This paper describes the potential benefits of using combinations of horizontal injection and production wells for EOR processes or waterflooding.
Our results show that a very favorable configuration occurs when two opposed horizontal wells are drilled from injection and production wells so that the opposed laterals are parallel in the patterns, and extended until the horizontal segments almost meet midway between the like wells. Compared to five-spot patterns with vertical wells, opposed horizontal wells can increase injectivity (injection rate per applied pressure drop) by as much as a factor of ten, depending on well spacing and formation thickness. Areal sweep efficiency can be increased by 25% to 40%. The horizontal-well advantages are greatest for thin formations with wide spacing, and decline significantly for thick formations and/or close spacing. Also, for a given injection pressure, the pressure gradient in the bulk of the reservoir can average several times greater when using opposed horizontal wells than when using vertical wells. This could significantly improve microscopic displacement efficiencies for EOR processes, such as micellar/polymer flooding, that are sensitive to interfacial tensions.
Because of the better sweep efficiencies, faster flooding rates, and/or lower injection pressures that are possible with horizontal wells, all EOR methods should benefit by their use. For example, polymer floods can be improved by the higher injectivity and lower rates of shear at the injection sandface. The advantages of horizontal wells for CO2 flooding include: (a) delayed CO2 breakthrough because of the better sweep efficiency, (b) the potential for maintaining the MMP in more of the reservoir with no increase in the injection pressure, (c) better injectivity at the same pressures, and (d) the opportunity to convert more pumped producers to flowing wells. Thermal EOR was not investigated in this work, but the cited references show that horizontal wells have been successful in several field applications and more projects are being planned.
