CO2 Tracer as an Alternate Data Acquisition Strategy to Accelerate Gaslift Optimization and Maximize Oil Production

Abstract

This paper serves to share the success story of utilizing Carbon Dioxide (CO2) well tracer surveys to conduct gaslift optimization, resulting in identifying additional oil production of 650 bopd and gaslift savings of 8 MMscf/d. In field B, located in the East Malaysia Region, wells in production are mainly operated with the assistance of gaslift. With over 70 active strings requiring gaslift, this creates a predicament in data acquisition of each string through the conventional Flowing Gradient Survey (FGS) method for gaslift optimization. The main setback of performing FGS in each string includes prioritization of slickline intervention for data acquisition against production enhancement activity, operation windows availability and production deferment. From the CO2 tracer survey, the root causes of well lifting issues such as multi-pointing, Gaslift valves malfunctioning, and tubing leaks can be identified. The accuracy of gaslift injection rate transmitters and total gas output from well test separators are also established together with the gaslift split factor for dual string wells. In the CO2 well tracer campaign in field B, 55 surveys were conducted of which 21 were on single string and 17 performed on dual strings. Around 20-30 pounds of CO2 was injected into the gaslift injection line and its concentration recorded at the well head. Injected CO2 travels through the tubing-casing annulus into the tubing through injection point/s. The travel velocities inside the tubing and casing were used to back calculate the operating lift depths. By importing the results of the CO2 well tracer survey into a software, the exact depth of injection can be measured, and any indication of multi-pointing can be seen. Accurate gaslift modelling can be conducted by incorporating actual measured injected gas rate, well test rate at time of survey and single/multi-point depth obtained from the survey. The CO2 well tracer campaign has proven to provide effective and reliable data on the lift gas entry points in the well, especially for fields with large number of gaslift strings. A total of around 650 bopd oil gain with gaslift savings of 8 MMscf/d was identified and will be realized by conducting Gaslift Valve Change (GLVC). CO2 well tracer campaign should be considered for fields with high quantity of gaslift wells as an alternative to FGS as it requires minimum equipment hook-up, has minimal production deferment, and does not require invasive well intervention. A presentation and discussion of the successful results, limitations, best practices, and lessons learnt from the CO2 tracer campaign aspires to be additive to the production surveillance tools in the oil and gas industry by providing alternatives in data acquisition from the conventional FGS.