Pore pressure prediction using the seismic velocity produced by multi-attributes analysis in carbonate reservoirs

Abstract

There are various methods for pore pressure prediction in hydrocarbon (HC) reservoirs which have their advantages and disadvantages. Herein seismic velocity was used to evaluate the pore pressures in one of the Iranian HC reservoirs along with its creation mechanisms. Seismic velocity was derived by seismic multi-attributes analysis method, to study interval velocities. The overburden pressure cube was estimated from the density cube. Thereafter effective pressures were obtained with Terzaghi equation at well locations by using well pressure tests (RFT) and overburden pressures. The velocity-density cross-plots represent that disequilibrium compaction is the main mechanism of pore pressure creation. Thus, an initial relationship was obtained by fitting of the effective pressure and seismic velocity data and it was then used for determining the calibration coefficients required for conversion of seismic velocity cube to the effective pressure cube. Finally, the effective pressure cube was converted to pore pressure cube by Terzaghi equation. The obtained results with high consistency, high correlation coefficient and low mean squares error indicate that pore pressures could be perfectly predicted by multi-seismic attributes method in carbonate formation before drilling. Moreover, comparative studies of the pore pressure cube estimated from the proposed model indicates that the pore pressure model obtained by multi-attribute analysis is precise enough to separate the reservoir layers from its upper and lower sections. This predicted pore pressure can be used to evaluate the drilling risk and also to estimate the required mud weights.