Chemical injection has been identified as one of the upstream strategies by PETRONAS for maximizing oil recovery from a Malaysian offshore oil field which is currently operating under waterflooding and declining in oil production. A chemical application roadmap from laboratory to full field scale was established with numerous technical evaluation stages. The recipe and formulation for this chemical injection were obtained from inclusive laboratory experiments studies including chemical screening, fluid-fluid, and fluid-rock evaluations.
Pilot field trial tests by single well chemical tracer (SWCT) technique were designed and executed to validate the laboratory results, chemical injection response, and to obtain an operating experience prior full field scale implementation. A simulation modelling study was carried out to obtain a scheme of injection, proper wells pattern, and amount of incremental oil recovery expected from this application. Moreover, an integration study from subsurface to surface including reservoirs, wells, and surface facilities were conducted to find an appropriate development concept and reduce the overall project costs for ensuring being a techno-commercially viable project.
Laboratory results verifies that a chemical injection consist of 1.0 wt. % alkali and 0.075 wt. % surfactant in an optimum salinity range of 5,000-10,000 ppm and adsorption of 0.30 mg/gr-of-rock should establish an ultralow IFT of 0.001 dyne/cm system and result in 50-75 % Sorw reduction. Favorable results achieve from pilot testes where successfully mobilized substantial amounts of Sor and chemicals easily mixed with no injection problems encountered. They were consistent with laboratory findings and validated a 50-80 % Sorw reduction. Minimum residual oil saturation of 0.06 and 0.08 were seen after chemical application. Soft-water buffers were planned to minimize competing reaction of alkali and allow surfactant to work in more favorable lower salinity water and fortunately, results show that it was not severe enough to prevent the AS system from working. The contrast of initial waterflooding Sor after first pilot completion in two wells indicate an increase of 0.04 in Sorw (0.16 to 0.20 and 0.27 to 0.31) which, interestingly it could be due to a shift in rock wettability toward more water wet system. Modelling study shows a four-year plan including three-year of AS slug and six-month of pre and post buffers is an optimum injection scheme.
This paper presents an outlook of the chemical project. This knowledge is extremely useful in guiding future laboratory studies and field implementation. Although, chemical was verified technically but significant efforts were made to gauge the development concept with harsh offshore environment, large well spacing, and chemical handling. This study can be used as a technical reference address various challenges that are often encountered in implementing chemical EOR, particularly at an offshore environment.