Sour gas injection (SGI) pilot was successfully implemented in Tengizchevroil (TCO) in 2008, successfully achieving pressure maintenance in Tengiz platform, re-injecting gas with high H2S concentration and improving oil recovery within pilot area. Over the years, gas breakthrough and GOR increase has been observed in majority of producers in SGI pattern. Due to limited surface gas handling capacity, producing SGI pattern wells with elevated GOR and H2S has been a challenge. At the same time, it is critical to manage voidage replacement ratio in the pilot area to maintain sufficient miscible gas sweep and ensure enough pressure release. Inability to inject all the sour gas to the reservoir leads to equivalent oil production cut at the Plant.
Specialized SGI Operating Strategy has been in place since the commencement of the project with the aim of developing broader understanding of injected gas front evolution and operating the SGI Pilot in a way to maximize value for TCO by balancing between maximizing lower GOR/H2S front-end plant production vs. maintaining sufficient well injectivity. The production and injection well targets and surveillance activities were tailored towards fulfilling these strategic objectives. The operating strategy has been revisited several times to ensure appropriateness to business needs at any given time.
Specialized reservoir simulation model is utilized for short and long-term injection forecasts to develop plans to provide sufficient well injection capacity at any given time.
This paper will discuss challenges and best practices associated with (1) operating elevated GOR/H2S wells in a gas constrained environment while performing reservoir data acquisition program in highly congested area to fulfill SGI pilot objectives and (2) finding the trade-off between front-end plant production and injection goals.