Integrated Multi-Disciplinary Approaches to Predict Fluid Contacts in a Partially Appraised Field - A Case Study of Yoko Field in Niger Delta

Abstract

The need for the estimation or evaluation Original Oil Water Contact (OOWC) prior to reservoir development is very pertinent to appropriate well placement within a reservoir. Oil and gas water contacts are determined via various sources including but not limited to Petrophysical logs, RCI data, Reservoir Simulation, Fault Seal Analysis (FSA), Quantitative Interpretation and Hydrocarbon Column Analogues. This paper focuses on an integrated approach of predicting OOWC using some of the methodologies highlighted above. The study explores the feasibility of further oil development in the Yoko field to grow production and increase reservoir ultimate recovery. Three wells have been drilled so far in the field and none encountered OOWC. Three (3) key reservoirs account for about 69% of the total field hydrocarbon resource but with significant uncertainty in fluid contacts column (about 132ft) and wide static and recoverable volume range. An effective and commercially viable field development plan is premised on the reduction of contact uncertainty. In order to narrow the contact uncertainty, multidisciplinary approaches has been used and they include (a) Petrophysical Logs (b) Structural Spill Point (c) Analogue oil column studies from adjacent fields (d) Fault Seal Analysis (FSA) to determine maximum column in the reservoir (e) Quantitative Interpretation (QI) and (f) Dynamic simulation. The analogue oil column from neighbouring field was used to benchmark the possible oil column for Yoko field. FSA which relies on the sealing capacity of the faults due to the amount of mechanical mixing from fault throws was also considered. The upper and lower limits of the fluid contacts were estimated from acoustic impedance amplitude plotted against depth. The reservoir dynamic models was also history-matched (7 years of production history) to calibrate and ascertain the limits of the possible contacts for the reservoirs. The result of the evaluation is a significantly reduced volumetric uncertainty range. In one of the reservoir, there was a progressive reduction in fluid column uncertainty from 232 ft to 90 ft. In general 55 - 85% reduction of the initial uncertainty was achieved. This reduced range enabled a commercially viable Development Plan for the field.