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. Inorder to narrow the contact uncertianty, a multidisciplinary approach has been used and they include (a) Petrophysical Logs (b) Analogue oil column studies from adjacent fields (c) Fault Seal Analysis (FSA) to determine maximum column in the reservoir (d) Quantitative Interpretation (QI) and (e) 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 132 ft to 11 ft. In general 55 – 92% reduction of the initial uncertainty was achieved. This reduced range enabled a commercially viable Development Plan for the field.

Managing uncertainties during subsurface modelling in brown field re-development requires robust identification and quantification of impact of the underlying uncertainties. Within a given cycle of integrated reservoir modelling, a modelling strategy can only be defined based on associated uncertainties and development options. This paper focuses on using the Design of Experiment to screen and quantify the impact of uncertainties and evaluate development outcomes in a brown field.The paper details steps taken to identify and quantify subsurface uncertainties in a multi stacked reservoirs that could impact development options. The overall development strategy was to: (a) Introduce artificial lift and offtake management to keep existing wells flowing, (b) Install gas lift supply lines from new gas-lift skid at the flowstation to existing wells requiring gas-lift, (c) drill and complete additional wells using existing locations, (d) hook up the new wells to existing remote manifold and route to flowstations via existing bulklines. To access the impact of uncertain parameters and its ranges of uncertainty were identified and quantified based on current understanding of the reservoirs. The PlackettBurman Design of Experiment was used to screen each parameter using the Tornado and/or Pareto Plots.The key uncertainties (heavy hitters) identified from the screening stage were carried forward to develop a Response Surface Model (RSM) using Box-Behnken experimental design in order to sample the full uncertainty space associated with each reservoir. The probability distributions of In-Place and cumulative production were generated using Monte-Carlo analysis and estimate of the Proved, Probable and Possible volumes and ultimate recovery were obtained (part of methodology)From the study results, the feasibility for further oil and gas development based on 3D reservoir simulation with several development scenarios and options were evaluated. Results of the deterministic possible outcomes were used to identify specific cases that closely matched the Proved, Probable and Possible volumes from the Monte-Carlo distribution. Model provides tool for better well and reservoir management.

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.