Abstract
Thin oil rim reservoirs are predominantly those with pay thickness of less than 100 ft. Oil production challenges arise due to the nature of the gas cap and aquifer in such reservoirs and well placement with respect to the fluid contacts. Case studies of oil rim reservoir and operational properties from the Niger-Delta region are used to build classic synthetic oil rim models with different reservoir parameters using a design of experiment. The black oil simulation model of the ECLIPSE software is activated with additional reservoir properties and subsequently initialized to estimate initial oil and gas in place. To optimize hydrocarbon production, 2 horizontal wells are initiated, each to concurrently produce oil and gas. Well placements of (0.5 ft., 0.25 ft. and 0.75 ft.) are made with respect to the pay thickness and then to the fluid contacts. The results show that for oil rim with bigger aquifers, an oil recovery of 8.3% is expected when horizontal wells are placed at 0.75 ft. of the pay thickness away from the gas oil contact, 8.1% oil recovery in oil rims with larger gas caps with completions at 0.75 ft. of the pay zone from the gas oil contacts, 6% oil recovery with relatively small gas caps and aquifer and 9.3% from oil rims with large gas caps and aquifers, with completions at mid-stream of the pay zone.
Highlights
The peculiarity of thin oil rim reservoirs irrespective of the depletion strategies used as described by Masoudi (2013) is such that at onset of production high water cuts and gas oil ratios are experienced
The results show that for oil rim with bigger aquifers, an oil recovery of 8.3% is expected when horizontal wells are placed at 0.75 ft. of the pay thickness away from the gas oil contact, 8.1% oil recovery in oil rims with larger gas caps with completions at 0.75 ft. of the pay zone from the gas oil contacts, 6% oil recovery with relatively small gas caps and aquifer and 9.3% from oil rims with large gas caps and aquifers, with completions at mid-stream of the pay zone
A conventional method of selecting well placement relative to fluid contact is done by viewing the section of the models with high oil saturation and varying the placements based on the pay thickness of that particular model and multiplying by some factors
Summary
The peculiarity of thin oil rim reservoirs irrespective of the depletion strategies used as described by Masoudi (2013) is such that at onset of production high water cuts and gas oil ratios are experienced. This is due to the nature of oil rim reservoirs with gas caps and aquifers larger in volume and size than the oil rim. Size of gas cap and aquifer, well placement and length, pay thickness and horizontal well placement are factors that affect oil rim productivity. The effectiveness of horizontal wells over vertical wells in normal reservoirs has been extensively studied
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