Dos Cuadras Offshore Polymer Flood

Abstract

Abstract An offshore polymer flood in the Dos Cuadras field near Santa Barbara, California was implemented early in 1986. The polymer selection process included laboratory screening and a month long field injectivity test with three prospective polymer suppliers. Polymer injectivity, required polymer concentrations Polymer injectivity, required polymer concentrations to meet design viscosities, the need for additional polymer inversion chemicals and core plugging polymer inversion chemicals and core plugging behavior of the polymer solution were critical parameters in this evaluation. Full-scale equipment parameters in this evaluation. Full-scale equipment design was aided by observing the performance of skids supplied by each vendor for polymer inversion and injection. Following the selection of a polymer product, shear tests were conducted to improve product, shear tests were conducted to improve polymer solution injectivity through Berea core polymer solution injectivity through Berea core plugs. Although these tests were sufficient to plugs. Although these tests were sufficient to ensure injection into the EP zone, additional shearing of the polymer solution was required to improve injectivity into the FP zone. A filtration test, which was found to be more sensitive than the core plug test to the plugging behavior of polymer solutions, was used to compare properties of injected solutions for the FP zone. Hall plots have been found to be useful for understanding the response of the injection wells to the various injectants. Introduction Lease OCS P-0241 has three offshore platforms, "A", "B" and "C", which stand in 190 feet (58 meters) of water. Peripheral waterflooding began in 1971 into the EP and FP zones. Dual well completions are used for the injection wells with one string in each zone. The EP zone has a nominal surface injection pressure limitation of 200 psi (1380 kPa) at a depth pressure limitation of 200 psi (1380 kPa) at a depth of 1150 feet (350 meters) subsea while the FP zone has a nominal limitation of 400 psi (2760 kPa) at a depth of 1700 feet (520 meters) subsea. The average thickness of the EP and FP zones are 151 feet (46 meters) and 87 feet (27 meters), respectively. Laboratory work showed the polymer flooding process could improve and accelerate oil recovery. The poor mobility ratio, low reservoir temperature and poor mobility ratio, low reservoir temperature and existing injection system were all favorable for polymer flooding. Conversely, the saline brine, polymer flooding. Conversely, the saline brine, the restricted wellhead pressure and the offshore location of the field were judged to be negative factors for implementing a polymer flood. Laboratory testing suggested that a three slug tapered design be used consisting of 5.5 cp, 3.5 cp and 2.2 cp (5.5 mPa s, 3.5 mPa s and 2.2 mPa s, respectively). Based on both laboratory data and the existing peripheral waterflood, a polymer slug size of 0.5 pore volume was selected. Background Polymer selection for the offshore polymer flood Polymer selection for the offshore polymer flood was made by comparing three emulsion polyacrylamides during a 30-day injectivity test. All three polymers were chosen for field testing based on polymers were chosen for field testing based on laboratory studies. The chosen polymer was selected based on lower overall cost and ease of injection even though some samples failed the core plug test for injectivity. Polymer injectivity was a critical parameter because of the severe pressure limitations of the shallow reservoir. No additional chemicals were required to assist the inversion of the chosen polymer, as were needed for the other candidates. This feature requires one less pump per skid and substantially reduces the possibility per skid and substantially reduces the possibility of injecting uninverted polymer into the well, which can result in major formation damage. Later studies showed the chosen polymer passed all core plug tests when mild shearing was performed on the concentrate stream prior to dilution. P. 391