Sabiriyah Upper Burgan (UB) is a giant clastic reservoir in North Kuwait undergoing development efforts with water flood. Productivity indices as per historical data indicated these to be less than adequate and mismatching with the intrinsic reservoir permeabilities. This was a puzzle till a comprehensive review of the past pressure build up data was made and the results integrated with the-then perforation practices. More than 85% of the wells showed formation damage with a positive skin of +2 to +7, as per PBU data. Efforts were made to perform mud acid jobs without much success. After detailed review and performance analysis, recommendations were made to perforate new producers with TCP under balance, in addition to improvements in drilling mud chemistry. Subsequent PBU results of these wells indicated negative skin, which was also supported by better PIs.
The situation became a serious issue during initial phase of water flood and Injectivity tests. Injectors showed poor Injectivity indices. Though there had been multiple reasons for poor Injectivity, formation damage due to progressive plugging of pore throats was one of the major contributors. Detailed review of the dynamic behavior of the injectors led to the recommendations for improving the injection water quality by proper filtration, back flowing of the injectors prior to injection start-up and performing proppant frac jobs, if warranted. The implementation led to significant improvement in Injectivity. Phase-1 injection in the pressure depleted crestal area is in progress since last 3 years, thus sustaining production staying above the bubble point pressure.
Simultaneous to above, pore throat studies were conducted, leading to the conclusion that the pore throat size is very small with inherent risk of progressive plugging of injectors with time. In order to have life-of-field solution to Injectivity issues, recommendation was made to inject above parting pressure during the full field expansion of the water flood in 2010–11, on the basis of the results of Step Rate tests.
The case history of understanding and combating the formation damage in UB was a giant leap for rationalizing the way forward for its full fledged development.
Upper Burgan reservoir in Sabiriyah field was discovered in 1950s. The Albian age Upper Burgan sandstone represents deposition in an overall paralic environment. The reservoir comprises a complex series of tidal, estuary, deltaic, valley fill and shoreface sands interbedded with semi continuous shales. The paleo-shoreline is interpreted as having a NW-SE trend with the field areas located slightly offshore. There are three dominant sand-prone facies present in the Upper Burgan.