Evaluation of Log-Derived Cation Exchange Capacity for Water Saturation Estimation

A common method to investigate the hydrocarbon content of a reservoir rock is through the evaluation of wireline logs. Lithology and Porosity logs combined with resistivity log are used to estimate the water saturation of a reservoir. However, several factors affect evaluation of wireline logs. One of such factors is presence of clay in the formation. Since clay mineral introduces additional conductivity, its presence is an extremely perturbing factor in formation evaluation. Many models are developed to account for the extra conductivity of clay minerals during log evaluation. Some of these models attempt to account for the extra conductivity due to clay presence through the introduction of cation exchange capacity (CEC). Usually, CEC is determined through a laboratory study and the process is complicated and tedious.