A deep fault identification method based on pumping test

Abstract

The application relates to a deep fault identification method based on a pumping test. The method comprises the following steps: designing a pumping well and an observation hole in an exploration area, performing a constant-flow non-steady pumping test, recording pumping quantity, pumping time, distance between the observation hole and the pumping well and drawdown data, drawing a drawdown-pumping duration time s-lgt relationship graph for analysis, determining a critical time point at which drawdown appears in the observation hole and a critical time point at which drawdown in the observation hole turns over; determining the properties of a deep fault in the exploration area according to drawdown change after the critical time point at which drawdown in the observation hole turns over; determining a suspected position and a suspected strike of the deep fault according to the distance between the observation hole and the pumping well, the critical time point at which drawdown appears in the observation hole and the critical time point at which drawdown in the observation hole turns over; and determining the exact position and the exact strike of the fault through drilling to obtain a core at the suspected position, so that 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, in particular to a deep fault identification method based on pumping test. BACKGROUND

[0002] As a common geological structure, faults have a significant impact on groundwater flow and resource distribution. In the fields of groundwater resource management, geological disaster prevention, and geological exploration, accurately exploring the location and nature of faults is crucial for developing reasonable development and utilization strategies and prevention measures.

[0003] Traditional fault exploration methods include geophysical prospecting and drilling, which use seismic wave reflection and geological structure analysis to explore faults. The traditional geophysical prospecting method of seismic wave requires manual tracking and selection of faults, which requires a lot of manual work and has low exploration efficiency. For experienced interpreters, it usually takes several weeks to several months to mark faults in a typical seismic volume, and the selection result is highly dependent on the experience of the interpreter, and manual errors can affect the interpretation result.

[0004] Therefore, the current fault exploration method has the problems of low efficiency and accuracy. SUMMARY

[0005] Therefore, it is necessary to provide a deep fault identification method based on pumping test to improve the efficiency and accuracy of fault exploration.

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

[0007] Designing pumping wells and observation holes in the exploration area, conducting constant-flow unsteady pumping test, recording pumping volume, pumping time, distance between observation hole and pumping well, and drawdown data;

[0008] According to the pumping time and drawdown data, draw a drawdown-pumping duration time s~lgt relationship graph in the observation hole;

[0009] According to the image features in the drawdown-pumping duration time s~lgt relationship graph in the observation hole, analyze and determine the critical time point when the drawdown in the observation hole starts to appear and the critical time point when the drawdown in the observation hole appears to turn;

[0010] According to the drawdown change after the critical point of the drawdown turning in the observation hole in the drawdown-pumping duration time s~lgt relationship graph in the observation hole, determine the nature of the deep fault in the exploration area;

[0011] According to the distance between the observation hole and the pumping well, the time critical point when the drawdown of the observation hole begins to appear, and the time critical point when the drawdown of the observation hole turns, a 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;

[0012] According to the distance between the observation hole and the virtual well, the suspected position and the suspected strike of the deep fault are determined;

[0013] By drilling to obtain the core of the suspected position, the exact position and the exact strike of the deep fault are determined according to the core properties of the suspected position.

[0014] In one of the embodiments, the method further comprises:

[0015] In the case where the strike of the deep fault in the exploration area is known, one observation hole, i.e., observation hole P, is designed;

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

[0017] In one of the embodiments, the drawdown change after the time critical point when the drawdown of the observation hole turns in the drawdown-pumping duration time s~lgt relationship graph of the observation hole is used to determine the properties of the deep fault in the exploration area, including:

[0018] In the drawdown-pumping duration time s~lgt relationship graph of the observation hole, if the drawdown amplitude increases after the time critical point when the drawdown of the observation hole turns, the properties of the deep fault in the exploration area are water-resisting fault;

[0019] In the drawdown-pumping duration time s~lgt relationship graph of the observation hole, if the drawdown no longer changes after the time critical point when the drawdown of the observation hole turns, the properties of the deep fault in the exploration area are water-conducting fault.

[0020] In one of the embodiments, the distance between the observation hole and the virtual well is plotted to determine the strike and the suspected position of the deep fault, including:

[0021] In the case where the strike of the deep fault in the exploration area is known, a vertical line of the strike of the deep fault is made through the pumping well, and an arc line is made 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 line is the position of the virtual well, and the perpendicular line of the connecting line between the pumping well and the virtual well is the suspected position of the fault;

[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 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, and the median of the line connecting the pumping well and the virtual well is the suspected position of the fault, and the strikes of the two medians of the line connecting the pumping well and the virtual well are the suspected strikes of the fault.

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

[0024]

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

[0026] In one of the embodiments, the distance relationship formula between the observation hole and the virtual well is determined in the following manner:

[0027] The distance relationship formula between the observation hole and the virtual well is determined by using the mirror method and the superposition principle based on the Jacob solution of the unsteady well flow formula.

[0028] In one of the embodiments, the distance relationship formula between the observation hole and the virtual well is determined by using the mirror method and the superposition principle based on the Jacob solution of the unsteady well flow formula, which includes:

[0029] The drawdown law of the water level in the observation hole is drawn based on the mirror method, and the influence range of the drawdown is determined as:

[0030] When 0 < t < t0, the influence range of the pumping well does not reach the observation hole, and then:

[0031] s = 0

[0032] wherein 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 hole, and the boundary does not work, and then the expression of the drawdown of the observation hole is:

[0034]

[0035] wherein T is the transmissibility coefficient, Q is the pumping well flow rate, r1 is the distance between the observation hole and the pumping well, and W is the storage coefficient.

[0036] When t≥t a , the boundary works, and then the expression of the drawdown of the observation hole is:

[0037]

[0038] Where r2 is the distance between the observation hole and the virtual well;

[0039] Substituting t = t0 and s = 0 into the case where t0 ≤ t ≤ t a When observing the bottom depth, the expression for the bottom depth is obtained:

[0040]

[0041] Depend on Solving for:

[0042]

[0043] Let t = t a s = s a Simultaneously, substituting the condition t0≤t≤t a When, the expression for the orifice drawdown and when t≥t a When observing the bottom depth, the expression for the bottom depth is obtained:

[0044]

[0045] And solve have to:

[0046]

[0047] Will Bring into Solving

[0048]

[0049] The deep fault identification method based on pumping test, by designing pumping wells and observation holes in the exploration area, performing constant-flow unsteady pumping test, recording pumping amount, pumping time, distance between the observation hole and the pumping well, and drawdown data; according to the pumping time and drawdown data, drawing a drawdown-pumping duration time s~lgt relationship graph in the observation hole; analyzing the image features in the drawdown-pumping duration time s~lgt relationship graph in the observation hole to determine the critical time point when the drawdown in the observation hole starts to appear and the critical time point when the drawdown in the observation hole appears to turn; according to the drawdown change after the critical time point when the drawdown in the observation hole appears to turn in the drawdown-pumping duration time s~lgt relationship graph in the observation hole, determining the property of the deep fault in the exploration area; according to the distance between the observation hole and the pumping well, the critical time point when the drawdown in the observation hole starts to appear, and the critical time point when the drawdown in the observation hole appears to turn, using 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; according to the distance between the observation hole and the virtual well, determining the suspected position and the suspected strike of the deep fault; by drilling to obtain the core of the suspected position, according to the core property of the suspected position, determining the exact position and the exact strike of the deep fault, thereby directly implementing pumping test, applying the theoretical method of groundwater dynamics to realize the rapid identification and accurate judgment of the fault position and property, greatly improving the efficiency and accuracy of fault exploration. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 It is a flowchart of the deep fault identification method based on pumping test in one embodiment;

[0051] Figure 2 It is a drawdown-pumping duration time s~lgt relationship graph flowchart of the property of the deep fault being a water-resisting fault in one embodiment;

[0052] Figure 3 It is a drawdown-pumping duration time s~lgt relationship graph flowchart of the property of the deep fault being a water-resisting fault in one embodiment;

[0053] Figure 4 It is a suspected position drawing schematic diagram of the deep fault with known strike in one embodiment;

[0054] Figure 5 It is a suspected position drawing schematic diagram of the deep fault with unknown strike in one embodiment;

[0055] Figure 6 It is a schematic diagram of the influence range of water level drawdown in three stages of the mirror image method observation hole in one embodiment. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

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

[0058] Step S1, a pumping well and an observation hole are designed in the exploration area, a constant flow unsteady pumping test is carried out, and the pumping amount, pumping time, distance between the observation hole and the pumping well and drawdown data are recorded.

[0059] Among them, as an important geological structure type, the fault is the key object in data processing. In actual processing, curvature, coherence and other seismic attribute techniques are often used for exploration. However, due to the complex environment of seismic data acquisition, there are often many noise interferences, which makes the fault exploration inaccurate. However, the deep fault identification method based on pumping test makes up for this problem, and the obtained fault position and property results are more accurate.

[0060] Among them, in order to ensure that the pumping test results are strongly related to the target fault and reduce the influence of other boundaries, first of all, according to the basic hydrogeological data of the study area, the study area is preliminarily divided. A pumping well and one or two observation holes are arranged at appropriate positions in the study area (such as near suspected faults), and pumping test is carried out in a constant flow manner. In order to ensure the accuracy of the results and the use conditions of the non-steady flow Jacob formula 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 meets the requirement of revealing that the fault has a significant influence 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 carried out to record the pre-pumping flow and roughly determine the boundary conditions to ensure that the pumping test process can cover the target fault area. During the pumping test process, the drawdown s, time t, distance r1 between the observation hole and the pumping well and other data are observed and recorded.

[0061] Among them, after setting a pumping hole and one or two observation holes in the exploration area, carrying out constant flow long-time pumping test, observing and recording the pumping amount and the water level drawdown in the observation hole at different times, the position and property of the deep fault can be calculated.

[0062] Step S2, according to the pumping time and drawdown data, a drawdown-pumping duration time s~lgt relationship diagram in the observation hole is drawn.

[0063] The study involved plotting the relationship between drawdown and pumping duration (s ~ lgt) to determine the water-impermeable nature of deep faults in the study area. Data on drawdown and pumping duration were collected from observation wells through pumping tests. The pumping test data were plotted with drawdown (s) on the ordinate and the logarithm of pumping duration (t) on the abscissa, as shown below. Figure 2 and 3 As shown. (Through) Figure 2 and 3 It can identify the nature of deep faults in the exploration area: if from t a Initially, as pumping continued, the drawdown of the observation well increased (e.g. Figure 2 As shown in the figure, this indicates that an impermeable fault has been exposed, blocking the recharge of groundwater; if from t a Subsequently, as pumping continued, the drawdown in the observation well ceased to change (e.g. Figure 3 As shown in the figure, this reveals a water-conducting fault, which connects to other sources of groundwater recharge.

[0064] Step S3: Analyze the image features in the relationship graph of drawdown-pumping duration s~lgt in the observation well to determine the critical time point when the drawdown in the observation well begins to appear and the critical time point when the drawdown in the observation well begins to turn.

[0065] Step S4: Based on the changes in drawdown after the critical point in the drawdown-pumping duration s~lgt relationship diagram in the observation well, determine the nature of the deep fault in the exploration area.

[0066] Step S5: Based on the distance between the observation well and the pumping well, the critical point at which the observation well begins to show a drawdown, and the critical point at which the drawdown of the observation well begins to turn in, the distance between the observation well and the virtual well is determined by using the formula relating the distance between the observation well and the virtual well.

[0067] Step S6: Draw a map based on the distance between the observation hole and the virtual well to determine the suspected location and suspected strike of the deep fault.

[0068] Step S7: Obtain rock cores from suspected locations through drilling, and determine the exact location and orientation of the deep fault based on the properties of the rock cores from suspected locations.

[0069] The deep fault identification method based on the pumping test comprises the following steps: designing a pumping well and an observation hole in the exploration area, performing a constant-flow unsteady pumping test, recording the pumping amount, pumping time, distance between the observation hole and the pumping well, and drawdown data; drawing a drawdown-pumping duration time s-lg t graph in the observation hole according to the pumping time and drawdown data; analyzing the image features in the drawdown-pumping duration time s-lg t graph in the observation hole to determine the critical time point at which the drawdown in the observation hole begins to appear and the critical time point at which the drawdown in the observation hole turns; determining the property of the deep fault in the exploration area according to the drawdown change after the critical time point at which the drawdown in the observation hole turns in the drawdown-pumping duration time s-lg t graph in the observation hole; analyzing the distance relationship between the observation hole and the virtual well according to the distance between the observation hole and the pumping well, the critical time point at which the drawdown in the observation hole begins to appear, and the critical time point at which the drawdown in the observation hole turns to determine the distance between the observation hole and the virtual well; determining the suspected position and suspected strike of the deep fault by plotting the distance between the observation hole and the virtual well; obtaining the core at the suspected position by drilling, determining the exact position and exact strike of the fault according to the core property at the suspected position, directly performing the pumping test, applying the theoretical method of groundwater dynamics to realize the rapid identification and accurate judgment of the position and property of the fault, and greatly improving the efficiency and accuracy of the fault exploration.

[0070] In one embodiment, the method further comprises: in the case that the strike of the deep fault in the exploration area is known, designing one observation hole, i.e., observation hole P; in the case that the strike of the deep fault in the exploration area is unknown, designing two observation holes, i.e., observation holes P1 and P2.

[0071] In the method, only one pumping well and one to two observation holes need to be constructed in a certain range, the pumping test is designed, the pumping test data are obtained, the position and property of the deep fault are accurately calculated and identified, the workload is effectively reduced, and the technical difficulty is reduced.

[0072] In one embodiment, the determination of the property of the deep fault in the exploration area according to the drawdown change after the critical time point at which the drawdown in the observation hole turns in the drawdown-pumping duration time s-lg t graph in the observation hole comprises:

[0073] In the drawdown-pumping duration time s-lg t graph in the observation hole, if the drawdown amplitude increases after the critical time point at which the drawdown in the observation hole turns, the property of the deep fault in the exploration area is a water-resisting fault; in the drawdown-pumping duration time s-lg t graph in the observation hole, if the drawdown no longer changes after the critical time point at which the drawdown in the observation hole turns, the property of the deep fault in the exploration area is a water-conducting fault.

[0074] In one embodiment, mapping is performed based on the distance between the observation borehole and the virtual well to determine the strike and suspected location of deep faults, including:

[0075] When the strike of a deep fault is known within the exploration area, draw a perpendicular line from the pumping well to the strike of the deep fault. Using the observation borehole P as the center and the distance between observation borehole P and the virtual well as the radius, draw an arc. The intersection of the perpendicular line and the arc is the location of the virtual well. The perpendicular bisector of the line connecting the pumping well and the virtual well is the suspected location of the fault. When the strike of a deep fault is unknown within the exploration area, draw an arc with the observation borehole P1 as the center and the distance between observation borehole P1 and the virtual well as the radius. Similarly, draw an arc with the observation borehole P2 as the center and the distance between observation borehole P2 and the virtual well as the radius. The intersection of the two arcs is the location of the virtual well. The perpendicular bisector of the line connecting the pumping well and the virtual well is the suspected location of the fault. The direction of the two perpendicular bisectors connecting the pumping well and the virtual well is the suspected strike of the fault.

[0076] When the fault strike is known, the distance r1 between an observation well and the pumping well, as well as the pumping time and drawdown data of the pumping test, need to be known. A drawdown-pumping duration s-lgt relationship graph should be plotted using the pumping time and drawdown data to determine t0 and t... a The value is then used to calculate the distance r2 between the observation well and the virtual well using the formula relating the distance between the observation well and the virtual well. A perpendicular line is drawn through the pumping well to the fault strike, and an arc is drawn with the observation well as the center and r2 as the radius. The intersection of the perpendicular line and the arc is the location of the virtual well; the perpendicular bisector of the line connecting the pumping well and the virtual well is the location of the fault. Figure 4 As shown.

[0077] When the fault strike is unknown, pumping time and drawdown data from two observation wells, P1 and P2, are needed to plot two curves: s1-lgt1 and s2-lgt2, to determine the critical point at which drawdown begins to appear in observation well P1 and the critical point t at which the drawdown intensifies. 10 t 1a And the critical time point at which the depth of observation hole P2 begins to decrease and the critical time point t at which the depth of observation begins to change. 20 t 2a Then, the distance r between observation hole P1 and virtual well is calculated using the formula relating the distance between the observation hole and the virtual well. 21 and the distance r between observation hole P2 and the virtual well 22 The distances between the virtual well and the two observation wells were obtained respectively. An arc was drawn with observation well P1 as the center and the distance between observation well P1 and the virtual well as the radius; an arc was also drawn with observation well P2 as the center and the distance between observation well P2 and the virtual well as the radius. The intersection of the two arcs represents the location of the virtual well. The perpendicular bisector of the line connecting the pumping well and the virtual well is the suspected location of the fault, and the direction of the perpendicular bisector of the line connecting the pumping well and the virtual well is the suspected strike of the fault. Figure 5 As shown.

[0078] It should be understood that Figure 4 and Figure 5 The pumping well and the midpoint of the line connecting the pumping well and the virtual well have two midlines, and each midline is a suspected location of the deep fault. Therefore, by plotting the distance between the observation hole and the virtual well, two suspected locations of the deep fault can be determined, and then only the cores of the two suspected locations need to be obtained by drilling. According to the core properties of the suspected locations, it can be determined whether the exact location of the deep fault is suspected fault 1 (i.e. fault 1 in Figure 4 or 5) or suspected fault 2 (i.e. fault 2 in Figure 4 or 5). 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 hole and the virtual well is:

[0080]

[0081] where r2 is the distance between the observation hole and the virtual well, t a is the critical time point at which the drawdown of the observation hole appears to turn, t0 is the time critical point at which the drawdown of the observation hole begins to appear, and r1 is the distance between the observation hole and the pumping well.

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

[0083] The mirror image method and the superposition principle are used to determine the distance relationship formula between the observation hole and the virtual well by using the Jacob solution of the unsteady well flow formula.

[0084] In one embodiment, the mirror image method and the superposition principle are used to determine the distance relationship formula between the observation hole and the virtual well by using the Jacob solution of the unsteady well flow formula, including:

[0085] The drawdown of the water level in the observation hole is determined based on the mirror image method, and the influence range of the drawdown is determined as:

[0086] When 0 < t < t0, the influence range of the pumping well does not reach the observation hole, 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 hole, and the boundary does not work, then the expression of the drawdown of the observation hole is:

[0090]

[0091] Where, T is the hydraulic conductivity, Q is the pumping well flow, 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 works, and the expression of the drawdown of the observation well is:

[0093]

[0094] Where, r2 is the distance between the observation well and the virtual well.

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

[0096]

[0097] From , we obtain:

[0098]

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

[0100]

[0101] Solving , we obtain:

[0102]

[0103] Substitute into , and we obtain

[0104]

[0105] Where, the values of t0(the critical point of time when the drawdown of the observation well begins to appear) and t a (the critical point of time when the drawdown of the observation well turns) are read from the drawdown-pumping duration time s~lgt graph, which are used to calculate the distance r2 between the observation well and the virtual well. The drawdown of the water level in the observation well experiences three stages, and the influence ranges of the drawdown of the water level in the three stages are shown in Figure 6 . The first stage: 0<t<t0, the influence range of the pumping well does not reach the observation well; the second stage: t0≤t≤t a , the influence range of the pumping well reaches the observation well, and the boundary does not work; the third stage: t≥t aThe boundary works at this time.

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

[0107] The deep fault identification method based on pumping test described above, based on the theory of groundwater dynamics, by delimiting the target research area (i.e. the exploration area), setting up pumping wells and observation holes, carrying out constant-flow pumping test, observing and recording data such as pumping well flow rate and observation hole water level drawdown at different times; draw the observation point water level drawdown-time image, identify the fault properties according to the image features, and determine the key parameters, and calculate the fault position by applying the theoretical formula. Thus, based on the pumping test data, the position and properties of the deep fault are identified by using the mirror method principle in groundwater dynamics, to make up for the shortcomings of the existing fault exploration methods, and significantly improve the accuracy of the boundary identification of deep faults.

[0108] It should be understood that, although Figure 1 The steps in the flowchart of the method for identifying the position and properties of the deep fault based on pumping test described above are displayed in sequence according to the direction of the arrows, but these steps are not necessarily executed in sequence according to the direction of the arrows. Unless otherwise stated in this document, there is no strict order restriction on the execution of these steps, and these steps can be executed in other orders. Moreover, Figure 1 At least part of the steps in the method for identifying the position and properties of the deep fault based on pumping test described above can include multiple sub-steps or multiple stages, which are not necessarily executed at the same time, but can be executed at different times, and the execution order of these sub-steps or stages is not necessarily sequential, but can be executed in rotation or alternation with at least part of other steps or sub-steps or stages of other steps.

[0109] The technical features of the above embodiments can be combined in any way. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described, but as long as the combination of the technical features does not exist contradictory, it should be considered as the scope of the present application.

[0110] The above-described embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method for identifying deep faults based on pumping tests, characterized in that, The method includes: Design pumping wells and observation wells within the exploration area, conduct constant flow unsteady pumping tests, and record pumping volume, pumping time, distance between observation wells and pumping wells, and drawdown data. Based on the pumping time and drawdown data, plot the relationship between drawdown and pumping duration (s) in the observation well (lgt). Based on the image features of the relationship between drawdown and pumping duration s ~ lgt in the observation well, the critical time point when the drawdown in the observation well begins to appear and the critical time point when the drawdown in the observation well begins to turn are determined. Based on the changes in drawdown after the critical point of the inflection point in the drawdown-pumping duration s~lgt relationship diagram of the observation well, the nature of deep faults in the exploration area is determined. Based on the distance between the observation hole and the pumping well, the critical point at which the observation hole begins to show a drawdown, and the critical point at which the drawdown of the observation hole begins to turn, the distance between the observation hole and the virtual well is determined by using the formula relating the distance between the observation hole and the virtual well. Based on the distance between the observation hole and the virtual well, a map is drawn to determine the suspected location and suspected strike of the deep fault; By drilling to obtain core samples from suspected locations, the exact location and orientation of deep faults can be determined based on the properties of the core samples from suspected locations.

2. The method according to claim 1, characterized in that, The method further includes: Given that the strike of a deep fault is known within the exploration area, an observation borehole, namely observation borehole P, is designed. In the absence of known deep fault strikes within the exploration area, two observation wells, namely observation wells P1 and P2, are designed.

3. The method according to claim 2, characterized in that, The determination of the nature of deep faults in the exploration area based on the drawdown changes after the critical point of inflection in the drawdown-pumping duration s~lgt relationship diagram of the observation well includes: In the relationship diagram of drawdown-pumping duration s~lgt in the observation well, if the drawdown amplitude increases after the critical point of the inflection point of the observation well, the deep fault in the exploration area is a water-resistant fault. In the relationship diagram of drawdown-pumping duration s~lgt in the observation well, if the drawdown no longer changes after the critical point of the inflection point of the observation well, the deep fault in the exploration area is a water-conducting fault.

4. The method according to claim 2, characterized in that, The step of determining the strike and suspected location of deep faults by plotting the distance between the observation well and the virtual well includes: If the strike of a deep fault is known within the exploration area, a perpendicular line is drawn through the pumping well to the strike of the deep fault. An arc is drawn with the observation well P as the center and the distance between the observation well P and the virtual well as the radius. The intersection of the perpendicular line and the arc is the location of the virtual well. The perpendicular bisector of the line connecting the pumping well and the virtual well is the suspected location of the fault. In the case where the strike of a deep fault is unknown within the exploration area, an arc is drawn with observation hole P1 as the center and the distance between observation hole P1 and the dummy well as the radius; an arc is also drawn with observation hole P2 as the center and the distance between observation hole P2 and the dummy well as the radius; the intersection of the two arcs is the location of the dummy well, the perpendicular bisector of the line connecting the pumping well and the dummy well is the suspected location of the fault, and the direction of the two perpendicular bisectors of the line connecting the pumping well and the dummy well is the suspected strike 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: Where r2 is the distance between the observation well and the virtual well, r a The critical time point at which the drawdown of the observation well begins to change is defined as r0, where r0 is the critical time point at which the drawdown of the observation well begins to occur, and r1 is the distance between the observation well 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, The application of the Jacob solution of the unsteady well flow formula, 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 well, and the boundary does not play a role, the expression for the drawdown of the observation well is: where 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; When t≥t a When the boundary conditions are in effect, the expression for the drawdown of the observation borehole is: where r2 is the distance between the observation well and the imaginary well; Substituting t = t0 and s = 0 into the case where t0 ≤ t ≤ t a When observing the bottom depth, the expression for the bottom depth is obtained: Depend on Solving for: Let t = t a s = s a Simultaneously, substituting the condition t0≤t≤t a When t≥t, the expression for the orifice drawdown and when t≥t a When observing the bottom depth, the expression for the bottom depth is obtained: And solve have to: Will Bring into Solving

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