The gas content distribution of coal reservoir at the Changzhi block, south-central Qinshui Basin, North China: Influences of geologic structure and hydrogeology

Abstract

Coalbed methane is now large-scalely explorated and exploitated in the world. The Changzhi coalbed methane block, south-central Qinshui Basin, is a new resource target zone for coalbed methane exploration and exploitation in China. However, the gas content distribution of this block and its influential factors have not yet studied. Based on the recent coalbed methane exploration and exploitation activities, the gas content distribution of coal reservoir in this block was studied. The results show that the gas content hold by the coal reservoir is 7.0 − 21.7 m3/t, which was determined by a combining control effect from geologic structure and hydrogeology. The Changzhi coalbed methane block has experienced multiple-stages geologic structure evolution, especially a tectonic-thermal event during the middle Yanshanian Orogeny improved the coal to the current R o,max 1.9 − 2.7% and meanwhile the coalbed methane was greatly generated. Subsequently, the widespreadly developed normal fault structures during the Himalayan Orogeny accelerated the coalbed methane escape through the “gas escape windows”, particularly where the location within the distance of about 1300 m to the “gas escape window” the gas content decreases significantly. Moreover, due to the action of the later Himalayan Orogeny, the slope areas of most Yanshanian fold structures were structurally cross-cut by the Himalayan normal faults, and thus an “open” syncline folds were formed. The coal reservoir was depressurized surrounding this “open” syncline structure and consequently the hydrodynamic losing effect has resulted in a comparatively lower gas content therein. By the control of geologic structure and hydrogeology, this block can be generally, compartmentalized into three hydrodynamic systems including the western groundwater stagnation region, the middle runoff region, and the north-eastern recharge region, where the hydrodynamic sealing effect at the groundwater stagnation region has made a comparatively higher gas content for the coal reservoir, but the hydrodynamic losing effect at the recharge region and runoff region has made a comparatively lower gas content of the coal reservoir.

Biogeochemistry and the associated redox signature of co-produced water from coalbed methane wells in the Shizhuangnan block in the southern Qinshui Basin, China

“…The Qinshui Basin is a tectonic Mesozoic basin which has evolved since the Late Paleozoic era in the North China Craton Basin in southeast Shanxi province (China), which is a complex synclinorium basin striking an NNE–SSW trajectory (Du et al., 2019). The southern Qinshui Basin CBM block is divided into SZN, Chengzhuang, Fanzhuang, Panzhuang, Shizhuangbei and Zhengzhuang, covering an area of approximately 23,923 km 2 (Figure 1(b)).…”

Implications of Geological Conditions on Gas Contents: A Case Study in the Pingdingshan Coalfield

“…Isobaric torsional faults, such as reverse faults, are generally used as barriers to gas migration, resulting in local gas enrichment . However, normal faults and other tensional faults act as cross-layer channels of gas migration, making the reservoir’s gas contents lower. ,, Well-sealed caprock is an important indicator of CBM enrichment , and CO 2 geological storage. , Hydrogeology has a direct or indirect effect on gas storage and migration. Atmospheric recharge water provides important microbial input for biogenic gas accumulation .…”

Influence of supercritical, liquid, and gaseous CO2 on fracture behavior in sandstone

“…Shanxi has the largest coal bed methane reserves, accounting for 91.5% of the national total. [20][21][22] Rock is damaged and destroyed to varying degrees under the influence of geological processes such as in situ stress, [23][24][25][26] temperature, 27,28 and hydrochemical corrosion. 29 For example, Ma et al 29 used the Forchheimer coefficient as an index to investigate the influencing mechanism of erosion on the nonlinear hydraulic properties of the broken red sandstones.…”

“…These reserves are mainly concentrated in the Shanxi, Shaanxi, and Guizhou provinces. Shanxi has the largest coal bed methane reserves, accounting for 91.5% of the national total 20‐22 …”