Sour Gas Injection project has been successfully implemented in Tengiz field, achieving long term pressure maintenance in the platform area by re-injecting gas with high H2S concentration and improving oil recovery. From the recent gas saturation campaign, sweep efficiency in injection pattern has varied from 10 to 70%, with the highest sweep, as well as most of gas breakthroughs observed in Bashkirian interval. This represents effective and uniform piston like miscible displacement across whole Bashkirian that enhances oil production. Similarly, surveillance monitoring shows that due to higher depletion rate in same Bashkirian, it experiences higher exposure to injectant fluid (sour gas) causing elevated GOR production at surface, whereas, lower intervals remain at near solution GOR with lower sweep efficiency. Such, anisotropy between the upper and lower intervals in terms of reservoir pressure and sweep efficiency creates an opportunity for the development of lower intervals by implementing conformance control technology.
Injectant breakthrough and GOR elevation in SGI wells create additional challenges for TCO, due to limited gas handling capacity at the plant processing facilities. Hence, isolation of Bashkirian will not only stimulate lower intervals to produce, but also, reduce GOR concerns. First pilot workover to isolate Bashkirian in SGI used chemical polymers. Polymers were injected into the formation and provided strong isolation of the target interval. As a result, time-lapse gas saturation logs confirmed significant increase in vertical sweep efficiency across whole Unit-1 intervals, plus lower GOR production lasted for more than 6 years. Completion type variety in existing SGI wells, make application of chemical polymers challenging, therefore, conformance control completions were introduced as an alternative solution. Conformance control liner provides mechanical isolation between compartments for more effective staged acid stimulation treatments and enable potential isolation of unwanted fluids.
This paper will introduce application of various conformance control techniques to alter production in SGI pattern by developing lower intervals and reducing elevated GOR. A gas shut-off campaign was initiated in Tengiz field after a decade of sour gas injection. Case studies will be presented to share challenges and results during planning and execution phases.