Abstract
The Burgan field, the second largest in the world and the largest clastic reservoir, has been in production for 66 years under primary production from natural water drive. The first phase of water injection has just begun in a small part of Burgan as a precursor to peripheral step-in water injection in the topmost Wara reservoir. Tertiary recovery schemes are being evaluated early in the life of this field with the foresight of reaping maximum benefits through early application before waterflood approaches maturity. Low salinity water (LSW) injection has been identified as a forerunner and apart from being very promising in itself; it will form an important base for the application of polymers and/or Alkaline/polymer/surfactant EOR schemes. Burgan is large enough to have a diversity that will require distinctive solutions for different areas of the field and different reservoir zones.
Produced water injection started in Wara formation in 2010 at 60mbwpd with next phase of 670mbwd injection arriving in 2014 to implement peripheral injection in the flanks. This is targeting just 5% of the reserves that will need future water injection. Confidence in the LSW trial will therefore change the course of our future water injection schemes in the remaining zones. Replacing secondary with tertiary recovery schemes early will benefit not just the operating costs of the volume of water handling and disposal/injection; the overall recoveries will be higher. The eyes of the world are constantly on the health of the 2 super giants, Burgan and Ghawar. Potential benefits from EOR will have a huge impact on the extension to the life of Burgan and its strategic importance worldwide.
This is the first time that KOC has taken a bold step into the field without extensive laboratory screening. As a result of taking this carefully calculated risk, KOC have soared ahead in experience on EOR in the Greater Burgan Field, within a small timeframe.
The presentation will discuss the results of the LSW trial injection into 2 producers and comparisons on Sorw are made of LSW versus High Salinity produced water injection. Key learnings are shared from operating the pilot and modeling of the results. Single well tracers were used to measure the Sorw and its interpretations can be quite challenging. The tests have been analysed using five different methods. From this work, it was concluded that
Low salinity water injection reduced Sorw by at least 3 s.u. (23.7% of remaining oil after effluent waterflood) in the best quality rock with the least clay content in Burgan, which would still be sufficient to make it economically attractive.
Additional tests are planned for the remaining rock types in Burgan, having higher clay content and the potential for a larger change in oil saturation.
Multiple models for evaluating the tracers response provide better insights to the interpretation of the Sorw.
Good surveillance during the test and careful control on injection/production volumes are essential when a small response in Sorw is expected. To reduce uncertainty in the results, it is preferable to use downhole pumps rather than gas lift, control the temperature of injected water and invest in lengthy overfishing back to base brine after LSW injection.
