Oil and Gas Co-Development of a Giant Offshore Carbonate Reservoir with Gas Cap: Feasibility Study and Expectations

摘要

Development of Giant carbonate reservoir considerable cap gas and condensate reserves along with oil rim is now being considered as one of the on-hand options to overcome shortage of gas in the long term and to add value to the company assets. This paper presents an overview of the study that was initiated to assess the feasibility of the simultaneous development of gas and oil and to evaluate its impact on the existing oil long term development plan. A compositional simulation study has been conducted by adding the co-development of the gas cap on top of the current Long Term Oil development plan. This development includes water injection at the original gas oil contact level to isolate the gas cap and to enable to develop gas cap independently from the oil rim. In this scenario, drilling of producers in the gas cap is considered and condensate is produced to the dedicated production system. Several prediction scenarios have been investigated to set up a development plan of gas: 1. Blow down or natural depletion, 2. Produced gas recycling, 3. Lean gas recycling. The best scenario has then been selected for further optimisation. (On gas injection recycling ratio, project start-up timing, gas production target, and water injection). After analysing the results, it was found that the blow down of the gas cap provides a good recovery of gas and condensates but has a negative impact on oil reserves. Gas recycling option proves interesting as it maintains pressure both for condensate (hence preventing drop-out) and for oil; therefore impact on Black-Oil recovery becomes minor. Oil recovery is higher with late starting time of the co-development or with high recycling ratio. Oil Recovery Factor depends mainly on the pressure maintenance of the reservoir. However excessive gas injection has a negative effect due to breakthrough of the gas into the oil producers which have GOR limit constraints. Co-development simulation study of the gas cap along with oil, through an inner ring of water injection at gas oil contact shows that the co-development is not only feasible but it will also bring significant value to the company future business plan. Gas cap being semi-isolated from the oil rim, the impact on the oil development plan is minimized. Co-development proves appealing to the different owners of the field since it brings more gas and LPG that is foreseen as valuable source of enriched gas for later EOR or WAG schemes