Monitoring The Mitsue Hydrocarbon Miscible Flood-Program Design, Implementation And Preliminary Results

Abstract The first two of three stages of a horizontal hydrocarbon miscible flood (HCMF) project have been implemented at the Mitsue Gilwood Sand Unit No.1, in Slave Lake, Alberta. Stage I was started up in May 1985 while the second stage commenced in May 1986. Stages 1 and 2 cover an area of 12500 ha with an original-oil-in-place of 57.2 × 106 m3. A project of this magnitude requires careful monitoring if the unit's technical and economic goals are to be achieved. A comprehensive monitoring program was developed to provide the data needed to evaluate and optimize flood performance. The program includes fluid sampling and analysis, tracer injection and analysis, pressure and profile surveys, numerical simulation, a data management system, and an observation well. This paper describes the monitoring program and the rationale for its different facets. The program for the surface sampling a produced well effluent is presented. Details are provided on the selection of five radioactive and two chemical tracers and the procedures used for their injection. In this tertiary project, produced fluid compositional changes are shown to be more reliable for estimating solvent breakthrough dates than GOR. Based on solvent breakthrough data to date, a correlation of solvent-oil ratio (SOR) to GOR was developed. The tracer breakthrough data are presented and analyzed. The tracer breakthrough data confirm that gravity override is taking place in the reservoir and, also suggest that the solvent is sweeping more than one sand layer. The implications of the tracer analysis results on reservoir continuity within the project area, areal sweep efficiency and on flood performance are discussed. Introduction The Mitsue Gilwood ‘A’ Pool was discovered in 1964. It is a sandstone reservoir, located 200 km northwest of the City of Edmonton, Alberta, near the town of Slave Lake (Fig. 1). It is a large pool, extending over an area of 48 000 ha or 475 km2 with an original oil-in-place of approximately 160 × 106 m3. The Mitsue Gilwood Sand Unit No. 1 commenced an HCMF in most of the waterflood swept areas of the unit in May 1985. Reservoir Geology The Gilwood sandstones are part of the Middle Devonian Watt Mountain Formation(l). The sands were deposited in a fluvial environment. This shallow dipping pool was formed by a stratigraphic trap (Fig. 2) with an extensive aquifer system located on the downdip, western edge. From depositional studies, the sands are divided into three groups-lower, middle and upper sands. The lower sands (layer 3) contribute less than 5% of the pool's reserves. They are made up of fine-grained, primarily non-channel, lower-meander reach and strand plain deposits. The lower sands are considered nonfloodable by the HCMF. The middle and upper sands (layers 1 and 2) are primarily channel deposits. The middle sands were deposited in the braided to coarse-grained meander reach of a fluvial system while the upper sands were deposited in the fine-grained braided to lower-meander reach regions of another fluvial system.