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ABSTRACT: Wildcatting the San Juan Sag, Interpretation of the Needham Medford #1-33

Wayne Loranc

In 1984 LoCo Exploration Corporation completed an investigative reconnaissance of the San Juan sag and the San Juan basin. The integrated scientific data were evaluated and the Needham Medford #l-33 location was staked. The objective was to achieve production under the Tertiary volcanics.

The primary technical problem was to obtain reliable seismic records below the volcanics. A check of the existing seismic data verified the problem; this was further substantiated by a literature search. An innovative and nonconventional solution resulted in acquisition of credible and useful data records. The use of Previous HitairNext Hit Previous HitgunTop sources and special processing techniques provided insight into the structural and stratigraphic framework. The integration of the surface geology and the seismic data confirmed the location of the Needham Medford #1-33 to be updip from a downdip show and separated by faults on either side.

Although the Needham Medford #1-33 proved dry, it is important because it encountered significant shows of oil and gas in sedimentary and igneous rocks underneath the Tertiary volcanics. The stratigraphic

section encountered was: Blanco basin, Conejos unconformity, Lewis Formation, Tertiary sill, Mancos Shale, Dakota Formation, Jurassic and Precambrian basement. Live hydrocarbon shows document the potential for production below the volcanics. Paradoxically, good shows were also encountered in the volcanic sill and the Blanco basin.

This exploration effort also documented the effectiveness of nonconventional seismic methods which resulted in interpretable records below the Tertiary volcanics.

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990