Structure mapping at Trap Spring Oilfield, Nevada, using controlled-source magnetotellurics

Hughes, L.J.; Carlson, Norman R.

doi:10.3997/1365-2397.1987021

Cited by 18 publications

(7 citation statements)

References 17 publications

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“…An example of the shift procedure is found in CSAMT data obtained over Trap Spring Field (Hughes and Carlson, 1987), a study which is described more fully in the Case Histories section. The data ( Figure 33) show layering effects due to stratigraphy in this area, a general trend toward lower resistivities toward the east due to higher groundwater salinity in that direction, and several pronounced lateral features.…”

Section: Figure 31 Is a Simplified Illustration Of Static Effects Ovementioning

confidence: 99%

“…An example is illustrated in data obtained over Trap Spring Field (Hughes and Carlson, 1987). But some situations, imposed either by geology or economics, make electrical a good complement or replacement for seismic.…”

Section: Petroleum Exploration (Structure Mapping)mentioning

confidence: 99%

“…In 1978 a full-scale development of CSAMT instrumentation and interpretation, begun by Zonge Engineering and Research Organization, Inc., (Zonge et al, 1980(Zonge et al, , 1985Ostrander et al, 1983;Hughes, 1984;Hughes et al, 1984Hughes et al, , 1986Hughes and Carlson, 1987;Carlson et al, , 1986Introduction Basic theoretical principles for natural-source magnetotelluric (MT) soundings are now well developed and understood (see Vozoff, 1986, for an excellent compilation of key papers on MT theory and practice and Vozoff, this volume). The theory for the MT case is conveniently formulated due to the assumed source independence of the EM field.…”

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confidence: 99%

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9. Controlled Source Audio-Frequency Magnetotellurics

Zonge¹,

Hughes²

1991

Electromagnetic Methods in Applied Geophysics

207

136

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INTRODUCTION Controlled source audio-frequency magnetotellurics (CSAMT) is a frequency-domain electromagnetic sounding technique which uses a fixed grounded dipole or horizontal loop as an artificial signal source.CSAMT is similar to the natural-source magnetotellurics (MT) and audio-frequency magnetotellurics (AMT) techniques; the chief differences center around the use of the artificial CSAMT signal source at a finite distance. The source provides a stable, dependable signal, resulting in higher-precision and more economical measurements than are usually obtainable with natural-source measurements in the same spectral bands. However, the controlled source can also complicate interpretation by adding source effects, and by placing certain logistical restrictions on the survey. In most practical field situations these drawbacks are not serious, and the method has proven particularly effective in mapping'the top 2 to 3 km of the earth's crust.The CSAMT source usually consists of a grounded electric dipole about ! to 2 km in length, ideally located at least four skin depths (4g = 2012 X/O/o/f; p = resistivity, f = signal frequency) from the area where soundings are to be made. Measurements are made within the 0.1 Hz to 10 kHz frequency band. Magnitude and phase are measured for two to five electric and magnetic field components (Ex, Ey, Hx, Hy, Hz), using either one or two sources. Grounded dipoles detect the electric field and magnetic antennas sense the magnetic field. The ratio of orthogonal, horizontal electric and magnetic field magnitudes yields the apparent resistivity. The difference between the phase of the electric and magnetic fields yields the phase of the impedance. In tensor measurements, these quantities may be treated by standard MT processing techniques. CSAMT depth of investigation is roughly equal to g/X/• m, when the separation between the transmitter dipole and the receiver station is greater than 4g, although we have found that maximum depth of investigation is limited in many cases to about 3 km due to the practical constraints of the measurements. Lateral resolution is controlled by the electric field dipole length, which normally is between 10 and 200 m. Vertical resolution is .5 percent to 20 percent of the depth of penetration, depending upon resistivity contrasts.Since its introduction in the mid-1970s, CSAMT has been used in exploration for petroleum, geothermal resources, massive sulfides, base and precious metals, structure, lithology, and sources of groundwater contamination. Much of this work has been quite successful due to the inherent capabilities of the technique.However, much remains to be learned about CSAMT interpretation, particularly in regard to static and source effects. By exploring the present understanding of the theory and practice of CSAMT we hope to provide a basis for further development. ObjectivesIn recent years the controlled source audio-frequency magnetotellurics (CSAMT) sounding technique has gained acceptance as a viable geophysical exploration tool. Its hig...

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Section: Figure 31 Is a Simplified Illustration Of Static Effects Ovementioning

confidence: 99%

Section: Petroleum Exploration (Structure Mapping)mentioning

confidence: 99%

mentioning

confidence: 99%

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9. Controlled Source Audio-Frequency Magnetotellurics

Zonge¹,

Hughes²

1991

Electromagnetic Methods in Applied Geophysics

207

136

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“…Since Goldstein and Strangway (1975) validated this technique in a massive sulfide deposit, CSAMT has been widely applied in a variety of exploration problems worldwide. These applications primarily focused on geothermal (e.g., Sandberg and Hohmann, 1982;Bartel and Jacobsen, 1987;Bromley, 1993;Wannamaker, 1997aWannamaker, , 1997b, mineral (e.g., Strangway et al, 1973;Boerner et al, 1993;Kellett et al, 1993;Chen et al, 2010;An and Di, 2010), and hydrocarbon (e.g., Hughes and Carlson, 1987). Other applications included groundwater surveys (e.g., Carlson et al, 2005), fault-zone mapping (e.g., Theodore and Sweetkind, 2011), and engineering detection (e.g., Unsworth et al, 2000).…”

Section: Introductionmentioning

confidence: 98%

Mineral Exploration using CSAMT data: Application to Longmen region metallogenic belt, Guangdong Province, China

Peng

Guiju

et al. 2013

GEOPHYSICS

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A controlled-source audio-frequency magnetotelluric (CSAMT) survey has been carried out to investigate potential iron (Fe) and polymetallic (Pb-Zn-Cu) deposits in Longmen region, which is one of the main metallogenic belts in southern China. Conducting geophysical surveys in this area is quite difficult due to mountainous terrain, dense forest, and thick vegetation cover. A total of 560 CSAMT soundings were recorded along twelve surveying lines. Two-dimensional Occam's inversion scheme was used to interpret these CSAMT data. The resulting electric resistivity models showed that three large-scale highly conductive bodies exist within the surveying area. By integrated interpretation combined with available geologic, geophysical, and geochemical data in this area, three prospective mineral deposits were demarcated. Based on the CSAMT results, a borehole penetrating approximately 250-m depth was drilled at the location of 470 m to the northwest end of line 06, defined with a massive pyrite from the depth of 52-235 m with 7%-16% Fe content, as well as locally highgrade Pb-Zn-and Ag-Ti-bearing ores.

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“…-I hydrocarbon (Hughes and Carlson, 1987;Ostrander, 1'990)' environments. Many other case I One major difference between the natural-field…”

Section: Introductionmentioning

confidence: 99%

Tensor controlled-source audiomagnetotelluric survey over the Sulphur Springs thermal area, Valles Caldera

Wannamaker¹

1991

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Structure mapping at Trap Spring Oilfield, Nevada, using controlled-source magnetotellurics

Cited by 18 publications

References 17 publications

9. Controlled Source Audio-Frequency Magnetotellurics

9. Controlled Source Audio-Frequency Magnetotellurics

Mineral Exploration using CSAMT data: Application to Longmen region metallogenic belt, Guangdong Province, China

Tensor controlled-source audiomagnetotelluric survey over the Sulphur Springs thermal area, Valles Caldera

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