Abstract

Since December, 1977, Gulf Canada has been operating a pilot project in West Willmar, S.E. Saskatchewan to establish the enhanced recovery resource base directly by initial determination of the production trend for waterflood and to determine the volume of oil that can be mobilized by the hydrocarbon miscible flooding process. Oil recovery due to waterflooding has been established and now enriched gas is being alternately injected with water.

This paper discusses important process design considerations related to this pilot. Such design parameters include:

  • enriched gas composition and slug size; and

  • mode of enriched gas placement.

Mathematical predictions of production performance are also compared with field data. Finally, comments are made on operating experience with certain specialized equipment used in this pilot operation.

Introduction

At the end of 1980 tertiary recovery development was expected to contribute 326*106 m3 (st) of oil as reserve additions to existing light crude oil pools in Western Canada, of which 23.7*106 m3 (st) was in Saskatchewan(l). This enhanced recovery reserve potential of Saskatchewan is concentrated mainly in the Mississippian formation with the Midale and Frobisher-Alida beds being the major targets.

After an initial review of the different enhanced recovery options available, it was concluded that hydrocarbon miscible flooding with alternating enriched gas and water injection offered the best recovery prospect for the pertinent carbonate reservoirs. Although a number of hydrocarbon miscible flood projects have been operated in Alberta no projects of this kind have been attempted in Saskatchewan. The reservoirs in Saskatchewan have geological and reservoir characteristics sufficiently different that a pilot test was warranted rather than immediate implementation of a full-scale recovery project. Therefore, a field pilot test was planned and a pilot location was chosen to be in a prolific part of the West willmar field.

Pilot Characteristics

The pilot site is 15 ha in area and surrounded by four existing producing wells as shown in Figure 1. Five new wells were drilled on 4 ha spacing in order to form two concentric inverted five-spot patterns centered on 3(3)-32, the injection well. As simulation and field results became available it was seen that, due to the proximity of wells J-J2, J(2)-32 and J(J)-32 and the specific configuration of these wells, a portionof the injected fluid is migrating directly towards 3–32. Thus, the actual injected fluid has a fiveway uneven split rather than a four-way split and the pilot may more realistically be considered a distorted six-spot pattern and is labelled the INNER pilot area.

The pilot rock and fluid properties have been discussed in detail elsewhere(2) and for convenience these characteristics are summarized in Table 1. Within the INNER pilot area, the oil-inplace at the beginning of the project was determined to be SO 400 m3 (st) whereas at the end of waterflooding there is left an unrecovered amount (enhanced recovery resource base) of 34 800 m3 (st).

The primary objective of performing the West Willmar pilot is to determine the ultimate oil recovery by hydrocarbon miscible flooding.

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