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The Sirikit Field, a mature onshore field operated by PTTEP in northern Thailand, derives production from sandstone reservoirs. While production from many of the shallow pays have been well-developed and optimized, comparatively few of the deeper and tighter sands have been similarly produced. Various methodologies have been trialed to enhance production from these tight sands and an examination of results will be presented in the context of geology, engineering and economics. This field, like most in the world, was produced initially by primary recovery (natural flow and various artificial lift mechanisms). Later in the development phase, secondary recovery (waterflooding) was implemented in the Sirikit Main area with the aim of improving production from the shallower, higher permeability, reservoirs. The deeper, lower permeability, sands have not undergone secondary recovery. It is foreseen that the vast majority of STOIIP can be extracted from these tight sands and will ultimately be the future of Sirikit long term production. Several secondary recovery methods were evaluated. Waterflooding was ruled out as an option due to poor reservoir properties which were not favorable for flooding displacement as well as a high injection pressure requirement. The focus then became well stimulation as the main strategy to enhance production from these tight reservoirs. Initial well stimulation technology was the use of larger size perforation guns for the low porosity sands in order to improve reservoir penetration and overcome damage zones. Analysis after field trials showed that the deep penetration perforations had insignificant production improvement. Consequently, solid-propellant technology, which is capable of creating near wellbore fractures, was field trialed. Two types of solid-propellant were tested: "regressive" burning propellant and "progressive" burning propellant. The "regressive" burning propellant results were inconclusive; however, the "progressive" burning propellant results showed clear improvements in production. Moreover, in order to create deeper fractures, "hydraulic fracturing", which requires higher investment, was tested in parallel to the smaller scale investment perforation guns and solid-propellant; however, the results were no better than the "progressive" burning propellant. Consequently, the "progressive" burning propellant provided the positive results at the best economics. Different well stimulation technologies may be appropriate for varying geologic, engineering and economic conditions. For tight or damaged reservoirs, progressively burning propellant may prove to be the most efficient and cost effective technology for secondary recovery. |
