Effect of Fracture Width and Fluid Rheology on Proppant Settling and Retardation: An Experimental Study

Abstract

Abstract Due to changes in fluid properties, porosity log responses change with pressure, especially for gas/water systems.Velocity data (compressional and shear) can be described using the Krief rock physics model.This model involves relationships among compressional and shear velocities, rock bulk density, elastic moduli of the matrix, shale and fluid components, shear modulus of the solids, and Biot coefficients.Density response is governed by changing gas density as a function of pressure.Neutron response is controlled by hydrogen indicies of the fluids and the excavation effect. A complete porosity log suite model is presented whereby pseudo porosity logs are calculated as pressure and gas saturation dependent functions. Matrix and shale properties are included.Additionally mechanical properties with changing pressure and saturation are available. From compressional travel time and density log responses, changes in synthetic seismograms as reservoir pressure is reduced can be calculated.This application has significant implications in the interpretation of 4-D seismic surveys over reservoirs undergoing pressure depletion. Estimates of changing mechanical properties as functions of saturation and pressure have a number of engineering applications, including stimulation design and sand control. Examples from a variety of clastic and carbonate reservoirs are presented, including intermediate depth hard rocks, deep offshore soft rocks, and shallow onshore soft rocks. Introduction Krief (1989) and Gassmann (1951)/Biot (1956) have independently developed rock physics models to account for velocity changes as gas saturation varies.A comparison of the two models, expressed in petrophysical terms, has been published by Holmes, et al (2004).Inherent in both models are effects of pressure on velocity responses, as a function of changing bulk moduli of the contained fluids (particularly gas).Pressure effects on density and neutron log responses in gas/water systems are a consequence of changing gas density and hydrogen indices. In this paper, the Krief and Gassmann models are expressed in petrophysical terms and extended to include neutron log responses.Pseudo logs are calculated for ranges of gas/water combinations and pressure:Acoustic compressionalAcoustic shearDensityNeutron These in turn can be used to estimate mechanical properties. The porosity modeling assumes an isotropic medium, and that porosity does not change with pressure variations.