It is challenging to increase oil recovery from a reservoir with a thin oil rim and large gas cap after a long depletion of the gas cap. Gas or water breakthroughs are commonly seen and are responsible for disappointing oil recovery. The development becomes more challenging when resources are needed to control depletion and maintain reservoir pressure.
This paper deals with challenges encountered in developing a thin oil rim and compares the recovery of the development scenarios.
The field under study is an offshore Carbonate reservoir consisting of multiple stacked thin porous layers separated by less porous layers. The gas cap was developed first, as at that time the oil rim was only poorly understood, and its potential was not fully recognized. Oil development only started after a prolonged period of gas depletion. Post depletion, gas injection has been introduced to control the depletion and to permit further development of the oil rim. The process followed in this study is summarized as follows:
Build a simulation model (static and dynamic) in order to simulate reservoir fluid movement due to periods of depletion or gas recycling.
Locate zones of remaining oil for development and suggest development options for these zones. Sweet zones to increase condensate production are suggested.
Compare hydrocarbon recovery for several development scenarios with different pressure support strategies (and well completions).
Finally a post gas production scenario to develop oil rim is presented as a revival scenario for oil rim development.
A representative fit for purpose sub-surface model to capture the high reservoir heterogeneities and the dynamic behavior was crucial.
It is demonstrated that despite the challenges inherent in this reservoir, it will be possible to increase the oil recovery. A number of locations for new oil production wells are identified and these allow recovery of additional oil through sustainable production.
Zones of high CGR in the reservoir are a good target to enhance condensate production. For gas recovery reservoir pressure is the main factor controlling recovery.
This paper shows that despite the early depletion of the gas cap there is a room to enhance oil rim recovery of thin oil rim reservoirs underlying extensive gas caps, by means of a development which targets remaining oil, complemented by injection to control reservoir pressure depletion or Low well head pressure system to produce from low pressure reservoir.
The post gas cap production scenario shows that theoretically there is an opportunity to recover oil after gas cap production.