Assessment of Produced Water Reinjection in a Giant Carbonate Reservoir

Abstract

Abstract Produced water reinjection (PWRI) is a proven field development technology which has been widely applied to numerous fields to optimize disposal of produced fluids while meeting reservoir injection requirements. However, PWRI has not been evaluated in many of the giant carbonate reservoirs which are relatively immature in the Middle East. In this paper, an on-going assessment of potential PWRI for a giant offshore field is presented. The giant offshore oil field in the Middle East has been extensively developed since the 1970's. Seawater injection has been applied in the field since the 1980's and the produced water is disposed of through dedicated wells. The daily water production rate from this field has been increasing over time, and the continuous addition of oil producers and water injectors to capture the field reserves will further accelerate water production. Developing the most cost-effective solution to handle the significant volumes of produced water is crucial to ensure long-term operability of facilities and continued field production. A strategy to derive value from the produced water, which otherwise is considered unwanted, is to utilize PWRI. Proper laboratory assessment to determine specifications for PWRI will ensure the re-injected produced water is compatible with the reservoir fluids and that the target injection rate can be sustained through matrix flow. The lab assessment to determine produced water quality specifications include an evaluation of the inorganic scaling potential of PWRI (fluid compatibility) and an analysis of the impact of oil carry over in the presence of fine particles on near wellbore injectivity. Thermodynamic modeling and bottle tests were performed to determine compatibility of PWRI with reservoir fluids (i.e. scale precipitation) and core flood tests at residual oil saturation with multiple rock types were completed to quantify the impact of oil carry over on PWRI specifications. Thermodynamic modeling and bottle tests show PWRI has a lower inorganic scaling tendency than conventional sea water injection, and that scaling does not appear to be aggravated by PWRI. Core flood experiments indicate injectivity is maintained under anticipated oil carry over conditions (including upset conditions) across the various rock types evaluated suggesting PWRI may be an attractive technology to mitigate produced water disposal requirements while also meeting a portion of future field-level injectivity demand.