Green light given to first full-scale enhanced-oil-recovery project
Posted: 12 January 2005
The shareholders of Petroleum Development Oman (PDO) have taken the final decision to invest in the company’s first full-scale enhanced oil recovery (EOR) project as part of the development of a cluster of oil fields near Harweel, in south Oman. The $600-million field development, known as Harweel Phase 2A/B, builds on the earlier Harweel Phase 1 pilot project that resulted in four oil fields coming on stream in 2004, beginning with the Zalzala field in March. And it is the Zalzala field that has now been earmarked for a full-scale EOR project. The other oil fields to be developed in Harweel Phase 2A/B—Sakhiya and Dafaq—will, for the time being, be developed by means of conventional recovery techniques.
The principle of the EOR technique being applied at Zalzala—miscible-gas injection—is based on the blending of the gas with the oil in the reservoir rock, to form essentially one fluid. The single-fluid nature of the mixture makes it move much more easily through the reservoir and into the producing wells. In essence, the injected gas acts as an oil solvent that “cleans” the reservoir of its oil. Without the miscible-gas injection, only about 10% of the oil originally in place in the Harweel-cluster reservoirs could be expected to be recovered. But with the application of miscible-gas injection, the percentage of oil recovered can be increased to 33% or more.
Part of the gas to be injected into the Zalzala reservoir will be produced from the nearby Government-owned Rabab gas field and transported by pipeline to the oil-production facilities, where it will be compressed into deep injector wells. The hydrocarbons flowing from the producing wells will be separated into oil and gas components. The oil will then be shipped by pipeline to the coast, but the gas will be re-compressed and re-injected again and again until as much oil as economically possible has been produced from the fields in the cluster. “This EOR process is applied elsewhere in the world, but it had never before been done in Oman,” points out Harweel project manager Steven van Rossem.
But it was not the unprecedented nature of the recovery technique that made the project particularly challenging for PDO; it was the sheer scale of the endeavour. “The compressors required to inject the gas must generate tremendous pressures and are consequently huge,” says Mr van Rossem. “We also need pipelines to bring in the gas and large separators to process the gas/oil mix that is eventually produced. Moreover, the gas we are using contains hydrogen sulphide, which is highly corrosive. So the materials we use have to be of a special type. All of these things make this project a costly one. Nevertheless, we have made it commercially viable.”
The Harweel Phase 2A/B development will constitute one of the largest oil-field projects that PDO has undertaken in many years. But by adopting a phased approach to the development of all the Harweel-cluster fields (the first of which was discovered in 1997), PDO has minimized the overall investment risk. The Phase 1 confirmed the viability of miscible-gas injection at Zalzala whilst delivering some 15,000 barrels a day by the end of this year. Phase 2A/B will confirm the viability of miscible-gas injection at Sakhiya whilst delivering 50,000 barrels of oil a day by the end of 2007. Investment proposals for further follow-up projects are currently being prepared that, if approved, could grow the oil production from Harweel even further, to some 100,000 barrels per day in 2010.
Posted by Editor Pipeline Magazine
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