Acoustic and mechanical response of reservoir rocks under variable saturation and effective pressure

Abstract

We investigate the acoustic and mechanical properties of a reservoir sandstone saturated by two immiscible hydrocarbon fluids, under different saturations and pressure conditions. The modeling of static and dynamic deformation processes in porous rocks saturated by immiscible fluids depends on many parameters such as, for instance, porosity, permeability, pore fluid, fluid saturation, fluid pressures, capillary pressure, and effective stress. We use a formulation based on an extension of Biot's theory, which allows us to compute the coefficients of the stress-strain relations and the equations of motion in terms of the properties of the single phases at the in situ conditions. The dry-rock moduli are obtained from laboratory measurements for variable confining pressures. We obtain the bulk compressibilities, the effective pressure, and the ultrasonic phase velocities and quality factors for different saturations and pore-fluid pressures ranging from normal to abnormally high values. The objective is to relate the seismic and ultrasonic velocity and attenuation to the microstructural properties and pressure conditions of the reservoir. The problem has an application in the field of seismic exploration for predicting pore-fluid pressures and saturation regimes.

Computational poroelasticity — A review

“…A plane-wave analysis predicts one shear (S-wave) and three compressional waves: a fast P-wave corresponding to the motion in phase of the solid and fluid phases, and two slow P waves associated with motions out of phase of the two fluids. An extension of this model to include in situ conditions of the single phases and viscoelasticity is given inRavazzoli et al (2003) andRavazzoli and Santos (2005), with a parametric analysis of the influence of effective pressure, abnormal pore pressure and saturation on the phase velocities and quality factors of the different waves.The first numerical evidence of the presence of a second slow wave in porous solids saturated by immiscible fluids is presented inSantos et al (2002) and later inSantos et al (2004b). It is shown that the second slow wave can be detected at ultrasonic frequencies, while at low frequencies is a source of attenuation of the fast waves (the mesoscopic loss).Partially frozen porous media and shaley sandstones are particular cases of fluid saturated porous media when the solid matrix is composed of two weakly-coupled solids Leclaire et al (1994).…”

Changes in the Physical Properties of Hydrocarbon Reservoir as a Result of an Increase in the Effective Pressure During the Development of the Field

“…From the known values of the velocities of propagation of elastic waves in rocks and the density of these rocks, it is possible to calculate the values of such elastic moduli as Young's modulus, Poisson's ratio, shear modulus, and bulk modulus [19] [20]. A decrease in reservoir pressure during field development will not only lead to a decrease in the porosity value but will also reduce the gas permeability values [21] [22]. The performed experimental studies made it possible to obtain the dependence of the gas permeability coefficient (K) on P eff (Fig.…”

Numerical simulation of ultrasonic waves in reservoir rocks with patchy saturation and fractal petrophysical properties

“…Our model is based on a generalization of Biot's theory [5][6][7] for porous rocks saturated by two immiscible fluids [36,39,40]. It takes into account the existence of capillary forces at the pore scale, assuming that each fluid phase has a continuous distribution within the tortuous pore space and that both fluids can flow (funicular saturation regime).…”