Innovative Subsurface and Surface Optimization of Well Placement in Stacked Heavy Oil and Light Oil Pools: A Case Study

This paper illustrates innovative application of integrated subsurface and surface optimization of well placement in stacked heavy and light oil reservoirs in M field, Sudan. Upper B reservoir is massive bottom water heavy oil reservoir with burial depth of 700 m. Well productivity was low, 200 to 300 BOPD under CHOPS, resulting in denser well spacing and extensive deployment of flowlines, de-sanding equipment etc., often forcing vertical infill wells drilled as directional wells due to footprints limitation. Lower AG reservoir is stratified light oil and gas reservoir with burial depth of 1500-2200 m, overlapped with above B reservoir to some extent. The operator intended to drill infill wells to grow production, whereas two major well placement challenges are confronted: 1) Integration of facilities and subsurface proposed well locations to reduce drilling costs; 2) Integration of lower AG and upper B reservoirs to maximize recovery; Well placement strategy has been optimized by following approaches: 1) firstly propose infill well locations based on history matching and scenarios screening; secondly input well locations into facilities maps and identify footprint contradiction; thirdly revise well locations to be compatible with facilities and input back into simulation to justify cumulative oil loss within reasonable range; 2) combine best locations in B and AG reservoirs and directionally deepen into AG reservoir to reduce unnecessary vertical wells in AG reservoir. Altogether 21 optimized well locations were put forward, totally avoiding 5 footprint-limited directional drilling and reducing 3 vertical wells in AG reservoir by directionally deepening into AG reservoir. Drilling costs were greatly saved and speed up field production growth process during 2010-2011. Conclusions drawn from successful well placement optimization were: 1) subsurface and surface optimization greatly contributed to drilling cost saving; 2) stacked AG and B reservoir optimization contributed to cost-effective development.