Abstract

In order to develop an enhanced recovery scheme for the Caroline Cardium E Pool, Alberta, the feasibility of waterflooding and gas injection have been examined. Due to the poor injectivity of the Cardium E wells and a postulated higher recovery under high pressure dry-gas miscible displacement, implementation of water flooding was eliminated.

Applying a 3-Phase, 3D compositional simulator the reservoir performance of a primary depletion and a gas injection scheme was developed. A compositional model was necessary to account for mass transfer and changes in composition of this undersaturated highly volatile oil system. Miscibility is expected to take place through interphase mass transfer during the gas injection period. Special volatile oil laboratory studies were used in the phase behaviour matching and considerable emphasis was placed in the history matching to predict the drastically different gas-oil ratio performance of the wells.

Results of the model study indicated that dry-gas miscible displacement will provide an ultimate oil recovery of approximately twice the recovery obtained under' primary depletion. Additional hydrocarbon 1iquids recovered from the separator gas, through vaporization, provided a total hydrocarbon liquid recovery equivalent to 43 percent of the original oi1-inplace. This model study formed the basis of an application filed with the Energy Resources Conservation Board of Alberta requesting approval to implement an enhanced recovery scheme by dry-gas injection in the Caroline Cardium E Pool. The scheme has been in operation for about seven months and the reservoir performance is showing positive response of the high pressure dry-gas miscible displacement scheme.

Introduction

The Caroline Cardium E Pool discovered in June 1974 is located approximately 40 miles southwest of Red Deer, Alberta as shown in Map 1. The discovery well was the HBOG lO-16-34-6W5 which was followed-up by the drilling of five additional wells in the Bearberry Cardium A Pool, Twp. 34, R6W5.

The existence of a fourteen mi1e northwest extension to this Cardium trend was confirmed by the drilling of the Pacific et al Ricinus 10-22-36-8W5 in August, 1975 and subsequently confirmed by the Pacific et al Ricinus 11-28-35-7W5 in January, 1976. The areal extension involving Twp. 36–8, Twp. 35–7 and part of Twp. 36–7 will be referred in this study as the Pacific operated area. The oil reservoir in these wells was initially referred to as Cardium U Pool.

In August, 1976 an application was filed with the Board requesting a special 320 acre spacing unit comprising either the north half or the south half of the section. This request was based mainly because of the marginal economics for developing this thin pay-narrow type reservoir. This request was approved by the Board in all order prescribing drilling spacing units in the Caroline Area2 to be effective November 1, 1976. On this basis the well allowable was approximately 58 STB/D.

By December, 1976 a total of 3 wells was drilled in the Pacific operated area. At that time, based on pressure data and reservoir fluid analysis, Pacific filed an application requesting that the Ricinus Cardium U Pool and the Bearberry Cardium A Pool be coalesced into the Caroline Cardium E Pool.

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