Rumaila is one of the world’s supergiant oil fields. At the end of 2009, BP entered into a Technical Service Contract as the lead contractor with the South Oil Company of Iraq (SOC) and PetroChina to develop the remaining resource. The Main Pay is one of the largest reservoirs in the field. It has played a large part in delivering production for more than 50 years and is expected to play a significant role in securing and sustaining field plateau production with billions of barrels yet to be recovered. The Main Pay is under active waterflood (aquifer support supplemented by water injection). In 2010, a massive program of cased hold saturation log surveillance was initiated, with logs acquired on 106 wells across the field with the objective of improving understanding of the current distribution of fluids in the reservoir. The acquisition of this data coincided with the beginning of an intense period of study on nearly 1 km of historical core released to BP by SOC that concluded in 2012. The Main Pay is interpreted to have been deposited in a largely progradational to aggradational, fluvially dominated and sand-rich deltaic environment. Occasional well-developed marine flooding surfaces are observed, usually succeeded by prodelta shales. These shales can be correlated widely and act to break up vertical connectivity and reduce vertical sweep efficiency. Whilst the majority of effective reservoir rock is found in high quality laterally and vertically amalgamated distributary channels, some lower quality reservoir is found in more distal or marginal argillaceous mouthbar, shoreline and tidal sand flat deposits. This heterogeneity is expected to reduce areal sweep efficiency.


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