Rock Physical Models Involving The Influence Of The Pressure

With the intensify of oil and gas exploration,deep,tight and unconventional reservoirs have gradually become the new focus of geophysical research.These reservoirs are more likely to have abnormal pressure conditions,which makes their geophysical properties significantly different from those of conventional reservoirs.To solve this problem,it is necessary to build new rock physical models and propose new pressure prediction processes on the basis of the results of rock physical researches involving pressure effects.In this paper,rock physical models for deep shale gas reservoir and tight sandstone reservoir involving the effect of effective pressure are proposed respectively.The former is based on the pore space stiffness theory which describes the quantitative relation between the effective pressure and pore space stiffness,and the latter is based on the relation between effective pressure and the aspect ratio of compliance pores in tight sandstone reservoir.Both of the two models are proved correct and reasonable by comparing the calculated elastic parameters and velocities with the real data.Then the effect of minerals,porosity,pore fluids and effective pressure on the moduli of shale gas reservoir are analyzed utilizing corresponding rock physical model to clarify the microcosmic controlling factor of the macroscopic moduli of shale gas reservoir.The effect of effective pressure on the aspect ratio of compliance pores is also analyzed utilizing the rock physical model for tight sandstone reservoir.Both of the two rock physical models can give reasonable results in practical shear wave velocity prediction.On the basis of rock physical analysis,two kinds of effective pressure seismic pre-stack prediction methods are proposed.The statistical rock physical relations between the bulk modulus,shear modulus,density,effective pressure,porosity and pore fluids are used to predict the effective pressure of deep shale gas reservoir by Monte-Carlo simulation and pre-stack inversion.Considering the uncertainty of statistic rock physical relations,a quantitative relation between the seismic reflection coefficient and the effective pressure,shale content,porosity,density and the properties of pore fluids is built and a new reflection coefficient equation on the basis of the rock physical model involving the effect of effective pressure is derived.Then the effective pressure is predicted by applying this reflection coefficient equation to the probabilistic statistical inversion process.Both of the methods are verified by real data application and analysis.