Fracture Geometries Consistent With Ttiltmeter Data And Pressure And Tracer Communication In The Glisp 1-1 Stimulation

Abstract

Abstract The Gregoire Lake In-situ Steam Pilot (GLISP) in the Athabasca tar sands, includes three producing u:ells surrounding an injection well. The authors modeled tiltmeter records of the fracturing treatment of the central injection well, and pressure and tracer communication from the central injection well to the producing wells, and investigated how these analyses support various fracture geometry scenarios. Several different fracture geometry scenarios have been examined. Theorencal surface tiltmeter vectors for these scenarios are compared with observed vectors. Also, theoretical time delays based on propagation of pressure transients and tracer material have been predicted for these scenarios, and compared with observed delays. The results of these comparisons are expressed in the form of a "range" of fracture geometries that are most consistent with measured tiltmeter data in the field, and pressure and tracer time delays in the three production wells. Interpretations within this range include complex fracture systems with one or two fracture components rising steeply from tire base of the McMurray Formation into the overlying depleted zone. Dominant horizontal fracturing does not appear to occur. Introduction The Gregoire Lake In-Situ Steam Pilot (GLISP), in the Athabasca tar sands, includes three producing wells, P-l, P-2, and P-3 surrounding an injection well, I-1 (Fig. la). On February 5, 1987, the injection well I-1 was fractured with about 114 m3 (30 000 gallons) of linear gel without proppant, to communicate with the producing wells. The cased well was fractured through notches near the bottom of the McMurray Formation. Profiles of bottomhole treating pressure and rate are shown in Figure 1b. A wide variety of diagnostic information has been evaluated in regard to the geometry of the induced fracture by MacKenzie, et al. (1). Several different fracture geometries are ranked, in order, according to how consistent they are with these data. The most probable fracture geometry is a U-shaped fracture, or variations of this generic shape, such as a non-symmetric U-shaped fracture, an L-shaped fracture, or an elongated bowlshaped fracture. The goal of this paper is to examine how consistent are three totally independent diagnostic observations of fracturing (tiltmeters and pressure, tracer communication). Delays in pressure transient peaks at the three production wells varied from 1.1 to 3.6 hours (from beginning of fracture). Hot water and tracers were injected after the treatment to assess communication with the other wells in the pilot The time to maximum tracer at the producing wells was 3 to 6 days. Several different fracture geometries scenarios have been examined. Using an in-house code, theoretical surface tilt meter vectors for these scenarios are compared with observed vectors. Also, theoretical time delays based on propagation of pressure transient and tracer material have been predicted for these scenarios, and compared with observed delays. The results of this analysis are expressed in the form of a "range" of fracture geometries that are most consistent with these data.