Successful Reservoir Monitoring With 4D Microgravity at Ras Laffan, State of Qatar

摘要

Recent advances in microgravity technology have improved precision, making the microgravity method a cost effective tool for reservoir monitoring in a time-lapse (4D) mode. Surface recorded gravity can now be reliably measured to five microgal accuracy, allowing small changes in fluid type in subsurface reservoirs to be monitored. RasGas Company Limited (RasGas) has successfully been using this 4D microgravity method to monitor waste gas injection near the LNG plants at Ras Laffan Industrial City (RLIC). This method has proved to be a very cost effective and intrinsically safe way to monitor the movement of gas injected into an aquifer at approximately 5000 ft depth in an industrial environment. Gas injection at RLIC started in 2005. A requirement of the injection permit was to monitor the movement of the injected gas. RasGas evaluated available monitoring technologies and chose 4D microgravity over monitoring wells and 4D seismic as the best method to achieve the monitoring objectives. Monitoring wells would have been costly and raised the risk of leakage behind the wellbore. Placing the wells in a congested industrial area would have been difficult because positioning these wells would require prior knowledge of where the dynamic gas front was likely to be encountered with time. 4D seismic would have been very expensive, intrinsically unsafe for this industrial environment, and adversely affected by LNG plant noise. The microgravity technology employed by RasGas is less sensitive to the LNG plant noise than 4D seismic, provides good coverage of the area, can be positioned dynamically, and has proven to be a robust technology even in this very active construction area.