Dynamic modeling of pressure and saturation effects in hydrocarbon producing reservoirs

Abstract

Proper modeling of the sensitivity of the seismic properties due to production effects, as alterations in gas-to-oil saturation and pore pressure, is important in reservoir monitoring. A change in pore pressure affects both the physical properties of the fluid and the elastic properties of the frame. In this paper we combine a fluid flow simulation and rock physics modeling to estimate the overall effects of saturation and pressure changes. Our modeling indicates that with decreasing pore pressure, the change in P-wave velocity is higher for gas saturation than water or oil saturation. Furthermore, for high pore pressure, the rock is more sensitive to fluid properties than for low pore pressure. This is due to the fact that at higher pore pressure there are more compliant pores (of low aspect ratios) which close with decreasing pore pressure. The fluid within the compliant pores have larger effect on the seismic properties than the fluid within the less compliant pores (higher aspect ratio pores). We also show the effect of the varying pore pressure, including both fluid and rock frame properties, on the amplitude versus incidence angle (AVA). This modeling shows that while the the pore pressure affect the general reflectivity, it has only a minor effect on the AVA. In a fluid flow simulation experiment we found that the changes in P-wave velocity was dominated by saturation effects in the early production stage, but that pressure effects dominated in the later stage.