Geoscience Assessment of Declined Production Rate and Recovery from a Reservoir in “ANDA” Field, Onshore Southwestern Niger Delta

Abstract

Declined production rates in wells producing from common reservoirs are enigmatic and generally viewed as phenomenal in some fields worldwide. The challenge posed by such discordant production trends forecloses the preponderance of totally and partially abandoned production, especially in aging fields. This study assesses possible factors associated with varying well production trends from a common reservoir in a field in the onshore western Niger Delta, by integrating multi-geoscience parameters including formation evaluation, 3D quantitative seismic analyses, paleoenvironmental diagnoses, paleobathymetric studies, and reservoir petrophysics to unravel the complexity of the reservoir. Composite well logs were collected from five wells selected for the study. Gamma-ray and SP logs were combined to delineate the depositional environment of "Heri sand" based on Schlumberger's (1985) log motif classification. The results were applied and found useful to develop an optimum recovery production plan for the study field.  It has been revealed from this study that declined production performances of the Heri sand reservoir are attributed to the deposition of the reservoir in three distinct paleoenvironments under different bathymetric settings within a coeval period. These factors constitute strong influences on the petrophysics of the reservoir which invariably influences’ the production performance of the reservoir.   Having realized the cause of the declined rate of the reservoir in the Anda field, the reservoir can be revitalized by well injection and fracturing.