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POTENTIAL FOR INVASION OF UNDERGROUND SOURCES OF DRINKING WATER THROUGH MUD-PLUGGED WELLS: AN EXPERIMENTAL APPRAISAL
Smith, M. D., G. F. Stewart, R. L. Perry, W. A. Holloway, J. D. Holman Jr., M. D. Smith, C. D. Tautfest Jr., AND G. Overton. POTENTIAL FOR INVASION OF UNDERGROUND SOURCES OF DRINKING WATER THROUGH MUD-PLUGGED WELLS: AN EXPERIMENTAL APPRAISAL. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-98/075 (NTIS 98-167976), 1998.
The main objective of the feasibility study described here was to test the hypothesis that properly plugged wells are effectively sealed by drilling mud. In The process of testing the hypothesis, evidence about dynamics of building mud cake on the wellbore-face was obtained, as well as comprehension of changes that occur in drilling mud from the time it is placed in a well until it reaches equilibrium. A system was developed to simulate (a) building mud cake in a borehole; (b) plugging the well; and (c) injecting sale water in a nearby well, with concomitant migration of salt water into the plugged well. The system "duplicated" reservoir pressures, mud pressures, and reservoir-formation characteristics that develop while mud cake is built, as in drilling a well. Salt-water injection was simulated, to monitor any migration of fluid through a cylindrical synthetic-sandstone reservoir that was 3 ft. in diameter and 2 ft. thick. Porosity and permeability of the sandstone were similar to those of several natural reservoirs. A 2100-ft. well and ancillary equipment permitted controlled variation of simulated depth, porosity and permeability of reservoir rock, fluid composition, fluid pressure, injection pressure, and mud properties. Data were recorded continuously by computer.