Pore Pressure (Gradient) Mechanism Of Rock Hydraulic Fracturing

Rock hydraulic fracturing plays an important role in a large number ofengineering practices. Therefore, it is much necessary to carry out researches on thecommon issue of many rock engineering-pore pressure mechanism. In this thesis, asthe author is with a large number of tests and field experience, rock pore structure isstudied as the research object for the process analysis of the rock microstructurefracture and damage under the function of the permeability pore pressure. Under theeffect of pore pressure, experimental studies are carried out for hydraulic fracturemorphology and fracture parameters. Then the pore pressure mechanism and thetheoretical application are analyzed.According to a large number of hydraulic fracturing tests and field practices andwith the pore structure of rock taking into consideration, a brief analysis of theformation of macro-hydraulic-cracks from micro-hydraulic-crack propagation is doneunder the pore pressure gradient. Otherwise, the main factors affecting hydraulicfracturing: mechanical properties of rocks, rock stress environment, water hydraulicfracturing drilling process as well as drilling layout and so on are studied. Thus, asingle-factor-affected test is done to study the effect of rock pore pressure on thehydraulic fracturing, while the hydraulic fracture morphology, water pressure curveand acoustic emission signals as well as the fracturing pressure are analyzed. Theresults show that: the fracturing pressure of rock hydraulic fracturing under the samestress conditions increases with the rock pore pressure.On the basis of others’ researches, the seepage mechanics and others are adoptedto analysis rock destruction of hydraulic fracturing under the influence of porepressure penetration. With the rock pore pressure and seepage taking intoconsideration, a fracturing pressure calculation model of hydraulic fracturing isestablished. From the perspective of the water and gas displacement, the relationshipbetween the microstructure destruction of rock and the macroscopic hydraulic crackpropagation and penetration zone expansion of hydraulic fracture is analyzed. Finally,the applicable conditions and the advantages and disadvantages of the model areanalyzed.