Abstract

Interdependence of effective pressure (Pe) and acoustic velocities (compressional Vp and shear Vs) in granular media is often exploited as one of the main rock physical attribute for reservoir characterization. This is particularly relevant for 4D feasibility investigations experiencing simultaneous pressure and saturation changes. Effective pressure changes in carbonate reservoir, however could be trickier because of the change in effective stress coefficient (?) as a result of rock and fluid interaction. Here, we calculated changes in effective pressure in a carbonate reservoir and its overburden shales based on commonly practiced; Terzhagi (1923), the Biot's and Willis (1957) using Biot's coefficient (?), and the experimentally determined effective stress coefficient (?) explained by Todd and Simmons (1972). We found that the calculated effective pressure was markedly different for the three methods, where Pe using ? exhibit values between the two extremes represented by other two methods. We consider this information crucial because it exhibits that correlations between acoustic velocities and effective pressure could change drastically leading to very different interpretations of the changes due to pressure and saturation. It also signifies that experimentally determined effective stress coefficient is crucial to prediction of effective pressure in carbonate reservoirs that generally do not follow compaction trends.