DZ/T 0173-1997 Technical specification for magnetotelluric sounding method
Some standard content:
ICS07.060
Record number: 199-1997
Geotechnical Specifications for Magnetotelluric Sounding in the People's Republic of China
Issued on March 19, 1997
Implemented on November 1, 1997
Ministry of Geology and Mineral Resources of the People's Republic of China
Circular calf dawg processing—website transfer pdf
DZ/T0173-1997
Appendix A and Appendix B of this standard are informative appendices.
This standard is proposed by the Geophysical and Geochemical Exploration Technical Committee of the National Committee for Geology and Mineral Standardization. This standard is drafted by the Fifth Geological Survey Office of the Physical Exploration Bureau of China National Petroleum Corporation. Drafter of this standard: Xiong Shizhong.
1 Scope
Technical Specifications for Magnetotelluric Sounding in Geological and Mineral Industry Standard of the People's Republic of China
This standard specifies the basic requirements for the technical work of magnetotelluric sounding. This standard applies to magnetotelluric sounding exploration in the geological and mineral industry. 2 Tasks and Application Conditions
2.1 Geological Tasks to be Solved
2.1.1 Study deep structures and detect the electrical structure of the crust and upper crust. 2.1.2 Detect the ups and downs and burial depth of the high-resistance basement of the basin, and define the scope of the basin and its secondary structural units. 2.1.3 Detect the underlying structure of the area covered by high-resistance layers (such as igneous rocks, carbonate rocks, and conglomerates). 2.1.4 Detect potential igneous rock bodies.
2.1.5 Study the distribution of faults and thrust structures. 2.1.6 Investigate geothermal resources and study magmatic activities related to geothermal resources. 2.2 Application conditions
2.2.1 There is an obvious and stable electrical marker layer in the survey area. 2.2.2
Each target layer in the survey area has sufficient thickness and significant electrical differences. 2.2.3 The electromagnetic noise in the survey area is relatively calm, and various human interferences are not serious. 2.2.4 The terrain is open and gently undulating.
3 Technical design
Preparation before design
3.1.1 Collect relevant information:
Geological data:
Drilling and electrical logging data;
Geophysical data;
Rock physical data;
Surveying and mapping data (topographic maps, triangulation results, etc.). DZ/T0173-1997
3.1.2 Organize survey of the survey area when necessary: understand the construction conditions (topography, transportation, residents, climate, etc.); investigate the interference sources that affect the magnetotelluric signal and their distribution range.
3.1.3 Using the collected rock electrical data, formulate a geoelectrical model of the survey area, perform forward calculations, study the characteristics of the main electrical marker layers to be detected on the magnetotelluric sounding curve, and reasonably design the observation frequency band. 3.1.4 Analyze the noise level in the survey area, study the accuracy that can be achieved through repeated observations, and determine the checkpoint error. 3.1.5 Considering the interference in the survey area, measures need to be taken to improve the observation quality. If necessary, a certain number of remote reference path measurement points can be designed. 3.1.6 If the geological task requires only some deep measurement points, the design should consider the reasonable layout of deep and shallow points. 3.2 Survey network design
Approved by the Ministry of Geology and Mineral Resources of the People's Republic of China on March 19, 1997 and implemented on November 1, 1997
DZ/T0173-1997
3.2.1 The distance between the magnetotelluric sounding lines (hereinafter referred to as the survey lines) and the magnetotelluric sounding points (hereinafter referred to as the survey points) designed for area survey. The general provisions are as follows:
Scale
1:100 000
1:200000
1:500000
Survey line distance, km
3.2.2 When conducting route survey for deep structure detection, the survey point distance should generally not exceed 40km. 3.2.3 The designed survey line should be basically perpendicular to the regional structural trend. Survey point distance.km
If there are seismic survey lines, vertical electrical sounding points, deep drilling holes, etc. in the survey area, the designed survey line should coincide with or be close to them. 3.2.51
The designed survey line should avoid towns or large settlements. 3.2.6 When solving special geological tasks, the designed The distance between survey lines and survey points should be increased as needed. 3.3 Contents of the design document:
》Geological tasks;
b) Location, geological profile and geophysical characteristics of the survey area; c) Layout of survey lines and survey points;
d) Working methods and technical requirements;
e) Planned work. Work arrangements and time allocation for each stage; f) Personnel, equipment and economic expenditure plan; g) Data processing and interpretation work requirements and expected results; h) Measures to complete the task;
i) Necessary drawings (such as survey line layout diagram, stratigraphic comprehensive columnar diagram, forward curve, etc.), and schedules. 3.4 Approval, execution and modification of the design document
3.4.1 Field work shall not be carried out without a design document or without approval of the design document. 3.4.2 When encountering insurmountable difficulties during construction and requiring modification and adjustment of the design task, it shall be implemented after approval. 3.4.3 The construction unit shall strictly implement the relevant provisions of the technical design and no changes without reason are allowed. 4 Field work
4.1 Survey line and survey point arrangement
4.1.1 Survey lines and survey points shall be arranged according to the design specifications. A small amount of adjustment within a certain range is allowed according to the actual situation. The movement of the survey line for area measurement shall not exceed 0.5cm on the map of the corresponding scale. The movement of the survey point for route measurement shall not exceed half of the point distance. 4.1.2 During area measurement, if significant anomalies are found within the survey area, the survey lines shall be increased in time, and at least 3 survey points (different survey lines) shall be located at the abnormal part.
If the magnetotelluric sounding curve is abnormal or loses continuity, the survey points must be increased. 4.1.4
The survey points shall not be selected at the top of the mountain or at the bottom of a narrow deep ditch. The survey points shall be selected in an open area, at least in a place where the ground is relatively flat within the range of two pairs of electrodes, and the ratio of the relative height difference to the pole distance is less than 10%. 4.1.5
The point selection shall take into account the uniformity of the surface soil within the range of pole arrangement, and the points shall not be set next to obvious local non-uniform bodies. The selected measuring point should be far away from the electromagnetic interference source. The general requirements are as follows: more than 2km away from large factories, mines, electric railways, and power stations; more than 1km away from radio stations and radar stations; more than 500m away from high-voltage power lines: more than 200m away from busy roads.
DZ/T0173-1997
4.1.7 When measuring the area, the plane coordinates and elevation of the measuring point should be measured by actual measurement (satellite positioning instrument or theodolite observation); when measuring the route, the point can be fixed on a large-scale topographic map that is - times higher than the map scale, but it should be ensured that the coordinate deviation is less than 1mm and the elevation error does not exceed the contour line distance on the map of the specified scale. 4.1.8 After the measuring point is completed, wooden stakes should be buried, and the stakes should be marked with the measuring point number, observation date and construction unit. 4.2 Observation equipment and digital design
4.2.1 Cross-type device: Two pairs of electrodes and two magnetic sensors (hereinafter referred to as magnetic bars) in the horizontal direction are laid perpendicular to each other, and the azimuth deviation is no more than 1°. The top of the horizontal magnetic bar is 8m to 10m away from the center point. If the two pairs of electrodes and the horizontal magnetic bar are arranged in the due north (x) and due east (y) directions, the vertical magnetic bar (z-downward) should be placed at an azimuth angle of 225° and no more than 10m away from the center of the measuring point (Figure 1). E
4.2.2 When the cross-type digital design is not suitable during construction, L-type, T-type devices (Figure 2, Figure 3), or oblique devices (Figure 4) can be used. The oblique angle should be greater than 70° and the azimuth deviation should be less than 1°. E
4.2.3 The receiving electrode distance should be determined according to the strength of the observed signal and the noise level, and is generally selected between 50 and 300m. If the surface around the measuring point is uneven, the electrodes should be arranged according to the measured horizontal distance, and the electrode distance error should be less than 1% of the soil. 4.2.4 The grounding resistance of the electrode is required to be no more than 2000α. In deserts, Gobi, and high-resistance rock outcropping areas, multiple electrodes should be connected in parallel, and soil should be placed around the electrodes and watered to reduce the resistance. 4.2.5 The electrode should be buried 20cm to 30cm in the soil to maintain good contact with the soil. The burial conditions of the two electrodes are basically the same. They should not be buried at the roots of trees, beside flowing water, on the side of busy roads and in villages. At the same time, they should be avoided from being buried in ditches and ridges. 4.2.6 The electrodes and magnetic ladders should be buried before observation. If instability is still found during observation, the electrode burial quality and grounding conditions should be checked, and they should be processed to achieve stability before recording.
4.2.7 The depth of the horizontal magnetic bar in the soil is 30cm, and it should be calibrated with a level to ensure horizontality; the depth of the vertical magnetic bar in the soil is more than 1/2 of the length of the magnetic bar, and the upper end should be buried with soil to ensure verticality. 4.2.8 The electrode connection line, magnetic bar connection line and the cables connected to the instrument or front box should not be suspended in the air or placed in parallel. They should be compacted with soil or stones every 3m to 5m to prevent shaking.
4.3 Setting of remote reference channel
DZ/T0173-1997
4.3.1 The setting of the remote reference track is divided into the fixed remote reference track method and the moving remote reference track method (mutual reference track method): a. The fixed remote reference track method is to set a magnetic bar fixed at a certain place (this point is called the base point or reference point), and arrange electrodes and magnetic bars at other points (called measuring points), and the measuring points move around the reference point; b. The mutual reference track method is to arrange electrodes and magnetic bars at two points in the same way, and the magnetic tracks (or electric tracks) of the two measuring points are used as references to each other. After the observation is completed, the two points move simultaneously.
4.3.2 When the fixed reference track method is used, the reference point should be selected at a relatively moderate position in the measurement area with a small interference background, an open and flat ground. 4.3.3 When the mutual reference track method is used, the distance between the two measuring points should be determined through observation tests based on the noise level of the measurement area. 4.3.4 The laying of the observation device of the remote reference track method is the same as the provisions in Section 4.2. 4.4 Observation
4.4.1 After the instrument arrives at the measuring point and the layout and connection of the electrodes and magnetic bars are ready, the following should be checked: a) The insulation between the electric and magnetic signal lines and the shielding layer should be greater than 1Ma; b) The resistance between each signal line and the ground should be greater than 1Ma; c) Whether the burial and laying of the electrodes, magnetic bars, and signal lines meet the requirements of Articles 4.2.5 to 4.2.8. 4.4.2 Before observation and recording, check whether the connection between the instrument and the transmission line is firm. After the instrument is started, various tests should be carried out according to the instrument operating manual, such as noise test, gain test, electrode comparison, polarity comparison, etc. 4.4.3 Various parameters read into the recording header during observation must be complete and correct. The observation of the earth's electromagnetic field at a measuring point needs to be carried out continuously, and the time when the interference background is relatively calm should be selected for recording. 4.4.4
4.4.5 Each measuring point should reach the minimum observation frequency required to complete the geological task. 4.4.6 Each additional point should have enough times of sending and adding, especially the data quality of low frequency band. If it does not meet the requirements, the observation time should be extended (the number of optional additions shall not be less than 3 times).
4.4.7 During the observation process, pay attention to monitor the changes of each channel at any time. If the recording channel is reversed, saturated, seriously interfered, etc., it should be re-measured in time. 4.4.8 Analyze the apparent resistivity and phase curve quality from the monitoring screen (or print results). If it does not meet the design requirements, it should be re-measured. 4.4.9 When working with the remote reference channel method, the reference point and the measurement point observation records should be synchronized. After the observation of a measurement point is completed, the data should be transcribed to the tape, one for archiving and another for data processing. 4.4.10
The tape disk should be labeled with the construction unit, measurement area, measurement line number, measurement point number, tape number, tape type, group number, operator name, date, etc. 4.4.11 The operator and surveyor should carefully fill in the work record (see Appendix Table A) and the measurement point layout record (see Appendix Table B). The handwriting should be clear and the symbols should be correct. There should be no erasure. 4.5 Checkpoint regulations
4.5.1 Checkpoints should be repeated observation points at the same measuring point, different dates, and re-arranged. 4.5.2 The checkpoints should be evenly distributed in the measuring area and should be selected in areas with relatively calm interference. They cannot be concentrated in a period of time.
4.5.3 The number of checkpoints shall not be less than 3% of the coordinate points in the entire measuring area. 4.5.4 The full-frequency apparent resistivity (pyPr) curve and phase (gry-9u) curve of the checkpoint and the checked point should have the same shape and the corresponding frequency values should be close, but the mean square relative error (m) of the same polarization of the checkpoint and the checked point after editing and interpolation should not be greater than 5% (i.e. m≤5%).
Calculate according to the following formula:
Where: i=1,2,3, n (frequency point)
A,-一PrwPyri+yi. (Apparent resistivity and phase of the i-th frequency point of the original measuring point) A—pwpy. (Apparent resistivity and phase of the i-th frequency point of the inspection point) 4
A=AA'
DZ/T0173--1997
4.5.5 In some strong noise areas, the mean square relative error of the inspection point cannot meet the requirements of Article 4.5.4, and specific requirements should be put forward in the design. 4.6 Inspection and maintenance of instruments and equipment during the field period 4.6.1 The calibration of instruments (or data synthesis test) should be carried out regularly according to the requirements of different instruments, and the relative error of two adjacent calibration results should not exceed 2%.
4.6.2 If two or more instruments are constructed together in the same measuring area, they should be compared for consistency at the same point using the same observation device, and the relative error of more than 80% of the frequency points should be less than 5%. 4.6.3 During the field work, if a major fault occurs in the instrument and it cannot be eliminated, it should be immediately sent back to the base for repair and shall not be disassembled by itself. It is strictly forbidden to carry out observations with faulty or abnormal instruments. 4.6.4 Instrument inspection and maintenance records should be established in the field, and detailed descriptions of faults that occur during instrument use and measures to eliminate them should be recorded. 4.6.5 The magnetic rod should be loaded and placed gently during transportation and burial to avoid collision. 4.6.6 Non-polarized electrodes should be cleaned frequently, and the solution should be replaced to keep sufficient and saturated electrolyte in the tank, with a range of less than 2mV. 4.6.7 When using the remote reference method, if the base point and the measuring point are synchronously observed by a quartz clock, the accuracy of the quartz clock shall not be less than 10-\s. 4.7 Data submitted in the field
4.7.1 Submitted original data;
a) Original data tape (or floppy disk);
b) Operator work record;
c) Measuring point layout record;
d) Point measurement record;
e) Instrument consistency check and calibration results. 4.7.2 In the field, the processing result tape (or floppy disk) and the corresponding full or partial printed data should be submitted according to different instruments: a) apparent resistance curve and phase curve;
b) dipole amplitude curve;
c) rotation main axis azimuth;
d) ellipticity;
e) deviation;
f) coherence;
g) other information.
4.7.3 The original data, processing calculation result tape (or floppy disk and corresponding printed data) submitted for each measuring point must be complete. The printed and filled data must be clear and correct.
4.8 Field data quality evaluation
4.8.1 The four curves of apparent resistivity and phase of each measuring point should be evaluated separately and registered according to grade. 4.8.2 The quality evaluation of full-frequency apparent resistivity curve and phase curve is divided into: a) (I) level, data of more than 85% of the frequency points, standard deviation does not exceed 20%, good continuity, can strictly interpolate the curve; b) (1) level, data of 75% of the frequency points, standard deviation does not exceed 40%, no obvious disconnection (no more than 3 frequency points); c) (II) level (unqualified), data points are scattered and cannot meet the requirements of level (I) 4.8.3 Evaluation of physical point quality: It should be evaluated based on the noise level of the survey area, the degree to which geological problems can be solved, and the quality level of the curve.
5 Indoor data processing and map preparation
5.1 Data processing
5.1.1 The interpreter should check the field data point by point and reprocess the original data if necessary. 5
5.1.2 Requirements for data editing and curve smoothing: DZ/T0173-1997
a) The measured magnetotelluric sounding curves should be analyzed and compared to determine the polarization mode (TE and TM) of each curve, and the polarization mode should be adjusted to select the wrong data points;
b) The frequency points deleted on a curve cannot exceed 20% of the total frequency points of the curve, and more than three frequency points cannot be deleted continuously. The retained frequency points should be evenly distributed on the entire curve, and the curve should not be irregularly distorted; c) The first and last branches of the curve should be in accordance with the design regulations to ensure that there are enough data points: d) For points with poor continuity of data points and large standard deviations, smoothing should be repeated with reference to adjacent curves to be objective and reasonable, so that the shape of the smoothed curve conforms to the general law of curve changes in the survey area. 5.1.3 The apparent resistivity curve with static displacement and the curve affected by terrain should be corrected. 5.1.4 After each survey point data is edited, smoothed, corrected for static displacement and terrain, a set of processing result tapes (or floppy disks) and printed data (curves and data) should be submitted.
5.2 Map preparationWww.bzxZ.net
5.2.1 Basic requirements for map preparation:
a) Maps must be prepared using data that has been accepted and repeatedly checked for accuracy; b) Necessary maps should be selected based on geological tasks, with clear purposes, prominent emphasis, and non-repetitive content; c) Maps can be prepared manually or by computer, but it should be ensured that the data on the map is correct, clear, and complete, the lines are smooth and symmetrical, and the layout of the map is reasonable and beautiful:
d) For combined maps compiled using other (geophysical, geological) data and magnetotelluric sounding data, the comprehensive maps should highlight the theme (magnetotelluric sounding results) and should not be confused;
e) The map size, format, symbols, fonts and names of similar maps in the same survey area must be consistent. 5.2.2 Basic maps compiled (including actual material maps and qualitative interpretation maps): a) Survey point location map; b) Curve type map; c) Frequency-apparent resistivity (or phase) pseudo-section map; d) Longitudinal conductivity map: e) Other maps (such as dipole, anisotropy, electrical trend and ellipticity maps, etc.). 5.2.3 Quantitative interpretation maps: a) Depth-resistivity (contour line) section map; b) Electrical marker layer burial depth map; c) Electrical marker layer thickness map; d) Electrical stratification profile map; e) Other maps. 5.2.4 Comprehensive interpretation maps: a) Geological, geophysical, and geochemical comprehensive interpretation maps; b) Tectonic unit division map; c) Other geological inference and prediction maps.
6 Writing of the results report
6.1 Basic requirements for writing the results report
6.1.1 After the magnetotelluric sounding work of a region or a project is completed, a complete results report should be submitted. If a region or a project is completed in several field work years, a stage results report or an annual work summary should be submitted every year. 6.1.2 The results report should be written in accordance with the requirements of the geological tasks and design documents. 6.1.3 The data used in the report must be reliable and the source must be well-founded. 6
0173-1997
6.1.4 The report should be substantial in content, concise in text, well-founded in discussion, reasonable inferences, and conclusions that conform to objective reality. 6.1.5 The report should be properly equipped with attachments and annexes, with reasonable layout and concise text descriptions. 6.2 Contents of the Achievement Report
6.2.1 Main body of the achievement report:
a) Geological tasks undertaken and task completion status; b) Geological and geophysical overview of the survey area; e) Field work methods and techniques;
d) Data processing;
e) Data interpretation and geological inference;
f) Conclusions and suggestions.
6.2.2 Attachments to the achievement report:
a) Basic maps;
b) Quantitative interpretation maps;
c) Comprehensive comparison maps;
d) Other maps.
6.2.3 Attachments and tables to the achievement report:
a) Description of rock electrical properties determination:
b) Description of forward and inversion methods;
c) Forward and inversion data table;
d) Data quality statistics table;
e) Others.
0173-1997
Limited wave color rate
Limited interruption rate
Magnetic sample model
Time shooting city
"Luqi
School of Science
D3-9022
234555
Operation number
Construction unit
Coordinate X
X-axis azimuth
Electrode distance length
Remarks:
0173-1997
Appendix B
(Suggested appendix)
Magnetotelluric sounding point layout record (general format) Date
Point layout officer
Topographic feature map of adjacent measuring points
Ground resistance
Magnetic sensor model
Insulation resistance
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.