Identifying the Cause of Unexpected Solids Deposition from a Sodium Bromide Completion Brine in a Giant Field, Offshore Abu Dhabi

摘要

To achieve the new increased production rate of a giant oilfield offshore Abu Dhabi, the operator started implementing a number of new technologies which push back the boundaries of technical expertise. Foremost among these is the construction of four artificial islands from which wells are being drilled using extended reach drilling (ERD) technology and the use of maximum reservoir contact (MRC) wells to maximise potential production. To ensure that the maximum benefit was obtained from these MRC wells, an extensive research and testing program was conducted to select an optimised completion fluid for use in the island wells to improve and maximise production. The resulting selected sodium bromide/sodium chloride (NaBr/NaCl) based completion fluid was used in the pilot MRC wells and is now being used successfully in new wells on the islands with significant improvement in production. However, shortly after the start of production from one well, an unexpected production upset occurred with the appearance of significant quantities of solids at the surface non-return valve (NRV). Laboratory analysis of these solids confirmed that they consisted primarily of mineral scales, with sodium bromide (NaBr) and sodium chloride (NaCl) predominant. To avoid major disruptions in the production system, the following key questions during the investigation required urgent answers: 1. Why were these salts depositing in this production system? 2. Why were similar issues not reported in other wells using the same completion brine? 3. Were there any specific differences in this well or its operation that could cause the solids being formed? 4. Are any mitigation measures required for the continued use of the NaBr/NaCl completion brine in the island wells? This paper describes the detective work undertaken to investigate the unexpected appearance of these solids in the production system. This involved a combination of field data review, mineral scale prediction modelling and laboratory tests and analysis. The cause of the solids deposition was identified as being due to the interaction of the completion brine with the hydrocarbon phase at very low water cuts. It should be noted that other wells are also being produced at low water cuts without any similar issues occuring. By investigating and understanding this problem more fully, a set of guidelines and improved testing protocol could be developed to use in any repeat investigation. At the time of writing this paper no further problems have occurred in any of the subsequent wells drilled and produced.