Seismic expressions of igneous sills in San Juan sag, south-central Colorado: Humps or bumps, tricks or traps

Conference · Fri Sep 01 00:00:00 EDT 1989 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:5631179

Ray, R R ^[1]

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1. Exploration Corp., Lakewood, CO (USA)

Petroleum exploration in the San Juan sag of south-central Colorado has been an exciting but frustrating experience. Thick surface volcanics cause seismic data to be fair to poor quality and often make mapping of the stratigraphy difficult. Some of the strongest reflections are igneous sills intruded parallel to the bedding planes of prospective horizons. Sills are dense, high-velocity (13,000-18,000 ft/sec) layers which stand out as high-contrast reflections in the lower velocity Cretaceous shales and to a lesser extent in the similar velocity Dakota, Morrison, and Junction Creek sandstone sections. Almost every well drilled in the San Juan sag has had at least one sill present in the Cretaceous or Jurassic section. Sills vary in thickness from 6 to 1,036 ft, with most common thicknesses from 200 to 500 ft. On seismic data the strong reflections caused by the velocity contrast of the igneous rock make the sills stand out as amplitude anomalies. Since the sills are additive to the section, they can cause bumping or thickening which may appear as a structural bump. Several wells have been drilled on these apparent structures. Color displays of seismic amplitude and phase can help detect igneous sills. Ironically, the only productive well in the San Juan sag to data has an igneous sill as its reservoir. The Del Norte field produced approximately 1,500 bbl of oil from fractured sill intruded into the Mancos Shale. The sill is 58-155 ft thick and is visible on seismic. Although rare, sills can be hydrocarbon traps as illustrated by the Dineh-bi-Keyah field of northeastern Arizona, which has produced more than 15 million bbl of oil.

• OSTI ID: 5631179
• Report Number(s): CONF-8910195-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (USA), Vol. 73:9; Conference: AAPG Rocky Mountain Section meeting, Albuquerque, NM (USA), 1-4 Oct 1989; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
COLORADO
PETROLEUM DEPOSITS
EXPLORATION
CRETACEOUS PERIOD
DATA ANALYSIS
GEOLOGIC FORMATIONS
GEOLOGIC TRAPS
JURASSIC PERIOD
RESERVOIR ROCK
SANDSTONES
SEISMIC SURVEYS
SHALES
VOLCANIC ROCKS
FEDERAL REGION VIII
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOPHYSICAL SURVEYS
IGNEOUS ROCKS
MESOZOIC ERA
MINERAL RESOURCES
NORTH AMERICA
RESOURCES
ROCKS
SEDIMENTARY ROCKS
SURVEYS
USA
020200* - Petroleum- Reserves
Geology
& Exploration