WAG Pilot Design and Observation Well Data Analysis for Hassi Berkine South Field

摘要

The Hassi Berkine South field (HBNS) is an undersaturated, low-viscosity, moderate permeability oil field within the center of the Berkine Basin in Algeria (Fig. 1). Discovered in January 1995, the HBNS field had first oil production in 1998 from the Trias Argilo-Greseux Inferieur (TAGI) reservoir with a reservoir development plan (RDP) of crestal, miscible gas injection and peripheral waterflood. Fullfield WAG, as a secondary recovery process, is currently under investigation for the potential increased oil recovery and higher oil rate. This paper describes the design of the miscible water alternating gas (MWAG) pilot test and presents novel techniques for correcting observation well log data to reflect the miscible displacement process. A simulator sector model for the pilot area was used to design the MWAG pilot parameters (e.g., solvent/water volume, WAG ratio, timing). Next, measurements from the first WAG cycle were used to calibrate key parameters in the sector model, and to define WAG parameters for subsequent cycles. For the initial pilot design analysis, the fine areal gridding and vertical layering were taken from the Prudhoe Bay pilot simulation experience. The objective of the pilot design is to collect optimal data from the observation well in the shortest possible time. The initial simulation work defined solvent injection rates, slug sizes, cycle lengths, and WAG ratios to achieve these goals. Subsequently, reservoir calibration with surveillance measurements from the first WAG cycle allowed for finetuning of key MWAG parameters. This work required correcting hydrocarbon saturations from the surveillance tools to be representative of the miscible displacement process. A method has been developed to correct log-derived immiscible saturations to reflect the miscible process occurring in the reservoir and simulated in the sector model.