Ever since the Bahrain field was discovered in 1932, the main focus of effort was on major formations of the field, leaving shallow formations not fully exploited. Today with the increase in oil price and the depletion of major formations, there is a greater preparedness to consider increasing production from these under developed zones.This case study was initiated with the purpose of increasing production from the Magwa zone, which is the most economically attractive of the shallow zones. The zone is the basal member of the Rumaila formation of the middle Cretaceous Wasia group. It is predominantly limestone with interbeded shale.This case study shows an integrated methodology to enable a better understanding of the reservoir production behavior and to explain the lateral heterogeneity of the formation. This investigation was triggered by the variation in the formation water salinity from North to South. Water saturation maps, production history, geochemistry and structure set-up were used as the main input in this analysis. The interpreted relations and trends between these factors were used to explain the behavior of the reservoir. The outcome of such investigations is of critical value in determining the location of new development wells, selecting candidate wells for workover and for EOR processes. This paper will explain how a better understanding of the reservoir through data integration has resulted in a significant increase in oil production.

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The onshore Bahrain Field is a multi-reservoir oil and gas field in the Kingdom of Bahrain. Hydrocarbons are found in various stratigraphic intervals from Devonian to Upper Cretaceous in mostly carbonate reservoirs. Clastic reservoirs are scarce in the post-Permian section but dominate in the pre-Permian section. The Lower Cretaceous Kharaib Limestone is an oil reservoir. The unit was tested in different exploratory wells in the early life of the Bahrain Field and it was found to be of low permeability but produced oil. The first phase of field development in Kharaib was initiated in the 1970s and after an initial period of dry oil production, the wells produced for a long time with high water cut (more than 90%). In the early 2000s, a horizontal well drilled in the reservoir provided encouraging results. Main development activities started from 2010 onwards, after Tatweer Petroleum – Bahrain Field Development Company W.L.L. ("Tatweer Petroleum") was formed. Thirty horizontal and fifteen deviated producers (a total of forty-five wells) were drilled during the period 2010–2014 and as a result, oil production from the reservoir increased significantly. However, within a short period of time, most of the wells started producing with high water cut (more than 90%) and image logs recorded in many horizontal wells showed presence of fractures. Based on this observation and 3D seismic analysis, Kharaib was characterized as a fractured reservoir and high water production was attributed to it. Later on, many wells had mechanical failure due to casing corrosion developed against the shallower Shuaiba aquifer. All development activities were subsequently stopped for the reservoir due to economic risk. In 2016, a renewed effort was undertaken to analyze all past data including; regional tectonics, core data, 1970s build-up studies, cement integrity, and image log interpretations. This back-to-basics analysis indicated that the primary cause of high water production in the Kharaib wells is lack of zonal isolation with Shuaiba (casing corrosion wells excluded) and not due to the presence of occasional fractures. Development activities restarted in 2017 that focused on addressing the zonal isolation and casing integrity issues. Seven wells have been drilled to date producing with an average water cut of 22%. More development wells are planned in the future thereby giving a new lease on life to the reservoir.