Genetic Siliciclastic Sedimentation Patten Drives Reservoir Development: Burgan Reservoirs of North Kuwait

Abstract

North Kuwait experienced two major clastic pulses in its stratigraphic succession- the Aptian Zubair_Ratawi Shale Formation and Albian Burgan Formation. The Burgan Formation is interspersed by two major deeper water carbonate sediementation of Shuaiba and Mauddud formations. Siliciclastic reservoirs of Burgan formation trap major hydrocarbon in North Kuwait structural and stratigraphic elements. Genetic sedimentation pattern and the resulting reservoir architecture has driven the development strategy of Burgan Reservoirs. With 59 years of production history and more than 1400 wells, there are critical insights into these reservoirs. North Kuwait experienced two major clastic pulses in its stratigraphic succession- the Aptian Zubair_Ratawi Shale Formation and Albian Burgan Formation. The Burgan Formation is interspersed by two major deeper water carbonate sediementation of Shuaiba and Mauddud formations. Siliciclastic reservoirs of Burgan formation trap major hydrocarbon in North Kuwait structural and stratigraphic elements. Genetic sedimentation pattern and the resulting reservoir architecture has driven the development strategy of Burgan Reservoirs. With 59 years of production history and more than 1400 wells, there are critical insights into these reservoirs. Burgan Sedimentation initiated in a deltaic environment above Shuaiba carbonate with a drop in Sea level. Fluvial sedimentation overlie the deltaic sedimentation and succeeded by estuarine settings. Successive rise in sea level resulted in shore face and deeper marine sedimentation in Middle Burgan. In upper part of Burgan deltaic and estuarine environment was re-stablished followed by deeper water carbonate sedimentation of Mauddud. Braided Channel environment of Lower Burgan held the major hydrocarbon reserves. It has strong bottom water drive with good areal and vertical sweep. Better sweep is observed in cleaner sands towards provenance to southwest and there was field wide water cone. In the Upper part of Lower Burgan, the estuarine and deltaic channels show directional sweep along the channel fairways. Genetic reservoir facies, Faults and structural compartments play important part in holding the remaining oil in the mature fields. Several innovative methods have been devised to locate and exploit the remaining oil from these swept reservoirs. The methodology includes innovative mapping of water encroachment using structural elements, locating lower reservoir quality sands and delineating areas undrained by past producers. Conventional water encroachment mapping involved use of PNL/PLT data and gridding them without constraint. Current approach involves gridding of current oil water contact in individual layers, subtracting it from top layer structure and containing the resultant grid to net reservoir thickness. This ensures higher thickness of oil column in attic areas and lower thickness in low relief areas. Constraining to reservoir thickness ensures removal on non-net thickness from resulting oil column. Remaining oil is observed to be confined to silty part of the layer. Maps of Sand and Sand with silt were prepared to delineate silty zones for well placement and completion. The areas having wells closed in past due to high watercuts were reviewed for the potential pay. Polygons were drawn to highlight such areas. Infill wells were planned in sweetspots having sufficient hydrocarbon thickness. Depositional trends and fault bound traps were given due consideration while identifying sweet spots. Horizontal wells were drilled to drain low thickness poor quality reservoirs. Subsequent Infill Drilling shows good results in terms of locating bypassed oil in several wells where structure and stratigraphic predictions are valid. Areas of poorer quality sands in different parts of the fields are being pursued. In Middle Burgan, shore face sands form the producing units. These are relatively thin layers with lateral discontinuity and show rapid drop in reservoir pressure. Exploitation strategy is to locate areas of better quality and more continuous reservoir from genetic aspects for development drilling. The Upper Burgan reservoirs are mainly in channels sands of deltaic and estuarine environments. Reservoir pressure support is along the channels and higher rate of withdrawal depletes the reservoirs faster. Development strategy for this reservoir is to support the reservoir pressure with peripheral and modified pattern injection along channel fairways and locate bypassed oil. The paper discusses the genetic elements, their impact on flow behavior and methodology adopted to maximize productivity from the siliciclastic reservoirs of Burgan Formation in detail.

AAPG Datapages/Search and Discovery Article #90360 © 2019 AAPG Middle East Region Geoscience Technology Workshop, 3rd Edition of the Siliciclastic Reservoirs of the Middle East, Muscat, Oman, October 28-30, 2019