Magnetotelluric survey of San Juan sag
- Phoenix Geoscience Inc., Denver, CO (USA)
The San Juan Mountains of southwestern Colorado, consisting almost entirely of Tertiary volcanic rocks, are bounded on the southwest by the mature oil and gas province of the San Juan basin and on the east by the San Luis basin, continuation of the sediments from the San Juan basin eastward beneath the volcanics was suspected based on the reported presence of seeps and the evaluation of regional gravity and magnetic data. The probability greatly increased when Milestone drilled Tertiary and Cretaceous sediments beneath 3,000 ft of volcanics, 37 mi northeast of the nearest Cretaceous outcrop. The MT (magnetotellurium) program described in this presentation is part of a nonexclusive survey that included magnetotelluric soundings, time-domain electromagnetic soundings, gravity stations, and geochemical sampling. MT data were acquired at 20 sites along an east-west profile centered on the Milestone 1 AMF well, five sites along a north-south cross profile, and three more sites around the wells northeast of the Milestone well. Site spacing was of the order of 1 to 3 mi except for the cross line. The program was designed to map the thickness of the surface volcanics and the thickness and resistivity of the underlying sediments. The MT data acquired near the Milestone well indicated that the Cretaceous sedimentary rocks are characterized by an average resistivity of the order of 4-12 ohm-meters. The MT data acquired in the San Luis basin east of Del Norte also shows 4-12 ohm-meter rocks in the subsurface, correlated in this case with Tertiary volcanics, volcaniclastics, and continental sediments. The MT data show that the low-resistivity 4-12 ohm-meter section extends continuously beneath the more resistive surface volcanics from the San Luis Valley to at least 16 mi west-northwest of Del Norte.
- OSTI ID:
- 5499223
- Report Number(s):
- CONF-8910195--
- Journal Information:
- AAPG Bulletin (American Association of Petroleum Geologists); (USA), Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Vol. 73:9; ISSN AABUD; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
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