Abstract
Lower Burgan, a giant clastic reservoir in Sabiriyah field of North Kuwait was discovered during mid 50s (Location map shown in Figure-1). An integrated performance analysis recently carried out indicated that the reservoir has a much higher potential than anticipated earlier. Though the cumulative recovery till date was more than 70% of the initial recoverable reserves, the reservoir pressure decline was insignificant with average water cut of about 20% only in this active water drive reservoir. Significant additional open hole data in new well penetrations, cased hole log data, seismic reinterpretation, additional production performance and pressure data acquired since last major reservoir update in 1998, has considerably improved the reservoir potential understanding of Lower Burgan.
Although reservoir performance suggested possibility of larger STOIIP base, lack of sufficient mapped net pay area impacted the deterministic STOIIP estimation negatively in the past. The additional information obtained in the new wells has opened up a large additional pay area by way of structural refinement, lowering of OOWC and additional net sands mostly in L-member. Whilst number of wells drilled in southwest flank and in north and south indicated possible occurrence of a deeper OOWC than earlier interpretations, SA-X1, the well drilled and tested beyond the reservoir limit in southern area, produced dry oil from sands with high Sw.
In order to assess the full potential of new reservoir area and to test the mobility of oil below the hitherto OOWC, a detailed testing program was formulated and implemented. MDT sampling was undertaken at several wells with successful results to prove the mobility of oil. Rigless perforation/ testing job were done at one of the identified wells, showing only traces of oil. Cores were cut with full suite of open hole logs and the RFT data. Production testing at newly completed wells, long term build up tests, PLT data and RST logs confirmed the additional potential for this mature reservoir, which was supposed to be on decline as per earlier predictions.
The paper is a classic example as to how a mature reservoir has been re-assessed and brought to the development limelight in terms of enhanced STOIIP, Reserves and production.
