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Water and Gas Injection Methods |
Mobil Research and Development Corporation, Mobil Exploration and Producing Technical Center, 13777 Midway Road, Dallas TX 75244, USA
A method involving the addition of water-soluble gas to exploit relative permeability relationships is evaluated for its potential to modify a waterflood profile. In this process, a soluble gas is added to injected water in an amount such that a single-phase aqueous solution enters the formation; however, the bubble point pressure is crossed in the steeply varying pressure profile around an injector. Solution gas alters the relative permeability to water in those zones taking water. Thus, the current water injection profile transports profile modification agent to the zones which need it most. Analytical model results for the radial flow of dissolved gas and subsequent gas evolution indicate that gas saturation is partitioned according to the permeability-porosity ratio. For most cases, this results in beneficial profile modification by three-phase relative permeability effects. Relative permeability reduction by a factor of three is anticipated through the nucleation of a trapped gas saturation. Gas saturations accumulate with time, making the process more beneficial with continued implementation. Though initially this process yields a near-wellbore treatment, prolonged application produces a trapped gas zone deep into the reservoir. Gas evolution away from the injector aids in injectivity maintenance. Increase in microscopic displacement efficiency, in addition to volumetric sweep, is also expected. Nitrogen, methane, and carbon dioxide are screened as potential water-soluble additives.
