Deep fault identification method based on water pumping test

Abstract

The invention relates to a deep fault identification method based on a water pumping test. The method comprises the steps that a pumping well and an observation hole are designed in an exploration area, a constant-flow unstable pumping test is conducted, the pumping amount, the pumping time, the distance between the observation hole and the pumping well and drawdown data are recorded, and a drawdown-pumping duration s-lgt relational graph in the observation hole is drawn for analysis; determining a critical time point when the observation hole begins to be deepened and a critical time point when the observation hole is deepened to be turned; according to the drawdown change condition after the time critical point when the drawdown of the observation hole turns, the property of the deep fault in the exploration area is determined; determining a suspected position and a suspected trend of a deep fault according to the distance between the observation hole and the pumping well, the time critical point when the observation hole starts to be deepened and the time critical point when the observation hole deepened to be turned, and obtaining a rock core at the suspected position through drilling to determine the exact position and the exact trend of the fault. And the efficiency and the accuracy of fault exploration are greatly improved.

Description

Technical Field

[0001] The present application relates to the technical field of hydrogeological exploration, and in particular to a method for identifying deep faults based on a pumping test. Background Art

[0002] As a common geological structure, the existence of faults has a significant impact on groundwater flow and resource distribution. In the fields of groundwater resource management, geological disaster prevention and geological exploration, accurate detection of the location and nature of faults is crucial for formulating reasonable development and utilization strategies and prevention and control measures.

[0003] Traditional fault detection methods include geophysical exploration and drilling, which use seismic wave reflection and geological structure analysis to detect faults. Traditional geophysical seismic wave methods require manual tracking and selection of faults, which requires a lot of manual work and has low detection efficiency. For experienced interpreters, it usually takes several weeks to several months to mark faults in a typical seismic volume, and the selection results are highly dependent on the interpreter's experience, and manual errors will affect the interpretation results.

[0004] Therefore, current fault exploration methods suffer from low efficiency and accuracy. Summary of the invention

[0005] Based on this, it is necessary to provide a deep fault identification method based on pumping test that can improve the efficiency and accuracy of fault exploration in response to the above technical problems.

[0006] A deep fault identification method based on pumping test, the method comprising:

[0007] Design pumping wells and observation holes in the exploration area, conduct constant flow non-steady water pumping tests, and record the pumping volume, pumping time, distance between the observation hole and the pumping well, and drawdown data;

[0008] According to the pumping time and drawdown data, a relationship diagram between the drawdown and the pumping duration s to lgt in the observation hole is drawn;

[0009] Analyze the image features in the depth drop-pumping duration s-lgt relationship diagram in the observation hole to determine the critical time point at which the depth drop of the observation hole begins and the critical time point at which the depth drop of the observation hole turns;

[0010] Determine the nature of the deep fault in the exploration area according to the change in depth after the critical time point of the turning point of the depth drop of the observation hole in the depth drop-pumping duration s-lgt relationship diagram of the observation hole;

[0011] According to the distance between the observation hole and the pumping well, the critical time point when the observation hole begins to drop and the critical time point when the observation hole drops, the distance between the observation hole and the virtual well is determined by analyzing the relationship formula between the observation hole and the virtual well;

[0012] Draw a map based on the distance between the observation hole and the virtual well to determine the suspected position and suspected trend of the deep fault;

[0013] By drilling to obtain rock cores at suspected locations, the exact location and exact direction of deep faults can be determined based on the properties of the rock cores at the suspected locations.

[0014] In one embodiment, the method further comprises:

[0015] When the deep fault trend is known in the exploration area, an observation hole, namely observation hole P, is designed;

[0016] In the case where the deep fault direction in the exploration area is unknown, two observation holes are designed, namely observation holes P1 and P2.

[0017] In one embodiment, the method of determining the nature of the deep fault in the exploration area according to the change in depth after the critical time point of the turning point of the depth drop of the observation hole in the depth drop-pumping duration s-lgt relationship diagram in the observation hole comprises:

[0018] In the relationship diagram between the depth drawdown and the pumping duration s to lgt in the observation hole, if the depth drawdown amplitude increases after the critical time point at which the depth drawdown of the observation hole turns, the nature of the deep fault in the exploration area is a water-blocking fault;

[0019] In the depth drawdown-pumping duration s~lgt relationship diagram in the observation hole, if the depth drawdown in the observation hole does not change after the critical time point at which the depth drawdown of the observation hole turns, the nature of the deep fault in the exploration area is a water-conducting fault.

[0020] In one embodiment, the drawing of a map based on the distance between the observation hole and the virtual well to determine the strike and suspected position of the deep fault includes:

[0021] When the direction of the deep fault is known in the exploration area, a vertical line is drawn through the pumping well to the direction of the deep fault, and an arc is drawn with the observation hole P as the center and the distance between the observation hole P and the virtual well as the radius. The intersection of the vertical line and the arc is the virtual well position, and the perpendicular midline of the line connecting the pumping well and the virtual well is the suspected fault position;

[0022] In the case where the strike of the unknown deep fault in the exploration area is unknown, an arc is drawn with the observation well P1 as the center and the distance between the observation well P1 and the virtual well as the radius; an arc is drawn with the observation well P2 as the center and the distance between the observation well P2 and the virtual well as the radius; the intersection point of the two arcs is the position of the virtual well, and the perpendicular bisector of the line connecting the pumping well and the virtual well is the suspected fault position, and the strike of the two perpendicular bisectors of the line connecting the pumping well and the virtual well is the suspected fault strike.

[0023] In one embodiment, the expression of the distance relationship formula between the observation well and the virtual well is:

[0024]

[0025] where r2 is the distance between the observation well and the virtual well, t a is the critical time point at which the drawdown of the observation well turns, r0 is the time critical point at which the drawdown of the observation well begins to appear, and r1 is the distance between the observation well and the pumping well.

[0026] In one embodiment, the determination method of the distance relationship formula between the observation well and the virtual well is:

[0027] Apply the Jacob solution of the unsteady well flow formula, and use the image method and the superposition principle to determine the distance relationship formula between the observation well and the virtual well.

[0028] In one embodiment, the application of the Jacob solution of the unsteady well flow formula, using the image method and the superposition principle to determine the distance relationship formula between the observation well and the virtual well, includes:

[0029] Based on the image method, draw the drawdown law of the water level in the observation well, and determine the influence range of the drawdown as:

[0030] When 0 < t < t0, the influence range of the pumping well has not reached the observation well, then:

[0031] s = 0

[0032] where s is the drawdown and t is the pumping time;

[0033] When t0 ≤ t ≤ t a , the influence range of the pumping well reaches the observation well and the boundary does not play a role, then the expression of the drawdown of the observation well is:

[0034]

[0035] where T is the transmissivity, Q is the flow rate of the pumping well, r1 is the distance between the observation well and the pumping well, and W is the storage coefficient;

[0036] When t ≥ t a , the boundary plays a role, then the expression of the drawdown of the observation well is:

[0037]

[0038] Among them, r2 is the distance between the observation hole and the virtual well;

[0039] Substitute t=t0、s=0 into the case of t0≤t≤t a When , the expression of observation hole drawdown is obtained:

[0040]

[0041] Depend on The solution is:

[0042]

[0043] Set t = t a 、s=s a At the same time, when t0≤t≤t a When t≥t a When , the expression of observation hole drawdown is obtained:

[0044]

[0045] And solve have to:

[0046]

[0047] Will Bring in Solved

[0048]

[0049] The above-mentioned deep fault identification method based on pumping test designs a pumping well and an observation hole in the exploration area, conducts a constant flow non-steady pumping test, records the pumping volume, pumping time, the distance between the observation hole and the pumping well, and the drawdown data; draws a depth drawdown-pumping duration time s~lgt relationship diagram in the observation hole according to the pumping time and drawdown data; analyzes the image features in the depth drawdown-pumping duration time s~lgt relationship diagram in the observation hole to determine the critical time point when the observation hole begins to draw down and the critical time point when the depth drawdown of the observation hole turns; determines the depth drawdown change after the critical time point when the depth drawdown of the observation hole turns down in the depth drawdown-pumping duration time s~lgt relationship diagram in the observation hole according to the change in depth Determine the properties of deep faults in the exploration area; according to the distance between the observation hole and the pumping well, the critical time point when the observation hole begins to drop in depth and the critical time point when the observation hole drops in depth and a turning point, use the distance relationship formula between the observation hole and the virtual well to analyze and determine the distance between the observation hole and the virtual well; draw a map based on the distance between the observation hole and the virtual well to determine the suspected position and suspected direction of the deep fault; obtain the core at the suspected position by drilling, and determine the exact position and exact direction of the deep fault according to the properties of the core at the suspected position, thereby directly implementing the pumping test, applying the theoretical method of groundwater dynamics, realizing the rapid identification and accurate judgment of the fault position and property, and greatly improving the efficiency and accuracy of fault exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 A schematic diagram of a process of a deep fault identification method based on a pumping test in one embodiment;

[0051] Figure 2 It is a flow chart of a relationship diagram of drawdown-pumping duration s to lgt of a deep fault whose property is a water-blocking fault in an embodiment;

[0052] Figure 3 It is a flow chart of a relationship diagram of drawdown-pumping duration s to lgt of a deep fault with the property of a water-conducting fault in one embodiment;

[0053] Figure 4 Drawing a schematic diagram of a suspected fault location of a known deep fault direction in one embodiment;

[0054] Figure 5 Drawing a schematic diagram of a suspected fault location of an unknown deep fault trend in one embodiment;

[0055] Figure 6 Schematic diagram of the influence range of the water level drop in the three stages of the mirror image observation hole in one embodiment. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0057] In one embodiment, Figure 1 As shown, a deep fault identification method based on pumping test is provided, comprising the following steps:

[0058] Step S1, designing a pumping well and an observation hole in the exploration area, conducting a constant flow non-steady water pumping test, and recording the pumping volume, pumping time, the distance between the observation hole and the pumping well, and the drawdown data.

[0059] Among them, faults, as an important type of geological structure, are the focus of data processing. In actual processing, seismic attribute technologies such as curvature and coherence are often used for exploration. However, the seismic data acquisition environment is complex, and there is often a lot of noise interference, which makes fault exploration inaccurate. However, the deep fault identification method based on pumping test makes up for this problem, and the fault location and property results obtained are more accurate.

[0060] Among them, in order to ensure that the pumping test results are strongly correlated with the target fault and reduce the influence of other boundaries, the preliminary study area division is first carried out according to the basic hydrogeological data of the study area. One pumping well and one to two observation holes are arranged at appropriate locations in the study area (such as near suspected faults), and the pumping test is carried out in a constant flow manner. In order to ensure the accuracy of the results and the conditions for the use of the Jacob formula for unsteady flow in groundwater dynamics, it is necessary to ensure that the pumping time is long enough and the distance between the observation hole and the pumping well is moderate (such as the pumping time is sufficient to reveal that the fault has a significant impact on the drawdown of the observation hole, and the observation hole should be located within the influence range of the pumping well). Before the formal pumping test, pre-pumping can be performed, the pre-pumping flow rate can be recorded, and the boundary conditions can be roughly determined to ensure that the pumping test process can cover the target fault area. During the pumping test, observe and record the drawdown s, time t, and the distance r1 between the observation hole and the pumping well.

[0061] Among them, a pumping hole and one or two observation holes are set up in the exploration area. After a long-term pumping test with a constant flow rate is carried out in the holes, the pumping volume and the water level drop in the observation holes at different times are observed and recorded, and the location and nature of the deep faults can be calculated.

[0062] Step S2, based on the pumping time and drawdown data, draw a relationship diagram between the drawdown in the observation hole and the pumping duration s~lgt.

[0063] Among them, the relationship between drawdown and pumping duration s~lgt is drawn to determine the water-isolating properties of deep faults in the study area. The water level drawdown and pumping duration data of the observation wells are collected through pumping tests. The pumping test data are plotted with the drawdown s as the ordinate and the logarithm of the pumping duration t as the abscissa, as shown in the figure. Figure 2 and 3 As shown. Figure 2 and 3 , the nature of the deep faults in the exploration area can be identified: if t a As the pumping time continued, the water level drop in the observation hole increased (e.g. Figure 2 As shown in the figure, it shows that the water-isolating fault has been exposed, blocking the recharge of groundwater. a As the pumping time continues, the water level in the observation hole no longer changes (e.g. Figure 3 This indicates that the water-conducting fault has been exposed, opening up other sources of groundwater recharge.

[0064] Step S3, analyzing the image features in the depth drop-pumping duration s-lgt relationship diagram in the observation hole to determine the critical time point when the depth drop of the observation hole begins and the critical time point when the depth drop of the observation hole turns.

[0065] Step S4, determining the nature of the deep fault in the exploration area according to the change in depth after the critical time point of the turning point of the depth drop of the observation hole in the depth drop-pumping duration s~lgt relationship diagram in the observation hole,

[0066] Step S5, according to the distance between the observation hole and the pumping well, the critical time point when the observation hole begins to drop in depth and the critical time point when the observation hole drops in depth and the turning point, the distance relationship formula between the observation hole and the virtual well is used for analysis to determine the distance between the observation hole and the virtual well.

[0067] Step S6, drawing a map based on the distance between the observation hole and the virtual well to determine the suspected position and suspected trend of the deep fault.

[0068] Step S7, obtaining the core of the suspected position by drilling, and determining the exact position and exact direction of the deep fault according to the properties of the core of the suspected position.

[0069] The above-mentioned deep fault identification method based on pumping test designs pumping wells and observation holes in the exploration area, conducts a constant flow non-steady pumping test, records the pumping volume, pumping time, the distance between the observation hole and the pumping well, and the drawdown data; draws a depth drawdown-pumping duration s~lgt relationship diagram in the observation hole based on the pumping time and drawdown data; analyzes the image features in the depth drawdown-pumping duration s~lgt relationship diagram in the observation hole to determine the critical time point when the observation hole begins to draw down and the critical time point when the depth drawdown of the observation hole turns; and determines the depth drawdown change after the critical time point when the depth drawdown of the observation hole turns down in the depth drawdown-pumping duration s~lgt relationship diagram. , determine the properties of deep faults in the exploration area; according to the distance between the observation hole and the pumping well, the critical time point when the observation hole begins to drop in depth and the critical time point when the observation hole drops in depth, the distance relationship formula between the observation hole and the virtual well is used for analysis to determine the distance between the observation hole and the virtual well; according to the distance between the observation hole and the virtual well, the suspected position and suspected direction of the deep fault are determined; the core of the suspected position is obtained by drilling, and the exact position and exact direction of the fault are determined according to the properties of the core of the suspected position, thereby directly implementing the pumping test, and applying the theoretical method of groundwater dynamics to achieve rapid identification and accurate judgment of the position and nature of the fault, which greatly improves the efficiency and accuracy of fault exploration.

[0070] In one embodiment, the method further includes: when the direction of the deep fault in the exploration area is known, designing one observation hole, namely, observation hole P; when the direction of the deep fault in the exploration area is unknown, designing two observation holes, namely, observation holes P1 and P2.

[0071] Among them, this application only needs to construct a pumping well and one or two observation holes within a certain range, design a pumping test, and obtain pumping test data, so as to accurately calculate and identify the location and properties of deep faults, effectively reducing workload and technical difficulty.

[0072] In one embodiment, the nature of the deep fault in the exploration area is determined according to the change in depth after the critical time point of the turning point of the depth drop of the observation hole in the depth drop-pumping duration s-lgt relationship diagram in the observation hole, including:

[0073] In the relationship diagram between depth drawdown and pumping duration s~lgt in the observation hole, if the depth drawdown amplitude increases after the critical time point at which the depth drawdown of the observation hole turns, the nature of the deep fault in the exploration area is a water-isolating fault; in the relationship diagram between depth drawdown and pumping duration s~lgt in the observation hole, if the depth drawdown no longer changes after the critical time point at which the depth drawdown of the observation hole turns, the nature of the deep fault in the exploration area is a water-conducting fault.

[0074] In one embodiment, the distance between the observation hole and the virtual well is plotted to determine the strike and suspected position of the deep fault, including:

[0075] When the direction of the deep fault in the exploration area is known, a vertical line is drawn through the pumping well to the direction of the deep fault, and an arc is drawn with the observation hole P as the center and the distance between the observation hole P and the virtual well as the radius. The intersection of the vertical line and the arc is the position of the virtual well, and the median perpendicular line of the line connecting the pumping well and the virtual well is the suspected position of the fault; when the direction of the deep fault in the exploration area is unknown, an arc is drawn with the observation hole P1 as the center and the distance between the observation hole P1 and the virtual well as the radius; an arc is drawn with the observation hole P2 as the center and the distance between the observation hole P2 and the virtual well as the radius; the intersection of the two arcs is the position of the virtual well, the median perpendicular line of the line connecting the pumping well and the virtual well is the suspected position of the fault, and the direction of the two median perpendicular lines of the line connecting the pumping well and the virtual well is the suspected direction of the fault.

[0076] When the fault direction is known, it is necessary to know the distance r1 between an observation hole and the pumping well, as well as the pumping time and drawdown data of the pumping test. The pumping time and drawdown data are used to draw a drawdown-pumping duration s~lgt relationship diagram to determine t0 and t a The distance r2 between the observation hole and the virtual well is calculated by the distance relationship formula between the observation hole and the virtual well. Draw a vertical line through the pumping well to the fault direction, and draw an arc with the observation hole as the center and r2 as the radius. The intersection of the vertical line and the arc is the virtual well position; the perpendicular midline of the line connecting the pumping well and the virtual well is the fault position. Figure 4 shown.

[0077] If the fault direction is unknown, the pumping time and drawdown data of the two observation holes P1 and P2 are needed to draw two curves of drawdown-pumping duration s1-lgt1 and s2-lgt2, and determine the critical time point when the observation hole P1 begins to draw down and the critical time point when the drawdown turns. 10 ,t 1a , as well as the critical time point at which the depth of observation hole P2 begins to drop and the critical time point at which the depth drops to a turning point t 20 ,t 2a , and then calculate the distance r between the observation hole P1 and the virtual well using the distance relationship formula between the observation hole and the virtual well 21 and the distance r between observation hole P2 and virtual well 22 , respectively get the distance between the virtual well and the two observation holes. Take observation hole P1 as the center and the distance between observation hole P1 and the virtual well as the radius to draw an arc; take observation hole P2 as the center and the distance between observation hole P2 and the virtual well as the radius to draw an arc; the intersection of the two arcs is the position of the virtual well, the median perpendicular line of the line connecting the pumping well and the virtual well is the suspected position of the fault, and the direction of the median perpendicular line of the line connecting the pumping well and the virtual well is the suspected direction of the fault, such as Figure 5 shown.

[0078] It should be understood that Figure 4 and Figure 5 the real well in Figure 4 and Figure 5 refers to the pumping well. There are two perpendicular bisectors of the line connecting the pumping well and the virtual well, and each perpendicular bisector is a suspected location of the deep fault. Therefore, by plotting the distance between the observation well and the virtual well, two suspected locations of the deep fault can be determined. Furthermore, only by drilling to obtain the cores at these two suspected locations and according to the core properties of the suspected locations, the exact location of the deep fault can be obtained, whether it is the suspected fault 1 (i.e., the fault 1 in Figure 4 or Figure 4 ) or the suspected fault 2 (i.e., the fault 2 in Figure 4 or ). Thus, the efficiency and accuracy of fault exploration can be greatly improved.

[0079] In one embodiment, the expression of the distance relationship formula between the observation well and the virtual well is:

[0080]

[0081] where r2 is the distance between the observation well and the virtual well, t a is the critical time point when the drawdown of the observation well turns, t0 is the time critical point when the drawdown of the observation well starts to appear, and r1 is the distance between the observation well and the pumping well.

[0082] In one embodiment, the determination method of the distance relationship formula between the observation well and the virtual well is:

[0083] Apply the Jacob solution of the unsteady well flow formula, and use the image method and the superposition principle to determine the distance relationship formula between the observation well and the virtual well.

[0084] In one embodiment, applying the Jacob solution of the unsteady well flow formula and using the image method and the superposition principle to determine the distance relationship formula between the observation well and the virtual well includes:

[0085] Based on the image method, draw the drawdown law of the water level in the observation well, and determine the influence range of the drawdown as:

[0086] When 0 < t < t0, the influence range of the pumping well has not reached the observation well, then:

[0087] s = 0

[0088] where s is the drawdown and t is the pumping time;

[0089] When t0 ≤ t ≤ t a the influence range of the pumping well reaches the observation well and the boundary does not play a role, then the expression of the drawdown of the observation well is:

[0090]

[0091] ​​​​Among them, T is the transmissivity, Q is the pumping well discharge, r1 is the distance between the observation well and the pumping well, and W is the storage coefficient;

[0092] When t ≥ t a , the boundary comes into play, and the expression for the drawdown of the observation well is:

[0093]

[0094] Among them, r2 is the distance between the observation well and the imaginary well;

[0095] Substitute t = t0, s = 0 into the expression for the drawdown of the observation well when t0 ≤ t ≤ t a , and we get:

[0096]

[0097] From Solve to get:

[0098]

[0099] Substitute t = t a , s = s a into the expression for the drawdown of the observation well when t0 ≤ t ≤ t a and the expression for the drawdown of the observation well when t ≥ t a , and we get:

[0100]

[0101] And solve to get:

[0102]

[0103] Substitute into Solve to get

[0104]

[0105] Among them, by reading the values of t0 (the time critical point when the drawdown of the observation well starts to appear) and t a (the critical time point when the drawdown of the observation well turns) from the drawdown - pumping duration s ~ lgt relationship graph, the distance r2 between the observation well and the imaginary well is calculated. The water level drawdown in the observation well goes through three stages, and the influence ranges of the water level drawdown in the three stages are as Figure 6 shown. The first stage: when 0 < t < t0, the influence range of the pumping well has not reached the observation well; the second stage: when t0 ≤ t ≤ t a , the influence range of the pumping well reaches the observation well and the boundary has not come into play; the third stage: when t ≥ t a, the boundary takes effect.

[0106] It should be understood that Figure 6 The real well refers to the pumping well, the position coordinates of the real well in the coordinate system are (a, 0), the position coordinates of the virtual well in the coordinate system are (-a, 0), and the observation well refers to the observation hole.

[0107] The above-mentioned deep fault identification method based on pumping test is based on the theory of groundwater dynamics. By demarcating the target research area (i.e., the exploration area), setting up pumping wells and observation holes, conducting fixed-flow pumping tests, observing and recording data such as the pumping well flow rate and the water level drop in the observation hole at different times; drawing the water level drop-time image of the observation point, identifying the nature of the fault based on the image features, and determining the key parameters, and applying the theoretical formula to calculate and determine the fault location. Therefore, based on the pumping test data, the mirror method principle in groundwater dynamics is used to identify the location and nature of deep faults, so as to make up for the shortcomings of existing fault exploration methods and technologies, and significantly improve the accuracy of deep fault boundary identification.

[0108] It should be understood that although Figure 1 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover, Figure 1 At least part of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps.

[0109] 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.

[0110] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A deep fault identification method based on pumping test, characterized in that: The method comprises: Design pumping wells and observation holes in the exploration area, conduct constant flow non-steady water pumping tests, and record the pumping volume, pumping time, distance between the observation hole and the pumping well, and drawdown data; According to the pumping time and drawdown data, a relationship diagram between drawdown and pumping duration s and lgt in the observation hole is drawn; Analyze the image features in the depth drop-pumping duration s-lgt relationship diagram in the observation hole to determine the critical time point at which the depth drop of the observation hole begins and the critical time point at which the depth drop of the observation hole turns; Determine the nature of the deep fault in the exploration area according to the change in depth after the critical time point of the turning point of the depth drop of the observation hole in the depth drop-pumping duration s-lgt relationship diagram of the observation hole; According to the distance between the observation hole and the pumping well, the critical time point when the observation hole begins to drop and the critical time point when the observation hole drops, the distance between the observation hole and the virtual well is determined by analyzing the relationship formula between the observation hole and the virtual well; Draw a map based on the distance between the observation hole and the virtual well to determine the suspected position and suspected trend of the deep fault; By drilling to obtain rock cores at suspected locations, the exact location and exact direction of deep faults can be determined based on the properties of the rock cores at the suspected locations.

2. The method according to claim 1, characterized in that The method further comprises: When the deep fault trend is known in the exploration area, an observation hole, namely observation hole P, is designed; In the case where the deep fault direction in the exploration area is unknown, two observation holes are designed, namely observation holes P1 and P2.

3. The method according to claim 2, characterized in that Determining the nature of the deep fault in the exploration area according to the change in depth after the critical time point of the turning point of the depth drop of the observation hole in the depth drop-pumping duration s-lgt relationship diagram in the observation hole includes: In the relationship diagram between the depth drawdown and the pumping duration s to lgt in the observation hole, if the depth drawdown amplitude increases after the critical time point at which the depth drawdown of the observation hole turns, the nature of the deep fault in the exploration area is a water-blocking fault; In the depth drawdown-pumping duration s~lgt relationship diagram in the observation hole, if the depth drawdown in the observation hole does not change after the critical time point at which the depth drawdown of the observation hole turns, the nature of the deep fault in the exploration area is a water-conducting fault.

4. The method according to claim 2, characterized in that: The drawing of a map based on the distance between the observation hole and the virtual well to determine the strike and suspected position of the deep fault includes: When the direction of the deep fault is known in the exploration area, a vertical line is drawn through the pumping well to the direction of the deep fault, and an arc is drawn with the observation hole P as the center and the distance between the observation hole P and the virtual well as the radius. The intersection of the vertical line and the arc is the virtual well position, and the perpendicular midline of the line connecting the pumping well and the virtual well is the suspected fault position; When the direction of the deep fault in the exploration area is unknown, an arc is drawn with the observation hole P1 as the center and the distance between the observation hole P1 and the virtual well as the radius; an arc is drawn with the observation hole P2 as the center and the distance between the observation hole P2 and the virtual well as the radius; the intersection of the two arcs is the position of the virtual well, the perpendicular median of the line connecting the pumping well and the virtual well is the suspected position of the fault, and the direction of the two perpendicular medians of the line connecting the pumping well and the virtual well is the suspected direction of the fault.

5. The method according to claim 1, characterized in that The expression of the formula for the distance relationship between the observation well and the imaginary well is as follows: Among them, r2 is the distance between the observation hole and the virtual well, r a is the critical time point when the depth of the observation hole drops, r0 is the critical time point when the depth of the observation hole begins to drop, and r1 is the distance between the observation hole and the pumping well.

6. The method according to claim 5, characterized in that The determination method of the formula for the distance relationship between the observation well and the imaginary well is as follows: Apply the Jacob solution of the unsteady well flow formula, and use the image method and the superposition principle to determine the formula for the distance relationship between the observation well and the imaginary well.

7. The method according to claim 6, characterized in that Applying the Jacob solution of the unsteady well flow formula and using the image method and the superposition principle to determine the formula for the distance relationship between the observation well and the imaginary well includes: Based on the image method, draw the drawdown law of the water level in the observation well, and determine the influence range of the drawdown as: When 0 < t < t0, the influence range of the pumping well has not reached the observation well, then: s＝0 where s is the drawdown and t is the pumping time; When t0≤t≤t a When the influence range of the pumping well reaches the observation hole, the boundary does not work, then the expression of the observation hole depth reduction is: where T is the hydraulic conductivity, Q is the flow rate of the pumping well, r1 is the distance between the observation well and the pumping well, and W is the storage coefficient; When t ≥ t a When the boundary takes effect, the expression of the observation hole depth reduction is: where r2 is the distance between the observation well and the imaginary well; Substitute t=t0、s=0 into the case of t0≤t≤t a When , the expression of observation hole drawdown is obtained: Depend on The solution is: Set t = t a 、s=s a At the same time, when t0≤t≤t a When t≥t a When , the expression of observation hole drawdown is obtained: And solve have to: Will Bring in Solved

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