Pay attention to the pronunciation of the following words and word formations.

Read the following word-combinations and translate them into Russian.

To be produced by direct or alternating current; bodies furnish their electrical field; to be supplied to the ground by contact or by induction

four frequency bands may be used; the audio-frequency range of from 200 to 1000 cycles; methods are usually subdivided into galvanic-electromagnetic and inductive-electromagnetic; radio-frequency range is used in the radio methods of electromagnetic prospecting; owing to the lack of depth penetration; resistivity and potential-drop-ratio methods are comparable to refraction methods; inductive methods are applied to the mapping of horizontal beds; spontaneous electrochemical phenomena occur on placers; to be produced on formation boundaries; difference in the conductivity of drilling fluid and formation waters; materials of different solution pressure; act as wet cells; survey equipotential lines or potential profiles.

54. Which word-combination is out of place here? And why?

a) alternating current, electrode spacing, direct current

b) supply, furnish, provide, induce

c) self-potential, surface potential, refraction, electromagnetic

d) compare, formation boundaries, comparable, comparison

e) pressure solution, low frequencies, high frequencies, radio frequencies

f) fault, inductive, external circuit, ground current

g) milliammeter, transmitter, current generator, field intensity

h) resistivity, flux line, potential-drop-ratio, self-potential, surface potential

Make up word combinations from the given words.

survey equipotential lines or potential profiles

produce inductive methods and refraction methods

supply formation boundaries

apply alternating current

induce high radio frequency

radiate potential difference

furnish frequency bands

observe point electrodes

compare emission characteristics

detect potential drop

Read the text, do the exercises.

Electrical Methods

Mineral deposits and geologic structures may be mapped by their reaction to electrical and electromagnetic fields. These are produced by either direct or alternating current, except where ore bodies spontaneously furnish their own electrical field (self-potential methods). Electrical energy may be supplied to the ground by contact or by induction. Three main groups of electrical methods may be distinguished: (1) self-potential, (2) surface-potential, and (3) electromagnetic methods. Frequently the first two groups are combined into one group of potential methods; the electromagnetic methods are usually subdivided into galvanic-electromagnetic and inductive-electromagnetic.

Four frequency bands may be used in connection with alternating current electrical prospecting: (1) low frequencies of from 5 to about 100 cycles; (2) the audio-frequency range of from 200 to 1000 cycles; (3) high frequencies of from 10 to 80 kilocycles; and (4) radio frequency of from 100 kilocycles to several megacycles. The low frequency range is applied in most potential methods; the audio-frequency range is used in some potential and most electromagnetic methods; the high-frequency range in the high-frequency electromagnetic methods; and radio-frequency in the radio methods of electromagnetic prospecting. The application of high radio frequencies is limited owing to their lack of depth penetration; of greatest importance are the audio frequencies and the low frequencies. In a number of respects, electrical methods are similar to seismic methods; comparable to refraction methods are resistivity and the potential-drop-ratio methods; inductive methods as applied to the mapping of horizontal beds are comparable to reflection methods but lack their resolving power.

Self-potential method. The self-potential method is the only electrical method in which a natural field is observed; its causes are spontaneous electrochemical phenomena. These phenomena occur on ore bodies and on metallic minerals and placers; they are produced by corrosion of pipe lines and on formation boundaries in wells by differences in the conductivity of drilling fluid and formation waters. Ore bodies whose ends are composed of materials of different solution pressure and are in contact with solutions of different ion concentration, act as wet cells and produce an electrical field which can be detected by surveying equipotential lines or potential profiles. For the mapping of equipotential lines, a high-resistance milliammeter is connected to two unpolarizableelectrodes are used. One is kept stationary and the other is moved until the current vanishes. At that point the electrodes are on an equipotential line.

Date: 2016-01-14; view: 935