Optimized Cementation Factor (M) And Tortuosity (A) Values For Fields In The Northern Depo Belt Of The Niger Delta Province Using Nonlinear Regression Method

Abstract

Formation evaluation is key for effective exploitation of hydrocarbon bearing subsurface formation using Petrophysical parameters like porosity, permeability, saturation, net to gross ratio, area and thickness of reservoir for effective estimation of hydrocarbon volume in place. The water saturation gives us a clear indication of hydrocarbon saturation within pore space and over time it has been estimated from model and also determine from the laboratory. Several models have been developed in estimating the formation resistivity factor for sedimentary basins around the world for effective hydrocarbon saturation in place. Archie first developed a model relating the formation resistivity factor, porosity and cementation factor. Over 43 core samples information were collected and acquired from different oil companies operating within the northern depo-belt Niger delta Province, and analyzed using the Excel solverdotnet. A non-linear regression tool was used to obtain the best values for the tortuosity and cementation values for Archie’s equation, with a cementation value of 1.418 and a tortuosity value of 1.4785. The model gave the best minimum sum of square deviation value of 23.10, a correlation coefficient of 0.927was obtained when comparing the modelled and measured formation resistivity factor plot. A model relating the formation resistivity factor and porosity based on Archie equation was developed with the tortuosity and cementation values optimized. The porosity value decreased with depth on a general trend and likely areas of anomaly (increasing depth with increasing porosity) could possibly be as a result of fluid present or trapped liquid within pore space. The cementation values increased on a general trend with increasing depth within the northern depo-belt. The model developed appeared to be more efficient when compared to other models developed for the Niger delta province using the sum of square deviation as a measure for comparism. This modified Archie model can be used in predicting and evaluating formation resistivity factor for effective water and hydrocarbon saturation computation, thereby reducing the risk of over or under estimating hydrocarbon in place for effective planning and decision making by the exploration and production team.