In view of the characteristics of obvious changes in topography, geologic background and significant influence on geochemical element content in hilly area, this paper puts forward a method for geochemical investigation of land quality in hilly areas based on geological background analysis, with emphasis on soil geochemical survey of arable land, garden andgentle-slope land.According to the geological and geographical features of Ganzhou, detailed sample method laying in basins, valleys and mountains are,the method of plot-assignment based on geological background, the combination of eco-geological investigation and soil geochemical survey, the method of combining the pollution-free se-enriched concentration and the land quality files as the core.

We figured out the estimated values of 12 major elements and 40 minor elementsof the exposed crust of Inner Mongolia with 392 samples which are collected from five seismic sections of Inner Mongolia. And the weighted values are obtained by the thickness of different rocks in every stratigraphy and the areas of stratigraphies and magmatic bodies in the geology map. The estimated values are proved reasonable by surface heat flow value, average seismic wave velocity and elements ratio.Comparing the major element estimated values with ones given by other researchers, the average composition of Inner Mongolia is similar to others’, which are also granodioritic, except that the Ca and Mg abundances are a little low. Researching on the estimated values of minor element, rare earth element and some element ratio, we found that there is intense crust differentiation in thenorth margin of North China Plate, and intense accretion inXingmeng Orogenic Belt.

Through an analysis of the static observation data of gravity, the standard deviation (S.D.) and the rejection (REJ) of real-time observation data of gravimeter before and after the Ms 6.0 earthquake in Changning, the authors hold that the change of gravity value detected during vibration is usually the mistaken reading of gravimeter caused by the failure of vibration filtering function of gravimeter. In this earthquake of Ms 6.0, no effective signal of gravity anomaly was observed before the arrival of seismic wave, and this is because high-frequency noise greater than 4 to 6 standard deviations is automatically rejected when the gravimeter vibration filtering function is turned on, transient changes in the gravitational field are not reflected in static gravity observations, but can be reflected by the S.D. indicator. Since the value of S.D. includes high frequency interference signals such as gravimeter's own noise and environment vibration, it can be used to measure the size of signal noise. By analyzing the correlation between the S.D. value recorded by gravimeter and the earthquake magnitude in different time spans when the earthquake occurs, it is concluded that the earthquake magnitude and the S.D. value recorded by gravimeter have a significant positive correlation. Among the 21 earthquakes recorded, 2 had significant changes in S.D values recorded by gravimeters prior to the earthquake and a sudden change of REJ value was observed 8 minutes before the earthquake. It can therefore be held that the earthquake can be predicted in advance and the duration of single earthquake activity can be judged according to the sudden change of S.D. value, the change of gravity value and the REJ value.

Hebei Province is one of the major areas where strong earthquakes occur in China, and the study of seismic structures in this area is of great significance to the understanding of earthquake disasters. Based on the 1:200 000 regional gravity and 1:200 000~1:50 000 aeromagnetic data, the fault system in Hebei Province is systematically studied by using the wavelet multi-scale fault analysis method, and applied to seismological structure analysis. The characteristics of the seismogenic faults of the 1966 Xingtai M7.2,1976 Tangshan M7.8 and 1679 Sanhe—Pinggu M8 earthquake are emphatically analyzed. It is found that the shallow faults of Xinhe fault, Tangshan fault and Xiadian fault are closely related to the deep faults. The plane position of shallow faults overlapped with the deep faults of the Xingtai M7.2 earthquake. The Xingtai M7.2 earthquake is the result of the joint action of the lower deep faults and the shallow Xinhe fault. It is concluded that the processing and interpretation of gravity and aeromagnetic data is an effective, fast and economical method for studying seismogeological structures, which can provide important information for the study of Seismogeological structures.

WZA-7N structure is located in the intersection area of multiple provenances, which is generally the prospective zone of development of lithological reservoir. Due to the limitation of seismic resolution, conventional seismic data cannot accurately describe lithological boundaries, not only increase the exploration risk, but also affect the reliability of reserve calculation.in face of this exploration problem, according to the difference of every seismic trace in one prestack gather, resolution in every prestack gather in aspect of seismic resolution imaging quality and geological characteristics reaction, combined with the seismic wave group characteristics of well synthetic seismogram and VSP corridor stacking traces, author designed a set of technical process for advantage seismic tace stacking, which can effectively improve seismic resolution and interpreted lithological boundaries again. The subsequent drilling confirmed the correctness of the new lithological interpretation scheme. Practice further shows that the advantage tace stacking technique can effectively improve seismic resolution and interpretation accuracy of lithological boundary, which is a practical technique suitable for fine exploration of lithological reservoirs in weizhouA-7N structure.

In-well IP is one of the effective means to explore deep sulfide-type metal ore. In the well, the electric field-well method is used to find the bottom of the well and the blind mine near the well; in the well, the electric well-ground method is used to determine the ore body’s direction and judge its occurrence. The exploration examples of the Beiwopu copper deposit in Inner Mongolia indicate that the ground-well IP measurement corresponds to high polarization anomalies in the pyrite-rich and brass mineralization-enriched rock sections; the well-ground charging method is used to measure the occurrence of ore bodies. Judging, retrieving the direction of the ore body, guiding the drilling project, reducing the investment in exploration, and achieving A better prospecting effect.

With the electro-geochemical survey technology becoming more and more "portable", it is possible to conduct electro-geochemical survey of small or medium scales. In this paper, an effect comparison test of electro-geochemicalsurvey and soil survey at the scale of 1:50,000 was carried out within 40 km² of the hydrothermal type lead-zinc polymetallic ore district in the aeolian sand shallow covered area of Luokedun, Inner Mongolia. The results are as follows: ①Electro-geochemical survey can delineate comprehensive anomalies of Pb-Zn-Ag-As-Bi-Cd, which have the same composition as the known orebodies. The locations of the anomalies are consistent with the known orebodies/ore spots in spatial distribution. ② Compared with the soil survey results, the results of anomaly range, contrast and continuity from the electro-geochemical survey are more superior in that soil soil survey can only find anomalies of spotted distribution in the outcropping area of the hill residual soil. ③The electro-geochemical survey also finds comprehensive anomalies of multiple elements in the aeolian sand shallow covered area in the northwest of the survey area. Based on these anomalies, the 1:10,000 induced-current middle-gradient survey and drilling verification test was carried out. A 6-meter-thick Ag-Cu rich orebody was discovered at the depth of about 540 meter, which seems to have been a breakthrough in ore prospecting. The above test results show that the electro-geochemical survey at the scale of 1:50,000 can effectively delineate the prospecting targets in the shallow covered area of aeolian sand. The electro-geochemical survey can be popularized and applied in future work.

In this paper, geoelectrochemistry was used to carry out feasibility study above nickel deposits in Hejiaya area, Lueyang, Shaanxi Province. The results were compared with results obtained by traditional soil geochemical measurement methods. The results show that geoelectrochemistry and soil geochemical measurements above nickel deposit profiles show anomalies, but the soil geochemical anomalies are not good in content and morphology. It is inferred that the topography and epigenesis may influence the distribution of anomalies, which makes the distribution of anomalies slightly disordered and the clarity of anomalies reduced. Compared with soil geochemical anomalies, geoelectrochemical anomalies show a good correspondence above the ore site, and the anomalies show a steep double-peak or three-peak pattern. In order to further study the distribution characteristics of anomalies on the plane, the authors analyzed the element content of the two methods. It is found that geoelectrochemical method can strengthen anomalies to a certain extent, magnify the anomaly effect and easily summarize the law of element dispersion and enrichment. On such a basis and in combination with the results of geological and geophysical exploration, two favorable prospecting targets were delineated by geoelectrochemistry in the study area, which indicate the existence of concealed orebodies in its deep part, but this conclusion needs to be verified by engineering.

The regional metallogenic geological conditions of the study area are good. The Tongwei County is covered by Quaternary sediments. The traditional geochemical prospecting method is ineffective. In order to investigate the effectiveness of the geogas measurement method in loess-covered region, the authors selected the Chenjiacun area in Tongwei County to carry out effective experiment of the geogas measurement. The results revealed several geogas anomalies in the study area. The geogas anomalies are obvious, and the element correlation is good; in addition, they have good nesting and zoning relationships. Based on combining the geophysical data and verifying the conclusions in the field, the authors processed and analyzed the data. The geogas anomalies are in accord with the faults, mineralized bodies and geophysical anomalies in this area, and can clearly reflect the basic geological conditions of the loess-covered region. The result shows that the geogas measurement is effective in the loess-covered region, and it provides a new thinking for the prospecting in loess-covered region.

Fast imaging inversion method has been a hotspot in quantitative interpretation of gravity and magnetic exploration in recent years. Because it does not need to add prior information in the calculation, it can quickly estimate the source depth, density and other related parameters. DEXP (Depth from Extreme point) imaging method adds the corresponding structural index to the depth scaling function in the calculation, making the imaging results more accurate. Based on the basic theory of the DEXP rapid imaging method, firstly, transformation formulas for gravity field and gravity gradient tensor regarding depth from the extreme point method were calculated and applied to the causative source interpretation in this paper. Then, through different synthetic models tests, the effects of sampling interval, data error, computing range and background field on the imaging results were analyzed, respectively. Finally, the imaging method was applied to the full gravity tensor gradient field data, and the results were compared with those provided by previous researchers in the literature. Both the synthetic tests and the field example show that the DEXP imaging method not only has good suppression on the noise in the observation data but also shows the characteristics of computing stability and accuracy. In addition, the data sampling interval, calculation range and background field all have certain influences on DEXP imaging results. Therefore, when actual field data are interpreted, it is necessary to comprehensively consider their influences on the imaging results and perform the corresponding pre-processing to improve the accuracy of the quantitative interpretation.

The detection and identification technology in the maintenance and construction of submarine cables has become a very important research content. In this paper, a 2.5-dimensional high-precision finite element numerical simulation algorithm of the frequency domain CSEM method was used to simulate and analyze the submarine cable model. Based on the horizontal terrain and undulating terrain submarine cable models, this study focused on the simulation and analysis of the characteristics of the electromagnetic field distribution with the changing of seawater layer thickness and the submarine interface. Numerical examples show that the magnetic field component H_y is very sensitive to the thickness of the seawater layer. When the thickness is changed by 0.2m, the H_y error anomaly amplitude can reach 5%, thus demonstrating that the CSEM theory is feasible for detection and identification of submarine cables.

In the current engineering application, one-dimensional inversion result of TEM sounding is still an important basis for geological interpretation. In order to improve the computational efficiency and accuracy of one-dimensional inversion, it is necessary to analytically derive Jacobian matrix of one-dimensional forward. In this paper, the analytical formulas of Jacobian matrix in one-dimensional forward of central loop transient electromagnetic based on all-time resisitivity are derived in detail. It is proved that the formulas are correct and worth adopting, as shown by testing one-dimensional Occam inversion of theoretical model and measured data.

High productivity acquisition technology can improve the efficiency of seismic acquisition.However,the existence of blended noise between adjacent sources severely decreases the signal to noise (S/N) ratio of seismic data and limits the application in the field.To solve the issue,an improved blended noise suppression approach is proposed by combining NMO,median filter with the seislet transform based threshold de-noising.Firstly,median filter is applied to the original blended data with NMO correction.Next,we continue to extract the residual energy to get the de-blended result by the seislet transform based threshold denoising.Then,re-process the residual data by subtracting the original pseudo de-blended data and the pseudo de-blended data of the de-blended result from each iteration as the above processing flow.Finally,the final de-blended data is obtained by adding the remained energy of each iteration.Simulated data tests demonstrate the proposed approach can protect effective signal while suppressing the blended noise.

The injection of CO₂ into the coal seam changes the CO₂ saturation of the coal seam.According to Archie's empirical formula,there are obvious differences in coal seam resistivity before and after CO₂ injection,which provides conditions for TEM monitoring.In the development of coalbed methane in Shizhuang North Block,the electrical resistivity changes of coalbed methane before and after CO₂ injection were monitored by TEM. The results show that the increase of electrical resistivity of coal seam can be caused by CO₂ injection in coal seam, and can be monitored by TEM. At the same time,the induced voltage can directly reflect the change of formation electrical characteristics caused by CO₂ injection.The equivalent resistivity from the surface to the coal seam is calculated by using the calculation formula of formation equivalent resistivity,and the transient electromagnetic sampling delay and the corresponding induced voltage of the formation near the coal seam are solved.The variation of induced voltage relative to background value reflects the change of formation electrical properties.The variation and rate of formation induced voltage caused by CO₂ injection are analyzed and calculated.Combined with the error range,the range of CO₂ migration enrichment zone can be inferred.

The international geomagnetic reference field (IGRF) is a general international model for describing the earth’s main magnetic field. At present,this model can be used to calculate the seven elements of geomagnetic field at any point. However,with the development of aeronautical full tensor magnetic measurement technology,there is an urgent need for full tensor geomagnetic gradient data. In this paper,the calculation principle of the IGRF model is summarized and the expression of the full tensor geomagnetic gradient with spherical harmonic expansion is derived. The calculation of the seven elements of geomagnetic field and the full tensor geomagnetic gradient at any given point is realized. Comparing with the calculated data from the website of the National Oceanic and Atmospheric Administration of the United States (NOAA),the results are accurate and reliable. The contour map of the full tensor geomagnetic field in a region is drawn, and the results were in accordance with the Laplace equation. It provides the theoretical basis for the selection of learning flight working area and flight height in the aeromagnetic survey.

Accurate imaging of subsurface anomalous geological bodies with diffraction energy is one of the breakthrough technologies in seismic exploration in recent years.Stacking the dip gather after effective filtering is the main technical means to effectively utilize the seismic diffraction information.In this paper,the authors improved the calculation method of dip domain common image gathers in a more flexible and efficient way and,through model test,analyzed the differences and relations between reflected energy and diffracted energy in DDCIG(Dip Domain Common Image Gathers).Then,a new target dip filter was designed for dip domain common image gathers to achieve better diffraction information.The authors testified the new methods both on a model data and on actual production data of beaded reservoir in Northwest China which highly demands diffracted imaging.With achieving better diffraction energy, the authors finally succeeded in improving imaging for weak diffraction geological body with less calculation time.

At present,the geological situation of seismic exploration is becoming more and more complicated.With the continuous development of seismic exploration,especially for viscoelastic media,the technical requirements for surface wave exploration are getting higher and higher.Love wave refers to the horizontal polarization shear wave in the surface layer after repeated reflections at the boundary of the surface layer.Love wave detection is one of the shallow surface detection method.It is very convenient and has high detection precision.Therefore,the study of Love wave has important theoretical and practical significance.In this paper,the Love wave single shot record is simulated by high order finite difference method in the case of horizontal layered complex geological.The comparison of the dispersion curves with the theoretical dispersion curves proves that the method proposed in this paper is correct.The influence of the viscoelastic medium on the Love wave dispersion curve is also discussed.Then,the least squares inversion is used to verify this conclusion.This paper provides a more complete theoretical basis for the high-precision surface wave inversion method.Finally,the field data inversion results show that the proposed method is effective and practicable.

The 1:25 million land geochemical survey conducted in Enshi area shows that the surface soil in Enshi area is rich in selenium, and the content of cadmium is also high. Based on the data of 3 950 surface soil samples and 362 crop samples in this area, the geochemical characteristics of selenium and cadmium, co-generation factors, and the capability of different types of crops for absorbing and enriching the two elements are discussed.The results show that the selenium and cadmium in the surface soil of Enshi area is associated with each other. The distribution of the two elements is mainly controlled by the Permian soil parent material, and the occurrence of selenium and cadmium is closely related to organic matter and sulfide in soil. Comparison of BCF of selenium and cadmium in different crops shows that ginkgo, corn and tea have higher absorption capacity for selenium than for cadmium, and hence these crops could be used as the preferred crops for the development of selenium-enriched agricultural products in Enshi area. At the same time, the pH of the soil should also be considered. The medium alkaline soil may be more likely to avoid the risk of cadmium enrichment in agricultural products. In addition, selenium has a detoxifying effect on cadmium. Selenium-rich environment will significantly reduce the harm of cadmium to human body.

The traditional detection of foundation improvement mainly depends on dynamic penetration test,drilling holes test,standard penetration test and plate loading test;nevertheless,these methods are all characterized by inefficiency and high dispersion degree,and hence can't totally reflect the detection of foundation improvement.So it is necessary to develop a fast way to detect the dynamic foundation.Based on the Garden Expo Wetlands Project,the authors gave an in-depth discussion on the transient Rayleigh wave detection method.Through the processing and analysis of a large number of Rayleigh wave data collected in this project and comparing with the in-situ test results,the authors established the correlation between Rayleigh wave velocity and in-situ test data,and studied the application effect of Rayleigh wave technology in quality testing.

Concrete is the main material in construction engineering,and its quality is closely related to people's life and property.The strength grade is an important indicator of the quality of the concrete,so the strength of the concrete structure needs to be tested. In this paper,the surface wave velocity inversion is realized by the least square method to obtain the shear wave velocity structure of the target concrete structure,the strength value is calculated based on the elastic modulus method and the power function fitting method,and then the concrete strength is evaluated.The results are as follows:First,the shear wave velocity structure of concrete structure can be obtained effectively by using the ultrasonic surface wave method.Second,both the elastic modulus method and the power function fitting method can evaluate the strength of concrete,which is effective and the elastic modulus method can meet the actual accuracy requirements,thus providing a new way for the quality detection of concrete.

The approximate vertical reflection method is a seismic exploration technique with a minimum offset,which does not need a sufficiently large offset and is suitable for tunnel,roadway and other underground projects with narrow space.It can be used to locate and track medium and large geological structures such as faults and corrosion zones.Firstly,combined with the actual engineering situation,the tunnel and fault model are modeled,and the model parameters which are in accordance with the actual engineering are given.The forward simulation research is carried out,and the theoretical detection results of the fault are obtained.Then,approximate vertical reflection method detection is carried out three times in practical engineering by using forward simulation of seismic array parameters,and the results of forward simulation are compared and analyzed.Finally,the validity of approximate vertical reflection method in fault detection is proved by the actual excavation of tunnel.

In the detection of urban bedrock surfaces, due to the severe urban traffic and electromagnetic interference, direct current sounding is often used as the main geophysical method. The two-dimensional electrical sounding profile arranges electrodes along the survey line, collects the apparent resistivity data and performs two-dimensional inversion, and uses the obtained two-dimensional resistivity cross-sectional image in the direction of the profile to infer the location and attitude of the geological body. However, due to the complicated actual situation, it is not suitable for the two-dimensional inversion conditions (infinitely extending and orthogonal to the survey line), and the two-dimensional inversion will produce large errors. In view of such a situation, three-dimensional inversion of multi-section two-dimensional electric sounding data of the survey area can be used to obtain three-dimensional resistivity stereo images of the survey area, and the spatial form of geological body distribution can be inferred. In a geological survey of a city in Shandong Province, an electrical sounding network with a distance of 50m and a line spacing of 100m was set up to collect two-dimensional symmetrical quadrupole sounding data. After establishing a three-dimensional inversion data format for the two-dimensional electrode arrangement in the survey area, a three-dimensional resistivity inversion was performed to obtain a three-dimensional resistivity image of the survey area. The inferred bedrock surface is basically the same as the drilling verification.

The Sebei gas field is a Quaternary Huxiang sedimentary biogas reservoir with shallow burial and poor diagenesis.The reservoir has "four highs" background of "high porosity,high salinity,high clay content,and high conductivity of (yellow/magnetic) iron ore".A low gas barrier layer and a special ultra-low gas barrier layer were formed.Based on the electrical response characteristics of the low-resistance gas layer logging curve,the authors studied its spatial distribution and its influence on production characteristics,and made a mechanism analysis of the low-resistance gas layer.The results are as follows:First,geological backgrounds such as high porosity,high salinity,and high clay content are the main factors leading to the low resistivity of the gas layer in the Sebei gas field,and the thin interbeds of sand and mudstone also have a certain effect;Second,the existence of special conductive minerals is the direct factor responsible for the abnormal low-resistance gas layer;Third,the natural gamma-resistance intersection method can effectively identify the low-resistance gas layer formed by geological background and reservoir characteristics;as for lateral and induction logging,the double-resistance cross section improves the recognition effect of thin sand bodies;Fourth,on the basis of fine logging interpretation,it seems that strengthening the study of the planar distribution of iron ore layers and using dynamic methods to form plane monitoring by means of gas testing can improve the precision of the interpretation of low-resistance gas layers.

In recent years, more and more data show that the Songliao Basin has a large hydrocarbon generation potential and oil-gas resource prospect, and is expected to become the key stratigraphic horizon for the deep oil-gas exploration breakthrough in the Songliao Basin in the future. However, The distribution of the Carboniferous-Permian strata still has large uncertainties in terms of method, technology and understanding. In view of such a situation, the authors deployed a magnetotelluric sounding profile around the Heifudi- drill hole in the western slope zone of the Shenyang Geological Survey Center. The field parameters were used to optimize the acquisition parameters and thus high quality raw data were obtained. Through data analysis and conjugate gradient method, the electrical structural profiles were obtained and, in combination with drilling, seismic and other data, a comprehensive analysis was conducted. The results show that two horizontally stable low-resistance layers are developed near Heifudi-1 drill hole, and the first set of low-resistance layers is buried between 300 to 800 meters, which is the electrical property of the Cretaceous strata with high muddy content. In response, the second set of strata is located between 1.5 to 2.5km below the T5-Interface, and the lateral undulation is small. Combined with the drilling data, it is considered to reflect the mudstone strata of the Permian Linxi Formation. Combined with the main controlling factors of deep gas, the favorable zone of oil-gas has been predicted. These insights provide a reliable geophysical basis and technical reserve for the evaluation of the Carboniferous-Permian hydrocarbon resources in the Songliao Basin.

In the high exploration stage,the exploration target of the turbidite reservoirs of $\text{E}_{3}\text{S}_{3}^{2}$ in Niuzhuang sag has been gradually turned to complex subtle reservoir whose characteristics are small scale,thin thickness,rapid lateral variation and containing carbonate.It is difficult to describe the thin interbed reservoir using conventional seismic data,and is also difficult to identify sandstone in gray background.To tackle these problems,the authors studied the prediction of sand reservoir by combining the reconstruction of lithologic sensitive curve with the inversion of waveform indication.It turns out that seismic indication inversion obviously suppresses the interference of gray matter components,and the inversion using lateral variation of waveform instead of traditional variation function can improve the inversion accuracy,with the accuracy of thickness above 5 m being 88.5%,and that of thickness of 2~5 m being 80.2%.The inversion of sand conforms to the sedimentary law and the reservoir fluid distribution in the study area.By applying the reservoir prediction results,a total of 20 exploration wells were deployed in 5 development blocks,of which 8 wells were drilled and industrial oil was obtained after they were put into production,with the new expected capacity being about 4×10⁴ t.

A comparison with ground transient electromagnetic (EM) method shows that airborne transient EM is more affected by noise, such as sefrics and motion noise. And the influence of background field noise couldn't be neglected. The background contains primary field information, which causes the amplitude of background field to be much larger than the secondary field signal containing geological information. In order to obtain the underground electrical structure clearly, it is necessary to find an efficient method to remove background field. In this paper, the background field problem is studied by linear interpolation. First, according to the responses of the front and back line obtained from the high flight, after cumulative and average calculation, the responses of the same time channel of each measured line in a cycle can be obtained as the background field responses of the corresponding time channel of each line. Using interpolation principle, the background field above each measuring line in the working area is calculated by flight time, so as to remove the background field. Through the real data removal, this method can better remove the background field and then show the anomaly, and can clearly determine the location of the anomaly after removal. Time-domain AEM data preprocessing contains many processing modules. The linear interpolation method proposed in this paper lays a foundation for efficient data preprocessing.

In practical measurement of magnetotelluric sounding, the static displacement of apparent resistivity is a common phenomenon. Whether it can be identified and corrected efficiently will affect the accuracy of inversion and interpretation directly, especially on condition of regional static displacements. In a magnetotelluric profile with continuous static displacements, the apparent resistivity curves with the same polarization model of adjacent measurement points are less referable to each other, and how to make reasonable static displacement correction is the key to obtaining reliable inversion results. Based on lithologic analysis and experimental tests, a new static displacement correction method for large-point-distance condition is preliminarily summarized in this paper, which is named "the statistical averaging method of frequency points in first branch". In this method, statistical analysis is firstly conducted on the distortion measurement points in the study region, then the first three frequency points of each measurement point (same polarization mode) are averaged, and finally the gained averages of all the distortion measurement points are further averaged to obtain a target value, which is preset to the second frequency point of the first branch of the corresponding apparent resistivity curves with distortion. This method doesn't change the shape, but only changes the position of the first branch of the measuring point curve, so as to reach the preset position. Taking the measured data of magnetotelluric sounding in Zalut area as an experiment, the authors carried out the static correction test, and obtained a good application effect, which also indicates that the method is reasonable and applicable in the magnetotelluric sections with continuous static displacement under the condition of insufficient logging and physical property constraints.

After the induced eddy current in the conductive thin plate is transient, the eddy current distribution has become stable and decays exponentially. In the equivalent mathematical model, it is easier to calculate the late transient electromagnetic response by the equivalent eddy current method. This method can calculate the response of any combination of 1~4 blocks and conductive surrounding rock or cover layer, and has certain applicability. In this paper, the calculation method of late transient electromagnetic equivalent eddy current field induced voltage is deduced. By numerical simulation and typical characteristic analysis of four typical geoelectric models, some results have been obtained: ① When the power-off delay is short, the amplitude of the abnormal response of the conductor is large. When the borehole passes through the center of the abnormal body, the abnormal shape is a single-peak positive abnormal response; with the elapse of time, the electromagnetic response gradually decays. ② When the borehole is located at the boundary of the orebody, the horizontal orebody produces a three-peak symmetrical anomaly, and the anomalous peak value is a negative anomaly; when the inclination is 45°, the anomaly morphology of the orebody exhibits asymmetric positive and negative anomalies, and a negative anomaly appears on the top side of the orebody, with positive anomaly on the underside. ③ Under the same condition, the abnormal amplitude of the simple plate-shaped body is larger than that of the single plate-shaped body, and its abnormal shape conforms to the abnormal response characteristics of the single plate-shaped body. The research results have certain significance for the ground-well transient electromagnetic method to use forward fitting to improve the later interpretation work and to determine the layout parameters of the work area, such as loop size, section length, point distance, and emission current.

In recent years,the field of carbonate rocks of Tarim basin has gained rich oil and gas,especially Ordovician karst cave reservoir resource in deep seam of northern basin.For the purpose of accurate cognition,evaluation and management of the reservoirs,the application of geophysical exploration methods to fine characterization of reservoir and accurate quantitative description of production and reserves is very important.Previous quantitative description of reservoir and karst seam holes is mainly based on two-dimensional (plane) category.In this paper,the authors introduce the key description method based on high precision acquisition of 3D seismic data,drilling data and production performance data,activity union,properties characterization of seismic facies,and use phase inversion to determine the reservoir as well as porosity relation to establish geological and seismic bridge,eventually carving three-dimensional category in three dimensions to describe and quantify geological body.This method can effectively characterize and obtain the geometric shape and effective volume value of the three types of reservoir spaces in karst slotted reservoirs,and achieve accurate quantitative description of such reservoirs.At present,this technique has been applied to the establishment of quantitative description standard and the compilation of reserve calculation scheme of carbonate fissure and cave reservoirs in the depth of Tarim basin,in the hope of realizing the progress of quantitative description technology of carbonate karst fissure and cave reservoirs.

Conventional fault detection attributes can identify low-sequence faults with relatively flat stratigraphic attitudes and obvious seismic reflection characteristics.Low-order faults are poorly identified in places where strata are inclined or the dip angle of strata changes drastically.In view of the above difficulties,on the basis of an in-depth analysis of the geological characteristics and seismic response characteristics of low-order faults,the authors carried out the research based on a method for identifying low-order faults based on the structure-oriented Canny attribute edge detection according to the combination of 3D multi-level blind source separation and structural preservation filtering denoising,and formed an effective low-order fault identification method,which improved the capability of low-order fault identification.Compared with coherent attributes,the noise detection results of the structure-oriented Canny attribute edge detection are smaller,especially in places where the stratum is steep or the attitude of the formation fluctuates greatly (that is,the formation dip angle changes greatly).The results are better.The obtained results are in good agreement with real drilling results,and the oil-water relationship in the study area is solved.Five more low-order faults were discovered,and new drilling wells have achieved high oil production flow.

In this paper, the authors analyzed cases of applying EH-4 electromagnetic imaging system and 2D, 3D high density resistivity method to detecting seawater intrusion interfaces in Laizhou Bay area. The results show that the inversion profile of these methods provides rich and reliable geological information, which can help solve geological environment problem of this region, and these geophysical methods are effective and feasible in detecting seawater intrusion interfaces in Laizhou Bay area. Based on many profiles of EH-4 electromagnetic imaging system and high density resistivity method, the authors successfully figured out the distribution of the seawater intrusion interface, compiled the map of the seawater intrusion interface, and analyzed and sorted out electrical features of the region. These results has laid a solid foundation for the future geological survey in Laizhou Bay area.