AU2021107040A4 - A comprehensive method for deep geological exploration in urban areas - Google Patents

Abstract

The invention provides a comprehensive method for deep geological exploration in urban areas. This method comprises: conducting preliminary exploration using a gravity method to obtain the density information of the target body in the center of the urban area, conducting supplementary exploration using the electromagnetic method to obtain the electrical information of the target body; conducting fine exploration of typical sections by the seismic method to obtain velocity information of the target body. The comprehensive combination of gravity, electromagnetic, and seismic methods can be applied in the deep exploration in urban areas, acquiring more accurate and precise data of coal seam structure. -1- / 1 Drawings I. boundary of seismic and EM boundary and --------- _ point of gravity Fig. 1 60' Fig. 2 -1- / 3

Description

Drawings

I.

boundary of seismic and EM

boundary and --------- _ point of gravity

Fig. 1

60'

Fig. 2

-1- / 3

Description A comprehensive method for deep geological exploration in urban areas

The invention relates to the field of city, engineering environment and

geophysical exploration, in particular to a comprehensive method for deep detection

in urban environment.

Background technology

Underground targets such as cavities, water bodies and structures are

distributed in many cities in northern China, it is difficult to accurately locate

underground targets. Geophysical methods are commonly used to determine these

kind of special targets. However, due to large electromagnetic interference, dense

population and many buildings in urban areas, geophysical detection is limited

in many aspects. Therefore, it is very necessary to select appropriate geophysical

methods and their combinations, carry out effective exploration step by

step, make various achievements complement each other, and realize the

exploration of underground deep structures in urban areas.

Summary of the invention

In order to solve the above technical problems, the invention provides a

comprehensive method for deep detection in an urban environment. In order to have a

basic understanding of some aspects of the disclosed embodiments, a brief summary

is given below. This summary is not a general comment, nor is it intended to identify

key/important constituent elements or describe the scope of protection of these

embodiments. Its sole purpose is to present some concepts in a simple form as a

-1- / 12

Description preface to the detailed description later.

The invention adopts the following technical scheme:

In some optional embodiments, a comprehensive method for deep detection in

an urban environment is provided, including the following steps: conducting

preliminary detection by gravity method to obtain the density information of the

target body; conducting supplementary detection by electromagnetic method to

obtain the electrical information of the target body; conducting fine detection of

typical sections by seismic method to obtain the velocity information of the target

body.

The invention relates to a comprehensive geophysical methods for deep

detection in an urban environment is further characterized by comprehensively

analyzing the three geophysical data obtained by the preliminary detection of the

gravity method, the supplementary detection of the electromagnetic method and the

fine seismic detection of the typical section, so as to determine the accurate

geological information of the deep structure in the urban area.

Furthermore, the gravity method preliminarily detects and obtains the density

information of the target body, including: in the urban area to be evaluated where

there are a lot of electromagnetic noise and dense buildings, the gravity detection

method is used to preliminarily infer the buried depth and fluctuation characteristics

of the upper interface of the limestone of the basement of the deep structure, as well

as the fault structure, so as to determine the preliminary geological information of the

deep structure.

-2- / 12

Description Furthermore, the process of supplementary detection of the electromagnetic

method to obtain the electrical information of the target body includes: in the

periphery of the urban area, the electromagnetic interference is relatively small. The

electromagnetic sounding method is used to detect and form the electromagnetic

apparent resistivity section. Based on the electrical difference between the deep

structure and the surrounding rock, the occurrence characteristics and deep structural

characteristics of the basement limestone in the urban area are estimated

supplementarily on the apparent resistivity section, and further supplementary

geological information of deep structure is given according to electromagnetic

results.

Further, the process of obtaining the velocity information of the target body by

fine seismic exploration of the typical section includes: the seismic exploration

method is used to detect in the periphery of the urban area to form a seismic section.

Using the elastic wave velocity difference between the deep structure and the

surrounding rock, the occurrence characteristics and deep structural characteristics of

the coal measure strata and the base limestone of the coal measure strata in the urban

area are finely estimated on the velocity section, and the further fine geological

information of the deep structure is obtained.

-3- / 12

Description

Beneficial effects brought by the invention: the three geophysical methods of

gravity, electromagnetic and seismic are used to cooperate in comprehensive

exploration, so that the high-precision data of coal seam structure and shape in the

exploration area with the best effect can be obtained, which is more accurate.

Description of diagrams

Fig. 1 is the layout of gravity method in the central urban area of the invention;

Fig.2 is a schematic diagram of the principle of frequency-domain

electromagnetic sounding of the invention;

Fig.3 is the layout of electromagnetic exploration outside the urban area of the

invention;

Fig.4 is the inference diagram of the Austrian roof interface;

Fig.5 is the seismic geological section.

Specific embodiments

The following description and the accompanying diagrams fully show specific

embodiments of the invention so that those skilled in the art can practice them. Other

embodiments may include structural, logical, electrical, process, and other changes.

The embodiments represent only possible changes. Unless explicitly required,

individual components and functions are optional and the order of operation can be

changed. Portions and features of some embodiments may be included in or replace

portions and features of other embodiments.

In some illustrative embodiments, the invention provides a comprehensive

-4-/12

Description method for deep detection in an urban environment, comprising the following steps:

First, conducting preliminary detection by gravity method to obtain the density

information of the target body;

The specific process is that in the urban area to be evaluated where there are a

lot of electromagnetic noise and dense buildings, the gravity detection method is used

to preliminarily infer the buried depth and fluctuation characteristics of the upper

interface of the limestone of the basement of the deep structure, as well as the fault

structure, so as to determine the preliminary geological information of the deep

structure.

Then, conducting supplementary detection by electromagnetic method to obtain

the electrical information of the target body;

The specific process is that using the electromagnetic sounding method to detect

and form the electromagnetic apparent resistivity section in the periphery of the urban

area. Based on the electrical difference between the deep structure and the

surrounding rock, the occurrence characteristics and deep structural characteristics of

the basement limestone in the urban area are estimated supplementarily on the

apparent resistivity section, and further supplementary geological information of deep

structure is given according to electromagnetic results.

Then, conducting fine detection of typical sections by seismic method to obtain

the velocity information of the target body.

The specific process is that using the seismic exploration method to detect in the

periphery of the urban area to form a seismic section. Using the elastic wave velocity

-5- / 12

Description

difference between the deep structure and the surrounding rock, the occurrence

characteristics and deep structural characteristics of the coal measure strata and the

base limestone of the coal measure strata in the urban area are finely estimated on the

velocity section, and the further fine geological information of the deep structure is

obtained.

-6- / 12

Description

Finally, three kinds of geophysical data obtained from preliminary detection by

gravity method, supplementary detection by electromagnetic method and fine seismic

exploration of typical sections are comprehensively analyzed to determine the

accurate geological information of deep structures in the urban area.

The survey area is located in Yangqu county, Taiyuan. There are dense buildings

in the urban area, and many caves are distributed around the urban area.

Electromagnetic method and seismic exploration cannot be carried out normally. The

exploration with one geophysical method is obviously restricted, and the combination

of multiple methods must be used to effectively detect the undulating shape of the

basement of underground coal measures.

In this exploration, three geophysical methods of gravity, electromagnetic and

seismic are used for collaborative exploration. First, gravity exploration is used to

find out the undulating shape and buried depth of the fixed interface of Ordovician

limestone in the urban area of Yangqu county. Then, the electromagnetic exploration

is carried out to obtain the form and buried depth of Ordovician limestone outside the

urban area. From the gravity exploration results in the urban area and the

electromagnetic exploration results outside the urban area, the fluctuation form and

buried depth information of the fixed interface of Ordovician limestone in the whole

area are obtained. Finally, the exploration area is identified by seismic method, the

detailed information of the coal seam above the fixed interface of Ordovician

limestone is obtained, and the high-precision data of coal seam structure and shape in

-7- /12

Description the exploration area with the best effect are obtained by integrating the results of the

above three methods.

First, gravity exploration is carried out in the urban area of Yangqu county,

Shanxi Province, to understand the fluctuation of Ordovician limestone top interface.

The strata in the urban area of Yangqu county from old to new are Ordovician,

Benxi Formation of Middle Carboniferous, Taiyuan Formation of Upper

Carboniferous, Shanxi formation of Lower Permian and Lower Shihezi Formation of

Lower Permian, in which the coal seams are mainly distributed in Taiyuan formation.

The density of coal seam is the lowest in Yangqu area, generally 1.2-1.5g/cm 3. The

second is mudstone density of 2.0-2.2g/cm 3, Tertiary conglomerate 2.2-2.4g/cm 3. The

density of limestone is relatively high, generally above 2.7g/cm 3. It can be seen that

there is an obvious density difference interface between Ordovician limestone and

overlying strata, which provides an interpretation basis for gravity exploration in this

area. The layout of the gravity method in the urban area is shown in Fig. 1.

CG-3M automatic gravimeter produced by SCINTREX, a Canadian company,

was used to test at obstacles. It was found that the response of the building was 40

pgal, the response of the cave was 25 pgal, and the abnormal value caused by the

bottom interface of deep coal seam is 3419mgal3425mgal. The interference

anomaly is very small compared with the effective anomaly. Thus, the impact of

buildings and caves can be ignored.

Then, supplementary exploration was carried out by electromagnetic method to

determine the burial depth of coal seam bottom interface.

-8- / 12

Description

CSAMT adopts a controllable artificial source, which is connected to two

grounded electrodes through a certain length of wire to supply alternating current to

the earth for transmission. For the horizontal layered earth, the transmitted waves are

TE and TM mixed waves. Observe the electromagnetic response excited by the

source at an appropriate distance from the source, and judge the underground

geological structure through the analysis and interpretation of data with geological

information. The high frequency corresponds to the shallow part and the low

frequency corresponds to the deep part. CSAMT has the advantages of high

efficiency, large exploration depth, high resolution, flexible device, convenient

construction, multiple parameters, little influence by terrain, strong ability to

penetrate high-resistivity layer and so on. The schematic diagram of

frequency-domain electromagnetic sounding principle is shown in Figure 2.

CSAMT follows the Kania formula of MT. By observing a pair of orthogonal

electric field component and magnetic field component in the far field and calculating

the ratio between them, it is called the impedance of electromagnetic wave, so as to

obtain the resistivity p, of the earth in uniform half space, as follows:

Pa - Z = wP wp H, Wp H,

In the above formula, c is the frequency, p is the permeability of the earth,

E, and H, is the orthogonal electric field component and magnetic field component

respectively.

The formula of apparent resistivity p, defined by electric field component E0

is as follows: -9- / 12

Description 4xr3 E, Ia 3cos2O-1

In the above formula, Ia is the horizontal harmonic electric dipole and r is

the polar distance.

In the case of far field, the apparent resistivity defined is basically the same for

all frequency sounding curves of the same geoelectric section, whether according to

Kania ratio method or single component method. However, due to the use of artificial

source excitation, it can't ensure that all sounding data are in the far field. When the

low-frequency data is in the near field, the apparent resistivity data is distorted and

can't reflect the deep geological information.

According to the theory of electromagnetic field, after the source is established,

the electromagnetic field is distributed in any range of depth underground. However,

for convenience, it is necessary to define the depth of the electromagnetic field. The

skin effect of electromagnetic wave propagation in the earth medium is used, that is,

the detection depth is determined by the different skin depth of electromagnetic

waves with different frequencies in the stratum. The skin depth is calculated as

follows:

15= 503;

In the above formula, A represents the formation resistivity and f represents

the working frequency.

In the periphery of the urban area, the electromagnetic interference is relatively

small. The electromagnetic sounding method was used to detect and form the

-10- / 12

Description electromagnetic apparent resistivity section. Based on the electrical difference

between the deep structure and the surrounding rock, the occurrence characteristics

and deep structural characteristics of the basement limestone in the urban area were

supplementarily estimated on the apparent resistivity section. Further supplementary

geological information of deep structure is obtained according to electromagnetic

results. The layout of electromagnetic exploration outside the urban area is shown in

Figure 3, and the inference diagram of Austrian roof interface is shown in Figure 4.

Finally, the typical section is explored by seismic method to find out the

basement fluctuation.

The seismic exploration was carried out on the basis of gravity exploration and

electromagnetic exploration, and seismic exploration laid 1000mx2000m survey

network to cover the whole area. Based on the principle that the main survey line

should be perpendicular to the stratum and structural trend as far as possible and the

connecting line should be perpendicular to the main survey line, the survey line in

NW direction should be determined as the main survey line with a line distance of

1000m, and the survey line in NE direction should be the connecting line with a line

distance of 2000m. Using vibrator as the excitation, DFS-V type and corresponding

supporting equipment as the receiving, and geophones of 60Hz natural frequency

were used; sampling interval: 1ms; record length: Is; preamplifier gain: 28; record

format: SEG-D; recording density: 1600; driving capacity of vibrator equipment:

%; scanning length: 14 seconds; scanning frequency: 12-110Hz; scanning type:

nonlinear; nonlinear compensation coefficient: 0.15dB/Hz; vertical stacking times: 12

-11- / 12

Description times for single set and 5-8 times for double sets. A total of 20 survey lines, 7263

qualified physical points and 131.93km section length have been completed in

seismic exploration.

The key processing links such as static correction, velocity interpretation,

improvement processing, special processing and VSP data processing are focused,

analyzed and studied, and high-quality processing results were obtained.

As shown in Figure 5, through seismic exploration, the structure in the area is

further controlled and the depth of coal seam bottom interface is further determined.

Those skilled in the art should also understand that various illustrative logic

blocks, modules, circuits and algorithm steps described in connection with the

embodiments herein can be implemented into electronic hardware, computer software

or a combination thereof. In order to clearly illustrate the interchangeability between

hardware and software, various illustrative components, frames, modules, circuits and

steps are generally described around their functions. Whether this function is

implemented as hardware or software depends on the specific application and the

design constraints imposed on the whole system. Skilled technicians may implement

the described functions in a flexible manner for each specific application, but such

implementation decisions should not be interpreted as departing from the scope of

protection of the present disclosure.

- 12- /12

EDITORIAL NOTE 2021107040

There are 2 pages of claims only.

Claims (5)

1. Claims 1. A comprehensive method for deep geological exploration in urban areas,

   comprises:

   Conducting preliminary exploration using a gravity method to obtain the

   density information of the target body in the center of the urban area;

   Conducting supplementary exploration using the electromagnetic method

   to obtain the electrical information of the target body;

   Conducting fine exploration of typical sections using seismic method to

   obtain the velocity information of the target body.
2. 2. The method according to claim 1, wherein a fine data analysis is

   performed after the data acquisition;
3. 3. The method according to claim 2, wherein the preliminary exploration

   using the gravity method further includes:

   In the dense urban area with a high level of electromagnetic interference,

   the gravity detection method is used to preliminarily examine the fault

   structure, buried depth, and fluctuation characteristics of the upper

   interface of the limestone at depth, as well as the fault structure, so as to

   determine the preliminary geological information of the deep structure;
4. 4. The method according to claim 3, wherein the process of the

   supplementary exploration of the electromagnetic method further

   comprises:

   On the periphery of urban areas with low electromagnetic interference, the

   electromagnetic method is used to generate electromagnetic apparent

   Claims resistivity sections. Based on the electrical difference between the deep

   structure and the surrounding rocks, the occurrence characteristics and

   deep structural characteristics of the basement limestone in the urban area

   are evaluated, and therefore, further supplementary geological information

   of deep structure is acquired.
5. 5. The method according to claim 4, wherein the process of fine exploration

   of typical sections using seismic method further comprises:

   The seismic exploration method is used to explore the periphery of the

   urban area and generate seismic sections. Using the elastic wave velocity

   difference between the deep structure and the surrounding rocks, the

   occurrence characteristics and deep structural characteristics of the coal

   measure strata and the base limestone of the coal measure strata in the

   urban area are finely determined in the velocity section, and therefore,

   further fine geological information of the deep structure is obtained.