In Situ Stress Distribution and Its Control on the Coalbed Methane Reservoir Permeability in Liulin Area, Eastern Ordos Basin, China

Abstract

Permeability is one of the important factors that affect the production efficiency of coalbed methane, and it is mainly controlled by in situ stress. Therefore, it is very essential to study the in situ stress and permeability for the extraction of coalbed methane. Based on the injection/falloff well test and in situ stress measurement of 35 coalbed methane wells in the Liulin area in the east of the Ordos basin, the correlations between initial reservoir pressure, in situ stress, lateral stress coefficient, permeability, and burial depth were determined. Finally, the distribution characteristics of in situ stress and its influence on permeability were analyzed systematically. The results show that with the increase of burial depth, the initial reservoir pressure and in situ stress both increase, while the lateral stress coefficient decreases. The permeability variation is related to the type of stress field in different burial depths, and its essence is the deformation and destruction of coal pore structures caused by stress. The distribution characteristics of in situ stress at different depths and its effect on permeability are as follows: at depths < 800 m , the horizontal principal stress is dominant ( σ H ≥ σ v > σ h ) and the permeability is a simple decreasing process with the increase of the depth; at depths > 800 m , the vertical stress is dominant ( σ v ≥ σ H > σ h ). The permeability of most coal is very small due to the large in situ stresses in this depth zone. However, because of the stress release at the syncline axis, coal with high permeability is still possible at this depth zone. Due to the existence of high permeability data points at burial depth (>800 m) and the fitting relationship between permeability and vertical stress, the maximum and minimum horizontal principal stress is poor. However, the coal permeability and lateral stress coefficient show a good negative exponential relationship. This indicates that the lateral stress coefficient can be used to predict permeability better.

Productivity characteristics and controlling factors of coalbed methane vertical well in a coal block of Qinshui Basin

“…The productivity turns with the increase of cover depth, primarily because the in situ stress indirectly affects the gas production of CBM wells by controlling the permeability. Previous studies have found that in situ stress usually increases with the increase in depth of cover (Feng et al, 2021), and permeability shows a nonmonotone decreasing trend with the rise (Chen et al, 2016; Feng et al, 2021). Chen et al (2016) took the Zhengzhuang coal block as the research object and found that the permeability showed a decrease-increase-decrease characteristic with increased cover depth.…”

“…Chen et al (2016) took the Zhengzhuang coal block as the research object and found that the permeability showed a decrease-increase-decrease characteristic with increased cover depth. The permeability of coal seams in the Liupanshui coalfield also exhibits a similar change characteristic with the increase of cover depth (Feng et al, 2021). Low permeability makes it difficult for CBM to migrate and produce from the reservoir (Xu et al, 2023).…”

Unraveling the Nanopores Evolution: Chemical Structure Control in Coal during Coalification

“…Large-scale folds are present along the N–S and NE-SW directions, whereas the number and scale of faults remain relatively limited. , The Carboniferous Taiyuan Formation and Permian Shanxi Formation constitute the main coal-bearing formations within this basin. The sedimentary environment of Taiyuan Formation exhibits a marine-continental transitional nature in contrast to the continental characteristics of the Shanxi Formation. , Due to differential subsidence between the northern and southern parts of the basin, coal seams in the southern region are significantly deeper than those in the north, leading to diverse levels of coalification between the two areas. Overall, the vitrinite reflectance ( R o ) of coal exhibits a gradual increase from north to south, displaying a wide variation ranging from 0.44 to 3.20%…”