地应力与天然裂缝对煤储层破裂压力的影响

Effects of crustal stresses and natural fractures on fracture pressure of coal reservoirs

以山西晋城矿区为研究对象,运用有限元模拟方法,计算不同地应力条件下煤岩的破裂压力.分析水力压裂过程中地应力、天然裂缝对煤岩破裂压力的影响.无天然裂缝时,破裂压力随3倍最小水平主应力与最大水平主应力的差值增大而线性增大.有天然裂缝时,天然裂缝降低了煤岩的抗张强度,使压裂裂缝的启裂和延伸脱离井筒周围局部地应力的影响,破裂压力随主应力差减少而增大;天然裂缝与最大水平主应力的夹角在30°左右时,破裂压力最小,大于30°时,破裂压力随夹角的增大而增大;破裂压力随垂直于天然裂缝的正应力的增大呈指数形式变大.

Selected Jincheng mining area as a research object in Shanxi Province, used the finite element simulation method, calculated coal fracture pressure in different crustal stress conditions, and analyzed the effects of crustal stresses and natural fractures on fracture pressure. Without natural fractures, fracture pressure linearly increases with the increase of the difference among triple minimum horizontal principal stress and maximum horizontal princi- pal stress. In naturally fractured coal, the natural fractures can cause the decrease of tensile strength. The local crustal stresses near a borehole may not affect crack initiating and propagating. Fracture pressure increases with decreasing principal stress difference. When the angle between a natural fracture and the maximum horizontal principal stress is about 30°, fracture pressure reaches the minimum value. The angle exceeding 30°, fracture pressure increases with the increase of the angle. Fracture pressure exponentially increases with increasing normal stress perpendicular to a natural fracture.