Simulation of Horizontal Well Performance While Waterflooding the Weyburn Midale Beds Pool of Southeastern Saskatchewan

Abstract

Abstract The feasibility of infill drilling and waterflood modification in the Weyburn Midale Beds Voluntary Unit No.5 in Southeastern Saskatchewan was assessed.Detailed geological and reservoir simulation studies were conducted toinvestigate the various alternatives for further development drilling usingvertical and horizontal wells. Various single well radial, two-dimensional and three-dimensional models wereemployed to better understand the main reservoir drive mechanisms duringprimary and waterflood operations. The models were calibrated by historymatching of actual pool production performance. Simulation results clearlyestablished the need for infill drilling, particularly with horizontal wells.which outperformed vertical wells by an order of magnitude. An 800 m horizontalwell was drilled and placed on production in September 1991. The earlyproduction results of the tirst horizontal well are compared to the modelpredictions. Introduction The Weyburn Field is located in the province of Saskatchewan, approximately 130km southeast of the city of Regina as shown in Figure 1. The Weyburn Midale Beds Pool was discovered in 1955 with the completion of Central-Del Rio Ralph1-06-7- 13W2M1 and was subsequently developed on 32 ha spacing. The main Weyburn Unit was formed in 1963 and an invented nine-spot waterflood scheme wasimplemented in April 1964. In 1977, Saskoil Weyburn 4-11-7-1 3W21M was drilled and completed in the Midale Beds extending the Weyburn Midale Beds Pool beyond the boundary of the main Weyburn Unit. Development of this extension by various operators has proceededsince 1977 on 32 ha spacing. In 1988, the Weyburn Midale Beds Voluntary Unit No.5 (the "Unit") was formed (Figure 1) and waterflood operations commenced in March 1988. A successful 40-acre infill well located at 3-11-7-13W2M wasdrilled in 1989 and prompted the initiation of an infill drilling: andwaterflood optimization study. The main objective of the study was to evaluatethe potential of further development drilling and modification of thewaterflood to increase production and improve the oil recovery from the Unit. Asecondary objective was to evaluate the merit of horizontal infill well versusvertical infill wells. Soon after the completion of the study in 1990, five more 40 acre verticalinfill wells were drilled and one existing producer was converted to waterinjection. Most of the five wells were drilled for both Midale and Frobishnerproduction and some wells were dually completed in both zones. Based on therecommendations of the infill drilling study, an 800 m horizontal well wasdrilled and put on production in September 1991. Currently the Unit consists of13 vertical producers, one horizontal producer, four water injectors and onewater source well. FIGURE 2: North Weyburn: permeability vs. porosity. Graph Available In Full Paper. Pool. The drilling, completion and initial production of the first horizontalwell in the Unit are also discussed in the paper. Geology The Weyburn Field is situated along the northeastern flank of the Williston Basin in southeastern Saskatchewan(1). The oil accumulation isconfined by an upper anhydrite seal and, at the Midale Beds subcrop, by lowpermeability Jurassic Red Beds silts.