Permeability Sandstone Effective Stress Equation And Stress Sensitivity Of Northern Hubei TIGHT

The reasonable exploitation of low permeability reservoir rocks entails the correctunderstanding of stress sensitivity of reservoir rocks to which the key rests with thedetermination of effective stress, but unfortunately no generally accepted achievementshave been ever obtained on effective stress and stress sensitivity till now. Started frommicrocosmic characteristics of rocks, this thesis, with E-bei low permeability sandstonebeing the sample, is aimed at exploring effective stress law for permeability of reservoirrocks and stress sensitivity including its related influence upon productivityexperimentally and theoretically with the knowledge of rock mechanics, fluidmechanics and porous flow mechanics, etc. The main achievements and findings arelisted as follows:（1）By means of Rock Slice Micrograph、Scanning Electron Micrograph andMercury Penetration, microcosmic characteristics of25rock samples are analyzed.（2）By summarizing some common effective stress theories for permeability, thevaried range and characteristics of the effective stress coefficient are obtained in theory.（3）Laboratory experiments with the improved experimental devices andmodified factorial designs were performed to determine the effective pressure law. Wealso proposed the response surface method, which is suitable to analyze theexperimental data and by which we obtained the varied range and characteristics of theeffective stress coefficient experimentally.（4）Based on the microcosmic characteristics of rocks and the effective stresstheories for permeability, the change law of the permeability-effective-stress coefficientand deformation mechanism of E-bei low permeability sandstone are analyzed.Simultaneously, the reasonability of the permeability-effective-stress coefficient isverified based on the concept of effective stress（5）By analyzing the relations between the effective stress and the permeability ofE-bei low permeability sandstone, the function between effective stress and thepermeability is obtained.（6）Conventional stress sensitivity experiments of E-bei low permeabilitysandstone are completed according to the trade standard for effective stress sensitivity,and at the same time, the stress sensitivity of E-bei low permeability sandstone isevaluated by different effective stress theories and stress sensitivity evaluation methods.（7）Combining with different effective stress theories for permeability and therelations between the effective stress and the permeability, the relationships of the porepressure and the permeability under different effective stress theories are established.（8）By introducing the concept of pseudo-pressure for varied permeability and under guidance of porous flow mechanics, both differential equation for plane radial gasstable flow and mathematical model with varied permeability and the productivityformula with pseudo-pressure form are established.（9） In view of the relations between permeability and pore pressure and theproductivity formula of pseudo-pressure form, the productivity formula under high andlow pressure is derived and the impact of permeability-stress-sensitivity on theproductivity is analyzed with different effective stress theories.The knowledge about stress sensitivity of reservoir rocks is deepened through theanalysis both in theory and experiment in our research, which will provide thetheoretical evidence in respect of efficient gas exploration.