The effects of heterogeneity on pressure derived porosity changes in carbonate reservoirs, Mishrif formation in SE Iraq

Abstract

The effects of overburden pressure on porosity and permeability are often neglected in formation evaluation, while it has important influences on reservoir storage and flow capacities. The present work focuses on the effects of overburden pressures on porosity changes in carbonate Mishrif Formation, Iraq. The porosities of 73 core plug samples have been measured under 4 overburden pressures. Winland Equation was reconstructed using the pore throat size of 165 samples which were measured by mercury injection. The Winland, FZI, Lorenz, and porosity data ranges rock typing methods have been used to manage the heterogeneity. Winland recognized as the most suitable method, because porosity, permeability and pore throat sizes are considerably affected by overburden pressures. Two factors of porosity and permeability are affected by overburden pressures in FZI method. In data grouping using ranges of porosity, the effective factors reduce to one. Lorenz method groups successive data and so is not effective for grouping the samples. Results showed that the best methods of managing heterogeneity for overburden tests are Winland, FZI, porosity data range, and Lorenz method, respectively. These new findings can help for better understanding of porosity–pressure relationships with respect to the reservoir heterogeneity.