Abstract: Determination of Flow Potential from Oil Reservoirs to Underground Sources of Drinking Water (USDW) in the San Juan Basin, New Mexico

R. C. Laudon, D. L. Warner, L. F. Koederitz, S. Dunn-Norman

As part of the permitting process for all new or newly converted class II injection wells (salt water disposal and secondary recovery injection wells), an Area of Review (AOR) study is required according to the Underground Injection Control Regulations promulgated in 1980 under the Safe Water Drinking Water Act of 1976. An exemption from the AOR requirement may be granted for a single well, a specific area, or a whole basin if it can be shown that the oil reservoir is underpressured relative to the USDW.

To demonstrate the underpressure relationship, the procedure requires that reservoir pressures be converted to freshwater hydraulic-head elevation equivalents using the base of the USDW as the datum. These elevation heads are then compared against USDW elevation heads, and residuals are generated either graphically (using map overlays) or by subtracting grids on a computer and contouring. A negative residual implies that the hydraulic gradient between the oil reservoir and the USDW is such that there is no potential for contamination from the oil reservoir to the USDW. Examples from the San Juan basin of New Mexico indicate that the procedure is simple in concept but complicated in practice.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994