ABSTRACT

This study evaluated the application of low-salinity water flooding (LSWF), whose predominant oil recovery mechanisms strongly depend on reservoir properties and conditions, to a clastic reservoir in an offshore field in Vietnam through laboratory work and simulations. In the laboratory, three coreflood experiments with tertiary low-salinity water (LSW) injection were conducted. An increased recovery of 2–17% over that for secondary high-salinity water (HSW) injection was observed, with an increase in differential pressure. Through pre- and post-coreflood analyses, some existing ideas on the alteration of rock surface conditions were discussed; however, emulsification was found to be one of the possible dominant phenomena. In cases where emulsions were observed, blockage and path-change by emulsions were suggested based on oil recovery and differential pressure behaviors. The relationship between the degree of blockage and the pore structure was discussed to support this. These results offer additional insight into the enhanced oil recovery (EOR) effects of LSW.

In simulation studies, low-salinity relative permeability curves for coreflood experimental results were derived via the black-oil reservoir model, in which the effects of EOR on characteristics such as the recovery factor and differential pressure were reflected based on the permeability distribution. The water treatment capacity of a desalination plant using reverse osmosis and nano-filtration membranes in parallel was considered as the simulation constraint. A 3.5% increase in the recovery factor was achieved for the full-scale application of low-salinity case, but a sensitivity study considering the water treatment capacity constraint suggested lower performance upon LSW injection. Thus, while a desalination system is installed on the existing platform, the extension of the platform and its facilities, such as the water intake system, is important.

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