Views: 255 Author: pqwt Publish Time: 2022-06-08 Origin: pqwt
Three frequencies and multi-frequencies are closely combined to see both trees and forests
It is difficult to read the map, difficult because it is a wordless book, difficult because it is a thousand different patterns, difficult because it is a map of multiple interpretations of the true and false, which is a common feature of all the methods of physical prospecting, including the Tiandian method.
pqwt one key into the map instrument can do both triple frequency measurement, but also multi-frequency measurement, most users only use multi-frequency, not triple frequency. The use of multi-frequency using the pole distance is mostly 1 meter, a survey line 15 ~ 20 points, the control range is only 15 ~ 20 meters, the electrical characteristics of this range outside of nothing, whether there is a better well location is not known, equivalent to the blind man touching the elephant, or called only see the trees but not the forest, to find a good well from the dozen meters is not easy, if it is more difficult in poor water areas. To get twice the result with half the effort and see both trees and forests, the best way is to do three frequencies first, select a few target sections, and then do multi-frequency on the target section, combining the two closely.
1, pqwt production of ground water detector to do multi-frequency measurement, 150 type has 33 frequencies, 300 type has 40 frequencies, 500 type has 56 frequencies, can automatically draw a dipole profile. Do three frequency measurements have three frequencies, each model of the instrument is 170, 67, 25 Hz, you can automatically draw three numerical curves, the three curves are measured at each measurement point with three frequencies of the potential difference between the value of the line rather than the contours of the profile.
2, the three frequencies of the three frequencies, 170 Hz reflects the shallowest, 25 the deepest, 67 in the middle. It does not correspond well with the depth of the multi-frequency measured profile, because the depth of the multi-frequency chart is determined by the development unit after a lot of experimental corrections, while the three frequencies of the three frequencies are the original values of the frequency measured. According to Maxwell's equations, the penetration depth of a certain frequency is also related to the resistivity, not a constant. It has been proposed that the penetration depth of electromagnetic waves of 170, 67, 25 Hz are 148, 215, 300 meters, respectively, if this statement is correct, it is not possible to correspond exactly to this depth. Any frequency of electromagnetic waves in the shallow to deep propagation of the measured value will certainly also be affected by the shallow part, is the result of the combined effect of the resistivity of the layers. For example, some places three frequency 170 line measured high value, in the multi-frequency profile, the upper part of a high value layer, but the depth of the high value layer is only 30 to 40 meters or more, and then down are low value layer, which is sufficient to prove that the 3 frequencies reflect the depth is only relative, can only say that the measured value is a depth of all the strata above the integrated value, the smaller the frequency, the greater the depth of penetration, the influence of the upper The smaller the frequency, the greater the penetration depth, the less it will be affected by the upper part, and the greater it will be affected by the deep part. My alumnus, Professor Han Rongbo, used 3 frequencies to measure the ancient tomb, which was buried only a few meters deep, and the 170 Hz was reflected very clearly, and the other two frequencies were also reflected, but they were getting weaker.
3, three frequencies and multi-frequency close combination can do comprehensive control, focus on fine measurement, improve efficiency and achieve preferential selection. Three frequency only three frequencies, measurement speed, and is a combination of shallow and deep, and so do a simplified multi-frequency, the effect is intuitive. If a line measured twice is more convenient to compare, a glance will be able to see two lines repeatability good or bad, to determine the strengths and weaknesses of the electromagnetic environment within the measurement area, you can quickly select the best possible line segment, and then do multi-frequency measurement on the selected line segment, the best from the best. If we only do multi-frequency, not tri-frequency, the measurement and control range is very small, it is difficult to say that the selected point is necessarily the best point in the survey area, and the well completion rate will be much lower.
4, three frequency and multi-frequency closely combined, how to choose the point distance of the two, how can be done against each other, is crucial. At present, pqwt users do multi-frequency point distance used mostly for 1 meter, there are many users do three frequency point distance also use 1 meter, the two are identical, the measurement range is also identical, which lost the meaning of three frequency, can not play its proper role, is not desirable.
5, in order to make the triple frequency and multi-frequency measurement points against each other, the triple frequency point distance is best for multi-frequency point distance of 1 to 2 times, for example, triple frequency point distance according to 10 meters, multi-frequency point distance is 5 meters or 2.5 meters. Three frequency point distance according to 5 meters, multi-frequency point distance is 2.5 meters or 1.25 meters. When the point spacing of the two match in this way, the correspondence of their measurement point numbers is: if the point spacing differs by a factor of 1, the point numbers of tri-frequency 1, 2, 3, 4, ..., the point numbers of its corresponding multi-frequency are 1, 3, 5, 7, .... If the point distance differs by a factor of 2, the corresponding multi-frequency point number is 1, 5, 9, 13, ... etc. In a measurement line measurement of three frequency measurement points should not exceed 34, and then more better to replace the line number. In the measurement process, if there is a flying point, the whole line is depressed, to be found in time, delete the retest.
6, the three frequencies of the point distance selected how many meters is best is not set in stone. In a large measuring area to 10 meters is good, in most cases to 5 meters is good.
Multi-frequency measurement is plotted out of the contour, each measurement once as long as the value of a slight change in the contour will change, in places with greater interference will be measured once a kind. Three frequency measurement plotted not iso-value line, but the value of the line, the value of a slight change only affects the value of the high and low, not easy to affect the trend change, easier to analyze, you can use three frequency more lines, each line of the original position of the original point measured several times, very fast, from the line of multiple measurements to select a higher probability of three frequency anomalies directly set the well, to multi-frequency as a reference. The point distance of three frequencies in this case can be a little denser, choose 2.5 meters.
7, from the three frequencies to select the section, from the multi-frequency selection of points, if the section is not selected points will not be selected well, it is very important to do the three frequencies first and retest.
Three frequency how to choose a section and multi-frequency how to choose points, the two selection principles are the same. What geological conditions to choose high value anomaly? What geological conditions to choose low value anomalies? What is an anomaly? How to master the selection of low in high and high in low? These questions must be combined with geological conditions and flexible mastery, like treating difficult diseases as serious analysis, to learn by doing, accumulate experience, do not simply engage in. Choose high or low, just like doctors diagnose stroke patients, is it good to stop bleeding or good to unblock? Once the diagnosis is reversed the wrong medicine will be killed.
8, although the three frequencies have many advantages, but in most cases we do not advocate the direct use of three frequencies to determine the well. What are the causes of the abnormalities found by triple frequency? How to determine the depth of the well? Questions such as these are not well answered by triple frequency. Some v-shapes may also be caused by low value downgradient, which also needs to be identified by multiple frequencies. Some details in the contour plot are not reflected in the triple frequency curve. Therefore, the value of the three-frequency line can not replace the multi-frequency contour line, the two must complement each other and closely integrated.
9, there is a special situation, that is, to find hard rock interlayer in the thick layer of soft rock, it is often shown in the profile as a horizontal multi-layer type. This kind of graph requires that the more layers of hard rock interlayer the harder the better. Most of the hard layers are shown as several layers of blackish horizontal strips, which correspond to frequencies that are difficult to coincide with the three frequencies of the triple frequency method, and it is difficult to find hard layers in this case by sweeping the surface with the triple frequency method, and it is impossible to compare where the hard layers are the most and the hardest.
If the geological condition is large, it is recommended to use the three-point multi-frequency to do the control measurement first, that is, to do multi-frequency in 4 corners or 4 sides of the survey area, and only 3 points are measured as a multi-frequency section with 5 meters distance, and each multi-frequency section is separated by an empty measurement, and then compare which section has the most and hardest hard rock layers after the measurement, and then you can do the work in detail near the section.
Currently, the most widely used method for finding water in wells is electrical exploration.
ground water detector
Electric detection method is divided into artificial electric field method and natural electric field method. Artificial electric field includes DC power supply, excitation, controlled source and other professional methods, these methods are mostly used in various types of large geological census projects, involving thousands of lines and points, but the use of inconvenience, especially the transport of power supply devices, often require a lot of manual. The natural electric field method has been used for decades
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