The design, construction, startup, and operating phases of major projects involve several different people. Operating problems encountered subsequent to initial startup are not always communicated to designers. This can result in design errors being repeated and costly modifications being required after initial construction.
The intent of this paper is to review several operating problems encountered in producing the Hanlan Swan Hills gas field since startup in March 1983. These problems and the resulting recommendations should be considered in the design and operation of future deep sour gas systems.
The Hanlan Swan Hills gas field is located approximately 25.7 miles (41.4 km) southeast of Robb, Alberta. The field has 8 gas wells producing to a central dehydrator station as shown in Figure 1. The well depths are all between 15,000 feet and 16,000 feet (4572 m and 4876 m). The Swan Hills formation pressure and temperature is 5700 psi (39,300 kPa) and 293deg.F (145deg.C) respectively. The produced fluids are sour with a composition shown in Table 1.
Gas from the wells flows through the first pass of a glycol bath heater, a choke valve, a meter run, the second pass of the of the heater and into an insulated multiphase gathering system. The maximum operating pressure of the gathering system is 1798 psi (12,400 kPa). Water is removed from the produced gas at a central desiccant dehydration facility. The dry gas and water are then transported via separate pipelines to the Hanlan Robb plant for further processing. The design production from the Hanian field is 220 MMscf/D (6243 103m3/D).
Since the startup of the Hanlan field in March 1983, several significant operating problems have been encountered these include higher than design pipeline operating temperatures, diamantane deposition, pyrite formation in the dehydrator regeneration gas piping, rapid well choke valve erosion and downhole scale formation.
The Hanlan gas gathering system was designed to operate at a maximum temperature of 122deg.F (50deg.C) assuming a -18.4deg.F (-28deg.C) installation temperature. After startup it was found that the actual operating temperatures were as high as 169deg.F (76deg.C)- On March 30. 1983. the pipeline from the 6-29 well ruptured at a 120 horizontal bend located in muskeg. At the time of rupture the pipeline was overpressure to 2284 psi (15750 kPa). Metallurgical investigation of the ruptured pipe indicated that the primary mechanism contributing to failure was high mechanical stress induced by thermal expansion.