This paper describes the integration of the development of a number of oil reservoirs by means of miscible gas injection with the development of a gas condensate field.
Around the year 2000 a number of oil reservoirs were discovered in south Oman. Material Balance calculations and early performance data confirmed the geological predictions that little or no aquifer support was to be expected from those reservoirs. Recovery factors based on primary depletion are limited to about 10%, and to boost recovery miscible gas injection (MGI) was identified as the most promising technique.
The gas needed for such miscible gas flood was found in the presence of a gas condensate field located nearby. The gas contains about 15% CO2 and 3% H2S and is considered a sour gas development. Originally the gas-condensate field was scheduled for stand-alone development, with gas sweetening and re-injection of the waste stream, containing about 70% CO2 and 30% H2S, to maximize condensate recovery. The integration of the gas and oil development offered an additional sink for the waste gas, as this could now be used for MGI.
To optimize the development, in terms of maximizing the Ultimate Recovery, a fully compositional model, integrating the 3D subsurface modeling and surface network, was constructed. The model was used to determine the best strategy for the MGI development of the portfolio of oil reservoirs, assess the impact of sour gas injection in those oil fields on existing production facilities, and select the optimum gas offtake from the gas field.
The integrated modeling enabled the selection of a development concept that maximizes the UR of the Oil and Gas fields, ensures the Gas sales commitments, while making maximum use of the existing facilities, thereby maximizing the monetary value of the project.