Critical review of field EOR projects in shale and tight reservoirs

The current routine practice to produce oil in shale and tight reservoirs is the primary depletion by combining horizontal well drilling and fracturing. The technology can only produce less than 10% of shale oil, and the oil recovery in tight reservoirs is also low. There is a big prize to be claimed in terms of enhanced oil recovery (EOR) in such reservoirs. To enhance the oil recovery in these reservoirs, a few ideas have been proposed and studied in laboratory (experimental and theoretical or modeling studies). Such ideas include gas injection, water injection, and surfactant injection, especially in huff-n-puff mode. This paper briefly summarizes the research results or conclusions from the laboratory studies first, then focuses on the practices and applications in fields. Field tests of different methods are reviewed and analyzed. It is shown that water injection has been applied in large scale field projects in tight formations and proved successful in China. CO2 injection has been tested many times in small scales in China. Several gas injection and water injection have been tested in US and Canadian shale reservoirs. Detailed results of those projects have not been reported, with test benefits mixed. Although surfactants are added in fracturing fluids to improve oil recovery performance, the mechanisms are not well understood.