Depositional Control on Reservoir and Production Performance of a Mature Field Onshore Niger Delta: Implication for Work-Over and Infill Drilling

Abstract

A typical sandstone reservoir in a mature field, onshore Niger Delta has being in production for about thirty (30) years. Initial oil rate in the reservoir was about 300 bopd average on natural drive. The production peaked to an average of about 3000bopd after one year before a decline phase with average oil rate below 600 bopd. Effective well reservoir management (WRM) through workover operations and infill drilling are required to sustain oil production. Hence, sequence stratigraphic analysis of sediment stacking pattern and the possible influence of depositional trend on previous well performance is critical to understanding key attributes of hydrocarbon recovery and production. Hence, the aim of this study is to correlate depositional pattern with production history in order to identify candidates forinfill drilling and workover operations. Approximately 1000 km2 of three dimensional (3D) seismic volumes of post stack and limited angle stacks, 38 well logs, and production data from 12 wells were integrated to evaluate the reservoir of interest. A systematic interpretation methodology involving structural mapping, sequence stratigraphy, well correlation, petrophysical analysis, decline curve analysis, material balance production modeling was used to identify short-term oil gain and infill drilling opportunities. Sediment stacking pattern and depositional trend from logs reveal a strong relationship between parasequence stacking pattern and oil production rate from the reservoir. On gas lift recovery, oil production from retrogradationalsand facies are associated with average rate of 500 bopd, while blocky aggradational sand facies have average rate greater than 1000 bopd. Also, the aggradational sand facies have very good reservoir quality with average porosity and permeability of 0.27 and 4000 mD respectively. Consequently, the analysis of the depositional trend and past production history, has shown potential for short-term oil gain in the wells producing from the aggradational sand facies In conclusion, the observed differential oil production rate between the retrogradational and aggradational sand facies, suggest that there is a strong correlation between depositional pattern, reservoir quality and production performance. Finally, the understanding of the depositional sequence stacking pattern has guided the selection of producing wells as candidates for water shut-off, and opportunities identified for infill drilling and well placement.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018