Reservoir Characterization of Heavy Oil in Burgan Formation of North Kuwait

Abstract

Abstract A regional study of the Burgan formation has been carried out over the North Kuwait Fields to understand the variation in depositional environment, oil occurrence and control of trapping mechanism on the quality of oil. The Burgan Formation in North Kuwait comprises fluvial, deltaic and marine sediments deposited during the Lower Albian period in response to global changes in sea level. There is a systematic gradation of depositional environments in Burgan during this period. Oil entrapment in this formation shows regional variation. Both stratigraphic and structural controls on oil accumulation are dominant in the region. The oil quality becomes heavier towards North and has a strong structural control. Significant volume of inplace oil has been estimated during this study which would be pursued for commercial exploitation of this deep heavy oil reservoir. Burgan clastic sedimentation over Shuaiba carbonates was initiated by a regional fall in sealevel and establishment of a deltaic setting. Reservoir facies include mouth bars and distributary channels along with non-reservoir facies of interdistributary bay and shallow marine environments. After a significant hiatus, the braided channel systems with massive amalgamated sand bodies were established in response to significant fall in seal level. Subsequently a significant marker in form of a marine and shoreface sand with associated marine shale was deposited with a rise in sea level. Estuarine channels and bay shales were deposited above this surface. The upper part of Lower Burgan has transgressive sand bodies. The Middle Burgan is dominated by marine shale and shoreface sand deposits in response to further rise in sea level. The Upper part of Burgan is mainly comprising estuarine channel sands and interdistributary bay deposits. In a regional context, the sedimentation pattern shows increasing marine influence to East-Northeast directions. The oil quality in Burgan is intricately related to the structure and trapping mechanisms. A post Mishrif time tilt in structure has resulted in a deeper relict oil water contact in Lower Burgan towards West of Sabiriyah. In the area towards North of Raudhatain structure, the fluid contact shows significant tilt towards North with a rising structure. The doubly plunging anticlines of Raudhatain and Sabiriyah structures have lighter oil in Burgan formation in a structural trap. Further north of Raudhatain, the oil is heavy although there is lateral reservoir continuity. Significant faults have been mapped in this area. The structure is shallower towards North with progressively deeper fluid contact in Lower Burgan. Origin of heavy oil appears be due to significant spilling of lighter oil along faults and upstructure migration due to structural tilting and transtensional deformation. Significant accumulation of heavy oil has been established in Basal Burgan, Lower Burgan and Upper Burgan Formations. Heavy oil inflow in form of testing and sampling is seen in 12 wells. Aggressive plans are in place to map the oil quality and to formulate a long term exploitation strategy.