As part of Dunga oil field water flooding program, well injectivity impairment analysis through series of core flood laboratory experiments was conducted with the primary objective to ascertain reservoir plugging possibility of the solids/fines contained within injection water that comprises combination of Produced Water (PW) and planned Caspian Sea Water (CSW). The quality of water and its compatibility as re-injection fluid requires investigation to ensure considerations from a reservoir management perspective are built into the facility water handling design criteria.
The scope of this study utilizes industry standard workflows of core flood experiments customized to suit required conditions using real CSW and PW samples. The later stage of the analysis uses various combinations of synthetic brine representing compositions of PW and CSW covering various levels of turbidity. The use of synthetic brine enables varying water filtration standards to be applied/simulated, and to determine the impact of individual elements on formation damage / permeability degradation.
Based on observations, CSW Core flood tests do not exhibit plugging/formation damage effect. This implies that formation fines migration or clay swelling in low saline water environment is not an issue for the Dunga field. Furthermore, the relatively low volume of total suspended solids (TSS) and low fluid pH index explain no detrimental impact of its injection into the tested core plugs.
Variation of total suspended solids content in injection water imparts significant damage to the tested core plugs. PW Core flood with high TSS shows instantaneous severe plugging with drastic permeability degradation. Whereas, PW Core flood with low TSS displays slight (tolerable) level of plugging that could be partially restored by chemical acid treatment. When CSW and PW blend is injected into formation, no fluid compatibility issues were observed. Instead, the plugging potential of the mixed injection water is diluted via increasing CSW content which contains lower TSS volumes.
All key findings related to real water samples have been ratified with synthetic brine experiments that helped identify an impact of individual water property on deliverables. Recommendations for injection water filtration scheme for the Dunga field were delivered as a result of this study which should positively impact the ultimate recoverable volumes of the development.