TOUGH-FLAC^3D热流固耦合模拟煤储层水力压裂过程

A coal-bed methane reservoir of the Anze Block, southern Qinshui Basin, is the chosen study area. The research developed a simulator linking TOUGH with FLAC^3D to analyze thermo-hydro-mechanical coupling during hydraulic fracturing in the coal reservoir, and then to reveal the rules of fracture propagation and bed-penetrating under the constraint of multiple fields. The results show that hydraulic fractures that propagate along the pre-existing natural fracture's direction, tend to occur when the two fractures intersect with a small approaching angle; otherwise, hydraulic fractures will propagate along the direction of the maximum horizontal principal stress. Due to the distinctive difference of rock mechanical properties between coalbed and its roof and floor beds, and high density of micro-fractures in the coalbed, the pressure in the coalbed propagates faster than that in the roof and floor rocks seen from vertical profiles, which results in two relatively higher pressure zones near the boundaries from coalbed to roof and coalbed to floor rocks respectively. In addition, compared with the shallowly buried coalbed, the deeply buried one is subjected to plastic deformation under an existing bigger in-situ pressure. The major reason for roof/floor fracture penetration is the occurrence of flow pressure accumulation, caused by the relative small leak-off rate of fracturing fluid and relatively bigger vertical stress than that of the shallow bed. The results of sampled coal experiments and fracturing curve analysis verify the accuracy of the simulation.