The Introduction of the Microchanneling Phenomenon to Cyclic Steam Stimulation and Its Application to the Numerical Simulator (Sand Deformation Concept)

Ito, Yoshiaki, SPE, Gulf Canada Resources Inc. Abstract Historically, a vertical or horizontal fracture is believed to be a main recovery mechanism for a cyclic steam-injection process in unconsolidated oil sands. Most current computer process in unconsolidated oil sands. Most current computer models for the process are based on the fracture concept. With the postulated sand deformation concept, on the other hand, the injected fluid is able to penetrate the unconsolidated oil sand by creating micro channels. When the pore pressure is reduced during production, these secondary flow channels will collapse totally or partially. Condensed steam tends to sweep fluids where the bitumen had been heated and imparts mobility as a result of the injected hot fluid. Flow geometry of the new concept is described in this paper. The physical differences between the sand paper. The physical differences between the sand deformation zone and the no-deformation zone are also investigated. The three major differences between these two zones are porosity change, pressure level, and energy and flow characteristics resulting from the existence of micro channels. All these modifications were incorporated successfully into a conventional numerical thermal simulator. The new model provided an excellent match for all the field observations (steam-injection pressure, oil-and-water production rates, fluid production temperature, downhole production rates, fluid production temperature, downhole production pressure, and salinity changes) of a production pressure, and salinity changes) of a steam-stimulated well in an unconsolidated oil sand. The study indicates that the most important phenomenon for in-situ recovery of bitumen is the one-way-valve effect of the micro channels, which are opened during injection and closed during production. Introduction A physical interaction between the injected fluid and the reservoir formation is required to inject large volumes of steam into the oil sand formation. Until now, this physical interaction was believed to be a vertical or a physical interaction was believed to be a vertical or a horizontal fracture, depending on the strength of the directional stress. Many authors investigated and incorporated this concept into numerical thermal simulators and used it for history match and prediction studies. There are many difficulties in analyzing the actual performance of steam stimulated wells by means of the performance of steam stimulated wells by means of the fracture concept. Some of the evidence is extremely difficult or impossible to explain with the conventional fracture concept. A few of these problems are discussed later. I, therefore, have postulated a new flow geometry to achieve a realistic interpretation of well performances. The new flow geometry has been termed the "sand deformation concept." The well performance characteristics for the bitumen recovery process can be described more clearly with the new concept process can be described more clearly with the new concept than with the conventional fracture concept. Sand Deformation Concept Although unconsolidated oil sand might not behave like a consolidated rock under stress, fracturing is assumed to be an important mechanism in most mathematical models for in-situ recovery of bitumen by steam injection. Fig. 1 A shows this process when the horizontal fracture is assumed to be the main recovery mechanism. Injected steam and condensate are contained primarily in a thin fracture zone so the fluid accommodated in the fracture will leak off. The process is similar to a linear displacement of oil by hot fluid. With the sand deformation concept, on the other hand, the injected fluid is able to penetrate oil sand through the creation of micro channels. Fig. 1 B shows this process. Since the micro channeling is postulated in the new model, a significant amount of resident fluid, including oil and connate water, will remain around the well without contacting the injected fluid. The extra space required to create the channels may be obtained by overburden heaving. Therefore, overburden movement will control the directional orientation of the channel creation. The preferential directional orientation is likely to be created as a result of preferential overburden movement. preferential overburden movement. Fig. 2 shows the rough dimensions of the pressurized channeling envelope surrounding the well when approximately 10 000 m3 [353,147 cu ft] of cold water equivalent as steam was injected. The shape of the areal extension is determined from the strength of the overburden stresses. SPEJ p. 417