A new velocity-pressure-compaction model for uncemented sediments

Knowledge of the pressure dependence of rock properties is useful for a wide range of earth science problems, especially related to pore pressure changes caused by fluid injection or withdrawal, as often occurs in groundwater, hydrocarbon and CO2 sequestration reservoirs. A long-standing problem is that theoretical models of velocity-pressure response often do not match laboratory measurements, and alternately, empirical regressions fit to such data do not extrapolate accurately to wider pressure ranges since they have little or no physical basis. Accurate determination of the dry rock frame properties at low effective pressure is a key aspect of the problem, particularly when ultrasonic laboratory measurements are not available in this pressure range. We present a new model to describe the pressure sensitivity of the bulk and shear moduli for uncemented sedimentary rocks. Our model incorporates effects of sedimentary compaction and critical porosity, including a relationship to account for porosity and density change with pressure. The model is tested on laboratory measurements for various rock samples and fits well over a wide range of pressures. The new velocity-pressure model should be useful for improved prediction and interpretation of pressure-dependent rock properties and seismic data.