Handling Production-Data Uncertainty in History Matching: The Meren Reservoir Case Study

Abstract

Summary History matching reservoir performance ordinarily implies adjusting geologic and rock-fluid flow properties until a satisfactory match is attained between the observed and model responses. Property adjustments inevitably imply a trial-and-error approach. Regardless of the approach used in any study, we presuppose the integrity of observed data. Unfortunately, measurements of gas and water do not have the desired precision when oil is the primary fluid of interest. For instance, when gas is flared, the quality of metering suffers. In some operations, withdrawal of small samples of a three-phase mixture near the wellhead becomes the sole basis for establishing water content in a production stream. These practices often introduce large uncertainty in the reported data of all three phases. This paper explores how we dealt with some of these issues while attempting to match 30-year performance in the Meren field in offshore Nigeria. Results show that production data affected by wellbore mechanical problems can be diagnosed with log-log type curves. Furthermore, this work shows that discerning water cut from wellhead samples is prone to errors, and issues with wellbore flow calibration can lead to large uncertainties in performance prediction. Identification of various issues helped mitigate the risks, leading to successful infill wells as testified by their production performance.