The paper presents the results of an empirical investigation of the behavior of pressure transients in two South Swan Hills Unit wells equipped with electric submersible pumps. Simultaneous pressure measurements taken at the intake and discharge of electric submersible pumps during build-up testing are compared. A comparison of predicted and measured pump intake pressures is made. Pressure transient testing using conventional pressure recorders located within the tubing (near the pump discharge) is discussed in terms of the accuracy of the results obtained. As well, the accuracy of acoustic well sounders and pressure sensors are evaluated by means of direct comparison with conventional pressure recorders.
The South Swan Hills Unit (SSHU) is located approximately 225 km northwest of Edmonton, Alberta (Figure 1). The Unit (Figure 2), operated by Amoco Canada Petroleum Company Ltd. since 1962, has produced 48.41 × 106m3 of 42 ° API oil from the Swan Hills member of the Beaverhill Lake formation (average depth – 2438 m, BHT – 112 °C). There are currently 187 producing wells and 62 injection wells in the Unit. During 1983, daily production averaged 4062 m3 of oil, 2076 × 103m3 of gas and 25,800 m3 of water. The Unit has operated under several recovery schemes (Figure 2) beginning in 1963 with secondary waterflood operations in the west side of the field. In 1973, a secondary hydrocarbon miscible flood project was initiated in the central portion of the Unit(l). In 1978, the east portion of the field was placed on a secondary waterflood. A tertiary hydrocarbon miscible flood scheme was initiated in the west waterflood area of the field in September of 1982.
Of the 161 producing wells located within the miscible flood portions of the Unit, 124 are equipped with electric submersible pumps (Figure 3). These wells account for 94% of the total liquid produced in the Unit (Figure 4). The balance of the producing wells either flow or are equipped with rod pumps.
Previous pressure surveys conducted within the miscible flood portion of the field were restricted to either injectors or wells equipped with rod pumps. While surveys conducted in this manner provided an accurate representation of average reservoir properties, pressure transient information valuable for stimulation design and problem diagnosis was not available from producing wells located in the more prolific portions of the reservoir. The pulling and rerunning of submersible pumps strictly for the purpose of installing pressure recorders for well testing was neither economically nor technically feasible. Acoustic well sounders, bottomhole pressure sensors and pressure recorders located at the pump discharge have all been used in the past to conduct pressure surveys on wells equipped with submersible pumps. However, data obtained by these methods was not thought to be sufficiently accurate for well test purposes.
Because of these problems, it was considered desirable to develop a technique to conduct pressure transient tests on wells equipped with submersible pumps which would both minimize costs and provide pressure transient data needed for well stimulation design and reservoir monitoring.