Characteristics of in situ stress and its influence on coalbed methane development: A case study in the eastern part of the southern Junggar Basin, NW China

Based on 54 sets of well test data of 29 coalbed methane (CBM) wells, the distribution characteristic of in situ stress in the eastern part of the southern Junggar Basin and its control on permeability (K), reservoir pressure (Po), and gas content (G) were discussed systematically. The results show that three types of in situ stress regime exist and are converted corresponding to a certain depth, (1) <600 m is the strike‐slip fault regime (σH > σv > σh); (2) 600‐1050 m is the stress transition zone (σH ≈ σv > σh); and (3) >1050 m is the normal fault regime (σv > σH>σh). Regionally, with depths < 1050 m, stress regime also changes from west to east, that is, σH > σv > σh type in the western Miquan, σH ≈ σv > σh type in the middle Fukang, and σv > σH > σh type in the eastern Jimushaer, respectively. Controlled by stress regime and vertical belting, coal K shows a trend of “remarkably decreased, rebounded increase and greatly decreased,” and two decreasing stages (<600 m and > 1050 m) are mainly influenced by horizontal stress and vertical stress, respectively. Taking a burial depth of 1000‐1150 m as a boundary, the relationship between G and depth converts from “continually increasing” to “gradually decreasing,” which is in good agreement with the converted interface of stress regime from σH ≈ σv > σh type to σv > σH > σh type. Taking the converted interfaces of G (1000‐1150 m), K (800 m), and the prediction depth of the weathered zone (400 m) into consideration, CBM development potential in the study area can be divided into three grades, that is, (1) 400‐800 m (high K and medium G), (2) 800‐1150 m in Miquan and 800‐1000 m in Fukang (medium K and high G), and (3) >1150 m in Miquan and >1000 m in Fukang (low K and poor G). Overall, a key CBM development breakthrough will most likely be made in the study area within the scope of 600‐800 m due to the better G and higher K.


| INTRODUCTION
In situ stress is a type of internal stress in the earth's crust that is mainly controlled by gravity and tectonic movement, and the latter has a greater impact on in situ stress formation. 1,2 Based on this, in situ stress can be divided into overburden stress (σ v ) and tectonic stress (σ H and σ h ), and the former is mainly influenced by the overlying rock mass, whereas the latter is mainly related to tectonic movement and rock geological structures. 3 According to the relative relationships of three principal stresses, the classification schemes for in situ stress regime have been divided into the normal fault regime (σ v > σ H > σ h ), the reverse fault regime (σ H > σ h > σ v ), and the strike-slip fault regime (σ H > σ v > σ h ). 4 Stress field data from coal-bearing basins at home and abroad indicate that in situ stress regime often shows an obvious belting phenomenon in the vertical direction. [5][6][7][8][9][10] Moreover, vertical variations of the current in situ stress regime have obvious influence on CBM enrichment mechanisms and development conditions. [11][12][13][14] By controlling the opening or closing of the coal reservoir pore-fracture system, the current in situ stress regime has obvious control effects on K, P o , G, artificial fracture expansion, and the process of drainage and pressure lowering. 8,11,[15][16][17] K is one of the most important factors in the determination of CBM productivity. 8 The K values of coal reservoirs are mainly composed of 0.01-5 mD in China, which is lowered by 1-2 magnitudes than overseas, for example, the Powder River Basin in North America (>10 mD) and the Surat Basin in Austria (10-30 mD). 10,18 The research showed that in situ stress had obviously affected coal K, and the latter exponentially declined with the increasing of the former. 8,9,[19][20][21] The methane adsorbability of coal reservoirs tends to increase with increasing P o and decreasing T em . 22 By changing the confining pressure of pore fluid, the in situ stress regime can directly control P o and influence the gas-bearing conditions of the coal reservoir. 8 In general, coal reservoirs usually have greater P 0 and G 0 values within a compressive stress regime, whereas smaller P 0 and G 0 values exist in a tensional stress regime. 23 During the 13th Five-Year Plan period (2016-2020), the southern Junggar Basin becomes the key target zone of CBM exploration and development in China, and its CBM resources (<2000 m) were predicted to be 0.95 × 10 12 m 3 . 24,25 To date, CBM exploration has achieved major breakthroughs in Fukang, southern Junggar Basin, with the highest daily production per well of 1.7125 × 10 4 km 3 . The first demonstration base of CBM development and utilization was established in Xinjiang in 2013. 26 However, CBM exploration and development are still confronted with a series of difficulties in the southern Junggar Basin, for instance, (1) better gasproduction efficiency has only been achieved in Fukang, and the CBM exploration results are relatively poor in other regions; (2) at depths > 1000 m, gas-production efficiency and CBM development are also relatively poor in Fukang; and (3) the lower P o and gas saturation seriously restrict CBM development efficiency and economic benefits. The studies suggest that the current in situ stress regime should significantly contribute to the differential distribution of CBM enrichment conditions and development potential.
To date, scarcely any studies of in situ stress and its effect on CBM development have focused on the Jurassic coals of the southern Junggar Basin, and it has never been reported in international literature. To systematically discuss the characteristics of in situ stress and its effect on CBM development, a series of well test data from the eastern part of the southern Junggar Basin was systematically collected for the first time ( Figure 1). A number of geological analyses were carried out, that is, (a) the distribution rules for in situ stress regime of the Jurassic formations in two-dimensional space, (b) the control mechanisms of stress vertical belting on K, (c) the control effects of stress vertical belting on G, and (d) the grade division of CBM development potential and (e) the optimization of favorable targets. Both of them can provide a geological basis for the reasonable establishment of a CBM exploration-development program.

| GEOLOGICAL SETTING
The Junggar Basin has experienced the Hercynian, Indosinian, Yanshan, and Himalayan tectonic movements since the late Paleozoic, and the additive effects of multiphase stress fields lead to a complex structural configuration. [27][28][29][30] As one secondary structural unit of the Junggar Basin, the piedmont thrust belt of the North Tianshan Mountains is a multiphase superimposed inheritance structural belt, which is usually divided into five secondary structure units (ie, the Sikeshu sag, Qigu fault-fold belt, Huomatu anticlinal zone, Huan anticlinal zone, and the Fukang fault zone) ( Figure 2A). Among them, the Fukang fault zone is the main research target in this study, and it is mainly located north of Bogda Mountain and east of the Urumqi-Miquan strike-slip fault and is now shown as a "NE-EW-NW" arcuate tectonic belt on the plane. 31 The front structural belt of Bogda Mountain mainly underwent the Yanshan and Himalayan movements. The Himalayan movement was the main developmental phase of the fault and fold structures, and the critical period of CBM enrichment and adjustment in the study area. 25 Overall, the formation and evolution of Bogda Mountain have obvious controlling effects on the current structural framework and stress field distribution of the study area. The rapid uplift of Bogda Mountain occurred from the late Oligocene to the early Miocene, and a large-scale thrust nappe began to form north of Bogda Mountain. 31 According to the difference between the hanging wall and footwall, the thrust nappe can be divided into an overthrust fault-fold zone and a back-thrust fault-block zone from north to south ( Figure 2B). Among them, the overthrust fault-fold zone located between the Fukang and Yaomoshan faults was the main target for CBM exploration and development in the study area. Overall, the overthrust fault-fold zone was also shown as a "NE-EW-NW" arcuate tectonic belt, along with a series of anticline and syncline structures. Regionally, tectonic deformation can be characterized as "strong in the center and weak on two sides." In the eastern part of the southern Junggar Basin, that is, the Fukang region, tectonic deformation is the strongest, whereas in the Miquan and Jimushaer regions, it is relatively weaker. 32,33 The surface of the southern Junggar Basin is mostly covered by Quaternary strata, and the Jurassic strata are partly exposed at the same time. The Badaowan and the Xishanyao Formations are the coal-bearing strata in the study area, and the Sangonghe Formation that developed between them contains only a small amount of coal streak or nothing ( Figure 3). There are differences in the sedimentary environments between the Badaowan and the Xishanyao Formations. The former mainly developed in the fluvial and swamp facies environments, whereas the latter developed in the delta, lacustrine, and swamp facies. 30 Controlled by tectonic and sedimentary environments synthetically, the coal-rich center of the Badaowan Formation is mostly located in the Fukang region, and the coal-rich center of the Xishanyao Formation is located in the Miquan and Jimushaer regions. Therefore, the Badaowan coal in the Fukang region and the Xishanyao coal in the Miquan and Jimushaer regions are selected as prospective targets for CBM exploration and development in the eastern part of the southern Junggar Basin.

| METHODOLOGY
As a common transient well test method, the injection/falloff well test has been widely applied in the CBM field. 12,34,35 The schematic diagram of the injection/falloff well tests and in situ stress measurement is shown in Figure 4. Based on log interpretation, the packer is installed on the immediate roof using tubing strings, and the pump injection system and underground equipment are connected through the pipelines. Then, the injection/falloff test and in situ stress measurement are carried out successively. To ensure the data are representative and comparable, all the test data are performed by the same procedure and equipment.
The injection/falloff test was performed in accordance with the Chinese National Standard GB/T 24504-2009 before the in situ stress measurement, 36 including two stages: (I) the steady injection stage (14 hours) and (II) the shut-in stage (24 hours) ( Figure 5). Thus, the bottom-hole pressure varies with the change of time that can be recorded using an electric pressure gauge, and the related data are used to calculate F I G U R E 3 Composite stratigraphic column showing coal-bearing formations in the eastern part of the southern Junggar Basin the reservoir parameters such as reservoir pressure and permeability. In general, straight-line analysis and chart board matching analysis are usually used for analyzing the injection/ falloff well test data. Here, the data were analyzed by both the semilogarithm and double-logarithm fitting analysis method and were further verified with a historical fitting curve. The permeability obtained from the injection/falloff test is near to the cleat permeability of single-phase fluid.
In situ stress parameters are measured by the multiloop hydraulic fracturing method, according to the China earthquake industry standard DB/T 14-2000. 37 To conduct a full cycle in situ stress measurement, fluid is injected into the wellbore at a higher injection rate for a very short time. Once the pressure is greater than p f , and the coal seams will be opened, pressure value recorded by the electric pressure gauge at this moment is the P f ( Figure 6). To ensure the accuracy of in situ stress measurements, three other cycles are completed by repeating the above steps. Two cycles with good fracture creation and closure are selected to calculate the P c value following the time square root method.
In this study, 54 seams from 29 vertical wells were tested after completion and before production. According to the onshore vertical well hydraulic fracturing methods, the shut-in pressure (p c ) is equal to the minimum horizontal principal stress (σ h ). 38 In the initial hydraulic fracturing cycle, the rock is complete ( Figure 6, Circle 1). According to the theory of elasticity, the maximum horizontal principal stress (σ H ) can be expressed as follows: 39 where P f is the breakdown pressure in MPa, P o is the reservoir pressure in MPa, and T is the tensile strength of coal or rock in MPa.
For two to four circles during the in situ stress measurement, the water is injected into the wellbore again, and the crack will reopen and the refracturing pressure will be gotten. Since the cracks have been produced in the cycle 1, the tensile strength (T) of the rock is equal to 0, and therefore, the σ H can be expressed as follows: 40 The vertical principal stress (σ v ) can be estimated from the density and depth of the overburden strata.   1.82 mD), which is lower by 1-2 orders of magnitude than overseas. 18 With Equations (1), (2), and (4), the values of σ h , σ H , and σ v have been calculated (  9 the in situ stress strength in the study area is relatively high that is not beneficial for CBM development. The research shows that the P 0 , P f , Pc, and T em all have linearly increasing trends with the increase in H (Figure 8). The relevant relationships are as follows. where H represents the burial depth of coal reservoirs, m, and R 2 represents the correlation coefficient.
Moreover, the P f has a linear positive correlation with P c and can be written as follows. , and if 28 of 54 test points more than 1.0, this indicates that the horizontal stress shows no advantage to the vertical stress in the study area. In general, λ is often used to characterize the relative relationship between horizontal and vertical stress, and it is expressed as Equation 10.

|
The study results from several coal-bearing basins indicate that the λ value usually decreases with increasing H. 1,5,9 The statistics suggest that the λ value ranges from 0.5 to 5.0 in the world, and most of them lie within 0.5-1.5. 41 According to Equation 10, the λ value of the study area has been calculated as 0.49-1.46 (avg. 0.87), belonging to the scope of the λ values all around the world. In this study, the λ value shows a "three-section" change rule with increasing H (ie, decrease, stabilize, and decrease) (Figure 9). At depths < 600 m, the λ value is approximately 0.45-1.46 (avg. 0.9) and shows a dispersed and gradually decreasing trend; from 600 to 1050 m, the λ value is approximately 0.49-1.18 (avg. 0.87), with a stable distribution range; at depths > 1050 m, the values of λ (0.55-0.93, avg. 0.76) show a convergent and ever-reducing trend. Overall, λ decreases with increasing H, and the λ value changes from dispersed to convergent, indicating that the proportions of the horizontal stress in the current stress regime weaken gradually with increasing H.

| In situ stress regime change with the depth
Meng et al proposed that the σ h values of sedimentary rocks were approximately equal to 70% of the σ v values, but the former in the study area are less obvious than the latter. 12 In addition to that, the above phenomenon can also be observed in other coal-bearing basins due to high organic matter and the weak rock mechanical strength of coal petrography. 9,42 As shown in Figure 10, both σ H and σ h of the Jurassic formations decrease with increasing H in the study area, and the relevant relationships are expressed as Equations (11) and (12). In addition, the linear relationship between σ H and H is not obvious, showing a "three-section" change rule ( Figure 10).
where H represents the burial depth of the coal seam, m; and R 2 represents the correlation coefficient. In this study, the division scheme of Anderson (1951) has been used to characterize the current in situ stress regime. 4 Seen from Figure 10, a general trend of in situ stress change can be observed, and three in situ stress regimes transform one another as follows. I: At depths < 600 m, the in situ stress regime of coal reservoirs is σ H (avg. 12

| Regional variation of in situ stress regime
It was generally considered that tectonic deformation of the Jurassic formations can be characterized as "strong in the center and weak on the two sides" in the study area. 32,33 The studies show that the current stress strength of the Jurassic coal appears as an "increase first and then decrease" trend, and the middle Fukang is the distribution zone of the strongest tectonic stress field (Table 1) and has a good correlation with the tectonic deformation. The contrast analysis shows that the in situ stress regime also changes from west to east, with depths of the coal seam < 1050 m. Regionally, a strike-slip fault regime (ie, σ H > σ v > σ h ) occurs in the western Miquan, and a normal fault regime (ie, σ v > σ H > σ h ) develops in the eastern Jimushaer. Moreover, the in situ stress regime is in the transition state from σ H > σ v > σ h type to σ v > σ H > σ h in the middle the Fukang, that is, σ H ≈ σ v > σ h type (Figure 11). At depths > 1050 m, the in situ stress regime of the deep coal all show a unified normal fault regime, that is, The combined geological setting and field investigations suggest the current stress regime is strongly associated with the Himalayan tectonic movement. Since the Himalayan movement began, the study area has been infected by N-S extrusion stress from Bogda Mountain. The high-dipping strata (60-70°) and more complex fold types are found in the middle Fukang due to the nearest stress source and the strongest tectonic deformation; therefore, its stress regime appears as the coexistence of the strike-slip fault and the normal fault stress regime, that is, σ H ≈ σ v > σ h type. In general, the Urumqi-Miquan sinistral strike-slip fault has obvious effects on the current stress regime of the western Miquan, showing a σ H > σ v > σ h type. Moreover, the eastern Jimushaer is far from the stress source, and a significantly smaller horizontal stress leads to the σ v > σ H > σ h type. Finally, the horizontal principal stress of the Fukang (avg. 6.86 MPa) is significantly larger than the Miquan (avg. 5.52 MPa) and Jimushaer (avg. 3.87 MPa) ( Table 1), which is beneficial for forming artificial fracture networks during the process of CBM development. 32

| In situ stress influence on coal permeability
As one of the most important factors in the determination of CBM productivity, K has been influenced by complex geological factors, for example, structural framework, in situ stress regime, burial depth, coal structure, and development of natural fractures. 20,27,[43][44][45][46][47] Among them, the influence of in situ stress regime on K occurs throughout the whole process of CBM exploration and development. In other words, the pore-fracture system varies with the change of in situ stress regime, along with K of coal reservoirs. 9,48 The permeability mainly includes matrix permeability and fracture system permeability, and the latter is the main factor that controls the percolation conditions of the coal reservoirs in the actual formation conditions, with the former almost negligible. 49 In general, paleo-tectonic stress fields determined the formation, distribution, and development degree of natural fractures, whereas the current stress regime can control opening/ closing of pore-fracture systems, and it then influences the permeability of the coal reservoirs. 22 Based on different coal-bearing basins, the relationships between in situ stress and the initial K have been discussed by several scholars, [50][51][52] and a unified understanding is that in situ stress has a negative exponential correlation with K. To discuss the relationship between the current stress regime and K in the study area, the control action of the effective stress σ e (ie, (σ H + σ h + σ v /3)-P o ) on K has been discussed, except for three principal stresses (ie, σ H , σ h , and σ v ). As shown in Figure 12, in situ stress parameters have the best pow-exponent correlations (superior to exponent) with K, and the latter F I G U R E 9 The lateral pressure coefficient (λ) vs depth F I G U R E 1 0 Scatter diagrams of maximum horizontal principal stress (σ H ), minimum horizontal principal stress (σ h ), and vertical stress (σ v ) vs depth decrease with increasing of the former. The R 2 values between the stress parameters with K are σ H (0.5031), σ h (0.4613), σ v (0.4472), and σ e (0.2262), indicating that permeability of coal reservoirs is mainly controlled by tectonic stress (ie, horizontal main stress), with a weaker influence from overburden stress. Moreover, coal K drastically reduces when the σ H , σ h , σ v , and σ e values are more than 10 MPa, 15 MPa, 20 MPa, and 10 MPa, respectively, and high values of K begin to disappear ( Figure 12). The low K is not conducive to the drainage and pressure lowering of coal reservoirs and CBM seepage effect, so the tectonic position with suitable stress field conditions may be selected for CBM development in the study area.
The research shows that the K value is not a simple decreasing process with the increase in H, but appears as a trend of "remarkably decreasing, rebounded increase and greatly decreasing" (Figure 13). The contrast analysis shows that the change rule for K has an obvious correlation with the vertical change of in situ stress regime. (a) At depths < 600 m, K drastically decreases with increasing H, and the current stress regime is the σ H > σv > σh type. The analysis suggests that the pore-fracture system closes gradually under the horizontal crushing stress, and K decreases from 13.48 to 0.0041 mD (avg. 4.16 mD). (b) At depths of 600-1050 m, K has a short-resilient process (ie, 600-800 m), which is closely associated with the coexistence of the strike-slip and the normal fault regimes (ie, σ H ≈ σ v > σ h type). In this stage, the extensive stress can open the pore-fracture system or some weak interface, leading to abnormally high-value sectors of coal K. the current in situ stress is beneficial to normal fault activity with an extensional stress environment. However, vertical stress dramatically increases with increasing H in this stage, leading to a quick closing of the pore structure and a sharp decrease in K. The normal fault regime existing in deep formations can also be observed in the eastern Ordos Basin and the Qinshui Basin. 8,9 The change rule for coal K is mainly controlled by the influence of the current in situ stress on the pore-fracture system.
At depths > 600 m or < 1050 m, the coal pore-fracture system twice experiences quick closing under the actions of horizontal stress and vertical stress, respectively, along with two decreasing stages of coal K. Overall, the important challenge for CBM exploration and development of deep formations (>800 m) is "extremely low K and strong stress field" in the eastern part of the southern Junggar Basin (Figure 13).

| In situ stress influence on initial reservoir pressure
The P o is the fluid pressure of the pore-fracture system prior to the CBM development. 22,23 The P o reflects the flowing capacity of methane gas and formation water from the porefracture system to the wellbore, and it has great significance for the CBM development effect. 53 The P o is closely related to the current in situ stress regime, and the latter can affect the former by exerting confining pressure on the fluid of the pore-fracture system. 54 In general, coal reservoirs usually have greater P 0 and G 0 values within a compressive stress regime, whereas smaller P 0 and G 0 values existed in a tensional stress regime. 23 In the study area, the The research shows that the P o value linearly increases with increasing σ H , σ h , and σ v values in the study area ( Figure 14A-C). Among them, the R 2 value between the stress parameters with P o is σ v (0.8397), σ h (0.6989), and σ H (0.4568), that is, σ v has the most effective control on P o , followed by σ h and σ H . The main reason is that the σ H > σv > σh type only occurs in shallow formations (<600 m); at depths > 600 m, the growing rate of vertical stress begins to be more than horizontal stress, along with the stress field changing from the σ H > σv > σh type to the σ v > σ H > σ h type, and vertical stress provides a more important contribution to increasing P o . Meng et al also proposed that vertical stress has obvious influences on P o under the normal fault regime. 23 Moreover, the σ h and σ H are often perpendicular and parallel to the pore-fracture system, respectively, so the σ h may have the more obvious influence on P o than the σ H . Based on the relationships between the tectonic stress field (ie, horizontal stress) and reservoir characteristics, Qin et al proposed that the G o of coal reservoirs logarithmically increases with increasing the horizontal differential principal stress (ie, σ H -σ h ). 55 However, there is no correlation between the G o value and the "σ H -σ h " value ( Figure 14D) in the study area, further indicating that the horizontal stress has poor control action on P o .

| In situ stress influences on gas content
The gas content (G) of coal reservoirs is influenced by complex geological factors, for example, coal rank (R o ), T em , P o , and coal macerals. 24,56,57 Among them, the G value tends to increase with the increase in the R o and P o , whereas the T em , moisture content, and ash yield are not beneficial to gas absorption of coal reservoirs. 58,59 When the R o , T em , and coal macerals are relatively stable, as discussed above, the current in situ stress regime controls the P o and affects the G and saturation of coal reservoirs. To discuss the influence of the vertical change of in situ stress regime on the G of coal reservoirs, two CBM wells (A and B) from the Miquan and Fukang regions have been selected to analyze the relationship between the G and the P o with the H. Seen from Figure 15, the G obviously increases with increasing H (<1000-1150 m), though the outliner of the G might occur in local positions, due to the difference of hydrodynamic or roof lithology. However, the G values begin to dramatically decrease with increasing H, when the depths in Miquan and Fukang are more than 1150 m and 1000 m, respectively. The analysis suggests that the changing interface of the G is rather consistent with the interface of in situ stress changing from the σ H ≈ σ v > σ h type to the σ v > σ H > σ h type. Overall, the vertical belting of in situ stress regime may have a vital effect on the vertical change of the G, and the H (1000-1150 m) may be used to divide the shallow and deep CBM in the study area. Moreover, the change rule for the G has good consistency with the G o , that is, the larger the G o , the higher the G. The analysis indicates that a sharply decreasing G value is mainly caused by two main reasons within the depths > 1000-1150 m. The first is F I G U R E 1 5 Gas content and reservoir pressure gradient vs depth that in situ stress regime begins to become a normal fault regime, and the extensional stress environment is not beneficial to CBM preservation. The second is the negative effect of T em on methane adsorbability is stronger than the positive effect of the P o , leading to a sharp decrease in the G, which is consistent with Qin et al. 60 Overall, the current in situ stress regime has an important effect on the P o and the G, and further affects gas saturation of CBM reservoirs. The statistics show that gas saturation greatly varies from 1.62% to 83.07% (avg. 15.87%) in the study area, and low P o plays an important role in the formation of undersaturated CBM reservoirs.

| Grade division for CBM development potentiality
In general, CBM development potential is mainly influenced by two key geologic parameters (ie, G and K), and the higher the G and the larger the K, the greater the CBM development potential. [61][62][63] The current in situ stress regime controls opening/closing of the pore-fracture system and affects the K, P o , and G of coal reservoirs. As discussed above, under the dominance of the current stress regime, there is an obvious transition interface for the gas content (A) that is controlled by the positive effect of the P o and the negative effect of T em , and the G apparently decreases below interface A. Moreover, the K also has an obvious converted interface (B) under the influence of in situ stress regime, and the K values sharply decrease below interface B. Overall, the converted interface B for the K (800 m) is slightly shallower than the G for interface A (1000-1150 m). The gas composition data indicate that the depth of the weathered zone is approximately 400 m, 30 and the G value increases with increasing H (<1000-1150 m).
Combined with the transition interfaces A (1000-1150 m) and B (800 m), and the depth of the weathered zone (400 m), CBM development potential in the study area is divided into three grades vertically (Figure 16), that is, (1) 400-800 m (high K and medium G); 2) 800-1150 m in Miquan and 800-1000 m in Fukang (medium K and high G); and (3) >1150 m in Miquan and > 1000 m in Fukang (low K and poor G). Therefore, under the dominance of the current stress regime, the main targets of CBM development in the study area should be positioned on 400-800 m, and the 600-800 m is the most probable to make a key breakthrough, due to better G and higher K. Regionally, with depths < 1050 m, in situ stress regime changes from west to east, that is, σ H > σ v > σ h type in the western Miquan, σ H ≈ σ v > σ h type in the middle Fukang, and σ v > σ H > σ h type in the eastern Jimushaer, respectively. For coal depths > 1050 m, the regional stress regime all appears as the σ v > σ H > σ h type. 2. The change rule of K is mainly controlled by the influence of the current stress regime on the pore-fracture system. K is not a simple decreasing process with increasing H, but appears as a trend of "remarkably decreasing, rebounded increase and greatly decreasing." At depths > 600 m or < 1050 m, the coal pore-fracture system twice experiences quick closing under the actions of horizontal stress and vertical stress, respectively, along with two decreasing stages of coal K. 3. Take the depths of 1000-1150 m as a boundary, the G value changes from "remarkably increasing" to "dramatically decreasing" in the study area. The vertical belting of in situ stress regime may have a vital effect on the vertical change of the G value, and the changing interface of the G value is rather consistent with the interface of the current stress regime changing from the σ H ≈ σ v > σ h type to the σ v > σ H > σ h type. 4. Combined with the transition interfaces A (1000-1150 m) and B (800 m), and the depth of the weathered zone (400 m), CBM development potential is divided into three grades vertically in the study area. The main targets of CBM development in the study area should be positioned on 400-800 m, and the 600-800 m is the most probable to make a key breakthrough, due to better G and higher K.