Use Of Production Logging And Reservoir Simulation To Improve Waterflood Conformance And Oil Recovery From The Hemlock Reservoir, McArthur River Field, Alaska
Authors: Cordiner Frank S. , Carlson Gary E. , Scheve Don F. 
Published: December 2007

Efficient oil recovery from layered reservoir systems by water flooding is dependent on knowledge and control of both vertical and areal conformance. This paper describes causes of poor conformance as well as the techniques for defining conformance of a large waterflood. These techniques have been useful and successful in improving conformance which has resulted in improved oil recovery.

Introduction

The McArthur River Field is the largest of several oil and gas fields located offshore in the upper Cook Inlet of Alaska (Fig. 1). The field was discovered in 1965 and unitized in 1967. Development of the field followed the setting of three drilling and production platforms. A total of 78 wells have been drilled to the Hemlock from the three platforms. Of these, 56 currently produce oil while the remaining 22 are water injection wells. The field produces oil from three reservoirs, with the Hemlock produces oil from three reservoirs, with the Hemlock being the major producing formation. The Hemlock reservoir has produced more than 370 million barrels of oil. This represents a recovery of more than 30 percent of the original oil-in-place.

Pressure maintenance by water injection was initiated in the highly undersaturated Hemlock reservoir during 1969 to arrest the rapid decline in pressure. Nearly 540 million barrels of water have been injected into the multi-layered reservoir through the 22 water injection wells situated around the periphery of the field. The current rate of water injection is approximately 160,000 barrels per day, with peak rates having been as high as per day, with peak rates having been as high as 184,000 barrels per day. Water for injection is taken from the glacial silt-laden waters of the Cook Inlet. All equipment for filtering, treating, and injection are located aboard the platforms. Because of the layered nature of the Hemlock, production logging was employed early in the life of production logging was employed early in the life of the field as a means of monitoring the productivity and injectivity of individual zones, or benches, which make up the reservoir system. A large amount of production and injection profile data in individual wells have been accumulated. These data have been useful in analyzing the changes in productivity and injectivity which have occurred during the course of the waterflood. The accumulated data have provided evidence that water breakthrough has provided evidence that water breakthrough has occurred prematurely in certain benches in some wells while other benches have not yet been invaded. They have also shown that the uninvaded benches are sometimes severely damaged following the appearance of water in the wells. These problems have had an adverse effect on the conformance of the waterflood, which, if not managed properly, will result in a substantial loss of production and oil recovery.

Profile data were used to determine the relative vertical distribution of produced and injected fluids between the various benches. By incorporating these data into reservoir models of the individual benches, it has been possible to gain a better understanding of the areal conformance of the flood as well. These techniques have been effective in evaluating the overall efficiency of the waterflood, and in developing plans for management of the Hemlock reservoir.

GEOLOGY AND CHARACTERISTICS OF THE HEMLOCK RESERVOIR

The geology and physical characteristics of the Hemlock reservoir are important to the understanding and analysis of performance of the water injection program. Figure 2 is a structure map of the program. Figure 2 is a structure map of the McArthur River Field showing contours on top of the Hemlock. The field consists of two anticlinal features having axes which trend generally north and south. The total productive area of the two adjoining features is approximately 12,000 acres. The main feature contains approximately 9,500 acres. The productive area is bounded by an oil-water contact, except on the northwest feature where the boundary is a northeast-southwest trending thrust fault.