Recoverable potential of coalbed methane in the Wangying-Liujia depression, Fuxin basin, China

摘要

The Wangying-Liujia depression in the Fuxin basin covers a 20 km~2 area and has abundant coalbed methane resource with in-place gas resource 51.81 × 10~8 m~3. Compared with the basins where coalbed methane (CBM) development is successful, the recoverable potential of CBM is evaluated in the investigated district. In the Lower Cretaceous Fuxin Formation, the coal seams are thick (averagely 35.21 m - 42.96 m), the coal adsorption capacity is comparatively high with about 18-34 m~3/t, and the gas content is relatively high (8 m~3/t - 10 m~3/t). Vertical lithological sealing, lateral fault sealing and hydrodynamics are favorable for the preservation of CBM. Thermogenic gas generated at the end of early Cretaceous and Himalayan Orogeny is the main gas source. Secondary biogenic gas generated from the end of the Cretaceous to now increases gas content. All these provide resource basis for CBM development, and the recoverable resources is 15.543 × 10~8 m~3. Though the permeability is low (well test 0.323 md - 0.469 md), coal can be fractured to improve the reservoir permeability. The coal reservoir is saturated gas or oversaturated, and the ratio of critical pressure to reservoir pressure is high (>0.74), which indicates that a little pressure need be decreased to make CBM desorbed from coal matrix and gas production. In one word, there are preferable recoverable potential in Wangying-Liujia depression, especially in the area limited by Piangan F2 fault, Liujia F2 and β_(5-2) dike. At present, 17 CBM production wells with 50 000 m~3 per day operate in this area.