Fracture Stimulation In The Glisp Tar Sands Pilot-Case History

Abstract

Abstract This paper reviews fracture stimulation of the McMurray formation in the Gregoire Lake In Situ Steam Pilot Project (GLISP), in northeastern Alberta. The purpose of the stimulations was to effect interwell communication between the injection and production wells prior to steam injection. In situ stresses measured at shallow reservoir depths, indicated a possibilityfor horizontal fractures, a very desirable prerequisite/or the potential success of the experimental pilot. Analyses of data collected during and following the final fracture stimulation in the pilot area on the I-I central injection well (i.e. tiltmeter data, bottomhole pressures, temperature profiles, tracer surveys, production response, laboratory experience, field observations) and fracture theory indicate that a very complex fracture geometry resulted with both horizontal and vertical components. These data were used to address an array of nine possible fracture geometries to determine the more probable fracture configurations). Interwell communication by hydraulic fracturing was achieved over short distances but not over the full well spacing of the pilot. Introduction Amoco Canada Petroleum Company Ltd., Petro-Canada, Inc., and the Alberta Oil Sands Technology and Research Authority (AOSTRA) are participants in an in situ experimental recovery pilot to investigate the feasibility of producing the heavy oil reserves in the McMurray formation in the Gregoire Lake area of the Athabasca tar sands deposit. This pilot known asthe Gregoire Lake In-Situ Steam Pilot or "GLISP" is located as shown in Figure 1. The pilot area, shown in Figure 2, was selected on the stratigraphy seen in the C-l abandoned core hole as being the preferred lithology in the general area. Three confirmation wells (D-l, D-2 and P-l) were drilled. Log evaluation indicated that the P-l well had the most suitable reservoir properties and therefore it was selected as the central injection well for the pilot. One observation well (O-1) was drilled and three producing wells were planned to be drilled triangularly spaced around this injection well (see original pilot configuration, Fig. 2). Drilling the three production wells was deferred pending the possible fracture stimulation of the central injection well. In addition, a tiltmeter survey was planned to monitor fracture evolution and better define the optimum locations for the wells. Injectivity tests run on the three confirmation wells indicated that fracturing would be required to accomplish communication between wells. Concurrent with the injectivity tests, in situ stress tests were also conducted to obtain fracture design data. The majority of these stress tests indicated closure pressures approximating the overburden pressure. In some tests there was also evidence of a much lower closure pressure. These data suggested the strong possibility of a horizontal fracture which would be preferred for the pilot. However, there was the distinct possibility of a vertical fracture, or more likely, a complex fracture geometry with both horizontal and vertical components. The P-l central injector was fracture stimulated through perforations at the base of the McMurray formation.