Abstract

Waterflood development on 160 acre well spacing has been staged over a period of several years in the Kuparuk River Field. The waterflood is implemented in two distinct reservoir sands which flood at significantly different rates due to differing reservoir permeabilities. This paper presents field data and analysis of waterflood performance in presents field data and analysis of waterflood performance in the Kuparuk River Field.

Analysis methods of decline curves, log WOR versus cumulative oil production, and the frontal advance X-plot technique are used and results compared. The importance of analyzing data by well and by zone in this dual-zone flood is demonstrated. The method of plotting log WOR versus cumulative oil recovery and the frontal advance X-plot technique result in very similar projections of ultimate recovery. Interpretation of the WOR versus cumulative oil plots are used to diagnose inadequate pattern performance. Waterflood performance trends indicate that decline curves are harmonic or hyperbolic, showing a decline exponent significantly higher than those suggested in industry literature.

Numerical simulations of C Sand waterflood patterns were performed to model layers of different permeability-thicknesses performed to model layers of different permeability-thicknesses and match observed behavior. Resulting understanding of the C Sand reservoir description is discussed, as well as the implications to projecting waterflood recovery. This understanding is important to investment decisions in continuing field development, as well as to evaluating the potential of infill drilling and enhanced recovery methods.

Introduction

The Kuparuk River Field, located on the North Slope of Alaska, is under waterflood in 85 percent of the 100,000 acres currently developed. Waterflood performance evaluation is important to management of the existing waterflood, assessment of ultimate production, and evaluation of the potential for infill drilling and enhanced recovery processes potential for infill drilling and enhanced recovery processes in the field. Decisions regarding further development involve very large economic stakes and require early commitment of multi-million dollar investments. Therefore, early evaluation of the Kuparuk waterflood is an important, yet very complex task, given the staged waterflood development and its implementation in two zones that flood at significantly different rates.

The objectives of this work were 1) to investigate empirical methods of analysis best suited to the Kuparuk waterflood, 2) to project ultimate recovery where the waterflood is sufficiently mature, and 3) to assess waterflood performance relative to expectations and identify areas of performance relative to expectations and identify areas of poor performance. poor performance. This paper will discuss the methods employed to distinguish waterflood performance in the individual reservoir sands, the empirical methods used to project ultimate waterflood recovery, and comparison of results from different projection methods. projection methods.

Background
Geology

The Kuparuk River Field is located on the North Slope of Alaska approximately 40 miles west of the Prudhoe Bay Field (Figure 1). The Kuparuk reservoir is a lower Cretaceous sandstone formation deposited in a shallow marine environment, and contains in excess of 5 billion barrels of oil in place 1. The field produces from two physically separated zones, termed the A Sand and the C Sand, physically separated zones, termed the A Sand and the C Sand, which are shown on the log section in Figure 2. The A Sand, which is the lower sand member, consists of sequences of interbedded sandstones, siltstones, and mudstones. The A Sand reservoir rock is very fine- to fine-grained quartz and has an average permeability-thickness of 1000 md-ft (0.3 um2-m).

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