Integrated Reservoir Study to Maximize Oil Recovery by Optimizing Shuaiba Dump Flooding into the Kharaib Reservoir

A significant number of Kharaib horizontal and deviated producers drilled over the last decade have suffered from casing leaks, with many occurring in the first two years of production due to the exposure to highly corrosive water from the overlying giant water-bearing formation known as Shuaiba formation, resulting in production losses and water dumping from Shuaiba formation into the Kharaib reservoir through these damaged wellbores. This paper investigates the impact of Shuaiba dump flooding on the Kharaib reservoir’s performance, the integrated reservoir management study that was conducted and the implementation of the study’s findings to achieve the best results. Severe casing leaks are the main production problems facing the Kharaib reservoir. A few repairs were attempted initially, however, high costs and failure rates led to a decision to cement squeeze all remaining casing leak wells, recomplete them in shallower reservoirs, and drill new replacement wells. All new Kharaib wells were designed with an extra casing to protect against the Shuaiba reservoir’s corrosive water. Although there are no longer any casing leak wells in Kharaib, their impact remains. The pre-casing leak production numbers and well counts are yet to be matched, and there is a large volume of hydrocarbons to be produced from the Kharaib reservoir. In addition, wells that are offset of old casing leak wells showed an increase in water cut, while the performance of new wells drilled down-structure of casing leak wells suffered from early water breakthrough. There is also strong evidence that the isolation in many casing leak wells, performed during the recompletion workovers, may be unsuccessful. All these factors indicate that dump flooding is likely ongoing in the Kharaib reservoir. The consequences of dump flooding have not all been negative. An increase in average reservoir pressure and a strengthening of the reservoir’s weak water drive mechanism were observed. Currently, many wells have shown an increase in oil production, while other wells have shown steady oil production with a very gentle decline which is particularly reflected in wells located up-structure of the casing leaks. As a result of the study, many wells have been drilled in carefully selected locations in order to take advantage of the flooding, and the results of the study concluded a sustained production with a low water cut. Moving forward, there are further opportunities to increase the recovery factor by mitigating the unwanted effects of Shuaiba dump flooding and utilizing the phenomenon to its best potential.