The objectives of this study were to identify factors controlling the performance of the horizontal well 10HZ-I 1-6-14W2 and make recommendations to improve the well's performance. A geological and reservoir model for the area around 10HZ-II was developed and simulated. A good history match of both the waterflood in the area and the horizontal well was obtained. The predictions of the performance of the well under various scenarios were generated. The recovery is improved by maintaining voidage replacement and by increased liquid production rates.
A workover on the "toe" of the well could increase the oil rate initially. but the well would water-out faster, for a lower ultimate recovery. If the well had been landed at the top of the Marly zone over its entire length, the production would have been better.
The Weyburn Unit is located approximately 130 km southeast of Regina, Saskatchewan (Figure I). The field covers approximately 180 km2 and consists of 627 producing wells and 162 water injection wells.
Oil is produced from the Midale Beds of the Mississippian Charles Formation, which were deposited on a shallow carbonate shelf in the Williston Basin. The reservoir is informally subdivided into an upper Marly and a lower Vuggy zone (Figure 2).
The Weybum field was discovered in 1954 and was completely delineated by vertical drilling by 1960. In 1964, the field was unitized and a waterflood was implemented using inverted nine spot patterns oriented in the NE-SW direction. Between 1985 and 1992 over 150 vertical infill wells were drilled within the Unit resulting in substantial incremental oil recovery. The infill drilling program concentrated on improving the waterflood performance and vertical wells were drilled on both 24 ha and 16 ha spacings within some areas of the field.
To date, only 25.8% of the 178 million stock tank m3 of medium gravity crude oil have been produced. The remaining oil in place represents a significant large for improved recovery schemes such as horizontal drilling.
In 1991, a horizontal drilling program was conducted in the Weyburn Unit. Three wells were drilled in different pans of the Unit to evaluate the potential and technical feasibility of applying horizontal technology in the field. With the number of economically attractive vertical infill targets declining, it was concluded that the future development of the Unit would be dependent on the successful application of this technology. Although promising, the results of this drilling program fell far short of what had been anticipated with only one well (10HZ-II) producing any appreciable amount of oil. The low overall productivity of these wells and the success of other wells in the area drilled by other operators led to an evaluation of the design parameters for horizontal wells, which included the development of a parametric numerical simulation study and a simulation evaluation of 10HZ-II, which is the subject of this paper The area simulated is shown in Figures 3 and 6. The reservoir properties are summarized in Table I.
The Marly is a chalky lagoonal dolostone with occasional by or limestone interbeds.