Archie formula, which contains three fundamental parameters (a, m, n), is the basic equation to compute the water saturation in a clean or shaly formation. These parameters are known as Archie parameters. To identify accurately the water saturation for a given reservoir condition, it depends critically on the accurate estimates of the values of Archie parameters (a, m, n). These parameters are interdependent and hence it is difficult to identify them accurately. So we present a new hybrid global optimization technique, where a gradient-based method with BFGS update is combined with an intelligent algorithm called Artificial Bee Colony. This new hybrid global optimization technique has both the fast convergence of gradient descent algorithm and the global convergence of swarm algorithm. It is used to identify Archie parameters in carbonate reservoirs. The results obtained are highly satisfactory. To further test the effectiveness of the new hybrid global optimization method, it is applied to ten non-convex benchmark problems. The outcomes are encouraging.
Keywords Archie parameters • Hybrid global optimization • ABC algorithm • Gradient-based method
IntroductionAn accurate identification of oil reserve in either an undeveloped or a developed reservoir is a significant task for a petro-physicist and reservoir engineer. To calculate the hydrocarbon reserve in its formation, it is required to know the amount of the water saturation. Inaccurate calculation of the amount of the water saturation will lead to a large error in the estimation of the hydrocarbon reserve.Archie equation, which is the underlying foundation for analyzing water saturation in potential oil and gas zones, is commonly used in the calculation of the amount of the water saturation of a reservoir rock, and hence providing an estimate of the initial hydrocarbon reserve of the reservoir. The values of the input parameters of Archie water saturation model in a clean or shaly formation must be estimated as accurately as possible. From field experiments, it is observed that the values of the following three input parameters, the cementation exponent m, the saturation exponent n, and the tortuosity factor a, depend critically on the petro-physical properties of a given rock. Thus, these parameters will take different values for different fields. Furthermore, the values of a, m and n in Archie formula are interdependent. Therefore, it is of critically importance that the estimations of the values of the parameters a, m and n are done accurately (Mabrouk et al. 2013;Michael et al. 2013;Makar and Kamel 2012).There are several techniques available in the literature for estimating the values of Archie parameters a; m and n. A conventional technique is to determine n separately, independent of a and m. This approach may not be valid in real situations, as it may lead to large error in the estimation of the amount of the water saturation (Archie 1942). In (Maute et al. 1992), a data analysis approach is proposed to determine the Archie parameters m; n an...