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JCPT92-04-07 BEST PAPER PRESENTED AT THE 42nd ANNUAL TECHNICAL MEETING A multiple-zone acid stimulation treatment of a horizontal wefl, Midale, Saskatchewan PATRICK J. McLELLAN, KEN H. LAWRENCE and KEN W. CORMIER Shell Canada Ltd. Calgary, Alberta ABSTRACT This paper describes an analysis of a multiple-zone acid stimulation treatment of a horizontal well in the naturally fractured Midale reservoir of southeastern Saskatchewan. Extensive characterization of the naturalfractures with a wellbore imaging tool and core studies indicated that most of the natural fractures in the stimulated section were nearly perpendicular to the well trajectory and were spaced at 1. A total of twenty seven, 4.5 m long, selected intervals of the openhole completed section were stimulated with retarded 15% HCl acid. Many of the pres:sure records also show cbmic fracture breakdown, propagation and shut-in characteristics. The well had a modest productivity improvement after the treatment although most of the producedfluid was water.
The 500 million barrel Midale oilfield is part of a trend of large Mississippian oil accumulations located in southeastern Saskatchewan, along the northern margin of the Williston Basin. The field was discovered in 1953 and developed on 80-acre spacing. In 1962 Midale was unitized for waterflooding, with 83 320-acre inverted ninespot patterns (Figure 1).
Waterflood performance in Midale is dominated by a system of oriented natural vertical fractures typically spaced 1-4 feet apart. Production wells located "ontrend" from injectors (aligned with the fractures) showed sharp early response to waterflood. In contrast, response of "off trend" producers was smooth and delayed. Oil produced to-date represents recovery of 20% of the original oil in place (OOIP); ultimate waterflood recovery is predicted to be only 24% OOIP. Current watercut in the mature operation is about 80% (Figure 2). Even with the natural fractures, the Midale Unit is a low-productivity reservoir, with average production rates of 75-100 STB/D/well.
A major reservoir and process mechanism characterization effort began in the mid-1980s to guide ongoing Midale field development opportunities. A detailed study team consisting of a geologist, a petrophysicist, and production, reservoir, and research engineers spent three years analyzing waterflood performance. The large-scale effort was dictated by the complexity of predicting performance in a heavily fractured reservoir. Obviously, good communication and cross-discipline integration of expertise was a key to the project's success. The resulting reservoir and process model honors all available data and can match performance of the field-scale waterflood as well as a tertiary CO2 flood pilot.
Ko, Stephen C.M. (SCMK Development And Engineering Ltd.) | Bakes, Phillip A. (SCMK Development And Engineering Ltd.) | Kehrig, R. (Saskatchewan Oil And Gas Corporation) | Chodzicki, John (Saskatchewan Oil and Gas Corporation)
EASKATCHEWAN The feasibility of infill drillin_g and waterflood modification in the Weyburn Midale Beds Voluntary U it No. 5 in Southeastern Sask wa was assessed. Detailed geol ical 0 REGINA and reservoir simulation studies were conducted to @inve tigate the various altematives for further development drilling using vertical and horizontal wells. WE'BURN* Various single well radi, two-dimensional and -dimensional models were employed to better unde tand the main