Subsurface Acid Gas Disposal Scheme in Wayne-Rosedale, Alberta

Abstract

Abstract The technology of disposing acid gas in subsurface formations is relatively new. In the past two years, this technology has been used increasingly by Alberta producers to handle small and uneconomic volume of acid gas. Prior to 1994, there was only one scheme in operation. at the end of 1995, 19 disposal schemes were operating or in the process of construction. PanCanadian Petroleum made a Nisku oil discovery in 1993 at Wayne-Rosedale, Alberta. In order to proceed with pool development and produce the reserves economically, a sulphur handling scheme had to be in place. The scheme chosen was subsurface acid gas disposal. Information on disposal technology available during the conceptual and design stages of this project was very limited with respect to published literature and operating experience. This paper is written to provide the reader with some details of the scheme and an overview of the steps taken to execute the project from conceptual evaluation to regulatory submission to start up and operation. The safety measures that PanCanadian has taken to ensure a safe operation are discussed. Introduction PanCanadian Petroleum made a Nisku oil discovery in the Wayne-Rosedale area, located approximately 100 kilometres northeast of Calgary, Alberta (see Figure 1) in October, 1993. The Wayne-Rosedale D2A Pool produces a 340 API oil with its associated solution gas containing 4 % hydrogen sulphide (H2S) and 17 % carbon dioxide (CO2). Subsequent delineation and development drilling indicated the pool has an estimated reserves of some 2.5 106m3 of oil and 250 106m3 of raw associated solution gas. To exploit these reserves economically, sour processing facilities would be required in this environmentally sensitive area. As shown in Figure 1, the pool and facilities are within 4 kilometers of Horseshoe Canyon, a very popular scenic view point that attracts many local residences and visitors. In 1988 the Alberta Energy Conservation Board (ERCB, now Energy Utilities Board - (EUB)) issued Information Letter (IL) 88-13 outlining a set of guidelines for sulphur recovery in sour gas plants. These guidelines stipulated that a gas plant with a sulphur throughput between 5 to 10 tonnes per day (Wayne-Rosedale was estimated at 5 tonnes per day sulphur) had to recover 90% of that sulphur. Even with sulphur recovery, the tail gas containing the remaining 10 percent sulphur and carbon dioxide still would have to be incinerated and the sulphur dioxide (SO2) and carbon dioxide would still be emitted to the atmosphere. The development project proceeded with the construction of an oil battery, gathering satellite, gas plant with sweetening facilities and an acid gas disposal scheme with a disposal well, compressor and a dehydration unit. The oil battery and gas plant came on stream in July 1995 with the acid gas disposal scheme commencing operations in December 1995. A Schematic of the facilities is shown in Figure 2. Evaluation of Sulphur Handling Scheme To meet regulatory requirements and satisfy public expectations on sulphur emission, some form of sulphur emission reduction was needed. The composition of the solution gas from the Wayne-Rosedale D2A Pool is summarized in Table 1. The estimated average daily solution gas production rate was approximately 100 103m3/d resulting in about 21 10m3/d of acid gas. In early 1994, a multi-discipline team (consisting of reservoir engineering, production engineering, geology, facility engineering and operation engineering personnel) were charged to develop a viable acid gas handling scheme. The options that the team evaluated were sulphur recovery, incineration, third party processing and subsurface disposal. P. 691