This paper presents a short analysis of the mechanisms which may increase oil recovery by using high pH injection water in the Wainwright field, and the screening techniques used to determine the feasibility of a pilot scheme. The pilot equipment is described and reservoir performance for the first ten months of pilot operation is reported. The pilot is the first caustic flood to use gas plant spent caustic as the injected material. It is also rather unique in that it was designed to test the economics of caustic flooding on an 80 acre area, which is relatively large compared to previous work.
Over 60,000 barrels of water at 240 barrels of water per day with an average pH of 12.5 have been injected into the Wainwright pilot injector. No production response has occurred; however, injection well injectivity index doubled in the two months after caustic injection commenced. An increase in new oil recovery in the order of 5% original oil in place may be predicted from initial results. The recovery increase needs to be confirmed after more data is obtained, and investigation into optimum slug size and concentration is complete.
In June, 1974 an investigation into improved oil recovery from the Wainwright area was commenced. A review of polymer, surfactant, gas injection and thermal processes showed that they would probably not be economically competitive with the present waterflood. After some laboratory work and screening a caustic waterflood was initiated in the Wainwright field on May 27, 1976. This pilot is the first sodium hydroxide flood attempted in Canada and the first waterflood that we know of which uses gas plant spent caustic in the injected fluid. The pilot was tailored so that Pacific's Empress gas plant spent caustic could be disposed as a beneficial side-effect of the project. Figure 1 shows the location of the Wainwright field and Figure 2 the well status within the pilot area.
The Wainwright-Lloydminster area has been assigned approximately 160 million stock tank barrels of remaining oil reserves under present primary and waterflood recovery schemes. Oil gravity varies from 15 ° API to 25 ° API.
The Wainwright pool was discovered in 1923 and has been extended and developed sporadically up to the present time, influenced by economic conditions and market demand. The first water injection project commenced in 1962(1). The pool has been developed under 20 acre drilling spacing units using an inverted 9 spot injection pattern over an area of about 15 Sections.
The reservoir was formed by combined structural and stratigraphic trapping with localized gas caps and water zones occurring within the undulating sand body. Deposition of the 12 foot Wainwright sand occurred in a marine environment during Lower Cretareous times in a sand-shale sequence of about 500 feet thickness. The sand is very fine grained, well sorted and friable. Permeability varies from greater than 500 millidarcies in the top three or four feet of net pay down to 10 millidarcies at the bottom.