Development Strategies of JZ25-1S Thin Oil Rim Reservoirs with Big Gas Cap

JZ25-1S oil field located in Bohai bay which has a thin oil rim with a gas cap on top and aquifer below, and this field has to supply fuel gases to the residents. To achieve maximum oil recovery, force balance between aquifer drive, gas cap expansion, and viscous withdrawal shall be carefully studied for this type of reservoir at various stages of the production life cycle. Available methodologies including analytical, and simulation are used to optimize the development strategies, including well type, the well location, drawdown and so on. Using horizontal wells to develop the thin oil rim, the horizontal length parallels with the GOC and OWC, the horizontal section length is 300-400m nearby, the stand off over the OWC is 1/3 of the oil column if the gas cap index is more than 1.5, and the optimized drawdown of the horizon well is recommended 0.3-0.6MPa ; while the gas cap index is less than 1.5 and the aquifer is stronger, the stand off over the OWC is 1/2 of the oil column, the drawdown is recommended 0.5-0.8MPa; And making good use of the gas and aquifer energy at initial stages of production, then using waterflooding for the reservoir which gas cap index is less than 1.5 and the aquifer is weak. A number of horizontal wells were optimized and drilled in JZ25-1S field after optimizing the development strategies. The initial oil rates are from 943-2830bbl/d under the optimized drawdown. The management of GOC and OWC movement is extremely critical in this kind of oil field. Based on the achieved parameters, these wells display significant higher oil production with delayed water coning and slower gas channeling. Both simulations and production data demonstrate that the JZ25-1S development strategies gain success, using horizontal wells balance GOC and OWC to explore hydrocarbon, and achieve maximum results, which provides the theoretical and production data for development optimization of thin oil rim reservoirs with gas cap in Bohai Bay.