Pressure Effects on Porosity-Log Responses Using Rock Physics Modeling:Implications on Geophysical and Engineering Models as ReservoirPressure Decreases

摘要

Due to changes in fluid properties, porosity log responsesrnchange with pressure, especially for gas/water systems.rnVelocity data (compressional and shear) can be describedrnusing the Krief rock physics model. This model involvesrnrelationships among compressional and shear velocities, rockrnbulk density, elastic moduli of the matrix, shale and fluidrncomponents, shear modulus of the solids, and Biotrncoefficients. Density response is governed by changing gasrndensity as a function of pressure. Neutron response isrncontrolled by hydrogen indicies of the fluids and thernexcavation effect.rnA complete porosity log suite model is presented wherebyrnpseudo porosity logs are calculated as pressure and gasrnsaturation dependent functions.rnMatrix and shale properties are included. Additionallyrnmechanical properties with changing pressure and saturationrnare available.rnFrom compressional travel time and density log responses,rnchanges in synthetic seismograms as reservoir pressure isrnreduced can be calculated. This application has significantrnimplications in the interpretation of 4-D seismic surveys overrnreservoirs undergoing pressure depletion.rnEstimates of changing mechanical properties as functions ofrnsaturation and pressure have a number of engineeringrnapplications, including stimulation design and sand control.rnExamples from a variety of clastic and carbonate reservoirsrnare presented, including intermediate depth hard rocks, deeprnoffshore soft rocks, and shallow onshore soft rocks.