The Effect of Geological Parameters on the Ratio of Horizontal to Vertical Permeability in Carbonate Reservoirs of Kangan and Upper Dalan Formations

The aim of the present study is to investigate the permeability changes and the ratio of horizontal to vertical permeability in Kangan and Upper Dalan carbonate reservoirs. The effect of geological parameters such as lithology, texture, facies and porosity has been investigated on the amount of horizontal and vertical permeabilities and their changes as well as the ratio of horizontal to vertical permeability in these formations in the central part of Persian Gulf. For this purpose, statistical methods have been used on the data obtained from the study of plugs and microscopic thin sections prepared from the 402 meters of cores. The results showed that the mean value of horizontal permeability is closed to the mean value of vertical permeability in the two types of dolomite and limestone lithology as well as crystalline carbonate and mudstone textures. By increasing porosity without considering other geological factors, permeabilities increase and the ratio of horizontal to vertical permeability decreases. Also, the two factors of heterogeneity and increase in the amount of grains (from mudstone to grainstone texture) are more effective in comparison with micrite and cement in the changes of permeabilities. The presence of grains increases heterogeneity. Horizontal permeability will be higher than vertical permeability in energetic sedimentary environments and in grain-supported facies. It was also observed that dolomitization increases the ratio of horizontal to vertical permeability due to increased mineralogical heterogeneity. The ratio decreases in very high amounts of this mineral (more than 90 percent) due to the homogeneity of rock texture. Therefore, this ratio depends on the degree of heterogeneity of rock, the amount of grain, and lithology. Increasing porosity and permeability, homogeneity of the sample both in terms of the type of mineral forming the rock and in terms of texture, causes closer horizontal and vertical permeabilities.