Reservoirs quality assessment and application of capillary pressure models in understanding saturation relationship in ‘Keyz’ field, Niger Delta Basin, Nigeria

Abstract

Semi-empirical models have been employed alongside capillary pressure information obtained from core plugs to predict capillary pressure, for the analysis of reservoir saturation occurring at interface that separates two or more immiscible fluids. These models cannot independently predict the interaction of more than one phase fluid when the fluids are immiscible in the absence of core information. As such, this limitation has inspired the formulation of optimized models that can be used to describe the interaction of immiscible fluid within reservoirs in the absence of core capillary information. This study is focused on applying two models (Wu's and Goda's model) for predicting capillary pressure using data from ‘Keyz’ well, Niger Delta Basin in order to describe the reservoir saturation trend and consequently to discuss conformity and disparity in the saturation trend as revealed by the respective models. Two reservoirs (Y and Z) were utilized for this study and the results were presented as histograms, charts, curves and well sections. The findings from this work revealed that the reservoirs have high net-to-gross ratio (0.86–0.90), good effective porosity (25–27%), good permeability (>500 mD), low volume of shale (<10%), relatively high hydrocarbon saturation (50–75%) and water saturation of 25–50% for reservoir Y and Z. From the poro-perm plot generated it is observed that the dominant lithofacies (sandstone) within this reservoir has low degree of cementation, good porosity and permeability which is indicative of reservoirs that can house economic quantity of hydrocarbon. The results of the capillary pressure derived reveals that, reservoir Y has capillary entry pressures of 0.02 and 1.5 PSI and maximum capillary pressure of 2.7 and 35 PSI as observed for Wu's and Goda's model respectively. For reservoir Z, Wu's model is observed to have an entry pressure of 0.03 PSI and a maximum capillary pressure of about 2.75 PSI while Goda's model has entry pressure of 1.23 PSI and a maximum capillary pressure of 35 PSI. For both reservoirs, Wu's model reveals a discontinuous trend in saturation and a sharp L-shaped capillary pressure curve while no visible discontinuous trend was observed for Goda's model however, it has a steeply L-shape curve. These models proved valuable in describing the saturation trend of the reservoirs utilized for this study.