Nahr Umr Classical Waterflood: From Pattern Pilot to Peripheral Waterflood, Bahrain

Abstract

Tatweer Petroleum completed the first successful Bahrain Field waterflood in 2014. The waterflood pilot and ultimate peripheral development was completed in the NahrUmr "CC" Reservoirs and demonstrates classical and economic waterflood performance. This paper describes the initial pilot and ultimate peripheral design and results. The paper also describes the systematic effective and efficient Tatweer pilot management approach which allowed an impressive pilot to peripheral time frame less than two years. Early in 2013, a 30 acre waterflood pilot was initiated in Cc reservoir in the central structural area, consisting of an inverted 5-spot pattern; one injector and four surrounding producers. The pilot was selected in a confined area where there was good pressure data coverage, relatively low GOR and WC, good reservoir continuity, high productivity and good reservoir characteristics (So, Net Pay). Initial pilot results showed classical reduction of gas production and increase gross production within a couple of months of injection. Based on this observation, the pilot team reassessed overall structural reservoir performance and determined the structure would benefit from a peripheral waterflood to augment natural water influx. The peripheral design covered 870 acers and was completed with 11 injection wells and 21 producers. The analytical approach designing the peripheral flood fell into five categories listed below: Re-assessed natural water influx; This was done by comparing voidage pulled from the reservoirs vs. pressurePetrophysical and Geological revision to the area of interestRe-evaluated the size of the prize; using analytical and simulation modelsInterpreting results and observations from the inverted 5-spot pilotRe-assessed development costs and reserves impact for pattern vs. peripheral considerations. Since the peripheral waterflood implementation in late 2014; 170,000 barrels of incremental oil has been recovered through February 2016 and reservoir pressure has increased by 50 psi. Current injection rate is 18,500 BWIPD in 11 injectors. Current incremental oil production is nearly 400 bopd from 21 producers. In this paper, the key elements of waterflood surveillance and assessment are described and used to help Tatweer Reservoir Management Team (RMT) to effectively and efficiently determine that the structure would benefit from a peripheral waterflood rather than a pattern design. An impressive multi-disciplinary work was done in order to change the plan and still execute the project in less than two years. In addition to that, this paper covers the process followed by the RMT to manage the waterflood conformance and monitor the injection and production simultaneously.