Waterflooding Optimisation Using a Multi-Action Technology in the Mature West Siberian Oil Field

Abstract

In mature fields developed by water flooding, oil companies keep trying to fight premature water encroachment in producing wells caused by heterogeneous reservoir permeability and non-uniform displacement front advance. Changes in pressure gradients and flow rates and increased effects of adsorptive, osmotic and capillary forces result in significantly reduced oil permeability and low production from low-permeability intervals. The chemical technology has been developed for the combined effect of selective water shut-off and change of rock properties from water wet to oil wet or visa versa to form a new phase on the rock surface, which produces significant excess energy used to recover residual oil. The effectiveness of this technology has been tested in a reservoir modelling laboratory by studying the compatibility between the agents employed and reservoir fluids and flow tests conducted on three areal heterogeneous reservoir models. Tests have shown that the agents used in the technology retain their functionality at high temperatures of up to 120°C and a formation water salinity of 10–127 g/l with no adverse effect on oil quality. The ultra-fine reagent reducing interfacial tension at the oil-water interface under reservoir conditions to 0.005 mN/m was studied in the laboratory. Geological and production data show that the main problem of the pilot areas is early encroachment of production wells by injected water because of its breakthrough and subsequent unwanted flow through the most permeable and depleted layers. Tracer studies, conducted in injection wells using tracers that moved through flushed channels towards wells with high production rates and high-water cuts, identified zones of ineffective injection. Treatments using multi-action technology in four pilot areas of the field produced the following effects: Redistribution of injected water flows by increasing the residual resistance factor in high-permeability zones and redirection of flows into previously inactive reservoir zones.Incremental oil production from four areas over 10 months was 2745 tonnes with a lasting effect. The novelty of the multi-action technology consists in targeted treatment of oil reservoirs and displacement of residual oil through selective isolation of water-encroached zones. The energy produced at the phase interface is used to separate film-bound oil, move globular oil through pore throats and increase oil flow rate and oil permeability in the reservoir irrespective of its geological and mineralogical characteristics or formation fluid properties.