水力压裂缝延伸方向分析及其应用

ANALYSIS AND APPLICATION ON FRACTURE PROPAGATION DIRECTION OF HYDRAULIC FRACTURING

水力压裂是油井增产通常采用的一种措施.对地层压裂时产生的裂缝形态、走向进行了阐述;根据井孔周围应力集中现象,利用地层破裂机理分析了发育有直劈裂缝的地层压裂时人工裂缝产生条件,定量分析了压裂缝延伸与地层应力状态、天然裂缝走向、施工压力、岩石抗张强度的关系.并在沙南油田梧桐沟组油藏开发生产中,应用该方法来判断人工裂缝和天然裂缝以及预测它们的延伸状况得到了非常好的验证.

Natural fracture and artificial fracture are all controlled by stress field. Oil reservoir development design and project of oil reservoir transforming and fracturing design and design of horizontal well are connected with natural fracture and artificial fracture and direction of fracture propagation. Fracturing fracture can be forecasted by researching natural fracture and analyzing character of stress, what's more, it can guild the oil field being explored reasonably and increasing measure being made. Under the condition that there is not crevice in oil formation, strike of fracturing fracture lies on direction of the most horizontal stress, and style of fracturing fracture lies on the value of vertical and horizontal stress. It produces vertical fracture if the state of crustal stress is σv>σH>σb and σH>σV>σh.-The strike of fracture is the direction of the most horizontal stress. It produces level fracture if the state of crustal stress isσH>σh>σv The direction of fracturing fracture propagation is relatively complexity while there is crevice in oil formation. The pattern of fracture propagation depends on not only the angle position of horizontal stress and crevice but also the value of horizontal stress and working pressure. The theory and practicing made it clear. It come down to the mechanics character of rock and state of crustal stress and style of crevice and fracture strike etc. The fracturing liquid pushes along the natural fracture, while the working pressure is between the sum total of stress and the least horizontal stress. The sum total of stress equals to the axial stress plus the rocky tensile strength. The hydraulic fracture is produced when working pressure is greater than the sum total of stress. Since the stress of sum surrounding is disappeared, pattern of the fracture expending lie on the state of stress on the face of crevice. There is NNE and NEE crevice in Shanan oil reservoir, direction of the horizontal stress is about N11.5°W. There is different crevice in different part of oil reservoir. The new fracture is produced when the working pressure is greater than fracturing pressure. The new fracture is not produced when the working pressure is smaller than fracturing pressure. Even though existing these conditions, the fracturing liquid push along the natural fracture first.