Enhancing the Oil Potential of Secondary Triassic Reservoirs in the Beryl A Field, UK North Sea
The Beryl A field is a north-south trending tilted fault block structure in Block 9/13 of the UK Sector of the northern North Sea. As production from the main reservoir, the Jurassic Beryl Formation, declines the need to offset this decline with production from the Triassic and other secondary reservoirs becomes more important. Extensive remapping and recorrelation of the Triassic reservoirs has led to a better understanding of reservoir distribution and performance. Hydraulic fracturing has been used to improve the economic viability of the Triassic reservoirs. So far, two wells have had their initial flow rates doubled and total recovery is estimated to have increased by 1 million barrels (MMbbl) per well.
The Triassic Lewis Formation reservoirs are mainly confined to the crestal region of the Beryl A structure. Estimated STOIIP is 324 MMbbl, 20% of the total STOIIP for the field. Significant additional potential resources exist in downthrown terraces to the east. Formation lithologies are interbedded lacustrine shales and finegrained sheet sands with extensive calcrete horizons. Porosity and permeability values range from 10–16% and 10–200 mD, becoming poorer in the eastern terraces. Historically, due to the reservoir quality, well performance has been poor and recovery factors may have been underestimated. The technical and economic success of the fracture stimulations highlights the potential for improving recovery from existing Triassic reservoirs.
KeywordsHydraulic Fracture Crestal Region Reservoir Distribution Fracture Stimulation Average Water Saturation
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