Characteristics of in situ stress and its influence on coal seam permeability in the Liupanshui Coalfield, Western Guizhou

Abstract

Abstract The current in situ stress regime is of great significance to the exploration and development of coalbed methane (CBM). In this study, the vertical stress (σV), maximum horizontal principal stress (σH), and minimum horizontal principal stress (σh) in the Liupanshui Coalfield were studied. Variations of the maximum and minimum envelopes and trend lines of the lateral pressure coefficient (λ) with depth were obtained, and the non‐monotonic decrease of permeability with burial depth was determined. On this basis, the effect of in situ stress on the coal reservoir permeability was evaluated. The results show that the average vertical stress gradient of the main coal seam in the Liupanshui Coalfield is 0.024 MPa/m. Generally, there are two stress regimes of σH > σV > σh (44.23%) and σV > σH > σh (46.15%); σH > σh > σV accounts for a smaller proportion (9.62%), and only occurs in relatively shallow coal seams ( σV > σh is dominant; σV > σH > σh is dominant between 600 and 800 m; and between 800 and 980 m, the coal reservoir is affected by both σH > σV > σh and σV > σH > σh, representing a transition zone between the two stress states. With the increase of burial depth, the permeability of the coal reservoir shows a complex non‐monotonic decline, and the variation of the permeability of the coal reservoir differs under the influence of different stress regimes. Further analysis shows that under the background of stress regime transformation, permeability is mainly affected by the stress value, horizontal principal stress difference, stress regime, and coal cleat, indicating that in situ stress is the main controlling factor of coal reservoir permeability in the Liupanshui Coalfield.

Keywords

• coalbed methane
• in situ stress
• Liupanshui Coalfield
• permeability
• synthetic density logging