Magnetotellurics case history: frontier basin analysis (Amazon Basin, Colombia)

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Exploring for Oil and Gas Traps
Series Treatise in Petroleum Geology
Part Predicting the occurrence of oil and gas traps
Chapter Applying magnetotellurics
Author Arnie Ostrander
Link Web page
Store AAPG Store

A regional exploration program to study a large unexplored area in the Colombian Amazon basin was conducted by Amoco Production Company in 1987 and 1988.[1] This study area was very large approximately 300,000 km2 (115,000 mi2) and remote with dense jungle cover, rugged terrain, and limited road access.

The first phase of the program consisted of 31,700 km (19,700 mi) of airborne gravity and magnetics. The large-scale structures delineated in these surveys were then further investigated by magnetotellurics (MT). The MT survey was feasible with a light helicopter because the crew was small and equipment was light and compact. Data were collected from 43 sites, with a typical spacing of 10–20 km (6–12 mi).

Survey results[edit]

Figure 1 Simulated cross section in the Amazon basin based on MT data. Drafted from data in Burgett et al.[1]

The MT data clearly delineated a thick sedimentary section with internal units that could be correlated from site to site. Three resistivity “packages” were observed:

  • 40–100 ohmm (sedimentary)
  • 150–250 ohmm (sedimentary)
  • >1000 ohmm (crystalline basement)

Figure 1 shows a simulated cross section in the Amazon basin based on MT data.

Post-MT program[edit]

Encouraged by the evidence from the MT survey, Amoco decided to shoot a small seismic program and drill a shallow stratigraphic test. This program was positioned on the edge of a subbasin defined in the MT data. There generally was good agreement between the MT data, the seismic data, and the borehole geology.

The airborne gravity and magnetic data, followed by the surface MT survey, provided a very cost-effective means of regional basin definition and led directly to a well-positioned seismic survey and well site.

See also[edit]

References[edit]

  1. ↑ 1.0 1.1 Burgett, W. A., A. Orange, and R. F. Sigal, 1992, Integration of MT, seismic, gravity, and magnetic data for reconnaissance of the Colombian Amazon: 54th meeting, European Association of Exploration Geophysicists, Expanded Abstracts, p. 428–499.

External links[edit]

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