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About the Journal

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Journal:
Coal Geology & Exploration
Establishment year:
1973
 
Periodicity:
Biomonthly
Supervised by:
Xi’an Research Institute Co. Ltd., China Coal Technology and Engineering Group Corp.
Sponsored by：
Xi’an Research Institute Co. Ltd., China Coal Technology and Engineering Group Corp.
Editor-in-chief:
 DONG Shuning
 
Associate E ditor-in-chief:

 LIU Cheng, James W. LaMoreaux 

 

Executive Editor-in-chief:
JIN Xianglan 

 

ISSN:
1001-1986
CN:
61-1155/P
Web:
www.mdkt.cbpt.cnki.net

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2021年02期目次

  • Progress of coal fines agglomeration and settlement mechanism based on high efficiency coalbed methane drainage

    LI Yong<sup>1</sup>; HAN Wenlong<sup>1</sup>; WANG Yanbin<sup>1</sup>; MENG Shangzhi<sup>2</sup>; WU Xiang<sup>2</sup>; WANG Zhuangsen<sup>1</sup>; MA Zhentao<sup>1</sup>; LIU Du<sup>1</sup>; ZHAO Shihu<sup>1</sup>

    Significant low-yield and inefficient wells seriously hinder the development of China’s coalbed methane (CBM) industry, and the coal fractures and production pipes blocking caused by the coal fines settlement are the key influencing factors. This paper systematically investigates the latest research progress in the composition, generation mechanism, suspension transport and output control of coal fines produced by coalbed methane wells at home and abroad, summarizes the control mechanism and key issues of coal fines agglomeration-settlement and dispersion behavior, and proposes research prospects. The coal fines problem accompanies the entire process of CBM exploration and development, involving all aspects of geological selection evaluation, engineering fracturing construction, and drainage management control. The coal fines include the primary fines generated by the destruction of the coal body structure and the secondary fines formed by the engineering construction. The fines produced from the CBM wells are mainly a mixture of organic debris and clay minerals, with some samples of high clay minerals content. The suspended migration of coal fines is controlled by coal structure and surface properties, nm-μm coal particles interaction, the role of organic matter and clay minerals, and the flow of gas and water in the channel. The moderate and stable output of coal fine is the key to the management and control of drainage, involving the influences and mechanism of formation water environment on coal fines wettability, surface electrical properties and steric effects; and effect of dispersant ion addition on the desorption and seepage capacity of CBM. Focusing on “whole process experimental simulation of coal fines adhesion-wetting-agglomeration-settlement” and “optimization of coal fines dispersion stability and its moderate drainage”, accurate characterization of the physical and chemical properties of coal fines, the mechanism of agglomeration and settlement, the boundary conditions of the scattering behavior are carried out. Then the flow rate suitable for the stable migration control of coal fine is put forward to form the basic basis for maintaining the suspended production of coal fines, which provides theoretical and technical support for ensuring the stable and efficient output of methane-water-coal fines.

    2021 02 [Abstract][OnlineView][Download 20042K]

  • Geological unit division and development countermeasures of deep coalbed methane in Southern Yanchuan Block

    CHEN Zhenlong

    Deep coalbed methane resources have great potential, accounting for 62.8% of the total resources. However, effective development faces many challenges such as strong heterogeneity, high geostress, difficult process matching and low production capacity. Taking the deep coalbed methane in Southern Yanchuan Block as an example, the key parameters are overlaid and analyzed, the development geological units of the gas field are finely divided according to the five controlling factors of “sedimentation coal-control, tectonic influenced accumulation, hydrodynamic gas-control, geostress seepage-control, physical property production-control”. The key geological attributes and development constraints of each development geological unit are clarified, and the differentiated development countermeasures are formulated. It has formed a series of treatment countermeasures for different main causes of low efficiency, such as blocking in the formation, scaling near the well, difficult transformation of deep coal seam, high fluid volume and difficult pressure reduction, and a series of efficiency increasing technologies suitable for “dredging and plug removal, disturbance and permeability enhancement, effective support, liquid extraction and pressure reduction” under complex geological conditions of deep CBM. On this basis, a set of geological engineering integration and technology based on the geological attribute of “multi element coupling gas reservoir control unit” is proposed. In view of the decline of gas wells caused by coal powder blocking the seepage channel in high-yield area, the “nitrogen disturbance” is adopted to form pressure wave disturbance to solve the problem of inner layer dredging. The water breakthrough efficiency of 21 wells is 90%, and the daily increase of single well is 400 m<sup>3</sup>. It is recognized that the high mineralization degree of deep coal seam is easy to scale in the near wellbore area, resulting in low production. In order to realize the effective utilization of resources in high stress area, the effective transformation of deep coal reservoir is achieved through “long-distance effective support and large-scale volume transformation”. All the 16 wells have achieved good results, and the daily increase of single well is 1500 m<sup>3</sup>, and the gas production level is increased by 5-6 times. Meanwhile, the potential of high-yield and low-efficiency wells is continuously explored, and the effect of fluid lifting and pressure reduction is initially shown. The successful research and development of the key technology system of integrated efficiency enhancement has played a leading and exemplary role in the cost-effective development of deep coalbed methane in China.

    2021 02 [Abstract][OnlineView][Download 12850K]

  • Study on the main controlling geological factors of high yield deep CBM in Southern Yanchuan Block

    GAO Yuqiao<sup>1</sup>; LI Xin<sup>1</sup>; HE Xipeng<sup>1</sup>; CHEN Zhenlong<sup>1</sup>; CHEN Gang<sup>2</sup>

    The Southern Yanchuan Block belongs to a deep, high-rank coalbed methane(CBM) reservoir. Due to the influence of geological conditions, the single well productivity varies greatly. Researching on the main controlling geological factors and their changing mechanism of CBM accumulation, combined with the dynamic data of CBM development, the main controlling geological factors of the CBM well enrichment and high production are analyzed. The research results show that the productivity of the gas field is controlled by the geological factors of “tectonic, hydrology, coal structure”. Tectonic restricts the accumulation of CBM; the degree of salinity characterizes affects the preservation of CBM; and the coal structure restricts the reformation of the reservoir. The high-yield wells are mainly located in the wing parts of the local micro-uplift belt with a buried depth of 800 to 1 200 meters where the formation water salinity is 30 000 to 100 000 mg/L, with thickness of primary-fractured coal greater than 2.5 m, and the daily gas production is greater than 1 000 m<sup>3</sup>. The middle-production wells are located in the gentle tectonic in the western part of Wanbaoshan with a buried depth of more than 1 200 m, where the water salinity is greater than 100 000 mg/L, with a daily gas production volume of 500-1 000 m<sup>3</sup>; The low-yield wells are mainly distributed in the fault-sag zone near the middle level Ⅲ faults and local level Ⅳ faults where the salinity is less than 3 000 mg/L, with thickness of primary-fractured coal less than 2.5 m, and the daily gas production is less than 500 m<sup>3</sup>. The plane change of the block productivity confirms that the tectonic is the main controlling factor for the high production of deep CBM. Under the condition of underdeveloped tectonic activity in deep CBM reservoirs, the permeability of the reservoir is extremely low with the poor rebuildability, so it is difficult to obtain high production. The enhancement of tectonic activity achieves the goals of improving the reservoir, and the formation of fissures near the axis of the local anticline increases the permeability of the reservoir. Therefor, it is beneficial to CBM enrichment and reservoir reformation, and local small faults form micro-fractures, which are conducive to the desorption and seepage of CBM. However, the faults with violent tectonic activity and the vicinity of the depression zone form CBM escape channels, which has a negative effect on the enrichment and high yield of CBM.

    2021 02 [Abstract][OnlineView][Download 10877K]

  • Optimization on particle size fraction of lightweight coated ceramsite proppant in coal reservoir

    CHANG Xiaoliang<sup>1</sup>; LYU Runsheng<sup>2</sup>; WANG Peng<sup>1</sup>; LI Bing<sup>3</sup>; GAO Lin<sup>1</sup>

    Hydraulic fracturing is currently one of the main technical measures for enhancing coal reservoirs permeability. The spreading range and transportation distance of proppants in the fracture is an important indicator of hydraulic fracturing to evaluate fracturing effect. According to the characteristics of coal reservoirs in Lu’an mining area, physical experiments and numerical simulation methods are used to compare and analyze the effects of fracture conductivity, sand spreading range, particle size combination and other factors on conductivity of coalbed methane wells, and the best proppants particle size and particle size ratio are selected. The research results indicate that the fracture conductivity of proppants decrease with the increasing closure pressure. The length of the coated light ceramsite proppants in the cracks of the sand embankment and sand paving area is nearly twice that of ordinary quartz sand. Among the three sizes of 40-60 mesh, 16-40 mesh, and 12-20 mesh coated lightweight ceramsite, the 12-20 mesh fracturing fracture length, supporting fracture length and average proppants concentration are the smallest, while the conductivity is the highest; when ratio of particle size for 40-60 : 16-40 : 12-20=1 : 6 : 2, the best fracturing range was obtained by using coated lightweight ceramsite with an average fracture length of 320 m, fracture width of 0.672 cm, proppants concentration of 5.16 kg/m<sup>2</sup> and fracture conductivity of 1.263.

    2021 02 [Abstract][OnlineView][Download 10540K]

  • Causes for low CBM production of vertical wells and efficient development technology in northern Zhengzhuang Block in Qinshui Basin

    JIA Huimin; HU Qiujia; FAN Bin; MAO Chonghao; ZHANG Qing

    In order to realize the efficient development of deep CBM in the north of Zhengzhuang block in Qinshui Basin, firstly, the geological conditions and development data of coal reservoir are deeply analyzed, and the development data of shallow CBM are compared. Secondly, based on the evaluation of gas content, the difficulty of coalbed methane recovery is evaluated by comprehensive evaluation of reservoir permeability, reservoir-desorption pressure difference, coal structure and in-situ stress state-Finally, the reasons for low production of CBM wells in the northern Zhengzhuang Block are clarified, and the adaptive technology for efficient development is put forward. The results show that the gas content in northern Zhengzhuang Block is generally higher than 20 m<sup>3</sup>/t. While the permeability is extremely low, with the fracture development index below 140. And the difference between reservoir pressure and desorption pressure(reservoir-desorption pressure difference) of CBM formation is greater than 6 MPa, resulting in small desorption range of CBM wells. In most areas, the ratio of the thickness of broken coal to that of whole coal seam is above 0.7, leading to shorter hydraulic fracturing fractures. The vertical stress, a geostatic-field-type stress, is greater than horizontal stress and the hydraulic fracturing is prone to form vertical fractures with shorter fracture extension. So the coupling of the extremely low permeability, relatively high reservoir-desorption pressure difference, high broken coal ratio and geostatic-field-type stress, all these factors result in poor production in northern Zhengzhuang Block. Artificial borehole is established by tree type horizontal well to realize high efficient stimulation of coal seam, and the coordinated depressurization is realized and the negative effects are overcome by shortening the seepage distance of CBM and water. At the same time, the artificial borehole is used instead of the relative shorter hydraulic fractures. The production of the tree type horizontal well is over 10 000 m<sup>3</sup> per day. But the disadvantages of tree type horizontal well are risks such as unfavorable drainage and depressurization, easy hole collapse and high cost. Multi-stage hydraulic fracturing of L shaped horizontal well can overcome the disadvantages perfectly of tree type horizontal well. Compared with vertical well, the cost of L shaped horizontal well increases by 2 times while the production increases nearly by 100 times. The production of L-shaped horizontal well is as high as that of tree type horizontal well, while the cost of the L shaped horizontal well is only 40% of tree type horizontal well. In conclution, the L shaped horizontal well realize the efficient development of Northern Zhengzhuang Block.

    2021 02 [Abstract][OnlineView][Download 9989K]

  • Numerical simulation of the influence of no-flow recharge aquifer on CBM drainage

    LIU Bing<sup>1;2;3</sup>; ZHANG Songhang<sup>1;2;3</sup>; TANG Shuheng<sup>1;2;3</sup>; WANG Pengfei<sup>4</sup>; ZHAI Jiayu<sup>1;2;3</sup>; JI Chaoqi<sup>1;2;3</sup>

    Coalbed methane wells in southern Qinshui Basin have the characteristics of high water yield and low gas yield, while some wells present high water yield and high gas yield characteristics. Generally speaking, the high water yield of coalbed methane wells is mostly related to the aquifer with recharge. In this case, based on the coal reservoir geological condition of Shizhuangnan Block and the actual situation of coalbed methane vertical well production, the influence of non-flow recharge aquifer on reservoir pressure variation and CBM outflow rule was simulated by using a three-dimensional coal reservoir simulation software (SIMEDWin) with gas and water two phases and multiple components. The simulation results show that compared with the CBM Wells without connected aquifer, the CBM Wells that communicate with the confined aquifer without leakage water complement have significant pressure drop range in the far well zone, the time of high gas production is long, with large cumulative gas production and water discharge, but late gas discovery time. The higher the permeability of aquifer, the higher the peak value of gas production of the CBM Wells. The higher the daily water discharge of a gas well, the faster the gas will be produced, but the production rate will not increase when water discharge reaches a certain value. Considering comprehensively, similar to the high-permeability aquifer(lens aquifer) in Shizhuangnan Block, increasing the daily displacement to a certain value is more conducive to the increase of CBM production.

    2021 02 [Abstract][OnlineView][Download 7153K]

  • Numerical simulation and test of gas drainage with water jet layered pressure relief and permeability enhancement in soft coal seam

    LIU Xiao<sup>1;4</sup>; LI Yong<sup>1</sup>; XUAN Dequan<sup>2;3</sup>; HU Shixiong<sup>1</sup>; JING Tianxiang<sup>1</sup>; XU Sen<sup>1</sup>

    Hydraulic punching is the main technical measure to enhance permeability and drainage of coal seam gas. The pressure relief effect is mainly evaluated by the coal output. However, there are some problems such as large coal output, uneven pressure relief and easy stress concentration. Therefore, this paper puts forward the soft coal interlayer water jet layered pressure relief and permeability increasing gas drainage technology. Considering the influence of gas pressure compression and coal matrix adsorption gas expansion on the coal mass deformation, a multiphysics theoretical model under the coupling condition of stress field, fracture field and seepage field was established. With COMSOL numerical simulation software, the branch number of water jet、the variation law of gas pressure and gas content of coal within the influence range of pressure relief in soft coal interlayer were analyzed. The results show that when the long half axis of water jet branch is 2 m and the short half axis is 0.22 m, the number of jet branch number is 6 in numerical model which is more reasonable. Under the same coal output rate, the gas pressure and content decrease as the distance from the borehole increases. After 180 days of drainage, the effective drainage radius of layered pressure relief by water jet is about 2.14 times that of the conventional hydraulic punching. When the effective influence range is 2 m, the gas content of layered pressure relief by water jet is reduced by 7 m<sup>3</sup>/t, while that of conventional hydraulic punching is reduced by 4.1 m<sup>3</sup>/t. In the field application of Xinyi Coal Mine, it is found that when the layered coal discharge rate of water jet is 0.29-0.71 times of the conventional punching, and the time of extracting high concentration gas is still 2 times of the conventional hydraulic punching. The soft coal interlayer water jet layered pressure relief and permeability increasing gas drainage technology is of great significance to the development of soft coal interlayer hydraulic punching technology in the future, providing a new method and direction for coal mine gas control.

    2021 02 [Abstract][OnlineView][Download 10751K]

  • The enrichment and high yield law of CBM in Yanjiao syncline in Zhijin Block, Guizhou Province

    GUO Tao

    In view of the problems such as the large number of coal seams, the thin single layer, the complex structure, much mylonite coal and hard to evaluate favorable area in southern China, this paper makes use of the exploration achievements and tests data of Zhijin Block to study the reservoir-forming conditions of multiple coal seam CBM. The results show that the enrichment and high yield CBM in south China is characterized by “sedimentation storage-control, preservation gas-control, geostress coal structure control production”. The thickness, number and quality of coal are controlled by sedimentation, which determines the resource base of coal bed methane. The coalbed controlled by tidal flat marsh has stable distribution and good continuity. The ash content is less than 20% and the volume fraction of vitrinite is more than 80%. The structure and hydrogeology jointly control the gas content of coal seam, showing the characteristics of rich gas at the core of syncline and the wing part of Zhuzang sub-syncline develops towards the core. With the increase of burial depth, the mass concentration of chlorine root and the reservoir pressure gradually increase, and the gas content gradually increases from 8 m<sup>3</sup>/t to 28 m<sup>3</sup>/t. Tectonization affected coal structure, the magnitude and state of geostress, directly affects the productivity of coalbed methane wells by influencing the effect of fracturing and seepage conditions. NE trending structure and NW trending structure belong to different deformation areas. The Zhuzang, Agong and Santang subsyncline of NW trending structure formed later than Bide and Shuigonghe sub-syncline of NW trending structure, and the tectonic action is relatively weak. The present geostress is less than 20 MPa, and the coal body structure is mainly composed of primary structural coal or fractured coal, and the horizontal stress is bigger than the vertical stress, the fracture is mainly horizontal fracture, which is advantageous to the fracture extension in the coal reservoir, so the CBM development condition is more advantageous. Based on the study of the law of enrichment and high production, it is considered that the implementation of multiple coal seam resource base in south China and the effect of structure on geostress and coal body structure are the key factors for multiple coal seam selection evaluation, and it is clear that the Zhuzang, Agong, Santang sub-syncline in the Yanjiao syncline is a favorable area for CBM development. Regionally, the NE coal-bearing syncline, far from the Weining fault, is the key direction of multiple coal seam CBM exploration in southern China.

    2021 02 [Abstract][OnlineView][Download 10800K]

  • Practice of enhanced gas extraction by staged fracturing with comb-shaped long hole in coal mine roof

    JIA Bingyi<sup>1</sup>; CHEN Dongdong<sup>1</sup>; WU Jie<sup>2</sup>; SUN Siqing<sup>1</sup>; WANG Jianli<sup>2</sup>; ZHAO Jizhan<sup>1</sup>; ZHANG Jie<sup>2</sup>

    In order to solve the problems of drilling construction difficulty, low gas drainage concentration, poor drainage effect and inability to realize the predrainage of large area, based on the existing directional drilling technology and hydraulic fracturing technology in coal mines, combined with the previous research results, the staged hydraulic fracturing technology of comb-shaped long borehole in roof was proposed, and the field test was carried out in Sangshuping No.2 well in Hancheng mining area.The test results show that the main hole length of comb-shaped hole in roof was 588 m, including 8 branch holes, the total drilling footage was 1 188 m, the distance between main hole and coal seam was 0-3.28 m, and the plane coverage was about 12.5 m. The hole was divided into 4 stages with staged hydraulic fracturing technology of immovable pipe string. The cumulative injected water volume was 2 012 m<sup>3</sup> and the maximum pumping pressure was 8.74 MPa. After fracturing, the maximum influence radius was more than 30m, and the fractures were mainly located under the borehole and extended to the coal seam. During the stable drainage stage of fracturing borehole, the pure gas drainage volume was 1.18 m<sup>3</sup>/min, and the average drainage concentration was 43.54%. The pure gas drainage quantity of segmented hydraulic fracturing borehole with comb-shaped long borehole in the roof was 1.2 times of that of hydraulic slotting borehole and 4.0 times of that of bedding borehole in this coal seam. The test results show that the staged hydraulic fracturing technology of comb-shaped long borehole in roof can effectively avoid the problems such as collapsed hole, stuck hole, spray hole, etc in the conventional drilling process of this coal seam, and realize the pre-drainage of gas in a large area of broken soft coal seams of low permeability. It provides a new idea and new method for gas pre-drainage in the area of broken soft coal seams of low permeability.

    2021 02 [Abstract][OnlineView][Download 7408K]

  • New mathematical model and key parameters of capillary pressure curves of high-rank coal samples

    CHEN Ke; TANG Lei; YIN Chao; HE Wei; ZHANG Wei; QUAN Zheng

    Capillary pressure is an important parameter that affects the occurrence and development of coalbed methane. In order to establish an effective mathematical model to characterize capillary pressure curves of high-rank coalbed methane reservoirs, coal samples from No.3 coal seam in southern Qinshui Basin was taken as the research object, high-pressure mercury intrusion experiments were carried out, and the adaptability of the typical mathematical models of the capillary pressure curve currently in common use are systematically evaluated. Then a new mathematical model with higher fitting degree for high-rank coal is established. The results show that capillary pressure curves of 6 coal samples have no middle flat section, and the overall performance showed the protruding to upper left, which is obviously different from those of the conventional sandstone or low-rank coal reservoirs. BC model, He Chengzu’s model and Li’s model could not fit the capillary pressure curves of high-rank coal samples well. A new empirical model of capillary pressure curve, is established by processing capillary pressure data. The fitting degree of this model and capillary pressure curve data reaches over 97%, and the fitting effect is better than the existing models. In the log-log coordinates, the logarithmic difference between capillary pressure and the minimum capillary pressure is linear with the logarithmic difference between mercury saturation and the minimum capillary pressure, and the linear relationship can be used to directly obtain the slope <i>a</i> and power exponent <i>b</i> of the new capillary pressure model. The values of slope <i>a</i> and power exponent <i>b</i> are inversely proportional to the capillary pressure, when other conditions are equal.

    2021 02 [Abstract][OnlineView][Download 9568K]

  • Study on Mesozoic magmatic intrusion and Paleozoic multi-mineral genesis mechanism in Huanghebei Coalfield，Shandong Province

    WANG Huaihong<sup>1</sup>; SHEN Lijun<sup>1</sup>; WANG Dongdong<sup>2</sup>; ZHU Yuzhen<sup>1</sup>; LI Zengxue<sup>2</sup>; WANG Yongjun<sup>1</sup>; MAO Qiang<sup>2</sup>

    Accumulation of various minerals is common in strata, especially in areas invaded by magma, which is more conducive to the generation and preservation of various minerals and greatly improves the exploration benefit and development value of mineral resources. Taking Huanghebei Coalfield in Shandong Province as an example, this paper studies the genesis mechanism of Mesozoic rock intrusion and Paleozoic multiple minerals(coal, coal-bed methane, coal-measure shale gas and rich iron ore). Research shows that: Huanghebei Coalfield Carboniferous-Permian Period tectonic conditions and sedimentary environment are conducive to the development of coal seam, and coal seam distribution in the plane is characterized by more in the east and less in the west, thinner in the east and thicker in the west, thinner in the north and thicker in the south, longitudinally has the feature of lower thicker and upper thinner. Coalbed methane reservoir has the characteristics of medium thickness of coal seam, wide distribution of coal grade, medium gas content, good adsorption, ultra-low undersaturation, low porosity and high permeability, underpressure and moderate buried depth. The coal-measure shale gas reservoir has the characteristics of thick mud shale accumulation, high organic matter abundance, medium hydrocarbon generation capacity, typeⅡ kerogen, medium maturity, low porosity and especially low permeability. Mesozoic magma intrusions into the limestone formations of the Majiagou Formation of Ordovician, and mineral-bearing hydrothermal metasomatism and magnetization occurred, forming a contact-metasomatism type rich iron deposit. Due to the intrusion of Mesozoic magmas and magmatic thermal metamorphism, the coal zonation centered on magmatic intrusions appeared in the overlying coal measures in the study area, and a large number of coalbed methane and coal-measure shale gas were produced and accumulated in local areas. The gas content, porosity/pore size, thermal evolution degree of organic matter and hydrocarbon generation capacity are negatively correlated with the distance from the intrusive body. Moreover, the closer the coal seam is to the intruder, the weaker the gas adsorption performance is, which is mainly in the free state. In conclusion, the magmatic intrusion in Mesozoic controlled the formation and coexistence of many Paleozoic minerals.

    2021 02 [Abstract][OnlineView][Download 6685K]

  • 3D geological model construction and error analysis of intelligent mining working face

    WANG Xinmiao<sup>1;2</sup>; HAN Baoshan<sup>2</sup>; SONG Tao<sup>3</sup>; SHEN Kai<sup>2</sup>; YUE Hui<sup>2</sup>; LEI Xiaoyu<sup>2</sup>

    The complexity of geological conditions is one of the key issues affecting the further development of current intelligent mining, and there is an urgent need to build a high-precision 3D geological model of the mining face. This article analyzes the construction method of the intelligent mining geological model, and takes an intelligent working face of Huangling No.1 Mine as an example, combines all the geological exploration data of the working face, and uses the TIM-3D modeling software to construct the initial static model and the working face respectively. The dynamic model of the working face is equipped with a transparent face digital twin system to display the intelligent mining geological model; by comparing the actual coal thickness value revealed by the mining and the geological model predicting the coal thickness value, the error between the static geological model and the dynamic geological model was analyzed. The reasons for the model errors were explained. The analysis concluded that: The accuracy of the static geological model cannot meet the geological requirements of intelligent mining; the updated dynamic geological model can significantly reduce the coal thickness prediction error and basically meet the geological requirements of intelligent mining; the error of the model is the measurement error and the amount of sampled data It is caused by the selection of its distribution and interpolation algorithm. It is comprehensively believe that the establishment of the model should fully integrate all the geological information of the working face, the interval between the roadway marker points in the model establishment should be less than 10 m, and the advancing and mining distance for the dynamic update of the model should be less than 15 m. The research results are of great significance for fully understanding the accuracy of the current intelligent mining geological model, and for the next step of the development of intelligent intelligent mining geological support technology.

    2021 02 [Abstract][OnlineView][Download 9816K]

  • Different-source prediction of gas emission based on SAPSO-ELM and its application

    REN Haifeng; YAN Youji; WU Qinghai

    In order to improve the accuracy of gas emission prediction, in view of the multiple correlations and complexity of the influencing factors of gas emission, principal component analysis and separated source prediction theory were combined, the gas emission data of the mining layer, adjacent layer, and goaf were respectively subjected to principal component analysis to reduce dimensionality, and the predictor was obtained. Aiming at the problem that the input weight matrix and hidden layer threshold of the extreme learning machine were generated randomly, the simulated annealing particle swarm optimization algorithm was used to optimize the parameters of the extreme learning machine, and the gas in a coal mining face in Xinjiang was optimized. The output and influencing factors were used as the input of the SAPSO-ELM model for training, and then the trained SAPSO-ELM model was used to verify and predict the gas emission of a coal mining face in Shaanxi, and the prediction results of the original ELM model was compared. The results show that the average relative error of the SAPSO-ELM model is 3.45%, and the average relative error of the ELM model is 8.81%. Compared with the ELM model, the prediction accuracy and efficiency are better than the original ELM model. The combination of source prediction theory and principal component analysis effectively solves the multiple correlations among multiple factors and reduces the complexity of the prediction model. Meanwhile, the SAPSO-ELM prediction model realizes the rapid and accurate prediction of gas emission, which plays a guiding role in preventing gas accidents and ensuring safe and efficient mining of coal mines.

    2021 02 [Abstract][OnlineView][Download 6304K]

  • Mechanism and control of strong ground pressure in fully mechanized mining face

    ZHANG Yin; ZHAO Yi; LI Hao

    In order to ensure the safe use of the withdrawal roadway in the fully mechanized mining face of thick coal seam, taking the strong ground pressure behavior of the withdrawal roadway in 31102 working face of Nalinhe No.2 well as the method of combination of field monitoring and theoretical analysis, the strong ground pressure behavior of the withdrawal roadway in the mining process of fully mechanized mining face in thick coal seam was studied. The results show that: the strong ground pressure behavior of withdrawal roadway in fully mechanized mining face of thick coal seam is mainly the result of coupling effect of advance abutment pressure caused by working face mining, bidirectional supporting stress caused by adjacent gob hanging roof, and static load caused by withdrawal roadway excavation. According to the occurrence mechanism of strong ground pressure, the control scheme of combining borehole pressure relief and reinforcement support for withdrawal roadway and adjacent roadway is put forward to make it in the state of “strong support and strong unloading”. Through field observation and data analysis, it shows that the effect of strong ground pressure control technology is good, which can effectively ensure the safe use of the withdrawal roadway.

    2021 02 [Abstract][OnlineView][Download 7689K]

  • Evaluation of the development potential of the coalbed methane resources in mining area based on AHP-entropy method

    JIA Zhichao<sup>1;2</sup>; HUANG Huazhou<sup>1;2</sup>; HUANG Shaobo<sup>3</sup>; ZHOU Yu<sup>4</sup>; WANG Bo<sup>1;2</sup>

    The development of coalbed methane(CBM) in mining area is conductive to the efficient mining of pressure relief CBM in mining panels, and it reduces the risk level of underground gas. However, the difference in geological and coal mining conditions makes the development effect of surface wells quite different. Therefore, it is of guiding significance to evaluate the pre-mining panel selection. In order to explore an efficient selection method of CBM in mining areas, a complete evaluation system of CBM development potential in mining area is established by building one vote veto system and evaluation index system, combining analytic hierarchy process(AHP) and entropy method, finally quantifying the comprehensive score, and the method was applied to the Xiaonan Mine in Tiefa Mining Area. The results show that 4 of the 16 planned mining panels scored greater than 0.6, then it is recommended to develop CBM from them. At the same time, the units with higher ranking of evaluation results has higher income, and they are located in the favorable tectonic area for CBM in Xiaonan Mine, which is consistent with the evaluation results and verifies the rationality of the evaluation results. In conclusion, the evaluation results of AHP-entropy method are more reasonable, effectively avoid the blindness of CBM development in mining area, and have certain practical reference value for engineering development arrangement and economic benifits.

    2021 02 [Abstract][OnlineView][Download 6637K]

  • Multi-level fuzzy mathematics-based comprehensive evaluation model of CBM well productivity

    FENG Yulong<sup>1</sup>; ZHOU Linyuan<sup>2</sup>; WANG Qian<sup>1</sup>; LIU Chengrui<sup>1</sup>

    To accurately predict the productivity of CBM wells, a multi-level fuzzy mathematics method was used to establish a comprehensive evaluation model including 3 secondary evaluation parameters(i.e. resource conditions, development conditions, and transformation processes) and 10 tertiary evaluation parameters. Combined with the data of reservoir parameters and stimulation technologies of 15 coalbed methane target blocks in China, the comprehensive evaluation work was carried out using the model. Finally, the actual production of each block was collected to verify the evaluation results, and the corresponding relationship between the evaluation results and the production was obtained. The results show that, the average daily production per well in most blocks does not exceed 600 m<sup>3</sup>/d, and the evaluation score is relatively concentrated below 0.64, which is mainly due to the poor development conditions and unreasonable reservoir stimulation. The production per well has a good correlation with the comprehensive evaluation results, and the relationship between them is power function. According to the evaluation results, when the comprehensive score exceeds 0.660 6, the average daily production per well is expected to exceed 1 000 m<sup>3</sup>. The research results shows that, on the one hand, it is necessary to strengthen reservoir evaluation and optimize favorable areas; on the other hand, optimizing suitable reservoir stimulation measures, to maximize the production capacity of coalbed methane development.

    2021 02 [Abstract][OnlineView][Download 6274K]

  • Geochemical characteristics and genesis of coalbed methane in Baode area

    LI Yangbing<sup>1</sup>; ZENG Lei<sup>2;3</sup>; HU Weiqiang<sup>1</sup>; CHEN Xin<sup>1</sup>; MA Litao<sup>1</sup>; LIU Cheng<sup>1</sup>; HUANG Ying<sup>1</sup>; QIAO Fang<sup>1</sup>

    In order to find out the geochemical characteristics and origins of coalbed methane(CBM)in Baode area, coal, CBM and water samples were collected, gas component analysis, quality detection of CBM well-produced water and stable isotope analysis were carried out. The results show that CH<sub>4</sub> is the main hydrocarbon gas in CBM composition and its volume fraction ranges from 88.60% to 97.59%; a small amount of ethane is contained, and the volume fraction is only 0.01%-0.14%. The drying coefficient is greater than 0.99, the CBM belongs to the extremely dry CBM. The non-hydrocarbon components mainly contain CO<sub>2</sub> and N<sub>2</sub>, of which the CO<sub>2</sub> volume fraction ranges from 1.74% to 7.61% and N<sub>2</sub> volume fraction ranges from 0.04% to 8.18%. CBM <i>δ</i><sup>13</sup>C(CH<sub>4</sub>) value is between –56.8‰ and –47.7‰, the <i>δ</i><sup>13</sup>C(CO<sub>2</sub>) value lies between –6.6‰ and 13.9‰, the <i>δ</i>D(CH<sub>4</sub>) value is between –252.6‰ and –241.6‰.The water produced from coal seam is weakly alkaline, belonging to NaHCO<sub>3</sub> type water, which is similar to the ion composition, salinity, value of <i>δ</i>D(H<sub>2</sub>O) and <i>δ</i><sup>18</sup>O(H<sub>2</sub>O) of surface water, and the recharge from surface water is conducive to the proliferation of CH<sub>4</sub>-producing bacteria and the formation of secondary biogas. It is generally believed that CBM in the study area is a mixture of thermal and biogenic gas, formed mainly through carbon dioxide reduction, and “lightened” due to coal seam desorption, diffusion and migration, water dissolution and secondary biological action. The research results provide guidance for subsequent CBM exploration and development.

    2021 02 [Abstract][OnlineView][Download 7682K]

  • Characteristics of shale gas reservoir in Upper Paleozoic coal measures in Yangquan Block, Qinshui Basin

    LI Yangyang<sup>1;2</sup>; LI Xianqing<sup>1;2</sup>; ZHANG Xueqing<sup>1;2</sup>; XIAO Xianming<sup>3</sup>; YU Zhenfeng<sup>4</sup>; WANG Baoyu<sup>5</sup>

    Shale reservoir characteristics are the basic content of shale gas storage capacity evaluation. In order to explore the properties of high-evolved coal-measures shale gas reservoirs and optimize favorable reservoirs, various experimental methods of rock pyrolysis, X-ray diffraction, scanning electron microscopy, high-pressure mercury intrusion, low-temperature N<sub>2</sub> and CO<sub>2</sub> gas adsorption were applied to the Qinshui Basin. Reservoir characteristics were studied with core samples of coal-measure shale core from the Upper Paleozoic in Yangquan Block. The results show that the Upper Paleozoic coal-measures shale in Yangquan Block of the Qinshui Basin has a high content of organic carbon(average TOC is 4.9%), is in an over-mature stage(average <i>R</i><sub>ran</sub> is 2.32%), and has a high content of clay minerals(average is 50.0%), with the characteristics of low porosity and low permeability(average porosity of 6.61%, average permeability of 0.006 3&#215;10<sup>–3</sup> μm<sup>2</sup>). The pore types are mainly intergranular pores, intragranular pores and microcracks, and micro-nano-scale pores provide the storage space for the occurrence of shale gas; the total pore volume of pores is 0.025 5-0.051 7 mL/g, the average is 0.038 9 mL/g, the total specific surface area is 12.64-40.98 m<sup>2</sup>/g, the average is 28.43 m<sup>2</sup>/g, the pore volume of the micropores(&lt; 2 nm), and the mesopores(2-50 nm) has a good positive correlation with the specific surface area, while the pore volume of macropores(&gt;50 nm) has no obvious correlation with the specific surface area, indicating that the micropores and the mesopores are Yangquan blocks. The main carrier of coal-measure shale gas accumulation. In general, the Upper Paleozoic coal-measure shale in the Yangquan Block has good shale gas storage performance, but the shale reservoir has poor fracturing properties, which will affect the development of shale gas.

    2021 02 [Abstract][OnlineView][Download 13138K]

  • Prediction of coal seam gas content based on ABC-BP model

    ZANG Zijing<sup>1</sup>; WU Haibo<sup>1</sup>; ZHANG Pingsong<sup>1</sup>; DONG Shouhua<sup>2</sup>

    It is valuable to exploit the coalbed-methane which is rich in our country. The prediction of gas content in coalbed methane reservoir is a key step in the early stage of development and utilization. In recent years, BP neural network algorithm has been often used in coalbed methane prediction, but the model has some shortcomings in the training process, such as slow convergence speed, sensitive to initial value and easy to fall into local minimum value. Therefore, this paper proposed an improved BP neural network prediction model characterized by artificial bee colony algorithm. Firstly, R-type cluster analysis was used to classify the seismic attributes extracted from the 3D seismic data, four seismic attributes which are most sensitive to the change of coalbed-methane and independent of each other were selected. Secondly, the artificial bee colony algorithm(ABC) was used to find the optimal connection weight of the input layer and the hidden layer and the optimal threshold of the hidden layer of BP neural network, to build a robust ABC-BP neural network prediction model, and the seismic attributes of well location and gas content data was used as samples to train the model. Finally, the coal seam gas content in the work area was predicted by taking the optimal seismic attributes of the target reservoir in the whole work area as input. The prediction results are basically consistent with the change trend of gas content in each well. Among them, the average error rate at the training well is 0.23%, and the error rate at the verification well is less than 15%. Therefore, the prediction method has high reliability and strong applicability, and can be effectively used for coal seam gas content prediction.

    2021 02 [Abstract][OnlineView][Download 10712K]

  • Discussion on roof water loss control method of coal seam based on pre-splitting grouting reformation(P-G)

    ZHAO Chunhu<sup>1;2</sup>; WANG Hao<sup>1;2</sup>; JIN Dewu<sup>1;2</sup>

    In view of the technical requirements of roof water disaster prevention and water resources collaborative protection faced by coal mining in western coal mining area, this paper puts forward a technical idea of roof water loss control based on pre-splitting grouting reformation(P-G) according to the strain strength theory of material mechanics and the statistical results of mining fracture zones of different overburden types. The basic principle is that the continuous bedrock layer will be fractured into discontinuous rock layers by fracturing technology, and by weakening the “tip effect” of upward expansion of mining induced water flowing fracture in hard rock stratum to restrain the development height of water flowing fracture. Then, the soft clay grouting materials are used to modify the strata into relatively weak ones. Therefore, the P-G method plays a dual role in restraining the upward development of the water flowing fracture zone and reducing the water conductivity of the overlying strata, so as to realize the water loss control of the coal seam roof aquifer. Taking the Yushen Mining Area in the energy base of northern Shaanxi as the analysis object, this paper discusses the control method of P-G water loss in roof aquifer before mining, including the analysis of geological and hydrogeological conditions, the identification of water inflow(loss) pattern of aquifer in coal working face, prediction of development height of water flowing fracture zone, water gushing mode of overburden rock, determination of P-G time, horizon and time, horizontal hole hydraulic fracturing of roof strata and grouting modification. It has certain reference significance for roof water disaster prevention and water resources coordinated protection technology practice in Yushen Mining Area of the energy base in northern Shaanxi.

    2021 02 [Abstract][OnlineView][Download 7131K]

  • Comprehensive exploration of collaps column and three-dimensional construction technology of water plug based on directional horizontal drilling

    TIAN Gan<sup>1;2</sup>; NAN Shenghui<sup>1;2</sup>; LIN Xudong<sup>1;2</sup>; FAN Juan<sup>1;2</sup>

    The Ordovician limestone water inrush from floor caused by water-conducted collapse columns is the main water hazard threat in Tashan Mine of Tongmei Group. Water inrush from collapse columns once happened in the roadway excavation of 8228 working face. On the basis of comprehensive geophysical exploration above and below the well, the development boundary, the influence zone, the cementation of the fractured body and the distribution characteristics of the water flowing subsided column are found out by means of multi-layer and multi-branch surface directional horizontal drilling speed logging, drilling fluid leakage, cuttings logging and logging while drilling, and combined with data statistical analysis, so as to find out the development boundary of the water flowing subsided column and the distribution characteristics of the broken body filled in it, and to control the subsided column by Grouting. The results show that the length and short axis of the collapse column is 410 m, 200 m, and the broken area is mainly distributed in the right front of the driving head of the belt roadway near the water inrush roadway. The 3D geological modeling of the spatial structure and development characteristics of the collapse column is carried out by using Surpac software, and the main passageway area, fracture area and secondary fracture area are divided according to the crushing degree of the collapse column filling material. In view of the different zones of the collapse column broken body, the directional horizontal drilling control technology and separate zones of the grouting technology are used to construct the three-dimensional water-blocking plug. The safe mining of the working face is finally realized by the comprehensive treatment of cutting the source and reinforcing the water-flowing collapse column. The comprehensive exploration and treatment technology of directional horizontal drilling multi-branch collapse column provides a good reference for other similar projects.

    2021 02 [Abstract][OnlineView][Download 10600K]

  • Fracture feature recognition of sandstone after high temperature based on RA/AF

    GE Zhenlong<sup>1;2;3</sup>; SUN Qiang<sup>1;2;3</sup>; WANG Miaomiao<sup>4</sup>; ZHAO Chunhu<sup>1;2</sup>

    It is of great significance to carry out the research on rock high temperature damage information identification for geothermal development and underground coal gasification. Based on the changes of acoustic emission parameters RA and AF in the failure process of sandstone after different high temperature treatments, the development and evolution law of different types of cracks in sandstone after high temperature treatment are studied. The results show that tensile cracks are dominant in the whole loading process of sandstone. When the loading stress exceeds 80% of the peak stress, the proportion of shear cracks increases rapidly, which can be regarded as the precursor of sandstone failure. When the heating temperature exceeds 600℃, the proportion of shear cracks increases. When temperature exceeds 800℃, the proportion of shear cracks decreases rapidly. Therefore, 600℃ and 800℃ can be regarded as the threshold temperature of sandstone damage mutation. After high temperature treatment, the dislocation pileup phenomenon increases, the plastic characteristics of sandstone strengthen, and the proportion of tensile cracks increases. The research results will provide an important theoretical basis for the identification of precursor information of rock fracture and instability after high temperature treatent.

    2021 02 [Abstract][OnlineView][Download 0]

  • Development of deep geothermal energy and its influence on geothermal water flow field: Taking the development of deep geothermal energy in Lankao County for an example

    SONG Qianjin<sup>1</sup>; WANG Gang<sup>2</sup>; XU Yichuan<sup>2</sup>; CHENG Lei<sup>3</sup>

    In order to study the influence of deep geothermal energy development on the flow field of thermal reservoir, deep geothermal energy development in Lankao County is selected as the research object. The geological structure and regional structure of the study area since Cenozoic are analyzed, and the of geothermal exploitation and existing problems in the area are investigated. According to the types of geothermal energy, the characteristics of the Quaternary(Q), Neogene Minghuazhen Formation(N<sub>2</sub>) and Neogene Guantao Formation(N<sub>1</sub>) are analyzed. The conditions of fault distribution, thermal reservoir development and water-resisting boundary in the area are found out by using controlled-source audio-frequency magnetotelluric sounding. The parameters of thermal reservoir in different positions are found by field test and measurement, the amount of geothermal resources in each layer by region are calculated. The mathematical model is established according to the mining mode, boundary conditions and hydrogeological parameters. By numerical simulation, it is predicted that the flow field of Q reservoir will revert to the original flow field model in 2023, the funnel effect of N<sub>2</sub> thermal reservoir flow field continues to weaken, the funnel effect of N<sub>1</sub> thermal reservoir flow field is obvious and its distribution is irregular. To control the influence of geothermal resource exploitation on environment, the methods of closed cycle geothermal utilization, pressure reinjection in the same layer, rational distribution of wells and comprehensive utilization of multi-layer geothermal are put forward, which provides a reference for the development of geothermal resources and environmental protection in local and surrounding areas.

    2021 02 [Abstract][OnlineView][Download 38547K]

  • Long-term heat transfer performance of underground coaxial heat exchanger for medium-deep geothermal

    LI Fengcui<sup>1</sup>; HAN Ershuai<sup>1</sup>; LIANG Lei<sup>1</sup>; WU Jing'an<sup>1</sup>; LU Bingxue<sup>2</sup>

    Underground coaxial heat exchanger(UCHE) for medium-deep geothermal has the characteristic of the high heat transfer capacity and outlet water temperature, so it has attracted great attention in the heating industry. However, the current research mainly focus on the heat transfer performance of the UCHE during a single heating period, with insufficient analysis on the long-term heat transfer performance. In this paper, considering the operation characteristics of heat supply in heating season and stopping working in non-heating season for underground coaxial heat exchanger for medium-deep geothermal, a numerical heat transfer model is proposed based on the energy conservation equation. The numerical model is solved by the finite volume method and calculated in Matlab platform, which is used to analyze the heat transfer performance of UCHE during the long-term operation. The results show that the heat transfer performance of the heat exchanger declines with the operating years and the degree of decline decreases year by year, and finally reaches the quasi-steady state. Among them, the decrease proportion of the average heat transfer in the next year is the largest, and the greater the buried depth of the heat exchanger, the smaller the decrease proportion of the heat exchanger. The decline ratios of HTC in the second year are 4.00%, 3.78% and 3.56% for the heat exchangers with lengths of 2 000, 2 500, and 3 000 m, respectively, and the corresponding decline ratios of 30-year operations are 13.7%, 13.1% and 12.4%, respectively. Rock-soil temperature declines and its disturbed radius increase with operating years. During 30-year operations, the disturbed radius increases from 13 m to 105 m for heat exchanger with 2 000 m depth. Furthermore, the disturbed radius is larger for the deeper heat exchanger. The research results demonstrate the evolution of the heat transfer performance of UCHE during the long-term operation, which has the guiding significances to the UCHE design.

    2021 02 [Abstract][OnlineView][Download 6503K]

  • Effect of arbuscular mycorrhizal fungi and <i>Hippophae rhamnoides</i> on the improvement of the dump of open-pit coal mine in the eastern grassland

    MIAO Chunguang<sup>1</sup>; YANG Huihui<sup>2</sup>; BI Yinli<sup>2;3</sup>; SONG Ziheng<sup>2</sup>; GUO Nan<sup>2</sup>

    The land barren, grassland degradation and difficult ecological restoration are serious in the open-pit mining area of eastern China. The symbiosis between arbuscular mycorrhizal fungi(AMF) and <i>Hippophae rhamnoides</i> and the effect of mycorrhiza on the development of <i>Hippophae rhamnoides</i> root system and the improvement of soil in the dumping site were analyzed. It was found that the plant height and crown width of inoculated AMF(+M) were increased by 20% and 21%, respectively. The root length and root volume of +M were 1.46 and 1.97 times of CK, respectively. The content of Glomalin in the rhizosphere soil of <i>Hippophae rhamnoides</i> in +M was 3.22 mg/g, which was significantly higher than 2.16 mg/g in CK. The phosphatase activity of +M was 1.76 times that of CK, and the content of available phosphorus was similar. The results show that it is feasible to use microorganism to promote soil improvement and ecological restoration of the open-pit mine dump.

    2021 02 [Abstract][OnlineView][Download 6144K]

  • Vegetation disturbance analysis in coal mining area with high ground water level based on Landsat time series NDVI data

    FANG Liangcheng<sup>1</sup>; CHEN Yongchun<sup>2</sup>; AN Shikai<sup>2</sup>; XU Yanfei<sup>2</sup>; YIN Mengjie<sup>3</sup>; LI Zhihui<sup>3</sup>; ZHAO Ping<sup>3</sup>; CHEN Yeyu<sup>4</sup>

    The eastern mining area of China is an important coal and grain composite production area. Due to the flat terrain and high underground diving level, most of the subsidence caused by mining is perennial or seasonal water, which causes serious land, ecological and environmental problems. As an important part of the ecological environment in mining area, vegetation has dynamic characteristics due to the external disturbance and the change of environmental factors. The normalized difference vegetation index(NDVI) is a common indicator for remote sensing monitoring of vegetation growth. The analysis based on NDVI time series data can effectively reveal the disturbance effect of vegetation. Taking Guqiao Coal Mine in Huainan, Anhui Province as the research object, the temporal and spatial variation characteristics of NDVI values were analyzed based on the classification statistics of Landsat NDVI time series data from 2007 to 2018, as well as hot spot analysis, clustering and outlier analysis, and profile analysis, and then the disturbance effect of coal mining subsidence on the surrounding vegetation was discussed. Results showed that from 2007 to 2018, the vegetation growth in Guqiao Mine was generally good, while the dispersion degree of vegetation cover was increasing. The NDVI distribution in Guqiao Mine has obvious spatial clustering characteristics, both are “High-High” Cluster type or “Low-Low” Cluster type, and there is no abnormal appearance. Under the influence of coal mining, hot spots decreased and cold spots increased, and the conversion of hot spots to cold spots mainly occurred in the area of subsidence water, near the Deshang speedway and Yongxing River. Within a certain range around the subsidence water accumulation area, there was an obvious vegetation disturbance effect, and the initial disturbance of mining was small. With the growth of the water accumulation area and the lapse of time, the disturbance range gradually increased and finally tended to be stable, which showed temporal lag and spatio-temporal accumulation. The results would provide a reference for the determination of ecological influence range and the restoration of ecological environment in coal mining subsidence area.

    2021 02 [Abstract][OnlineView][Download 13539K]

  • Beneficial CBM area prediction based on structural elemental quantitative cluster classification

    LIU Jing<sup>1;2</sup>; CHANG Suoliang<sup>1;2</sup>; LIU Zuiliang<sup>3</sup>; ZHANG Sheng<sup>1;2</sup>; CHEN Qiang<sup>1;2</sup>; LIU Bo<sup>1;2</sup>

    In order to select optimally the CBM-enriched area of structural elements and delicately divide the advantageous blocks of CBM structural control under the development scale, this paper takes the Yongle south block in the southwest of Qinshui Basin as an example, subdivides the structural characterization elements and quantifies the indicators of structural elements, and puts forward the method of trend surface iteration to characterize different degrees of structural deformation, fuzzy clustering classification and element dichotomy to optimize the favorable area of CBM structural control. Based on the comprehensive interpretation results of seismic geology, the quantitative characterization of structural elements of No.2 and No.(9+10) coal seams in the study area is carried out from three aspects of structural deformation, fault system and burial depth. The quantitative classification of structural elements is carried out by Q-type clustering method. On this basis, the single element is divided by using factor dichotomy method under the guidance of the structural geological law affecting the enrichment and preservation of coalbed methane. The favorable and disadvantageous areas for gas control are finally synthesized into four types: the most favorable, the more favorable, the more disadvantageous and the disadvantageous under the influence of CBM enrichment structure, which are verified by the gas content data of coal drilling holes.

    2021 02 [Abstract][OnlineView][Download 18333K]

  • Analysis of geophone array method in low SNR complex area of Ordos Basin

    WANG Zhengliang; XIAO Guoqiang; FU Qunli; LYU Zhenchuan; YAO Zonghui; SHI Qingyang; GAO Bin; YI Hongbin; GAO Qiang; ZHANG Peng; HOU Jie; SHI Bingcheng; WANG Yanduo; JIAO Guixing

    In the northwest of Ordos Basin, there is serious random interference in the complex area, which leads to the low signal-to-noise ratio of seismic data in this area. In order to solve the problem of low signal-to-noise ratio(SNR) of seismic data in this area, a method study of suppressing random interference by geophone array is carried. The influence of random interference on the accurate calculation of NMO correction and static correction, the suppression of interference wave by geophone array, the influence of intra group height difference and array base distance on high frequency of seismic acquisition data are studied, and the attenuation effect of geophone array internal distance on random interference is compared and analyzed. The results show that: in the area with low signal-to-noise ratio in the basin, the field geophone array mainly suppresses the serious random interference wave and improves the signal-to-noise ratio of seismic data; the height difference of geophone array less than 1 m has limited influence on the high-frequency components below 110 Hz of the seismic acquisition data in this area, and the base distance less than 13 m has limited influence on the frequency within 70 Hz of seismic data of medium and deep target layers; The random interference radius determined by theoretical calculation and experimental data is 1.7-2.0 m. the inner distance of geophone array larger than the random interference radius can effectively suppress the random interference wave, among them, the effect of the geophone group inner distance of 3 m is more stable. The results show that the method of geophone array receiving with the above parameters can improve the signal-to-noise ratio and frequency in the limited frequency band of 70 Hz, and the cost is relatively low. This conclusion has a guiding role in seismic exploration field acquisition in low SNR complex area of Ordos Basin.

    2021 02 [Abstract][OnlineView][Download 13397K]

  • Forward simulation of fault detection by transmitting channel wave in thin alternating coal seams

    MA Yanlong

    In order to study the feasibility of the fault detection by transmitting channel wave in thin alternating coal seams of southwestern region, a representative area was selected, and a coal mine in Panzhihua Coal Industry Group was selected as the research object. A three-dimensional geological model with three alternating coal seams containing three partings, three partings and faults and without parting was established based on actual geological data. Through the forward simulation and analysis of the characteristics of the wave field and the frequency dispersion of the channel waves of the three dimensional elastic wave, the validity of the amplitude attenuation coefficient imaging in the channel wave detection of the development location and the extension direction of the faults in the thin alternating coal seams was summarized, and combined with the actual application, the propagation velocity, the frequency dispersion characteristics, the influence of the faults and the partings on the propagation of the transmitting channel waves in the thin alternating coal seams were discussed. The results indicated that for the detection of the transmitting channel waves in the thin alternating coal seams, the faults plaid a leading role in the influence on the propagation of the transmitting channel waves in thin alternating coal seams, a parting of less than 0.5 m had little influence on the development and energy imaging of the channel waves, in the case of the same thickness of the coal seams, the dominant frequency of the model with a parting was lower than that of the model without parting, the channel waves can detect relatively accurately the thin alternating coal seams of 2 m thick and with a parting of less than 0.5 m. the research indicate that the transmitting channel waves can detect the location, strike and extension of a fault with the throw bigger chan 1/2 thickness of the coal seam in the thin alternating coal seams, provide reference for the detection of the structures in the thin alternating coal seams in the southwestern region.

    2021 02 [Abstract][OnlineView][Download 7962K]

  • Rock breaking mechanism of composite impact of full-size PDC bit based on finite element analysis

    PENG Xu<sup>1;2</sup>; HAO Shijun<sup>1;2</sup>

    In order to solve the problems of low rock breaking efficiency in hard formation and the decrease of bit life caused by stick-slip vibration of drilling tools, the full-size bit composite impact rock breaking mechanism was studied by finite element method(ANSYS). The effects of impact frequency, WOB(weight on bit) and rotational speed on the efficiency of rock breaking were analyzed. It was found that both tensile and compressive stresses existed in rock during bit rock breaking, and rock failure was manifested in comprehensive failure of “tensile &amp; compressive shear”. It is concluded that under the condition of torsional impact frequency of 25 Hz, the optimal axial impact frequency is 13 Hz, and the drilling rate is the fastest under the combination of these two impact frequencies. The influence of WOB on rate of penetration(ROP) increases linearly, and the relationship between ROP and WOB under impact load or not is regressed. The influences of rotational speed on the ROP is relatively small and tends to increase slightly. It is considered that the hard rock layer causes PDC bits to be cut into abrasive state and causes little change in the mechanical drilling speed. Composite impact could significantly improve the ROP of drill bit in formation drilling. The research on composite impact rock breaking mechanism of full-size PDC bit is of great significance to the improvement of drilling efficiency and the development of composite impact technology.

    2021 02 [Abstract][OnlineView][Download 18035K]

  • Difficulties and optimization of wire-line core drilling technology for broken formation in complex structure area of northwest Hunan

    KONG Xiangwang<sup>1;2</sup>; ZHANG Shaohe<sup>1;2</sup>; WANG Wenbin<sup>3;4</sup>; SUN Pinghe<sup>1;2</sup>; WU Dongyu<sup>1;2</sup>; XIAO Jincheng<sup>3;4</sup>; HE Hongsheng<sup>3;4</sup>

    Taking Xiangcidi 1 Well in the complex structural area of northwest Hunan as an example, in view of the common drilling difficulties encountered during the drilling process such as low core adoption rate and stuck-drilling buried drilling, we adopted the self-developed pumpless reverse circulation advanced side spray line and optimized the drilling fluid system to effectively improve the core drilling rate of the drilling project. The new type of drilling tool can form a local reverse circulation at the bottom of the hole, and combined with the internal anti-clogging cone net of the drilling tool and the design of the advanced side jet bit can effectively improve the drilling core rate in broken formations. By applying the drilling tool in practice, the drilling core rate in the core broken formation reached 94.4%, so it has achieved good application effects.

    2021 02 [Abstract][OnlineView][Download 8057K]

  • Research on the grouting and setting pressure of the automatic hole sealing device in underground coal mine

    LI Chengcheng<sup>1;2</sup>; WANG Yi<sup>2</sup>; WANG Li<sup>1;2</sup>; DUAN Huijun<sup>1;2</sup>

    Grouting pressure and setting pressure are the main parameters for designing an automatic hole sealing device in coal mine, and they are also the important basis for the design of automatic hole sealing construction. Based on the radial sealing range of the slurry, the paper analyzes the sealing effect under different slurry pressure conditions by means of theoretical calculation and numerical simulation. Combined with the mechanical characteristics of the rubber Mooney-Rivlin model, extrusion seal and other principles, the optimal injection pressure and setting pressure are studied and determined. The results show that the radial sealing range of the slurry at a pressure of 2 to 4 MPa is 2 to 4 m, which can meet the sealing requirements for drilling. When the drilling diameter is 96 to 100 mm, the setting seal pressure of 2.2 to 8.4 MPa can make the device achieve the best setting sealing effect. The results can provide a theoretical basis for the design of the device and provides a theoretical basis for determining the technical parameters of the application of the device.

    2021 02 [Abstract][OnlineView][Download 6692K]

  • Numerical simulation of safe distance through roadway drilling under dynamic load of large diameter rescue well

    LI Bizhi; HAO Shijun; LIU Mingjun; ZHANG Qiang; BAI Gang; MO Haitao

    Aiming at the sudden inburst of formation water and drilling fluid into a roadway along the borehole during through roadway drilling operation, which results in the secondary injury of the trapped personnel, ABAQUS geotechnical numerical simulation method was adopted, the model was established with the surface rescue well of the roadway of No.3 coal seam in Pingshang Coal Mine as an example, the plastic deformation characteristics of the surrounding rock of the roadway roof and the optimization of safe through roadway distance under drilling dynamic disturbance were studied. The results show that the dynamic disturbance caused displacement deformation and plastic failure of the roof surrounding rock, and the distribution of the borehole center was symmetrical zigzag. The axial force had great influence on the surrounding rock of the roadway roof, the safe through roadway distance was 16.53 m. The simulation results provide reference for optimizing the safe driving distance, realizing the purpose of safe and efficient driving, providing the guarantee for the safe lowering and lifting of the rescue cabin in the rescue well.

    2021 02 [Abstract][OnlineView][Download 6591K]
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