The Preliminary Study On Elementary Theory And Methods Of Rock Hydraulic Fracturing

Rock hydraulic fracturing was a new technology which appeared in petroleum and natural gas industries in 1950s.while hydraulic fracturing can destroy engineering structures even cause disasters such as mine water irruption, water yield of deep-buried cavities, dam body and body foundation hydraulic fracturing of high dams and pumped storage power stations and inducing sliding of high slope affected by ground water permeation and so on. All of these belong to the problems of hydraulic fracturing. So, it is a considerable topic to know the mechanism of hydraulic fracturing and to avoid or minimize its damages.On the basis of existing hydraulic fracturing theories and according to the test results of high pressure permeability of Tianhuangping pumped storage power station, the happening, development and fracture permeability during hydraulic fracturing will be researched by the theories and methods of rock mechanics, fluid mechanics, groundwater dynamics and elastic fracture mechanics. The conclusions as follows:(1) In elasto-plastic mechanics, rock failure modes is given on the basis of strain to study the discrimination criteria and thinks that there are two types for rock failure: tension and shear. Under the different loading considerations and constraint conditions, rock failure happens with one type (tension or shear) or two types concurrence. Through case calculation, the fracture propagation should belong to crack â…¡.(2) The analysis to test results of high pressure permeability and different P^Q relationship curves shows that critical head pressure really exists in the relative closing cracks but not in certain aperture cracks. With the increase of head pressure, rock permeability becomes more sensitive. But in the continuing head pressure, rock available hydraulic slope value trends to decrease.(3) The sensitivity analysis to fracture aperture in hydraulic fracturing showsthat the crack increment â–³b* has good linear relationship with σ₃ and water pressure P, but with σ₁ crack, basic friction angle φb, β (the angle between long axisdirection of crack and maximum principal stress), the linear relationship is not obvious.(4) The analysis to hydraulic fracturing process through mode PKN and mode KGD shows that the mode has certain precision in the beginning phase of fracture. But in the growing phase, the calculation results of practical modes are different with fact.