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

Abstract

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.