Double-stage active fracturing grouting method

Abstract

The invention discloses a double-stage active fracturing grouting method, and belongs to the technical field of shaft inrush water plugging. The method comprises the steps that firstly, a plurality of fracturing drill holes are vertically and downwards constructed at equal intervals along a well side of a working face, cross-hole detection is carried out through a focusing electrical method to determine which two fracturing drill holes an existing crack is located between, then first-stage fracturing is carried out through cement-water glass double-liquid slurry depending on one fracturing drill hole, and nearly 90-degree rotation of the existing crack in the near-field principal stress direction is achieved; and after the slurry is solidified, hole sweeping is conducted, second-stage fracturing is conducted through ordinary cement slurry, after the fracturing crack is communicated with the existing crack, the cement slurry fills a crack network formed by the fracturing crack and the existing crack, and therefore targeted grouting plugging is completed. The method is suitable for targeted grouting plugging of the existing structure crack in the working condition that the cross-shaft structure crack is separated from the fracturing drill hole.

Description

Technical Field

[0001] This invention relates to a two-stage active fracturing grouting method, belonging to the field of vertical shaft water inrush sealing technology, and is particularly suitable for targeted grouting and sealing of cross-vertical structural cracks during the construction of deep vertical shafts. Background Technology

[0002] High-angle (nearly 90º) structural cracks across shafts are the main channels for water inrush at deep shaft working faces. Targeted grouting and sealing of these cracks can eliminate the risk of water inrush at the shaft working face and minimize water inrush, which is of great significance for the safe and efficient construction of deep shafts.

[0003] Existing technologies are mostly designed for coal-bearing strata (sedimentary rocks) with soft surrounding rocks and loose pores. However, igneous rocks commonly found in metal mines are hard rocks with low porosity. The applicability of high-energy gas fracturing technology, characterized by pulse loading, needs to be verified. There is an urgent need to develop an active fracturing grouting method with slow pressure increase, long duration, and quantitatively controllable effect to solve the problem of water diversion grouting and sealing of high-angle fractures in the shaft walls during shaft construction in igneous rocks.

[0004] The prior art disclosed in CN114482913A is a method for determining the plugging length of a horizontal well in a fractured oil well with water production, and a plugging method thereof. It includes the following steps: 1) determining the main water-producing section of the horizontal well; 2) predicting the comprehensive water cut and water drive volumetric sweep efficiency of the reservoir injection-production well group under different plugging schemes; each plugging scheme is centered on the main water-producing section, and the plugging length ratio of each section is different; the plugging section of each plugging scheme includes the main water-producing section; 3) weighted averaging the comprehensive water cut and water drive volumetric sweep efficiency of each plugging scheme to obtain evaluation index parameters, and then determining the plugging length of the horizontal well in the fractured oil reservoir. However, this method can only be used for plugging small-diameter oil wells and cannot effectively pre-treat fractures present in large-diameter vertical wells.

[0005] Existing fracturing technologies are mostly designed for large-volume formation fracturing. During fracturing, the propagation distance of the fracturing fractures is much greater than the propagation distance of the actively fracturing fractures in the local area of ​​the wellbore before connecting with existing fractures. Due to the heterogeneity of the formation, the stress distribution around existing fractures is uneven, so the effect of modifying the principal stress direction in the local area is highly uncertain. Moreover, existing fracturing technologies mostly use water of different viscosities, mainly to open up channels for oil and gas outflow in the formation or for water injection for extraction. However, in fracturing grouting, the grout flows from the outside into the surrounding rock fractures. The fluid viscosity and the physical interaction principle between the fluid and the rough fracture wall are different in these two processes. Existing fracturing technologies cannot be simply applied to fracturing grouting in deep wells. Summary of the Invention

[0006] Technical Issue: To address the aforementioned issues, considering the regulatory effect of the fracturing fracture filling and propagation process on the near-field principal stress direction of existing fractures, a dual-stage active fracturing grouting method is proposed, following the approach of first regulating the principal stress direction and then connecting the main control fractures. This provides an innovative approach for effectively preventing water inrush disasters in deep well working faces and reducing water inflow at the working face.

[0007] Technical Content: To achieve the above technical objectives, this invention discloses a dual-stage active fracturing grouting method, the steps of which are as follows: S1. Construct multiple fracturing boreholes at equal intervals along the circumferential direction of the shaft working face. Select two fracturing boreholes in sequence to perform cross-hole focusing electrical resistivity tomography to determine which two fracturing boreholes the existing fracture is located between. S2. In either of the two fracturing boreholes containing the existing crack, the first stage of grouting fracturing is carried out. Under the control of the near-field principal stress direction of the existing crack, the fracturing crack will extend in the direction parallel to the existing crack. During the crack extension process, the small principal stress direction in the area surrounded by the fracturing borehole and the existing crack gradually rotates towards the direction parallel to the existing crack due to the combined effect of grouting pressure and grout flow on the crack wall. S3. After the first stage of grouting fracturing, the grout immediately fills the first stage fracturing crack and solidifies, completing the adjustment of the principal stress in the local area. Then, a drill bit with a diameter smaller than the diameter of the fracturing borehole is used to clean the fracturing borehole of the first stage of grouting fracturing, and the second stage of grouting fracturing is implemented. Since the direction of the minor principal stress has become parallel to the direction of the existing crack after the first stage of grouting fracturing, the second stage of grouting fracturing crack will extend perpendicular to the direction of the existing crack until it connects with the existing crack. S4. Pressure grouting is carried out on the existing cracks through the second-stage grouting-induced cracks, and the grout fills the existing cracks and the second-stage induced cracks.

[0008] Furthermore, the number of vertically downward fracturing boreholes along the circumference of the shaft working face is 3 to n, where n = shaft circumference / 1.5.

[0009] Furthermore, the grout used in the first stage of grouting and fracturing is a cement-water glass two-component grout with a water-cement ratio of 0.6:1 to 1:1 and a cement:water glass volume ratio of 1:1, in order to achieve rapid curing of the grout and good interfacial bonding performance. The grout used in the second stage of grouting and fracturing and pressure grouting operations is ordinary cement grout with a water-cement ratio of 0.6:1 to 1:1, in order to fill the existing cracks.

[0010] Furthermore, the process of determining which two fracturing boreholes an existing fracture is located between using cross-hole focusing electrical resistivity is as follows: Transmitting and receiving electrodes are set at the same height in two fracturing boreholes to obtain the reciprocating resistivity. Transmitting and receiving electrodes are set at different heights in one fracturing borehole to obtain the adjacent resistivity. Based on the principle that the reciprocating and adjacent resistivities are not equal, the process determines which two fracturing boreholes the existing fracture is located between. In the reciprocating measurement, the transmitting and receiving electrodes are located at the same height in two fracturing boreholes, while in the adjacent measurement, the transmitting and receiving electrodes are located at different heights in the same fracturing borehole.

[0011] Furthermore, the lengths of the first-stage fracturing fractures and the second-stage fracturing fractures are both controlled to not exceed the distance between two adjacent fracturing boreholes, and the length of the second-stage fracturing fracture is approximately equal to the vertical distance between the fracturing borehole and the existing fracture.

[0012] Furthermore, the principal stress in the region enclosed by the first-stage grout-induced fracturing and the existing cracks gradually rotates towards a direction parallel to the existing cracks. It is expressed as follows: ; In the formula This represents the shear stress in the plane formed by the vertical and circumferential directions. These represent vertical and circumferential stresses, respectively.

[0013] Furthermore, considering the local expansion characteristics of cracks in the shaft working face, the pressure grouting equipment also serves as an active fracturing equipment, realizing the integration of fracturing and grouting systems.

[0014] Furthermore, during the second phase of grout-induced fracturing, the connection time between the fracturing crack and the existing crack was determined by real-time monitoring of sudden pressure drops and instantaneous flow increases.

[0015] Furthermore, during the pressure grouting operation on the existing cracks, the grouting pressure is observed through the pressure gauge at the orifice. When the grouting pressure suddenly increases, it is determined that the grout has filled the existing cracks and the second-stage cracking cracks.

[0016] Beneficial effects: After fracturing borehole construction, this method determines the location of existing fractures between two fracturing boreholes based on cross-hole detection results. Then, it selects one fracturing borehole to perform two phases of fracturing operations, efficiently establishing a connection with the existing fracture. Because the wellbore size is smaller than the oil and gas formation fracturing size, the influence of formation heterogeneity on fracture propagation is effectively reduced, resulting in the shortest connection path. Due to the high formation water pressure, the surrounding rock fracture strength is comparable to its tensile strength, and the high-pressure conditions required for large-scale fracture propagation are not needed. Therefore, during fracturing and grouting operations, only one grouting equipment needs to be deployed on the ground to simultaneously meet the requirements of fracturing and grouting sealing. Attached Figure Description

[0017] Figure 1 This is a schematic diagram showing the spatial relationship between existing cracks, fracture-causing boreholes, and wellbore in an embodiment of the present invention.

[0018] Figure 2 This is a schematic diagram of the two-stage active fracturing grouting method of the present invention. Detailed Implementation

[0019] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0020] like Figure 2 As shown, this invention discloses a two-stage active fracturing grouting method. The vertical shaft working face has 3 to n vertically downward fracturing boreholes along the circumferential direction of the shaft wall, where n = shaft circumference / 1.5. The existing fracture is assumed to be a penetrating structural fracture (controlling fracture) that intersects the shaft once. Figure 1 As shown.

[0021] The specific steps of this method are as follows: S1. In the circumferential fracture-inducing boreholes along the shaft wall of the vertical shaft working face, two fracture-inducing boreholes are selected sequentially for cross-hole focusing electrical resistivity tomography (EDT) to determine which two fracture-inducing boreholes the existing fracture is located between. Figure 2 The minor principal stress trace is represented by a dashed line in the middle; The process of determining which two fracturing boreholes an existing fracture is located between using cross-hole focusing electrical resistivity is as follows: A transmitting electrode and a loop electrode are set at the same height in two fracturing boreholes to obtain the reciprocating resistivity. A transmitting electrode and a loop electrode are set at different heights in a single fracturing borehole to obtain the adjacent resistivity. Based on the principle that the reciprocating and adjacent resistivities are not equal, the process determines which two fracturing boreholes the existing fracture is located between. In the reciprocating measurement, the transmitting and receiving electrodes are located at the same height in two fracturing boreholes, while in the adjacent measurement, the transmitting and receiving electrodes are located at different heights in the same fracturing borehole.

[0022] S2. In either of the two fracturing boreholes containing the existing crack, the first stage of grouting fracturing is carried out. The grout used in the first stage of grouting fracturing is a cement-water glass two-component grout with a cement-cement ratio of 0.6:1 to 1:1 and a cement-water glass volume ratio of 1:1 to achieve rapid curing of the grout and good interfacial bonding performance. Controlled by the direction of the near-field principal stress of the existing crack, the fracturing crack extends along the direction parallel to the existing crack. During the crack extension process, the small principal stress direction in the area surrounded by the fracturing borehole and the existing crack gradually rotates towards the direction parallel to the existing crack, achieving a nearly 90° rotation of the near-field principal stress direction of the existing crack. The first-stage grouting fracturing caused the minor principal stresses in the region to gradually rotate towards a direction parallel to the existing cracks. The rotation angle of the minor principal stresses in the region enclosed by the first-stage grouting fracturing and the existing cracks towards a direction parallel to the existing cracks is... It is expressed as follows: , In the formula This represents the shear stress in the plane composed of the vertical and circumferential directions. These represent vertical and circumferential stresses, respectively.

[0023] S3. After the first stage of grout fracturing, the grout immediately fills and solidifies the fracture, completing the adjustment of the principal stress in the local area. Then, a drill bit with a diameter smaller than the diameter of the fracturing borehole is used to clean the borehole from the first stage of grout fracturing, and the second stage of grout fracturing is implemented. Since the direction of the minor principal stress has changed to be parallel to the existing fracture direction after the first stage of grout fracturing, the second stage of grout fracturing will extend perpendicular to the existing fracture direction until it connects with the existing fracture. The length of the first stage fracturing fracture and the length of the second stage fracturing fracture are both controlled to not exceed the distance between two adjacent fracturing boreholes, considering the local expansion characteristics of fractures in the shaft working face. The pressure grouting equipment also functions as an active fracturing device, integrating fracturing and grouting systems. It determines the connection point between the initiating fracture and existing fractures by real-time monitoring of sudden pressure drops and flow rate increases. The length of the second-stage fracturing fracture is approximately equal to the distance between the initiating borehole and the existing fracture. The grout used in the second-stage fracturing and pressure grouting operations is ordinary cement grout with a water-cement ratio of 0.6:1 to 1:1, to fill the existing fractures. During pressure grouting of the existing fractures, the grouting pressure is observed through a pressure gauge at the borehole opening. When the grouting pressure suddenly increases, it is determined that the grout has filled both the existing fracture and the second-stage initiating fracture.

[0024] S4. Pressure grouting is performed on the existing cracks through the second-stage grouting-induced cracks, so that the grout fills the existing cracks and the second-stage induced cracks.

[0025] There are many specific ways to implement this invention. The above description is only a preferred embodiment of this invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of this invention, and these improvements should also be considered within the scope of protection of this invention.

Claims

1. A dual-stage active fracturing grouting method, characterized in that... The steps are as follows: S1. Construct multiple fracturing boreholes at equal intervals along the circumferential direction of the shaft working face. Select two fracturing boreholes in sequence to perform cross-hole focusing electrical resistivity tomography to determine which two fracturing boreholes the existing fracture is located between. S2. The first stage of grouting fracturing is carried out in either of the two fracturing boreholes containing the existing crack. Under the control of the near-field principal stress direction of the existing crack, the fracturing crack will extend in the direction parallel to the existing crack. During the crack extension process, the small principal stress direction in the area surrounded by the fracturing borehole and the existing crack gradually rotates towards the direction parallel to the existing crack. S3. After the first stage of grouting fracturing, the grout immediately fills the first stage fracturing crack and solidifies, completing the adjustment of the principal stress in the local area. Then, a drill bit with a diameter smaller than the diameter of the fracturing borehole is used to clean the fracturing borehole of the first stage of grouting fracturing, and the second stage of grouting fracturing is implemented. Since the direction of the minor principal stress has become parallel to the direction of the existing crack after the first stage of grouting fracturing, the second stage of grouting fracturing crack will extend perpendicular to the direction of the existing crack until it connects with the existing crack. S4. Pressure grouting is performed on the existing cracks through the second-stage grouting-induced cracks, so that the grout fills the existing cracks and the second-stage induced cracks.

2. The dual-stage active fracturing grouting method according to claim 1, characterized in that, The number of vertically downward fracturing boreholes in the circumferential direction of the shaft working face is 3 to n, where n = shaft circumference / 1.

5.

3. The dual-stage active fracturing grouting method according to claim 1, characterized in that, The first stage of grouting for crack initiation uses a cement-water glass two-component grout with a cement-cement ratio of 0.6:1 to 1:1 and a cement-water glass volume ratio of 1:1 to achieve rapid curing and good interfacial bonding performance. The second stage of grouting for crack initiation and pressure grouting uses ordinary cement grout with a water-cement ratio of 0.6:1 to 1:1 to fill existing cracks.

4. The dual-stage active fracturing grouting method according to claim 1, characterized in that, The process of determining which two fracturing boreholes an existing fracture is located between using cross-hole focusing electrical resistivity is as follows: A transmitting electrode and a loop electrode are set at the same height in two fracturing boreholes to obtain the reciprocating resistivity. A transmitting electrode and a loop electrode are set at different heights in a single fracturing borehole to obtain the adjacent resistivity. Based on the principle that the reciprocating and adjacent resistivities are not equal, the process determines which two fracturing boreholes the existing fracture is located between. In the reciprocating measurement, the transmitting and receiving electrodes are located at the same height in two fracturing boreholes, while in the adjacent measurement, the transmitting and receiving electrodes are located at different heights in the same fracturing borehole.

5. The dual-stage active fracturing grouting method according to claim 1, characterized in that, The lengths of the first-stage and second-stage fracturing fractures are both controlled to not exceed the distance between two adjacent fracturing boreholes, and the length of the second-stage fracturing fracture is approximately equal to the vertical distance between the fracturing borehole and the existing fracture.

6. The dual-stage active fracturing grouting method according to claim 1, characterized in that, During the first phase of grouting fracturing, the small principal stress in the region enclosed by the fracturing hole and the existing fracture gradually rotates towards a direction parallel to the existing fracture. It is expressed as follows: , In the formula This represents the shear stress in the plane formed by the vertical and circumferential directions. These represent vertical and circumferential stresses, respectively.

7. The dual-stage active fracturing grouting method according to claim 1, characterized in that, Considering the local propagation characteristics of fractures at the shaft working face, the pressure grouting equipment also serves as an active fracturing equipment, realizing the integration of fracturing and grouting systems.

8. The dual-stage active fracturing grouting method according to claim 1, characterized in that, During the second phase of grout-induced fracturing, the connection time between the fracturing crack and the existing crack was determined by real-time monitoring of sudden pressure drops and instantaneous flow increases.

9. The dual-stage active fracturing grouting method according to claim 1, characterized in that, During pressure grouting of existing cracks, the grouting pressure is observed through the pressure gauge at the orifice. When the grouting pressure suddenly increases, it is determined that the grout has filled the existing cracks and the second-stage cracking cracks.

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