Brine type sylvite ore detection method based on comprehensive geophysical technology

Abstract

The invention discloses a brine type potassic salt ore detection method based on a comprehensive geophysical technology, and relates to the field of geophysical detection and strategic mineral resources, the method comprises the following steps: adopting an audio magnetotelluric sounding technology to obtain audio magnetotelluric sounding data; determining a stratum resistivity profile of the audio magnetotelluric sounding line according to the audio magnetotelluric sounding data; acquiring shallow seismic exploration data of the same survey line by adopting a shallow seismic exploration technology; determining a seismic stack section according to the shallow seismic exploration data; the stratum resistivity profile and the seismic stack profile are combined to jointly reveal the stratum structure and construction characteristics of the research area; based on the stratum structure and construction characteristics, according to the low resistance abnormity of the stratum resistivity profile and the strong reflection event characteristics of the seismic stack profile, the sylvite mineralization favorable area and the brine reservoir interval are comprehensively detected, and the brine type sylvite ore identification precision can be improved.

Description

Technical Field

[0001] The present application relates to the field of geophysical exploration and strategic mineral resources, and in particular to a method for detecting brine-type potash mines based on comprehensive geophysical technology. Background Art

[0002] Geophysics, as an effective method of mineral exploration, studies geophysical fields or certain physical phenomena, such as the geomagnetic field, geoelectric field, gravity field, etc., to infer and determine the physical properties of the geological body to be investigated and the differences in physical properties between the geological body to be investigated and the surrounding geological bodies (i.e., geophysical anomalies), and then infer the geological properties of the investigated object, combined with geological data analysis, to achieve the purpose of discovering mineral deposits (bodies). Geophysical methods specifically include gravity, magnetic, electrical and seismic exploration methods.

[0003] Experts and scholars have conducted relevant research on geophysical exploration methods for potash reservoirs and achieved good prospecting results. Using gravity methods, the potash mineralization prospecting areas can be effectively delineated based on gravity anomalies; using audio-frequency magnetotelluric sounding, magnetotelluric sounding, and transient electromagnetic methods, the brine-enriched areas can be quickly determined based on low-resistance anomalies. Based on the reflection characteristics of seismic exploration wave groups, the top and bottom interfaces of potash ore layers can be finely divided, sedimentary laws can be revealed, and potassium-rich brine reservoirs can be tracked.

[0004] However, existing geophysical exploration technologies for potash minerals mostly operate with a single identification method, which has many limitations, does not reveal enough about the properties of potash reservoir segments, and the identification accuracy of a single detection method is low. Summary of the invention

[0005] The purpose of this application is to provide a brine-type potash mine detection method based on comprehensive geophysical technology to solve the problem of low identification accuracy of a single identification method for brine-type potash mines.

[0006] To achieve the above objectives, this application provides the following solutions:

[0007] In a first aspect, the present application provides a method for detecting brine-type potash mines based on integrated geophysical technology, comprising:

[0008] Using the audio magnetotelluric sounding technology, the audio magnetotelluric sounding data of each audio magnetotelluric sounding measuring point on each audio magnetotelluric sounding line are obtained;

[0009] Determining the formation resistivity profile of the audio frequency magnetotelluric sounding line according to the audio frequency magnetotelluric sounding data;

[0010] Using shallow seismic exploration technology to obtain shallow seismic exploration data of a shallow seismic exploration line; the shallow seismic exploration line and the audio frequency magnetotelluric sounding line are the same line;

[0011] Determining a seismic stacking profile of the shallow seismic exploration line according to the shallow seismic exploration data;

[0012] The formation resistivity profile and the seismic stacking profile are combined to reveal the formation structure and structural characteristics of the study area; the formation structure includes the burial depth, undulation and extension characteristics of each set of formation interfaces; the structural characteristics include faults and folds;

[0013] Based on the stratigraphic structure and structural characteristics, the favorable areas for potash mineralization and the brine reservoir sections are comprehensively detected according to the low-resistance anomaly of the stratigraphic resistivity profile and the strong reflection event axis characteristics of the seismic superposition profile.

[0014] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0015] This application combines two geophysical exploration technologies, namely, audio-frequency magnetotelluric sounding technology and shallow seismic exploration technology, to comprehensively characterize the stratigraphic structure and structural characteristics of the study area from the perspective of electrical and elastic characteristics, so as to identify the favorable areas for potash mineralization and the brine reservoir sections. Compared with a single identification method, it can clearly reveal the property characteristics of the potash reservoir section, which is more consistent with the actual drilling results, and improves the accuracy of identifying brine-type potash mines. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. The drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 A map of the study area provided for this application;

[0018] Figure 2 A flow chart of the brine-type potash mine detection method based on comprehensive geophysical technology provided in this application;

[0019] Figure 3 is the audio frequency magnetotelluric sounding resistivity and phase curve of a certain measuring point; Figure 3 (a) is the audio frequency magnetotelluric sounding resistivity curve of the measuring point; Figure 3 (b) is the audio frequency magnetotelluric sounding phase curve diagram of the measurement point;

[0020] Figure 4 This is a schematic diagram of a typical single shot record of shallow seismic exploration at a certain measurement point;

[0021] Figure 5is the resistivity profile of the audio frequency magnetotelluric sounding inversion; Figure 5 (a) is the resistivity profile of the MA10 line using audio frequency magnetotelluric sounding inversion; Figure 5 (b) is the resistivity profile of the MA20 line using audio frequency magnetotelluric sounding inversion; Figure 5 (c) is the resistivity profile of the MA30 line using audio frequency magnetotelluric sounding inversion; Figure 5 (d) is the resistivity profile of the MA40 line using audio frequency magnetotelluric sounding inversion; Figure 5 (e) is the resistivity profile of the MA50 line using audio frequency magnetotelluric sounding inversion; Figure 5 (f) is the resistivity profile of the audio frequency magnetotelluric sounding inversion of the MA60 survey line; Figure 5 (g) is the resistivity profile of the audio frequency magnetotelluric sounding inversion of the MA70 survey line; Figure 5 (h) is the resistivity profile of the audio frequency magnetotelluric sounding inversion of the MA80 survey line;

[0022] Figure 6 This is a superimposed profile of shallow seismic exploration; among them, Figure 6 (a) is the stacked profile of shallow seismic exploration of MA40 survey line; Figure 6 (b) is the stacked profile of shallow seismic exploration of MA80 survey line;

[0023] Figure 7 It is a comprehensive interpretation diagram of the resistivity profile inverted from audio frequency magnetotelluric sounding;

[0024] Figure 8 It is a shallow seismic exploration stratigraphic and structural interpretation map; among them, Figure 8 (a) is the stratigraphic and structural interpretation map of the shallow seismic exploration of the MA40 survey line; Figure 8 (b) is the stratigraphic and structural interpretation map of the shallow seismic exploration of the MA80 survey line;

[0025] Fig. 9 It is the surface geological boundary and comprehensive geophysical interpretation profile of MA80 survey line; among them, Fig. 9 (a) is the surface geological boundary map of the MA80 survey line; Fig. 9 (b) is the resistivity profile interpretation diagram of the audio frequency magnetotelluric inversion of the MA80 survey line; Fig. 9 (c) is the interpretation diagram of the shallow seismic exploration stacked profile of the MA80 survey line;

[0026] Fig.10 It is the surface geological boundary and comprehensive geophysical interpretation profile of MA40 survey line; among them, Fig.10 (a) is the surface geological boundary map of the MA40 survey line; Fig.10(b) is the resistivity profile interpretation diagram of the audio frequency magnetotelluric inversion of the MA40 survey line; Fig.10 (c) in the figure is the interpretation diagram of the shallow seismic exploration stacked profile of the MA40 survey line. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. The described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0028] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is described in detail below with reference to the accompanying drawings and specific implementation methods.

[0029] Taking the Qaidam Basin as the study area, the geological overview is as follows:

[0030] Tectonic background: The structure of the Qaidam Basin is mainly NW-oriented, and the overall structure is characterized by "anticlines and synclines arranged alternately, appearing in groups and belts". It is divided into five primary structural units, namely, the Qaidam Basin West Depression, the Altun Mountain Front Belt, the Qaidam Basin North Depression, the Qaidam Basin East Depression, and the Delingha Uplift, and 25 secondary structural units, namely, the Niuzhong Slope, the Lenghu Tectonic Belt, the Saishiteng Sag, the Mahai Uplift, and the Sanhu North Tectonic Belt. Since the Cenozoic, with the northward expansion of the Qinghai-Tibet Plateau, strong structural deformation has occurred, and fault structures have developed. The basin has rapidly subsided under the control of the NW-NWW-oriented fault zone, and has received thick Cenozoic sediments, becoming a large intermountain basin on the northeastern edge of the Qinghai-Tibet Plateau. A large number of fold structures have developed from the Lower Proterozoic to the Cenozoic. Due to the influence of faults, the Neogene fold structures in the basin have been destroyed to varying degrees, and the fold appearance is incomplete, with the main axial directions being NW and NWW. The uplift of the fold belt has led to the development of faults in the region, and faults have occurred in the Lüliang to Xishan cycles. It is mainly composed of the NEE-oriented Altun Mountain Fault, the NW-oriented and north-south (NS)-oriented Saishiteng Mountain Fault, and some NW-oriented and northeast (NE)-oriented faults. The Altun Mountain faults are complex and diverse, with different directions and properties. The southern and northern margin faults are the most significant, controlling the development of different tectonic units and tectonic contours in the region, and also have the characteristics of deep and large faults. The Saishiteng Mountain Fault is mostly torsional faults with a wide range of temporal and spatial distribution. In addition, the NW-oriented and NWW-oriented faults in the basin are oblique to the Altun Mountain Fault. These faults not only control the Quaternary salt deposition, but are also important channels for deep water to replenish the salt lake.

[0031] Stratigraphic structural characteristics: The Qaidam Basin is the largest and most complete sedimentary basin on the Qinghai-Tibet Plateau. At the end of the Neogene, the Qaidam area was still a complete ancient lake. By the late Pleistocene, the Qaidam ancient lake had basically disappeared and differentiated into dozens of semi-independent, semi-enclosed secondary salt lakes, which were connected only by underground "channels". The strata in the study area are developed from the Cambrian to the Quaternary except for the Permian. Previous researchers believed that the focus of potash research was on the Cenozoic strata, and divided the Cenozoic strata in the basin into 7 groups, determined the geological age of each group, and established a detailed stratigraphic age framework. Table 1 is a schematic diagram of the Cenozoic stratigraphic structural characteristics of the northeastern margin of the Qaidam Basin. The Cenozoic stratigraphic structural characteristics in the region are shown in Table 1.

[0032] Table 1

[0033]

[0034]

[0035]

[0036] Mineralization geological conditions: According to the classification of mineralization units, the Qaidam Basin is located in the Qinling-Kunlun metallogenic domain-Kunlun metallogenic province-Qaidam Basin lithium-boron-potassium-sodium-magnesium-salt-oil and natural gas metallogenic belt. Combined with the characteristics of the metallogenic belt, the Qaidam Basin metallogenic belt can be further divided into five metallogenic sub-belts: the northern margin of the Qaidam Basin, the central, northern Kunlun, Chaerhan and Delingha. The study area is located in the central metallogenic sub-belt (Ⅳ2), the Mahai potassium-rock salt-magnesium salt ore cluster (Ⅳ 2-1 ). The physical properties of strata and rocks are the basis and foundation of geophysical work, and their characteristic changes are the main factors causing changes in geophysical parameter characteristics, especially the differences in the degree of diagenesis and the strength of cementation, water-richness, and groundwater mineralization, which will cause a series of reaction changes in abnormal characteristics. The electrical properties of the Quaternary halite silt, clay silt, gypsum-containing silt clay, silt sand, fine sand, coarse sand, gravel sand, and silt clay in the study area do not change much, but there are still certain electrical differences in the above-mentioned strata when the mineralization is different. Among them, the resistivity values ​​of high-mineralized silt sand, fine sand, coarse sand, gravel sand, etc. are relatively low or extremely low (basically less than 1Ω×m), which are the main high-mineralized brine-enriched strata in the study area. The resistivity values ​​of high-mineralized clay and silt clay are relatively high (all above 1Ω×m) due to their small porosity and poor water-richness. The resistivity values ​​of low-mineralized clay silt, silt sand, silty fine sand, fine sand, coarse sand, gravel sand and other formations show relatively high resistivity characteristics. Figure 1 shown.

[0037] The present application embodiment provides a brine-type potash mine detection method based on comprehensive geophysical technology. In the present application embodiment, Figure 2As shown, the method includes the following steps.

[0038] S1: Use the audio frequency magnetotelluric sounding technology to obtain the audio frequency magnetotelluric sounding data of each audio frequency magnetotelluric sounding measurement point on each audio frequency magnetotelluric sounding line.

[0039] S2: Determine the formation resistivity profile of the audio frequency magnetotelluric sounding line according to the audio frequency magnetotelluric sounding data.

[0040] S3: shallow seismic exploration technology is used to obtain shallow seismic exploration data of a shallow seismic exploration line; the shallow seismic exploration line and the audio frequency magnetotelluric sounding line are the same line.

[0041] S4: Determine the seismic stacking profile of the shallow seismic exploration line according to the shallow seismic exploration data.

[0042] S5: The stratigraphic structure and structural features of the study area are jointly revealed by combining the stratigraphic resistivity profile and the seismic stacking profile; the stratigraphic structure includes the burial depth, undulation and extension characteristics of each set of stratigraphic interfaces; the structural features include faults and folds.

[0043] S6: Based on the stratigraphic structure and structural characteristics, and according to the low-resistance anomaly of the stratigraphic resistivity profile and the strong reflection phase axis characteristics of the seismic superposition profile, comprehensive detection of the potassium salt mineralization favorable area and the brine reservoir section is carried out.

[0044] This application mainly carried out audio frequency magnetotelluric sounding and shallow seismic exploration, and completed a total of 8 audio frequency magnetotelluric sounding profiles, including MA10, MA20, MA30, MA40, MA50, MA60, MA70 and MA80 survey lines from NW to SE. The length of each survey line is 10km, the line spacing is 4km, and there are 21 measurement points on a single survey line with a point spacing of 500m. At the same time, the audio frequency magnetotelluric sounding point encryption measurement and shallow seismic exploration of the same profile were also carried out on the MA40 and MA80 survey lines. The point spacing of the audio frequency magnetotelluric sounding encrypted measurement points is 200m, and there are 41 encrypted measurement points on each survey line, a total of 82 encrypted measurement points, and a total of 250 audio frequency magnetotelluric sounding measurement points have been completed; the shallow seismic exploration lines on the same profile are each 13km long, with a total of 26km, such as Figure 3 shown.

[0045] In an exemplary embodiment, S1 may be replaced by the following steps.

[0046] The SEP magnetotelluric instrument adopts four-component tensor observation to collect each audio magnetotelluric sounding data; wherein the four components include the horizontal electric field component in the x direction, the horizontal magnetic field component in the x direction, the horizontal electric field component in the y direction and the horizontal magnetic field component in the y direction; the electrodes of the SEP magnetotelluric instrument are arranged with the horizontal electric field component in the x direction and the horizontal magnetic field component in the x direction as 0° and the horizontal electric field component in the y direction and the horizontal magnetic field component in the y direction as 90°; the x direction is perpendicular to the y direction.

[0047] In an exemplary embodiment, S2 may be replaced by the following steps.

[0048] The original file format of the audio magnetotelluric sounding data is converted.

[0049] Based on the converted file format, the audio magnetotelluric sounding data is converted into a time-frequency format.

[0050] The audio magnetotelluric sounding data after time-frequency conversion and the audio magnetotelluric sounding data in the original file format are edited to generate an EDI impedance file.

[0051] The audio frequency magnetotelluric sounding data in the EDI impedance file is processed to generate a formation resistivity profile of the audio frequency magnetotelluric sounding line.

[0052] In an exemplary embodiment, the audio frequency magnetotelluric sounding data in the EDI impedance file is processed to generate a formation resistivity profile of the audio frequency magnetotelluric sounding line, specifically comprising:

[0053] Performing profile fitting on the audio frequency magnetotelluric sounding data under the EDI impedance file to determine profile fitting parameters; the profile fitting parameters include profile length, azimuth, and audio frequency magnetotelluric sounding measurement points involved in inversion.

[0054] The curve displacement is corrected based on the profile fitting parameters to determine a corrected profile curve.

[0055] The corrected profile surface is subjected to one-dimensional inversion and two-dimensional inversion to generate a formation resistivity profile of the audio frequency magnetotelluric sounding line.

[0056] In an exemplary embodiment, geophysical data collection and processing are as follows:

[0057] Four sets of SEP magnetotelluric instruments were used for audio magnetotelluric sounding data acquisition. Four-component (Ex, Ey, Hx, Hy) tensor observation was adopted. The electrodes were arranged in a standard positive "cross" shape. Ex and Hx were arranged at 0°, and Ey and Hy were arranged at 90°. After completing the electrical method start-up test, the final acquisition frequency was determined to be 1-10000Hz, and the acquisition time was not less than 1h. The resistivity and phase curves of a certain measuring point are shown in the figure below. Figure 2 shown.

[0058] After data processing was preprocessed using SSMT2000, MT Editor, etc., MT Pioneer inversion software was used. Table 2 is the audio magnetotelluric sounding data processing flow chart. The specific data processing flow and parameters are shown in Table 2. Finally, the TM mode two-dimensional inversion results were selected for interpretation to obtain the resistivity profiles of 8 survey lines.

[0059] Table 2

[0060]

[0061]

[0062] In an exemplary embodiment, S3 may be replaced by the following steps.

[0063] Determine the optimal excitation parameters of the controllable vibrator and the optimal receiving parameters of the node-type seismograph; wherein the excitation parameters include the mass of the weight, the weight of the source, the number of source stations, the scanning frequency, the scanning length, the source output, the number of vertical overlaps and the excitation mode, and the excitation mode is intermediate blasting; the receiving parameters include the natural frequency, the recording length, the recording format, the sampling interval, the track spacing, the shot spacing, the number of receiving channels, the maximum number of coverage times and the receiving mode, and the receiving mode is two-side reception.

[0064] Based on the optimal excitation parameters and the optimal receiving parameters, shallow seismic exploration data of the shallow seismic exploration line is acquired.

[0065] In an exemplary embodiment, shallow seismic exploration data acquisition uses 800 Node-X node seismometers and 1 ZF-15 controllable vibrator. After completing instrument consistency tests, acquisition parameter tests, and extended arrangement tests, the optimal acquisition parameters were finally determined to be 3m channel spacing, 15m shot spacing, 400 receiving channels, middle shot, two-side receiving, maximum coverage times 40 times, sampling interval 2ms, record length 5s, etc. Table 3 is a table of shallow seismic exploration data acquisition parameters. Typical single shot records are as follows: Figure 4 shown.

[0066] Table 3

[0067]

[0068] Before carrying out shallow seismic exploration data processing, all equipment needs to be installed in the cabinet, data is downloaded according to the acquisition time period, and then the Rocket software is used to extract the reflection signal according to the trigger time of the controllable source record to synthesize the final single shot record. In addition, Omega software is used for data processing, which mainly includes observation system definition, static correction, pre-stack denoising suppression, true amplitude recovery, deconvolution, velocity analysis, stacking migration and other steps. Table 4 is a shallow seismic exploration data processing flow chart, as shown in Table 4.

[0069] Table 4

[0070]

[0071]

[0072] In an exemplary embodiment, S4 may be replaced by the following steps.

[0073] An observation system file is generated based on the shot points, detection points and relationship files of the shallow seismic exploration data and stored in the data header.

[0074] Perform static correction on shallow seismic exploration data to determine the shallow seismic exploration data after static correction.

[0075] Prestack noise suppression is performed on the shallow seismic exploration data after static correction to determine the shallow seismic exploration data after noise suppression.

[0076] The shallow seismic exploration data after noise suppression is subjected to true amplitude recovery to determine the shallow seismic exploration data after true amplitude recovery.

[0077] Deconvolution processing is performed on the shallow seismic exploration data after the true amplitude is restored to determine the shallow seismic exploration data after deconvolution.

[0078] Velocity analysis and stacking migration processing are performed on the deconvolved shallow seismic exploration data to determine the seismic stacking profile of the shallow seismic exploration line.

[0079] In an exemplary embodiment, S5 may be replaced by the following steps.

[0080] Stratigraphic structure and structure: We completed the measurement of 8 audio-frequency magnetotelluric sounding profiles in the study area. At the same time, we also conducted in-depth measurement of audio-frequency magnetotelluric sounding points on the MA40 and MA80 survey lines and deployed shallow seismic exploration on the same survey lines, and obtained the corresponding resistivity profiles and seismic superposition profiles, such as Figure 5 and Figure 6 As shown, the stratigraphic structure and structural characteristics are interpreted, such as Figure 7 and Figure 8 As shown, 1) the stratigraphic structure mainly refers to the burial depth, undulation and extension characteristics of each set of stratigraphic interfaces; 2) the structural characteristics are mainly faults, folds, etc.

[0081] Electrical characteristics: Figure 5 It can be seen that although the overall resistivity of the strata in the study area is low, the electrical differences between the strata are quite obvious. Within the depth range of 300m, the electrical structure as a whole presents the characteristics of a "high-low-high" three-layer medium. The relatively low-resistance layers of each survey line are discontinuous, and the thickness and range are also different. According to the existing data, it is speculated that the first layer of strata with relatively high resistivity is clay containing gypsum or rock salt containing silt; the second layer has the lowest resistivity, which is speculated to be a clay or brine layer; the third layer has the highest resistivity, which is speculated to be the strata below the Quaternary loose sediments. The strata are relatively compact and the sand content is relatively high. Its undulating characteristics reflect the bottom boundary morphology of the Quaternary loose sediments.

[0082] In addition, structural interpretation was performed based on the lateral resistivity variation characteristics of the resistivity profile, and four faults, F1, F2, F3, and F4, were effectively divided, such as Figure 7 As shown, there is a certain correspondence with the previous remote sensing and seismic research results (Jiao Pengcheng et al., 2016; Cui Qinggang et al., 2019). The study believes that due to the NE-trending compression stress on the northern edge of the Qinghai-Tibet Plateau, the secondary structure inside the Mahai Basin is relatively developed, with faults and secondary folds arranged alternately, and all faults are thrust faults. Among them, the output characteristics of the two faults F1 and F2 on the north side correspond to the Quenan Fault and the Qiannan Fault respectively; the two faults F3 and F4 on the south side are newly identified hidden faults, located in the Mahai Lake secondary depression.

[0083] Elastic characteristics: Shallow seismic exploration was carried out on two key survey lines (MA40 and MA80) in the study area. The obtained seismic stacking profiles are shown in the following figure. Figure 6 As shown. The two profiles can clearly reflect the structural framework and stratigraphic distribution characteristics in the study area. The overall stratification is good. The strata in the northeastern region of the two are thicker, the phase axis is more continuous, the strata are relatively gentle, the phase axis is dislocated in some areas, and fault structures are developed. The shallow strong reflection phase axis is speculated to be the reaction of the interlayer of solid halite and mudstone or siltstone. In addition, the strata in the northeast of the MA40 survey line gradually rise to the core of the gentle anticline in the southwest direction, and the middle and southwest of the survey line are generally anticline; while the strata in the northeast of the MA80 survey line gradually descend to the core of the syncline in the southwest, and the southwest shows the structural characteristics of the syncline, and many faults are developed inside the syncline structure.

[0084] Based on geological data and combined with the reflection event characteristics of shallow seismic exploration stacked profiles, the stratigraphic structure of the MA40 and MA80 survey lines was interpreted, such as Figure 8 As shown. T0 is the bottom interface of the Quaternary system (Q), T 0-1 , T 0-2 and T 0-3 are the stratigraphic boundaries within the Quaternary System, which subdivide the Quaternary System into Q P1 , Q P2 , Q P3 and Q h The corresponding strata are the Lower Pleistocene (Seven Springs Formation), Middle Pleistocene, Upper Pleistocene and Holocene of the Quaternary System; T1 is the bottom interface of the Neogene (N), T 1-1 and T 1-2 are stratigraphic boundaries within the Neogene, which subdivide the Neogene into N 1Y1 、N 1Y2 and N 2S The corresponding strata are the Miocene (Lower Youshashan Formation and Upper Youshashan Formation) and Pliocene (Shizigou Formation) of the Neogene respectively; below the T1 interface is the Paleogene (E) strata.

[0085] Based on the dislocation and continuity characteristics of the reflection phase axis of the profile, combined with the regional tectonic data, the structural interpretation of the MA40 and MA80 survey lines was carried out. Since the study area is located on the northern edge of the Qinghai-Tibet Plateau and the edge of the Qaidam Basin, the region is subject to compressive stress. The four faults F1, F2, F3 and F4 are reverse faults with the upper plate rising and the lower plate falling. 3-1 and F 4-1 The secondary faults are F3 and F4, both of which are reverse faults. In terms of regional structure, F1 is the Quenan fault, F2 is the Qiannan fault, and F3 and F4 are internal faults of the Mahaihu secondary depression in the study area.

[0086] In an exemplary embodiment, the effectiveness of the method shown in this application is verified as follows:

[0087] Comprehensive geophysical exploration technologies including audio-frequency magnetotelluric sounding and shallow seismic exploration were used in the study area to reveal the stratigraphic structure and tectonic characteristics of the study area from the perspective of electrical characteristics and elastic characteristics respectively. Based on the stratigraphic structure and tectonic characteristics, the strata with "electrical low-resistance anomaly + seismic strong reflection phase axis" were identified as favorable areas for potash mineralization and brine reservoir sections.

[0088] Take the two measurement lines MA80 and MA40 as an example. Fig. 9 and Fig.10 As shown, both the resistivity profile and the seismic superposition profile can effectively characterize shallow faults. The location and dip of the faults are consistent and also appear to a certain extent on the surface geological boundary.

[0089] The two potash wells MH005 and MH015 located on the MA80 survey line, which have obtained good industrial grade, both show obvious low resistivity characteristics on the resistivity profile and strong reflection phase axis characteristics on the seismic stack profile, indicating that the potash reservoir is a brine-rich stratum with a certain porosity, and the lithology, density and velocity of the upper and lower media are quite different.

[0090] For the two wells MH004 and MH010 on the MA40 survey line, their resistivity profiles have the same low-resistance anomaly, but the reflection characteristics on the seismic stacked profiles are quite different. Specifically, the characteristics of the stratigraphic medium around the industrial-grade MH004 well are similar to those of the two wells MH005 and MH015, both of which are characterized by "electrical low-resistance anomaly + seismic strong reflection"; while for the MH010 well, where no brine and halite layers were found, the lithology revealed from top to bottom in drilling is mainly clay, and because clay has a lower resistivity than the surrounding rock, it is characterized by low resistance on the resistivity profile. Since the well is filled with clay, the medium is relatively uniform from top to bottom, so it is characterized by weak reflection on the seismic stacked profile, which further shows that the application of the comprehensive geophysical technology combination of "electrical method + seismic" in potash exploration is effective, and can effectively delineate the favorable areas for potash mineralization and reveal the characteristics of brine storage space.

[0091] in accordance with Fig. 9 Based on the comprehensive geophysical exploration results of the MA80 survey line shown in the figure, combined with the existing geological data and potash mineralization model of the study area, it is believed that the potash reservoirs in this area are mainly divided into two categories. One is the "layered" brine storage model controlled by the stratum distribution, such as Fig. 9 The nearly horizontal resistivity low-resistance anomaly and seismic strong reflection phase axis between the F2 fault and the F3 fault, where the MH015 well obtained good potassium brine resources; the other is the "steep dip" brine storage mode controlled by the fault, such as Fig. 9 The resistivity anomaly and strong seismic reflection phase axis between the F3 and F4 faults indicate that the MH005 well has obtained abundant brine resources here. In addition, there are brine extraction channels excavated from the nearby potash fertilizer salt field on the surface. A large amount of brine evaporates and crystallizes into salts in the channels, which further verifies the good brine resources in the area. At the same time, it is believed that the "steeply inclined" brine storage model is more water-rich and is a favorable area for the exploration of brine-type potash resources.

[0092] It can be seen that (1) in the study area of ​​the northeastern margin of the Qaidam Basin, comprehensive geophysical technologies such as audio-frequency magnetotelluric sounding and shallow seismic exploration were used to identify the shallow geological structure and structural characteristics in detail, and an effective comprehensive geophysical exploration technology combination of salt lake potassium salt based on "electrical method + seismic" was constructed, and the drilling verification effect was good.

[0093] (2) Effectively delineate favorable areas for potash mineralization and reveal the characteristics of potash reservoir sections, namely, the characteristics of “abnormal low resistivity + strong seismic reflection”. It is inferred that the potash reservoir model in the study area is mainly a “layered” brine storage model controlled by stratum distribution and a “steeply inclined” brine storage model controlled by fault development.

[0094] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0095] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A brine-type potash mine detection method based on comprehensive geophysical technology, characterized in that: The brine-type potash mine detection method based on comprehensive geophysical technology includes: Using the audio magnetotelluric sounding technology, the audio magnetotelluric sounding data of each audio magnetotelluric sounding measuring point on each audio magnetotelluric sounding line are obtained; Determining the formation resistivity profile of the audio frequency magnetotelluric sounding line according to the audio frequency magnetotelluric sounding data; Using shallow seismic exploration technology to obtain shallow seismic exploration data of a shallow seismic exploration line; the shallow seismic exploration line and the audio frequency magnetotelluric sounding line are the same line; Determining a seismic stacking profile of the shallow seismic exploration line according to the shallow seismic exploration data; The formation resistivity profile and the seismic stacking profile are combined to jointly reveal the formation structure and structural characteristics of the study area; the formation structure includes the burial depth, undulation and extension characteristics of each set of formation interfaces; the structural characteristics include faults and folds; Based on the stratigraphic structure and structural characteristics, the favorable areas for potash mineralization and the brine reservoir sections are comprehensively detected according to the low-resistance anomaly of the stratigraphic resistivity profile and the strong reflection event axis characteristics of the seismic superposition profile.

2. The brine-type potash mine detection method based on comprehensive geophysical technology according to claim 1 is characterized in that: The audio magnetotelluric sounding technology is used to obtain the audio magnetotelluric sounding data of each audio magnetotelluric sounding measurement point on each audio magnetotelluric sounding line, including: The SEP magnetotelluric instrument adopts four-component tensor observation to collect each audio magnetotelluric sounding data; wherein the four components include the horizontal electric field component in the x direction, the horizontal magnetic field component in the x direction, the horizontal electric field component in the y direction and the horizontal magnetic field component in the y direction; the electrodes of the SEP magnetotelluric instrument are arranged with the horizontal electric field component in the x direction and the horizontal magnetic field component in the x direction as 0° and the horizontal electric field component in the y direction and the horizontal magnetic field component in the y direction as 90°; the x direction is perpendicular to the y direction.

3. The brine-type potash mine detection method based on comprehensive geophysical technology according to claim 1 is characterized in that: Determining the formation resistivity profile of the audio frequency magnetotelluric sounding line according to the audio frequency magnetotelluric sounding data specifically includes: Converting the original file format of the audio magnetotelluric sounding data; Based on the converted file format, performing time-frequency conversion on the audio magnetotelluric sounding data; Edit the audio magnetotelluric sounding data after time-frequency conversion and the audio magnetotelluric sounding data in the original file format to generate an EDI impedance file; The audio frequency magnetotelluric sounding data in the EDI impedance file is processed to generate a formation resistivity profile of the audio frequency magnetotelluric sounding line.

4. The brine-type potash mine detection method based on comprehensive geophysical technology according to claim 3 is characterized in that: Processing the audio frequency magnetotelluric sounding data under the EDI impedance file to generate a formation resistivity profile of the audio frequency magnetotelluric sounding line specifically includes: Performing profile fitting on the audio frequency magnetotelluric sounding data under the EDI impedance file to determine profile fitting parameters; the profile fitting parameters include profile length, azimuth, and audio frequency magnetotelluric sounding measurement points involved in inversion; Correcting the curve displacement based on the profile fitting parameters to determine a corrected profile curve; The corrected profile surface is subjected to one-dimensional inversion and two-dimensional inversion to generate a formation resistivity profile of the audio frequency magnetotelluric sounding line.

5. The brine-type potash mine detection method based on comprehensive geophysical technology according to claim 1 is characterized in that: Use shallow seismic exploration technology to obtain shallow seismic exploration data of shallow seismic exploration lines, including: Determine the optimal excitation parameters of the controllable vibrator and the optimal receiving parameters of the node-type seismograph; wherein the excitation parameters include the mass of the weight, the weight of the source, the number of source stations, the scanning frequency, the scanning length, the source output, the number of vertical overlaps and the excitation mode, and the excitation mode is the middle blasting; the receiving parameters include the natural frequency, the recording length, the recording format, the sampling interval, the track spacing, the shot spacing, the number of receiving channels, the maximum number of coverage times and the receiving mode, and the receiving mode is the two-side reception; Based on the optimal excitation parameters and the optimal receiving parameters, shallow seismic exploration data of the shallow seismic exploration line is acquired.

6. The brine-type potash mine detection method based on comprehensive geophysical technology according to claim 1 is characterized in that: Determining the seismic stacking profile of the shallow seismic exploration line according to the shallow seismic exploration data specifically includes: Generate an observation system file according to the shot points, detection points and relationship files of the shallow seismic exploration data, and store it in the data header; Perform static correction on shallow seismic exploration data to determine the shallow seismic exploration data after static correction; Performing pre-stack noise suppression on the shallow seismic exploration data after static correction to determine the shallow seismic exploration data after noise suppression; Performing true amplitude recovery on the shallow seismic exploration data after noise suppression to determine the shallow seismic exploration data after true amplitude recovery; Performing deconvolution processing on the shallow seismic exploration data after the true amplitude restoration to determine the shallow seismic exploration data after deconvolution; Velocity analysis and stacking migration processing are performed on the deconvolved shallow seismic exploration data to determine the seismic stacking profile of the shallow seismic exploration line.

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