Well Testing in New Frontiers: Lessons Learned and Best Practices from an Ultra-Deepwater Well Testing Campaign in Namibia

Abstract The improved geological understanding of deep fan systems combined with the development of better geophysical acquisition and processing tools has pushed the limit of wildcats beyond 3000m of water depth. Dynamic evaluation of these potential future developments requires performing full-scale well tests. This paper presents a solution for well-testing in ultra-deepwater wells offshore Namibia, focusing on the flow assurance aspects during the design, planning, and well-test execution stages. Well-testing in remote deepwater environments introduces a set of unique challenges associated with the risk of hydrate formation. Such well-test operations are often designed on a case-by-case basis and require a long period of preparation and mobilization. To accelerate the exploration and appraisal of Block 2913B in Namibia, two drilling rigs equipped with bespoke surface well test packages were mobilized. This enabled the flow back and testing of the wells consecutively, and to rapidly collect an extensive amount of representative fluid samples and dynamic reservoir data. The exploration and appraisal campaign performed by Total Energies offshore Namibia demonstrated that it is possible to overcome flow assurance risks, perform ultra-deepwater well test operations safely, and to reduce costs by performing batch well testing while rapidly collecting significant amounts of dynamic reservoir data for field development decision-making. The fit for-purpose surface well testing packages, designed in compliance with the DNV standard and installed on the two drilling rigs, were optimized to efficiently process production fluid with a high gas-oil ratio at high flow rates, accurately measured by the Coriolis flow meters installed on the separator and a stand-alone multiphase flow meter. The selected drill stem test (DST) string design incorporated chemical injection lines, and an acoustic telemetry system. This allowed real-time monitoring through downhole gauges and the control of lower completion elements such as the downhole reservoir-isolation valve and dual-acting well tester valve. Long-term monitoring equipment was also deployed in the lower completion. The well test operations were designed using a transient wellbore simulator to determine operating parameters and identify mitigation measures to be employed, alleviating potential flow assurance risks such as hydrate formation. Precise planning and a robust maintenance plan between the wells were also required to conduct four ultra-deepwater DST operations successfully. This paper describes the consecutive drilling and testing of four wells in an ultra-deepwater environment with water depths up to 3100m, a record in the oil industry. This enabled to quick delivery of high-quality dynamic reservoir data to support potential development plans. The program was completed with zero HSE and environmental incidents