BP installed an extended well testing (EWT) facility to perform extended flow tests for appraisal of the tight gas reservoirs in the Sultanate of Oman. The EWT facility is a "mini-gas-plant" that processes appraisal well gas and delivers it into the national grid. It helps avoid excessive flaring of significant volumes of gas while providing valuable long term history matching data used to predict full field production profiles.
Middle East tight gas reservoirs are typically Pre-Cambrian to Ordivician in age situated in a high pressure and high temperature environment. A comparatively complex diagenetic history makes prediction of rock quality and fluid distribution very challenging. Key depletion planning uncertainties identified at the outset of appraisal were: the long term decline in gas production rates, the connected hydrocarbon volumes, the impact of condensate banking and the long term trends in water gas ratios. The EWT data gathering is helping to reduce these uncertainties to a level sufficient to inform an investment decision.
Four appraisal wells, ranging from good to poor quality, were tied into the EWT for long term testing for up to 2 years to date. The combination of this production history and downhole pressure data has markedly improves confidence in predictions of production profiles for the range of full field development wells.
The EWT operations have also revealed several potential full field development design and startup concerns. These were related to formation of hydrates due to gas expansion at the wellhead along with other potential integrity risks due to high chlorides content and the presence of minor H2S levels. The changing fluid chemistry was also identified which helped in redefining the fluid basis of surface facilities design to optimize operability of the full field development.