The PUT River, Appraisal and Development of a Minor Reservoir within the Prudhoe Bay Field, North Slope, Alaska

Abstract

Abstract PUT River formation is an early Cretaceous reservoir in the North Slope, Alaska. Stratigraphically it lies above the Lower Cretaceous Unconformity (LCU) and below the Highly Radioactive Zone (HRZ). The reservoir sands are near shore face to shallow marine deposits with heavy bio-turbation. In the Prudhoe Bay Field the PUT River reservoir overlays the Sadlerochit interval, the main producing horizon. A number of the Prudhoe Bay development wells penetrate the PUT River reservoir and provide well control for defining the areal extent and thickness of the reservoir. Four lobes of the PUT River were appraised by recompleting existing Sadlerochit wells that penetrated PUT River. The oil filled south-east lobe is the target of the current development plan. A key uncertainty of the development plan was the transmissibility across the faults. Three dimensional (3D) stochastic reservoir models were constructed and matched with the appraisal production data to determine the OOIP. VIP simulation models were generated to construct a development plan for this reservoir to determine the ultimate recovery. Significant uncertainties remained with regards to (1) location, number and type (horizontal vs vertical) of injectors, (2) number of producers to use, (3) geologic properties (in terms of correlation length and direction and facies distribution), and (4) fault transmissibility that could impact the choice of the plan of development (POD). To select the optimal POD in terms of ultimate recovery a Top Down Reservoir Modeling1 (TDRM™) process was set up. Several 3D models were generated to cover the geologic uncertainty. The TDRM™ process analyzed 960 discrete combinations of the above parameters. An optimal POD was selected from the analysis of the results. The range of possible recovery outcomes was also more clearly quantified. A development plan consisting of 1 horizontal injection well and 2 recompleted producing wells was chosen with an option to use two additional producers in the future. The injection well was drilled in early 2006 and the Southern Lobe of the PUT River began production in late 2006.