Flow-Assurance-Management Strategy Considerations for a Deepwater Gas Field

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202254, “Flow-Assurance Challenges for China’s First Deepwater Gasfield Development in South China Sea,” by Lawrence Khin Leong Lau, Kun An, and Xian Di Tang, CNOOC, et al., prepared for the 2020 SPE Asia Pacific Oil and Gas Conference and Exhibition, originally scheduled to be held in Perth, Australia, 20–22 October. The paper has not been peer reviewed. The complete paper describes the key flow-assurance challenges for a deepwater gasfield development in the South China Sea and the considerations and steps taken to achieve an overall flow-assurance-management strategy. The discussion covers early-stage feasibility studies through the stage of project execution at the time of writing. In addition, flow-assurance analysis is highlighted as a key input for startup and commissioning guidelines as well as operating procedures. Project Background This gasfield development consists of a semisubmersible more than 100 km offshore in the South China Sea. The water depth is approximately 1500 m, with a minimum seabed temperature of less than 4°C. The design incorporates Eastern and Western production loops spanning more than 40 km of the subsea production system (SPS) in total. Line size for the Eastern and the Western production loops are selected according to the total of production wells located in respective areas. The entire production system, including topsides facilities, subsea flowlines, risers, and other key SPS elements such as subsea manifolds, is designed with potential future development tie-ins in mind. Long subsea tiebacks, coupled with typical deepwater characteristics, require a robust flow-assurance- management strategy. A dedicated flow-assurance team was assembled across sectors such as subsurface, drilling and completion (D&C); subsea umbilicals, risers, and flowlines (SURF); control and instrumentation; and topsides process engineering. During the feasibility-study stage, more than 10 deepwater subsea production wells were grouped by characteristics. Analysis was performed for the most-representative wells selected from each group during this development stage to determine the range of the operating envelope and to identify all related risks. As development progressed into the detailed engineering-design stage, a detailed flow-assurance-scope analysis was completed for each well to ensure full coverage. This analysis considered scenarios including well unloading, well testing, precommissioning, first gas, steady-state production, planned and unplanned shutdowns, and hot and cold restarts. Any risks identified were assigned mitigation strategies and then were incorporated into design philosophy and operating guidelines or were specifically detailed in operating procedures. Primary Flow-Assurance Challenges Region-Specific Flow-Assurance Challenges. Flow Assurance as an Independent and Integrated Discipline. The creation of a cross-disciplinary flow-assurance team differs significantly from previous management approaches in which flow-assurance scopes were embedded in different disciplines and managed separately by teams such as subsurface, D&C, SURF, and topsides. The team described in the paper had the goal of implementing flow-assurance design and strategy with a truly integrated approach to maximize efficiency, optimize costs, and minimize impact on the environment.