Abstract

The Silverdale Wet In Situ Combustion Pilot in the Sparky Sand, Saskatchewan, was initiated in 1972 and was in operation until Dec., 1980. This paper discusses the basic design of the fireflood and compares performance with the predicted behavior. The detailed operation of the pilot is discussed in another paper (1).

The original design of the wet in situ combustion pilot was based upon the concept of a heat wave-type process. Air and water injection rates were selected to conform with this concept. The heat wave temperature was to be in the range of 400 °C initially, dropping to about 150 °C upon curtailment. The actual performance of the project seems to be in fair agreement with the design. The oil displacement efficiency in the swept region was high, being about 80 per cent. The oil production performance was close to the prediction, with the air-oil ratio being of the order of 756 sm3/sm3. In spite of the efficient drive underground, the project suffered from a series of operationa1 problems related to well pumping. These are discussed in Ref. 1, and were responsible for the poor economics of the pilot.

It is concluded that a heat wave type combustion drive is technically feasible and efficient in the Sparky Sand. In the Silverdale combustion pilot it was possible to operate at low temperatures, with a low air-oil-ratio and yet achieve high oil displacement efficiency.

Introduction

The Silverdale South Sparky Pool was developed in the fifties, with 36 producing wells on a 4 hectare spacing. Formation depth is 564 m. and thickness averages 5.5 m. Initial well productivities were 5.0 m3/day oil and 0.3 m3/d water. Final water cuts before field shut-in, in early sixties, were of the order of 90 per cent. Selected field data is given in Table 1. Reference can be consulted for a detailed description of reservoir geology and production behavior. In 1972, when the reservoir was considered for in situ combustion, the cumulative oil production from the pilot area was 20 740 m3, i.e. approximately 9 per cent of the oil in place. The oil saturation estimated to be 80 per cent. The oil is a 14 ° API asphaltic crude, with a viscosity of 4420 mPa.s at 21 °C (formation temperature is 28 °C).

PILOT OBJECTIVES

The principal objective of the pilot was to develop a recovery technique for a thin, marginal, depleted sand, that is to say, the Sparky sand in the pilot area, which would be applicable to other thin formations in the Lloydminster heavy oil reservoirs. The recovery methods of alkaline flooding and immiscible carbon dioxide flooding were considered for the pool. Both were ruled out in view of lack of field experience at the time (1972). (Unfortunately. the situation has not changed much in this regard over the intervening years). Thermal recovery methods considered, consisted of steam injection and in situ combustion.

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