Mobil's SAGD Experience at Celtic, Saskatchewan

Abstract

Abstract Following the 1996 success of two Single Well-Steam Assisted Gravity Drainage (SW-SAGD), wells in the Celtic Field, Saskatchewan, Mobil Oil Canada piloted a Dual Well-Steam Assisted Gravity Drainage (DW-SAGD), well pair in 1997. The well pair was located in the Sparky-General Petroleum, "channel" sands with a net pay thickness of about 20m and a dead oil viscosity of about 15,000 cP. The objective of the pilot was to obtain operational data for the design and drilling of horizontal wells, and the production performance of horizontal SAGD producers. The well pair has now been operating trouble free for over a year. A plateau oil rate of about 100 m3/d has been sustained during this period, at an extremely efficient Steam/Oil Ratio (SOR) of just under 2.0. This paper briefly reviews the geology and the reservoir in which the wells are located, the specifics of well design and construction, surface facilities, start-up procedure, and the performance of the wells. Introduction In November of 1996, Mobil Oil Canada (Mobil) submitted an application to Saskatchewan Energy and Mines (SEM) for an extension of the existing enhanced oil recovery project in Mobil's Celtic Field(1) (Figure 1). The application proposed to construct and operate two Dual Well-Steam Assisted Gravity Drainage (DW-SAGD) wells in the Celtic Sparky-General Petroleum (G.P.) sand pool. Approval was granted by the SEM on December 2, 1996. One DW-SAGD well pair was constructed to penetrate the optimum reservoir at a relatively horizontal position. Figure 2 shows the nature of the reservoir in the "channel" sands from log curves. The well pair is located in the southwest corner of section 16-52-23 W3M. Figure 3 shows a plan view of the surface locations and subsurface positions of both wells in relation to the SWSAGD wells (also drilled from the S.E. of section 17), and the thickest porous sand. The producing well was drilled over the period of December 16, 1996, to January 7, 1997, from 3A1-17-52-23 W3M with the bottom hole lying in 4B3-16-52-23 W3M. The steam injection well was drilled over January 8, 1997, to February 3, 1997, from 7A1-17-52-23 W3M with its bottom hole location in 8B3-16-52-23 W3M. The injection well uses the existing surface facilities that are in place for SW-SAGD pilot wells. The objective of the DW-SAGD pilot was to test the applicability and potential of DW-SAGD technology in Mobil's Celtic Sparky-G.P. "channel" sands. The pilot was implemented to FIGURE 1: Celtic field location: Upper Mannville Isopach (Available in full paper) obtain operational performance data for both the design and drilling of horizontal wells, and for sand containment and control of horizontal SAGD producers. Performance data will be critical for the design and operation of future DW-SAGD projects. Geology The Sparky and G. P. (General Petroleum) clastics of the Celtic Field represent a series of fluvial, estuarine, deltaic and marine environments. At Celtic, channels cut through the regional sands in a north-northeast direction. The widespread Rex Coal is always below the scoured surface of the valley and it forms the base of the described sequence.