Validation of Digital Rock Physics Based Water-Oil Capillary Pressure and Saturation Exponents in Super Giant Carbonate Reservoirs

Abstract

Abstract Digital Rock Physics (DRP) has progressed at a rapid speed since the first pore network models were developed. DRP has now evolved in to a new discipline and essentially involves use of X-ray CT scanning in micro and Nano-CT to capture the 3D network structure of representative reservoir rock types. The proliferation of the technique with powerful computers and robust network modeling means one can rapidly determine various Special Core Analysis (SCAL) properties that form the basis of reservoir characterization parameters: porosity, permeability, formation factor, cementation and saturation exponents, capillary pressure, relative permeability and elastic properties. A comprehensive DRP based validation study was performed on reservoir core plugs which had undergone rigorous Petrophysical SCAL at representative pseudo reservoir conditions. The objective was to assess the use of DRP in determining such data, and quantifying the relevant uncertainties. The plugs were chosen from two super giant carbonate reservoirs in the Middle East. The laboratory tests comprised cementation exponent ‘m’ at a range of pressures, water-oil capillary pressure (Pc) and electrical resistivity index (RI) tests at reservoir temperature and reservoir overburden pressure using specially designed Porous Plates. Capillary pressure under primary drainage and imbibition conditions, replicating reservoir conditions were established using multi-phase flow simulations on the pore network representation of the 3D rock model. Similarly, the cementation exponent ‘m’ was calculated using a solution of the Laplace equation with charge conservation; the equations were solved using a random walk algorithm. DRP based primary drainage and imbibition saturation exponents ‘n’ were also computed for cores samples of different reservoir rock types. The results were then compared to measured SCAL data, and validation criteria established along with possible uncertainties. DRP is extremely promising in generating fairly accurate SCAL parameters very fast from existing cores.