Accumulated water goaf fine detection method for anisotropic stratum

Abstract

The invention discloses a ponding goaf fine detection method for an anisotropic stratum. The method comprises the following steps: effectively utilizing resistivity logging and acoustic logging information of multi-vertical drill hole data in a detection area to obtain a stratum anisotropy coefficient near a drill hole; based on three-dimensional geological modeling, the stratum anisotropy coefficient in a detection area is effectively obtained, and prior information is provided for transient electromagnetic anisotropy constraint inversion interpretation. In addition, the real anisotropy coefficient of the stratum is taken as prior information to be substituted into transient electromagnetic anisotropy constraint inversion calculation, so that errors brought to transient electromagnetic inversion interpretation when the stratum is assumed to be uniform and isotropic are avoided; the explanation precision of the plane and space positions of the water-accumulated goaf under the anisotropic stratum condition is effectively improved, and scientific support is provided for follow-up coal mine safety production and water prevention and control engineering.

Description

Technical Field

[0001] The present invention belongs to the technical field of mine water prevention and control safety, and in particular relates to a fine detection method for water-filled goaf areas in anisotropic strata. Background Art

[0002] When it comes to formation conductivity, the difference between isotropy and anisotropy lies in the relationship between formation conductivity and direction. Isotropy means that the formation conductivity does not change with changes in direction, while anisotropy means that the formation conductivity changes with changes in direction.

[0003] Most strata develop into continuous sedimentary strata. When the sedimentary strata have obvious stratification, the conductivity of the conductive earth in different directions changes, and the underground rock strata show macroscopic conductivity anisotropy. There are a large number of pores and cracks in the strata during their formation. The pores and cracks will be filled with other solid substances or fluid substances, which will eventually cause the strata to have strong anisotropic characteristics. The mining of the strata will cause certain disturbances, change the tectonic stress of the original rock, cause the destruction of the overlying rock strata and the change of the distribution of cracks in the goaf, and produce goaf cracks and fissures of different shapes, heights and densities. After a certain period of time, the cracks and cracks will be filled with water to form fracture aquifers. Due to the structure and water filling, the fracture aquifers will produce conductivity anisotropy.

[0004] In order to meet the needs of safe production and water prevention and control projects, it is urgent to provide a precise detection method for the water-filled goaf areas in the above anisotropic strata to provide scientific support for subsequent coal mine safety production and water prevention and control projects. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for fine detection of water-filled goaf areas in anisotropic strata, so as to solve the problem in the prior art that due to the lack of relevant methods, scientific support cannot be provided for subsequent coal mine safety production and water prevention and control projects.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for finely detecting water-filled goaf areas in anisotropic formations comprises the following steps:

[0008] Step 1: Collect relevant information of the waterlogged goaf to be detected and determine the target area;

[0009] Step 2: Obtain the horizontal resistivity of the target formation by resistivity logging;

[0010] Step 3, calculating the vertical resistivity of the target area formation using the sonic logging method;

[0011] Step 4, calculating the anisotropy coefficient of the target area formation based on the horizontal resistivity and the vertical resistivity;

[0012] Step 5: Establish a three-dimensional geological model of the target area based on the multiple vertical drill hole positions in the target area and the anisotropy coefficient obtained in step 4;

[0013] In step 6, the three-dimensional geological model parameters of the target area are used as prior information to construct a transient electromagnetic constrained inversion objective function to achieve accurate detection of water-filled goaf areas under anisotropic formation conditions.

[0014] The present invention also has the following features:

[0015] Furthermore, the relevant information of the waterlogged goaf to be detected in step 1 includes:

[0016] Geological report of the water-filled goaf to be detected, upper and lower comparison diagrams of the well, mine production and excavation diagrams, drill hole coordinates, drill hole histograms and drill hole logging curves.

[0017] Furthermore, step 2 includes the following sub-steps:

[0018] Step 21: Drilling a hole in the target area for resistivity logging and determining all data acquisition points in the resistivity logging;

[0019] Step 22, placing an electrode system consisting of a power supply electrode and two measuring electrodes at the bottom of the resistivity logging hole, and placing a return electrode of the power supply electrode at the ground surface;

[0020] Step 23, lifting the electrode system from the bottom of the hole upwards, and measuring the corresponding potential difference at each data collection point;

[0021] Step 24 : performing borehole, surrounding rock and invasion effect correction operations on all measured potential differences, and obtaining the horizontal resistivity corresponding to each layer in the resistivity logging as the horizontal resistivity of the target formation.

[0022] Furthermore, in step 21, the distance between each data collection point is 5m;

[0023] In the area where the potential difference exceeds two times, the point distance of each data collection point is adjusted to 1m.

[0024] The distance between the loop electrode and the resistivity logging hole is not less than 2 km.

[0025] Furthermore, step 3 includes the following steps:

[0026] Step 31, performing acoustic logging on the borehole where resistivity logging is performed, and obtaining the propagation time of the acoustic wave in each layer of the borehole;

[0027] Step 32, calculate the time it takes for the sound wave to propagate in the borehole using the following formula:

[0028]

[0029] Among them, Δt represents the time it takes for the acoustic wave to propagate in the resistivity log, μ s / m;

[0030] n represents the total number of layers in the resistivity logging;

[0031] φ v represents the volume porosity estimated vertically from the resistivity log, %;

[0032] i represents any layer in the resistivity log;

[0033] Δt mai and Δt f represent the acoustic wave transmission time in the formation and fluid of layer i, μ s / m;

[0034] V mai represents the volume fraction of the mineral components in the i-th layer, %;

[0035] Step 33, use the following formula to calculate the vertical resistivity R of each layer in the borehole v , and the result is used as the vertical resistivity of the borehole in the target area;

[0036]

[0037] Among them, a v It represents the lithology coefficient related to lithology;

[0038] b v represents a constant related to lithology;

[0039] Sw represents water saturation, %;

[0040] Rw represents the resistivity of connate water, Ω·m;

[0041] m v represents the cementation index;

[0042] n v Represents the saturation index.

[0043] Furthermore, when measuring potential difference and acoustic logging, it is ensured that the stress is uniform during the measurement process and that the formation is in good contact with the electrode.

[0044] Furthermore, in step 4, the anisotropy coefficient within the full depth range of the borehole is calculated using the following formula as the anisotropy coefficient within the full depth range of the target area:

[0045]

[0046] Where λ represents the anisotropy coefficient;

[0047] R h Indicates the horizontal resistivity of the borehole.

[0048] Furthermore, step 5 includes the following sub-steps:

[0049] Step 51: construct the geological model parameter ρ of a single borehole based on the horizontal resistivity and vertical resistivity within the full depth range of the borehole. i =(R vi ,R hi ,λ i ,H i );

[0050] Among them, R vi =(R v1 ,R v2 ,…,R vn ), which represents the horizontal resistivity of different layers from the surface to the bottom of the borehole;

[0051] R hi =(R h1 ,R h2 ,…,R hn ), which represents the vertical resistivity of different layers from the surface to the bottom of the borehole;

[0052] λ i =(λ1,λ2,…,λ n ), represents the anisotropy coefficient of the resistivity of different layers from the surface to the bottom of the borehole;

[0053] H i =(H1,H2,…,H n ), which represents the top interface parameters of different layers from the surface to the bottom of the borehole;

[0054] Step 52: Based on the multi-borehole coordinates and the geological model parameters of a single borehole, a three-dimensional geological model of the target area is constructed using the following formula: xyhik =(x ik ,y ik ,h ik ,R vik ,R hik ,λ ik ,H ik );

[0055] Among them, x i =(x 1k ,x 2k ,...,x nk ) represents the x-coordinate of the full depth of the k-th drill hole;

[0056] y i =(y 1k ,y 2k ,...,y nk ) represents the y coordinate of the full depth of the kth borehole;

[0057] h i =(h 1k ,h 2k ,...,h nk ) represents the formation elevation at the full depth of the kth borehole.

[0058] Furthermore, in step 6, transient electromagnetic detection is carried out on the target area. During data processing, the three-dimensional geological model parameters of the target area are used as prior information, and one-dimensional resistivity anisotropy inversion is performed on the transient electromagnetic field response data to construct an inversion objective function with parameters of formation thickness, formation anisotropic resistivity and formation interface. The second norm of the difference between the vertical resistivity, horizontal resistivity, formation thickness and formation interface depth of the same layer of adjacent data acquisition points is minimized, and the data of all data acquisition points in the entire target area are collaboratively inverted, and the data of different data acquisition points are mutually constrained. The inversion objective function is solved to obtain the formation anisotropic resistivity and formation thickness of the entire target area, and then the formation interface is determined, so as to realize the accurate detection of water-filled goaf under anisotropic formation conditions.

[0059] Compared with the prior art, the present invention has the following technical effects:

[0060] The present invention's fine detection method for water-logged goaf in anisotropic formations effectively utilizes resistivity logging and acoustic logging information from multiple vertical borehole data within the survey area to obtain the anisotropy coefficient of the formation near the boreholes; based on three-dimensional geological modeling, the anisotropy coefficient of the formation in the detection area is effectively obtained, providing prior information for transient electromagnetic anisotropy constrained inversion interpretation.

[0061] In addition, by bringing the true anisotropy coefficient of the stratum as prior information into the transient electromagnetic anisotropy constrained inversion calculation, the error caused by assuming the stratum to be uniform and isotropic in the transient electromagnetic inversion interpretation is avoided, and the interpretation accuracy of the plane and spatial position of the water-logged goaf under anisotropic stratum conditions is effectively improved, providing scientific support for subsequent coal mine safety production and water prevention and control projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 It is a flow chart of the method for fine detection of water-filled goaf areas in anisotropic strata according to the present invention. DETAILED DESCRIPTION

[0063] It should be noted that, unless otherwise specified, all methods in the present invention adopt methods known in the prior art.

[0064] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0065] like Figure 1 As shown, a method for fine detection of water-filled goaf areas in anisotropic formations includes the following steps:

[0066] Step 1: Collect relevant information of the waterlogged goaf to be detected and determine the target area;

[0067] Step 2: Obtain the horizontal resistivity of the target formation by resistivity logging;

[0068] Step 3, calculating the vertical resistivity of the target area formation using the sonic logging method;

[0069] Step 4, calculating the anisotropy coefficient of the target area formation based on the horizontal resistivity and the vertical resistivity;

[0070] Step 5: Establish a three-dimensional geological model of the target area based on the multiple vertical drill hole positions in the target area and the anisotropy coefficient obtained in step 4;

[0071] In step 6, the three-dimensional geological model parameters of the target area are used as prior information to construct a transient electromagnetic constrained inversion objective function to achieve accurate detection of water-filled goaf areas under anisotropic formation conditions.

[0072] Specifically, the relevant information of the water-filled goaf to be detected in step 1 includes a geological report of the water-filled goaf to be detected, a top-bottom comparison map of the well, a mine production excavation map, borehole coordinates, a borehole histogram, and a borehole logging curve.

[0073] The purpose of this step is to comprehensively analyze suspected waterlogged goaf areas through data collection and geological surveys, thereby identifying target areas for exploration. Furthermore, the early data collection provides theoretical support for later production and flood control projects. Those skilled in the art are capable of determining target areas based on the collected data, drawing on their knowledge in the field. This process is well known in the art.

[0074] The collection of the above data is essential. It is also possible to collect sample porosity, stratum distribution characteristics, working face mining conditions, working face recovery time, surface subsidence conditions, nearby water supply conditions, rainfall conditions and formation water resistivity within the detection area based on actual conditions.

[0075] Furthermore, step 2 includes the following sub-steps:

[0076] Step 21: Drill holes in the target area for resistivity logging, and determine all data collection points in the resistivity logging;

[0077] In step 22, an electrode system consisting of a power supply electrode A and two measuring electrodes M and N is set at the bottom of the resistivity logging hole, and a return electrode B of the power supply electrode is set on the surface. In this embodiment, the letter labels of the electrodes are only used for differentiation.

[0078] Step 23, lifting the electrode system from the bottom of the hole upwards, and measuring the corresponding potential difference at each data collection point;

[0079] Step 24: perform borehole, surrounding rock and invasion effect correction operations on all measured potential differences, and obtain the horizontal resistivity corresponding to the resistivity logging as the horizontal resistivity of the target formation.

[0080] It should be noted that the correction operations for wellbore, surrounding rock and intrusion effects are well-known methods in the art and are beyond the scope of this embodiment, so they will not be described in detail.

[0081] Further preferably, in step 21, the distance between each data collection point is 5m;

[0082] In the area where the potential difference changes greatly, the distance between each data collection point is adjusted to 1m. In actual work, whether the potential difference changes greatly needs to be determined by those skilled in the art based on the actual situation.

[0083] This embodiment provides a specific determination method, that is, in an area where the speed difference exceeds two times, the point distance of each data collection point is adjusted to 1 meter.

[0084] The loop electrode B is placed on the surface, not less than 2 km away from the borehole mouth.

[0085] When the electrode system is lifted upward from the bottom of the resistivity logging hole, the current I is supplied by the A electrode.

[0086] Furthermore, the vertical resistivity of the target formation is calculated using sonic logging and the modified Archie formula. Step 3 includes the following steps:

[0087] Step 31, performing acoustic logging on the borehole where resistivity logging is performed, and obtaining the propagation time of the acoustic wave in each layer of the borehole;

[0088] Step 32, calculate the time it takes for the sound wave to propagate in the borehole using the following formula:

[0089]

[0090] Where Δ represents the time it takes for the acoustic wave to propagate within the resistivity log, μ s / m;

[0091] n represents the total number of layers in the resistivity logging;

[0092] φ v represents the volume porosity estimated vertically from the resistivity log, %;

[0093] i represents any layer in the resistivity log;

[0094] Δt mai and Δt f represent the acoustic wave transmission time in the formation and fluid of layer i, μ s / m;

[0095] V mai represents the volume fraction of the mineral components in the i-th layer, %;

[0096] In this embodiment:

[0097]

[0098] Step 33: Combine the above two formulas to calculate the vertical resistivity R of resistivity logging. v , and take the result as the vertical resistivity of the target area;

[0099]

[0100] Among them, a v The lithology coefficient is related to the lithology and is related to the actual geological conditions of the target area and is directly determined by those skilled in the art.

[0101] b v represents a constant related to lithology, which is related to the actual geological conditions of the target area and can be directly determined by those skilled in the art;

[0102] Sw represents water saturation, %; it is related to the actual geological conditions of the target area, can be obtained through conventional geological experiments, and can be directly determined by those skilled in the art;

[0103] Rw represents the resistivity of connate water, in Ω·m; it is related to the actual geological conditions of the target area, can be obtained through conventional geological experiments, and can be directly determined by those skilled in the art;

[0104] m v It represents the cementation index, which is related to the actual geological conditions of the target area and can be directly determined by those skilled in the art;

[0105] n v It represents the saturation index, which is related to the actual geological conditions of the target area and can be directly determined by those skilled in the art.

[0106] As a preferred solution, when measuring potential difference and acoustic logging, it is ensured that the stress is uniform during the measurement process and that the formation is in good contact with the electrode.

[0107] Furthermore, in step 4, the anisotropy coefficient within the full depth range of the borehole is calculated using the following formula as the anisotropy coefficient within the full depth range of the target area:

[0108]

[0109] Where λ represents the anisotropy coefficient;

[0110] R h Indicates the horizontal resistivity of the borehole.

[0111] Furthermore, step 5 includes the following sub-steps:

[0112] Step 51: construct the geological model parameter ρ of a single borehole based on the horizontal resistivity and vertical resistivity within the full depth range of the borehole. i =(R vi ,R hi ,λ i ,H i );

[0113] Among them, R vi =(R v1 ,R v2 ,…,R vn ), which represents the horizontal resistivity of different layers from the surface to the bottom of the borehole;

[0114] R hi =(R h1 ,R h2 ,…,R hn ), which represents the vertical resistivity of different layers from the surface to the bottom of the borehole;

[0115] λ i =(λ1,λ2,…,λ n ), represents the anisotropy coefficient of the resistivity of different layers from the surface to the bottom of the borehole;

[0116] H i =(H1,H2,…,H n ), which represents the top interface parameters of different layers from the surface to the bottom of the borehole;

[0117] Step 52: Based on the multi-borehole coordinates and the geological model parameters of a single borehole, a three-dimensional geological model of the target area is constructed using the following formula: xyhik =(x ik ,y ik ,h ik ,R vik ,R hik ,λik ,H ik );

[0118] Among them, x i =(x 1k ,x 2k ,...,x nk ) represents the x-coordinate of the full depth of the k-th drill hole;

[0119] y i =(y 1k ,y 2k ,...,y nk ) represents the y coordinate of the full depth of the kth borehole;

[0120] h i =(h 1k ,h 2k ,...,h nk ) represents the formation elevation at the full depth of the kth borehole.

[0121] Furthermore, in the three-dimensional geological modeling step of the anisotropy coefficient, according to the relative position of the borehole position and the transient electromagnetic data acquisition point, the geological model parameters at different depths of each data acquisition point are obtained based on the three-dimensional nearest neighbor interpolation method with the borehole position as the base point, mainly including layer thickness, horizontal resistivity, vertical resistivity and layer interface parameters.

[0122] Furthermore, in step 6, the three-dimensional geological model parameters of the target area are used as prior information to construct an initial inversion model with parameters such as formation thickness, formation anisotropic resistivity, and formation interface. The two-norm difference between the vertical resistivity, horizontal resistivity, formation thickness, and formation interface depth of the same layer at adjacent data collection points is minimized, achieving collaborative inversion of data from all data collection points in the entire survey area and mutual constraints between data from different data collection points.

[0123] By solving the set of equations, the anisotropic resistivity, formation thickness and formation interface of the entire target area can be determined, and accurate detection of water-filled goaf areas under anisotropic formation conditions can be achieved.

Claims

1. A method for fine detection of water-filled goaf in anisotropic strata, characterized in that: The following steps are involved: Step 1: Collect relevant information of the waterlogged goaf to be detected and determine the target area; Step 2: Obtain the horizontal resistivity of the target formation by resistivity logging; Step 3, calculating the vertical resistivity of the target area formation using the sonic logging method; Step 4, calculating the anisotropy coefficient of the target area formation based on the horizontal resistivity and the vertical resistivity; Step 5: Establish a three-dimensional geological model of the target area based on the multiple vertical drill hole positions in the target area and the anisotropy coefficient obtained in step 4; In step 6, the three-dimensional geological model parameters of the target area are used as prior information to construct a transient electromagnetic constrained inversion objective function to achieve accurate detection of water-filled goaf areas under anisotropic formation conditions.

2. The method for fine detection of water-filled goaf in anisotropic strata according to claim 1, characterized in that: The relevant information of the waterlogged goaf to be detected in step 1 includes: Geological report of the water-filled goaf to be detected, upper and lower comparison diagrams of the well, mine production and excavation diagrams, drill hole coordinates, drill hole histograms and drill hole logging curves.

3. The method for fine detection of water-filled goaf in anisotropic strata according to claim 1, characterized in that: Step 2 includes the following sub-steps: Step 21: Drilling a hole in the target area for resistivity logging and determining all data acquisition points in the resistivity logging; Step 22, placing an electrode system consisting of a power supply electrode and two measuring electrodes at the bottom of the resistivity logging hole, and placing a return electrode of the power supply electrode at the ground surface; Step 23, lifting the electrode system from the bottom of the hole upwards, and measuring the corresponding potential difference at each data collection point; Step 24 : performing borehole, surrounding rock and invasion effect correction operations on all measured potential differences, and obtaining the horizontal resistivity corresponding to each layer in the resistivity logging as the horizontal resistivity of the target formation.

4. The method for fine detection of water-logged goaf in anisotropic strata according to claim 3, characterized in that: In step 21, the distance between each data collection point is 5m; In the area where the potential difference exceeds two times, the point distance of each data collection point is adjusted to 1m. The distance between the loop electrode and the resistivity logging hole is not less than 2 km.

5. The method for fine detection of water-filled goaf in anisotropic strata according to claim 1, characterized in that: Step 3 includes the following steps: Step 31, performing acoustic logging on the borehole where resistivity logging is performed, and obtaining the propagation time of the acoustic wave in each layer of the borehole; Step 32, calculate the time it takes for the sound wave to propagate in the borehole using the following formula: Among them, Δt represents the time it takes for the acoustic wave to propagate in the resistivity log, μ s / m; n represents the total number of layers in the resistivity logging; φ v represents the volume porosity estimated vertically from the resistivity log, %; i represents any layer in the resistivity log; Δt mai and Δt f represent the acoustic wave transmission time in the formation and fluid of layer i, μ s / m; V mai represents the volume fraction of the mineral components in the i-th layer, %; Step 33, use the following formula to calculate the vertical resistivity R of each layer in the borehole v , and the result is used as the vertical resistivity of the borehole in the target area; Among them, a v It represents the lithology coefficient related to lithology; b v represents a constant related to lithology; Sw represents water saturation, %; Rw represents the resistivity of connate water, Ω·m; m v represents the cementation index; n v Represents the saturation index.

6. The method for fine detection of water-filled goaf in anisotropic strata according to claims 4 and 5, characterized in that: When measuring potential difference and acoustic logging, ensure that the stress is uniform during the measurement process and that the formation has good contact with the electrode.

7. The method for fine detection of water-filled goaf in anisotropic strata according to claim 1, characterized in that: In step 4, the anisotropy coefficient within the full depth range of the borehole is calculated using the following formula as the anisotropy coefficient within the full depth range of the target area: Where λ represents the anisotropy coefficient; R h Indicates the horizontal resistivity of the borehole.

8. The method for fine detection of water-filled goaf in anisotropic strata according to claim 7, characterized in that: Step 5 includes the following sub-steps: Step 51: construct the geological model parameter ρ of a single borehole based on the horizontal resistivity and vertical resistivity within the full depth range of the borehole. i =(R vi ,R hi ,λ i ,H i ); Among them, R vi =(R v1 ,R v2 ,…,R vn ), which represents the horizontal resistivity of different layers from the surface to the bottom of the borehole; R hi =(R h1 ,R h2 ,…,R hn ), which represents the vertical resistivity of different layers from the surface to the bottom of the borehole; λ i =(λ1,λ2,…,λ n ), represents the anisotropy coefficient of the resistivity of different layers from the surface to the bottom of the borehole; H i =(H1,H2,…,H n ), which represents the top interface parameters of different layers from the surface to the bottom of the borehole; Step 52: Based on the multi-borehole coordinates and the geological model parameters of a single borehole, a three-dimensional geological model of the target area is constructed using the following formula: xyhik =(x ik ,y ik ,h ik ,R vik ,R hik ,λ ik ,H ik ); Among them, x i =(x 1k ,x 2k ,...,x nk ) represents the x-coordinate of the full depth of the k-th drill hole; y i =(y 1k ,y 2k ,...,y nk ) represents the y coordinate of the full depth of the kth borehole; h i =(h 1k ,h k2 ,...,h nk ) represents the formation elevation at the full depth of the kth borehole.

9. The method for finely detecting water-filled goaf areas in anisotropic strata according to claim 7, characterized in that: In step 6, transient electromagnetic detection is carried out on the target area. During data processing, the three-dimensional geological model parameters of the target area are used as prior information, and one-dimensional resistivity anisotropy inversion is performed on the transient electromagnetic field response data to construct an inversion objective function with parameters of formation thickness, formation anisotropic resistivity and formation interface. The two-norm of the difference between the vertical resistivity, horizontal resistivity, formation thickness and formation interface depth of the same layer of adjacent data acquisition points is minimized, and the data of all data acquisition points in the entire target area are collaboratively inverted, and the data of different data acquisition points are mutually constrained. The inversion objective function is solved to obtain the formation anisotropic resistivity and formation thickness of the entire target area, and then the formation interface is determined, so as to realize the accurate detection of water-filled goaf under anisotropic formation conditions.

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