A New Cementation Factor Correlation in Carbonate Parts of Oil Fields in South-West Iran

Petrophysical parameters such as porosity, water an d oil saturations, formation resistivity factor, et c. describe the storage capability of the porous media or the capacity of rocks to hold fluids. The modified Archie’s equation � � � � ��. � � /�� . � � , also called the saturation equation, is used to determine the water saturation. Archie’s parameters , namely � , �, and �, are sometimes assumed constant to simplify petrophysical measurements. Bu t these parameters are not constant, particularly in heterogeneous reservoirs. Inaccurate estimates o f these parameters can cause significant errors in the calculation of water saturation when using Arch ie’s equation and lead to discrepancies between log interpretation and production test results. The re are many factors affecting cementation factor ( � ) such as porosity, pore throat size, type of rock gr ains, type and distribution of clay content, degree of cementation, and overburden pressure. In the presen t paper, the results of electrical resistivity experiments are used to derive a new cementation fa ctor correlation which can be applied to carbonate parts of Asmari and Sarvak formations located in so uth-west Iran. In Iran, the cementation factor is traditionally measured by Shell formula or is assum ed equal to 2 to avoid difficulty. In the new formula, � increases with increasing porosity; however, in th e Shell formula, � decreases with increasing porosity especially in the low porosity ranges, which is in disagreement with the current