Application of Experimental Design Techniques to Unravel Sub-Surface Complexity in Gravity Assisted Water Injection Project in the Niger Delta

Abstract A pilot Gravity Assisted Water (Dumpflood) Injection scheme was executed in 1997 in X1 reservoir of a Niger Delta field ‘Alpha’. Post performance analysis showed that the injection has been successful in maintaining good pressure support and in supporting future recovery from the reservoir. However due to X1 reservoir uncertainities and variabilities in Water Dumpfllod injection rates, expected range of future recoveries could not be quantified. This paper presents a case study of the application of Experimental Design (ED) to understand the historical performance and future predictions of a gravity-assisted water injection in ‘Alpha’ X1 reservoir. A range of static and dynamic models were constructed and experimental design methodology was used to map out the key uncertainties and to develop a range of history matched models which were used to assess the range of future hydrocarbon resource volumes likely to be produced from the reservoir under the existing development concept. In addition to the traditional sub-surface uncertainties, this project also assessed water injection rates as an additional uncertainty that significantly impacted the future recoverable from the reservoir. Experimental design was used to create a range of history matched dynamic models of a dumpflood development that captures the key uncertainties in the reservoir. Ten history matched models were developed and carried to the prediction phase of the study. A voidage replacement development strategy was applied and all ten models were used to predict the reservoir performance over a range of water injection rates. The outcome of the analysis was used to update recoverable volume estimates and to develop a well and reservoir management strategy for the reservoir.