Microcrack-based low-permeability sandstone uranium mine reservoir matrix permeability improving method

Abstract

The invention belongs to the field of uranium mine well drilling and completion mining, and particularly relates to a low-permeability sandstone uranium mine reservoir matrix permeability improving method based on microcracks, which comprises the following steps: acquiring a stratum stress field, hydrogeological conditions and mechanical property parameters of a sandstone uranium mine reservoir; calculating the micro-fracture initial pressure of a hydraulic fracture surface required to be reached by the fractured sandstone uranium mine reservoir, wherein the micro-fracture initial pressure is an upper bound value of a water pressure range; measuring a lower bound value of a water pressure range by adopting a test method; if the target sandstone uranium mine reservoir is under the geological condition containing confined water, low-pressure hydraulic pulse needs to be adopted for later-stage permeation enhancement construction, and pulse action parameters are calculated; and carrying out sandstone uranium mine reservoir permeation enhancement construction. According to the method, the permeability of the reservoir matrix is improved by forming the microcracks, new macroscopic cracks are not formed, damage to the well wall and the upper and lower water-resisting layers of the uranium mine reservoir is avoided, special drill holes do not need to be additionally constructed, construction can be conducted by directly using existing in-situ leaching drill holes of a mine, construction is simple, and the cost is low.

Description

Technical Field

[0001] The present invention belongs to the field of uranium ore drilling and completion mining, and in particular relates to a method for improving the matrix permeability of low-permeability sandstone uranium ore reservoirs based on microcracks. Background Technique

[0002] Natural uranium is an important raw material for the development of the nuclear industry and plays an important role in the fields of nuclear military industry, nuclear power, and civilian non-power nuclear technology. Sandstone uranium ore is the most important natural uranium resource in China. The uranium-containing solid minerals in sandstone-type uranium ore are widely distributed in the pores between sandstone mineral particles, but the grade can be as low as one in a million. At present, the main method for mining sandstone-type uranium ore is the in-situ leaching process. In this process, the leaching solution is first injected into the formation, and then the leaching solution enters the rock pores, converting the solid uranium minerals in the pores into ionic uranium dissolved in water. Then, the ionic uranium is pumped out of the formation with the leaching solution and further purified to obtain natural uranium. In the in-situ leaching process, the flow ability of the reservoir pore fluid has an important impact on in-situ leaching of uranium. However, more than 70% of sandstone uranium ore in China has low-permeability characteristics. And during the in-situ leaching of uranium, ion precipitation blocks the pores, which also makes the pores in the uranium ore reservoir blocked and shows low-permeability characteristics. The low permeability of the uranium ore reservoir will cause problems such as "difficult injection, difficult extraction, long leaching cycle, and low leaching rate" during the in-situ leaching of uranium, seriously affecting the production rate and resource recovery rate of uranium mines in China. Therefore, improving the matrix permeability of low-permeability sandstone uranium ore reservoirs is the key problem to break through the current technical bottleneck of in-situ leaching of uranium.

[0003] Traditional reservoir permeability characterizes the macroscopic permeability characteristics of the reservoir, which is the statistical average of the matrix permeability and fracture permeability in the reservoir. The in-situ leaching process of uranium depends on the leaching solution entering each tiny pore to leach the uranium-containing minerals. If there are macroscopic fractures in the reservoir, the macroscopic fractures will become the preferential seepage channels for the leaching solution, converging a large amount of the leaching solution and quickly passing through the reservoir, thus making the leaching process of uranium minerals worse or even ineffective. Therefore, for sandstone-type uranium ore reservoirs mined by the in-situ leaching process of uranium, it is necessary to improve the matrix permeability rather than the fracture permeability.

[0004] Since the formation fluid in the oil and gas reservoir is the ore body, the oil and gas reservoir needs macro cracks to collect the formation fluid to increase production capacity; the coal field needs macro cracks to cut the rock to transform the rock structure and optimize the surrounding rock stress. Therefore, the traditional reservoir permeability enhancement / rock structure transformation technology in the oil and gas and coal fields uses constant displacement fracturing, pulse fracturing, phase change fracturing, thermal shock fracturing, liquid-electric effect fracturing, perforation, water jet, high-energy gas fracturing, explosive blasting and other methods, which have the characteristics of high pressure, large displacement, and giant volume, forming a macro crack network in the reservoir; these methods are conducive to the formation of macro cracks / crack networks and improving the permeability of cracks; however, since the traditional reservoir permeability enhancement / rock structure transformation technology in the oil and gas and coal fields will produce macro cracks, it is not conducive to in-situ leaching of uranium, so it is difficult to apply to the permeability enhancement of low permeability sandstone uranium reservoirs. Therefore, how to improve the matrix permeability of the reservoir without generating macro cracks is a technical problem that needs to be solved in the current in-situ leaching of uranium.

[0005] In order to improve the permeability of sandstone uranium reservoirs, there are currently a uranium mine completion directional pipe string and directional method using hydraulic sandblasting (CN117703333A) and a sandstone uranium mining method (CN115788439A). These two methods first use hydraulic sandblasting or perforation treatment to eventually form macroscopic hydraulic fractures that expand in a directional manner, which is not conducive to in-situ leaching of uranium and cannot solve the problem of improving matrix permeability. 2 Fracturing-In-Situ Leaching and CO 2 The integrated storage method (CN202211183137.6) and a safe and efficient mining method for improving the permeability of low-permeability sandstone-type uranium ore layers (CN201910673538.1) are developed using supercritical CO 2 Fracturing, liquid CO 2 Phase change cracking and other methods act on uranium reservoirs. Due to the maintenance of CO 2 Supercritical state requires high pressure, CO 2 The phase change high pressure is as high as 270MPa, while the uranium deposit is shallow and has a low stress level, which inevitably forms macro cracks, making it unfavorable for in situ leaching of uranium. There is an existing in situ leaching method that uses blasting to increase infiltration (CN202011519240.4), in which explosives are placed in horizontal wells for blasting to increase infiltration. This method still relies on high pressure to form a crack network, but it increases the density of the crack network, and it is still difficult to solve the problem of improving the permeability of the matrix of the in situ leaching uranium reservoir. There is an existing rock formation variable frequency pulse fracture network fracturing method and equipment (CN202211261651.7) in the embodiment. It mentions a method of controlling the pulse time and the borehole spacing to avoid the destruction of the upper and lower impermeable layers of the uranium reservoir, but this method forms a crack network that runs through the boreholes, which is difficult to adapt to in situ leaching.

[0006] The ideas of the above technologies are all aimed at forming macroscopic cracks to achieve the purpose of converging formation fluids or cutting rock masses. The same technical indicators require that the pressure exceed the fracture pressure of the rock mass to achieve the ultimate goal of forming cracks. These solutions achieve enhanced permeability in uranium ore reservoirs by forming cracks / crack networks, belonging to the category of permeability enhancement through cracks, and cannot meet the special requirements for improving the matrix permeability of low-permeability sandstone-type uranium ore reservoirs suitable for in-situ leaching uranium technology. In view of the deficiencies of the existing technologies, the present invention proposes a method for improving the matrix permeability of low-permeability sandstone uranium ore reservoirs by forming microcracks in the reservoir. Summary of the Invention

[0007] The purpose of the present invention is to solve the shortcomings existing in the prior art, and to propose a method for improving the matrix permeability of low-permeability sandstone uranium ore reservoirs based on microcracks.

[0008] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0009] A method for improving the matrix permeability of low-permeability sandstone uranium ore reservoirs based on microcracks, comprising the following steps:

[0010] Step 1: Obtain the formation stress field parameters, hydrogeological condition parameters, and rock physical and mechanical property parameters of the target sandstone uranium ore reservoir;

[0011] Step 2: According to the parameters in Step 1, calculate the micro-fracture initiation pressure of the hydraulic fracture surface required for fracturing the sandstone uranium ore reservoir. This initiation pressure is the upper bound value p of the water pressure range max2 ;

[0012] Step 3: Use the experimental method to determine the lower bound value p of the water pressure range min1 , then p max2 - p min1 is the water pressure range used to form microcracks during the later permeability enhancement construction;

[0013] Step 4: If the target sandstone uranium ore reservoir is a geological condition containing confined water, then during the later permeability enhancement construction, it is necessary to cooperate with the hydraulic fracturing action form of low-pressure hydraulic pulses. According to p max2 , p min1 and the parameters in Step 1, calculate the pulse action parameters;

[0014] Step 5: Implement the permeability enhancement construction of the sandstone uranium ore reservoir; under the conditions of a hydrophobic sandstone uranium ore reservoir, use the water pressure range as the construction requirement; under the conditions of a water-bearing sandstone uranium ore reservoir, use the water pressure range and the pulse action parameters as the construction requirement.

[0015] As a further preferred solution, in Step 1, the formation stress field parameters include the maximum principal stress σ 1 , the intermediate principal stress σ 2, the minimum principal stress σ 3 ;

[0016] The hydrogeological condition parameters include the buried depth h of the uranium-bearing aquifer sandstone 1 and the initial pore water pressure p 0 ;

[0017] The rock physical and mechanical property parameters include the tensile strength T 0 and the average particle size r of the sandstone 0 .

[0018] As a further preferred solution, in step two, according to the parameters in step one, calculate the micro-fracture initiation pressure p of the hydraulic fracture surface max2 , and the formula is:

[0019]

[0020] As a further preferred solution, in step three, for the determination of the lower bound value p of the water pressure range min1 , the test method is used:

[0021] Take the core of the target sandstone uranium ore reservoir, and apply the σ 1 , σ 2 , σ 3 of the formation stress field parameters and the initial pore water pressure p 0 as boundary conditions on the core, then drill a hole in the core, and gradually load and increase the water pressure into the hole through the fracturing fluid containing the micro-crack fluorescent tracer. Set multiple loading water pressure values according to experience and conduct the loading respectively. The loading time for each time is 5 - 10 s. After each loading ends, observe the surrounding rock of the inner wall of the hole. When there is no hydraulic fracture surface generated and micro-cracks marked by the fluorescent agent appear under ultraviolet light irradiation, the water pressure value of this loading is the lower bound value p of the water pressure range determined by the test min1 .

[0022] As a further preferred solution, in step four, the pulse action parameters are calculated as follows:

[0023] (1) Calculate the pore water pressure gradient k for forming macro-fractures max ;

[0024]

[0025] (2) Calculate the critical pore water pressure gradient k for forming micro-cracks min ;

[0026]

[0027] Wherein, a and b are correction coefficients, used to compensate for the errors caused by the differences between the on-site complex conditions and the theoretical assumption conditions. Usually, a = 1 and b = 1. Empirical adjustments can be further made based on experiments or construction effects to improve the accuracy of the theoretical values;

[0028] The pore pressure gradient range k during the action of low-pressure hydraulic pulse is k min ~k max , and the range of the pore pressure gradient is specifically reflected in the frequency f of the pulse action, the peak pulse pressure p peak , and the valley pulse pressure p vall parameters. Among them, during the construction process, ensuring the range of p peak is p min1 ~p max2 ;

[0029] During the actual construction process, the peak pulse pressure p peak , and the valley pulse pressure p vall are variable values affected by the discreteness of rock properties and the factor of increasing fluid resistance with the increase of the extension distance. During the construction process, they are taken in real time according to the monitored pulse water pressure fluctuation curve;

[0030] During the actual construction process, in order to form microcracks and inhibit the generation of macroscopic cracks, it is necessary to control the output pressure p pump of the enhanced water pressure source to adjust the water pressure range in the enhanced permeability section of the reservoir, that is, the peak pulse pressure p peak ~the valley pulse pressure p vall ; At the same time, it is also necessary to adjust the pore pressure gradient range k in the surrounding rock; the adjustment method of the pore pressure gradient range k is to control the output frequency f of the enhanced water pressure source;

[0031] The relationship between the output pressure p pump of the enhanced water pressure source and the bottom-hole water pressure p bore is:

[0032] p bore = p pump +ρgh 1

[0033] In the above formula, ρ is the density of the leaching solution, and g is the acceleration of gravity;

[0034] The detection method of the peak pulse pressure p peak and the valley pulse pressure p vall is: Arrange a bottom-hole water pressure sensor in the enhanced permeability section of the reservoir in the borehole to detect the bottom-hole water pressure, and the bottom-hole water pressure is transmitted through the bottom-hole water pressure signal transmission line to the bottom-hole water pressure signal acquisition device to collect the bottom-hole water pressure p bore , and compare all the bottom-hole water pressures p collected within a certain time interval t gap collected within;bore Among them, the maximum value is the peak pulse pressure p peak Among them, the minimum value is the valley pressure p vall ;

[0035] In the experimental method, a cylindrical core with a length of L is loaded into the column leaching test device, and the initial pore pressure is applied. A sufficiently strong pressure fluctuation is generated at one end of the column leaching device, and then the interval time t when the pressure fluctuation arrives is synchronously detected at the other end of the column leaching device 0 The pulse wave propagation speed v = L / t 0 ; The frequency f is based on the time period t gap The peak pulse pressure p monitored within peak The peak pulse pressure p and the valley pulse pressure p vall are adjusted in real time to determine that these three parameters should satisfy the following relationship, so as to ensure that k is within the range "k min ~k max ". The pulse frequency parameter f under different pulse pressures is determined as follows:

[0036]

[0037] The enhanced water injection pressure source adjusts the output frequency of the pulse wave according to the calculated pulse frequency parameter f, and the time interval t gap is set manually and is related to the pulse frequency adjustment range of the equipment used by the enhanced water injection pressure source. The principle followed in setting is that the time interval t gap is greater than the 2 / f value calculated when the frequency f takes the minimum value

[0038] As a further preferred solution, in step five, the enhanced permeability construction process is as follows: First, use a borehole television to determine the fracture distribution and specific location of the uranium-bearing sandstone formation in the borehole, and then use a borehole packer corresponding to the borehole diameter for sealing; at the sealing position, for the case where no significant primary fractures are found in the borehole, seal the hole at the upper and lower water-resistant layers of the uranium ore reservoir. First, move the sealing device to the interface between the upper water-resistant layer and the sandstone uranium ore reservoir, and then the sealing pressure is provided by the sealing pressure source and transmitted to the packer through the sealing pressure transmission pipeline, so that the sealing device acts according to its design principle to achieve sealing

[0039] As a further preferred solution, in the enhanced permeability construction of the sandstone uranium ore reservoir containing confined water:

[0040] (1) Use the form of low-pressure constant displacement fracturing to act on the reservoir for enhanced permeability. The pressure range of the low-pressure water pressure source is between p min1 ~p max2 ;

[0041] (2) The reservoir permeability enhancement is achieved by the form of low-pressure hydraulic pulse. The water pressure source for permeability enhancement adopts the form of hydraulic pulse, and the water pressure range needs to be controlled between p min1 ~p max2 . The pulse action parameters are calculated according to the calculation method of pulse action parameters based on the monitored bottom-hole water pressure p bore and are adjusted in real time according to the calculated frequency f.

[0042] As a further preferred solution, when it is necessary to use the leaching solution as the permeability enhancement medium and carry out permeability enhancement construction through the injection well, if the flow rate of the leaching solution pumped and injected due to permeability enhancement in the injection well is less than or equal to the flow rate of the leaching solution extracted by the surrounding in-situ leaching pumping wells supporting the injection well, and the leaching solution injected into the injection well can be completely extracted by the surrounding pumping wells to ensure that the injected leaching solution does not diffuse out of the "injection well - pumping well" coverage area along the formation, the leaching solution can be used as the permeability enhancement medium, and the permeability enhancement - in-situ leaching combined construction can be carried out through the injection well. Then, step four and step five are carried out synchronously to form a permeability enhancement - in-situ leaching combined construction process. At the same time, the pumping wells around the injection well are responsible for extracting the formation fluid, and the pumping speed of the pumping wells is greater than or equal to the injection speed of the injection well;

[0043] Under this condition, the leaching solution physically enhances the permeability of the reservoir and chemically leaches the uranium-bearing minerals in the reservoir, that is, the permeability enhancement - in-situ leaching combined construction.

[0044] As a further preferred solution, the determination of the permeability enhancement time: The pumping and injection time is determined according to the actual pumping volume of the formation fluid and the uranium concentration of the leaching solution; When the uranium concentration of the leaching solution increases significantly, or when the uranium concentration of the leaching solution reaches the normal level designed for the mine, it can be stopped.

[0045] As a further preferred solution, for the formation with primary fractures in the borehole, the sealing position should avoid the position of the primary fractures, and multiple sealing and permeability enhancement operations should be carried out.

[0046] Beneficial effects:

[0047] The present invention improves the matrix permeability of the reservoir by forming microcracks, and no new macroscopic fractures will be formed in the reservoir, so it will not cause damage to the wellbore, etc., and will not cause damage to the upper and lower water - resistant layers of the uranium ore reservoir; It is not necessary to construct special boreholes additionally, and the existing in-situ leaching boreholes in the mine can be directly used for construction, and the construction is simple and the cost is low. Using the leaching solution as the construction medium for reservoir structure transformation is convenient for operation. Using the uranium ore reservoir permeability enhancement construction equipment of the present invention can be combined with in-situ leaching equipment, thus not delaying in-situ leaching production. Description of the drawings

[0048] Figure 1 It is a schematic diagram of the permeability enhancement construction for a hydrophobic low - permeability sandstone uranium ore reservoir;

[0049] Figure 2 Schematic diagram of permeability enhancement construction for water-bearing low-permeability sandstone uranium ore reservoir

[0050] Figure 3 Schematic diagram of permeability enhancement construction for avoiding wellbore cracks by multiple sealing of sandstone uranium ore reservoir

[0051] Figure 4 Flow chart for calculating frequency f

[0052] In the figure: 1 - sandstone uranium ore reservoir, 2 - water - isolating layer, 3 - reservoir permeability enhancement section, 4 - sealing device, 5 - borehole pipeline fixator, 6 - sealing pressure transmission pipeline, 7 - permeability - enhancing water pressure transmission pipeline, 8 - permeability - enhancing water pressure source, 9 - sealing pressure source, 10 - cracks on the inner wall of the borehole, 11 - leaching solution injection pump station, 12 - control valve of leaching solution conveying pipeline, 13 - control valve of permeability - enhancing water pressure transmission pipeline, 14 - control valve of sealing pressure transmission pipeline, 15 - leaching solution conveying pipeline, 16 - bottom - hole water pressure signal sensor, 17 - bottom - hole water pressure signal acquisition device, 18 - bottom - hole water pressure signal transmission line Specific implementation mode

[0053] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments

[0054] Embodiment 1

[0055] The method for improving the matrix permeability by forming micro - cracks in the hydrophobic low - permeability sandstone uranium ore reservoir through low - pressure constant - displacement fracturing is based on a method for improving the matrix permeability of low - permeability sandstone uranium ore reservoir based on micro - cracks

[0056] Formation water in some sandstone uranium ore reservoirs is drained by preferential seepage channels such as faults and large fractures. This type of uranium ore reservoir has low - permeability characteristics. Therefore, before in - situ leaching of uranium, it is necessary to improve the matrix permeability, carry out permeability - enhancement construction, and then supplement sufficient leaching solution to leach out the uranium - containing solid minerals in the pores. The initial pore - pressure gradient in this type of drained sandstone uranium ore reservoir is 0, and the conventional constant - displacement fracturing method can be directly used to easily form a pore - pressure gradient

[0057] The compressibility of liquid media is more than 2500 times that of gaseous media. Under the same conditions, the pressure propagation distance based on liquid conduction is longer, which is conducive to the long - distance extension of micro - cracks. By controlling the pressure range of constant - displacement fracturing, micro - cracks can be formed without forming macroscopic fractures, achieving the purpose of improving matrix permeability

[0058] The specific operation of carrying out low - pressure constant - displacement fracturing on the hydrophobic low - permeability sandstone - type uranium ore reservoir to form micro - cracks and achieve the improvement of the matrix permeability of the low - permeability sandstone uranium ore reservoir is as follows

[0059] 1. Obtain the formation stress field parameters, hydrogeological condition parameters, and rock physical and mechanical property parameters of the target sandstone uranium reservoir; the formation stress field parameters include the maximum principal stress σ 1 , the intermediate principal stress σ 2 , and the minimum principal stress σ 3 ;

[0060] The hydrogeological condition parameters include the buried depth h 1 of the uranium-bearing aquifer sandstone and the initial pore water pressure p 0 ;

[0061] The rock physical and mechanical property parameters include the tensile strength T 0 and the average particle size r 0 of the sandstone;

[0062] 2. Calculate the range of increased seepage water pressure;

[0063] The upper bound of the water pressure range is the critical water pressure at which the hydraulic fracture surface begins to form. In this regard, existing research has shown that the critical condition for the formation of the hydraulic fracture surface is not that the water pressure reaches the conventional fracture pressure, but that the water pressure reaches the micro-fracture initiation pressure. For different stages of the enhanced permeability construction, the micro-fracture initiation pressure for the formation of the hydraulic fracture surface from a circular borehole is calculated as follows;

[0064] (1) For the start and initial stage of the construction, the micro-fracture initiation pressure p max1 of the hydraulic fracture surface is:

[0065] p max1 = T 0 + 3σ 3 - σ 1 + p 0

[0066] (2) For the later stage of the construction, the permeability of the borehole surrounding rock increases, and the micro-fracture initiation pressure p max2 of the hydraulic fracture surface is:

[0067]

[0068] For safety, generally take p max2 as the upper bound value of the water pressure range.

[0069] For the lower bound value of the water pressure range, due to the complex composition of rock mineral particles and the large discreteness of the strength parameters of different component minerals, the experimental method is used to determine the lower bound value p min1 of the water pressure range. Then p max2 - p min1 is the water pressure range used to form micro-cracks during the later enhanced permeability construction. For the lower bound value p min1The measurement process by the test method is as follows:

[0070] Take the core of the target sandstone uranium ore reservoir, and in the laboratory, apply the σ 1 , σ 2 , σ 3 and the initial pore water pressure p 0 as boundary conditions on the core. The laboratory equipment is a true triaxial loading test frame with the ability to load pore water pressure, such as the GCTS true triaxial test system. Then, drill a hole in the core, and gradually load and increase the water pressure into the hole through the fracturing fluid containing the microcrack fluorescent tracer. Set multiple loading water pressure values according to experience and conduct the loading separately. Each loading time is 5 - 10 s. After each loading ends, observe the surrounding rock of the borehole wall. When there is no hydraulic fracture surface generated and microcracks marked by the fluorescent agent appear under ultraviolet light irradiation, the water pressure value of this loading is the lower bound value p min1 ;

[0071] The microcrack fluorescent tracer consists of a solute and a solution. The composition of the solute is a substance with a particle size less than 3 μm that can emit fluorescence under ultraviolet light irradiation. For the microcracks in sandstone, this organic optoelectronic material can be a stilbene derivative, a chloride ion fluorescent complex, etc.; the composition of the solution can be water or the configured leaching solution in in-situ leaching of uranium. Marking microcracks with organic optoelectronic materials is a relatively advanced and mature microcrack tracing technology in the field of microcrack propagation research. Generally speaking, the calculated low-pressure water pressure range is "p min1 ~p max2 ".

[0072] Three: Implement the permeability enhancement construction for the sandstone uranium ore reservoir.

[0073] As Figure 1 shown, in the sandstone uranium ore reservoir in the non-fractured section, the permeability enhancement construction process is as follows: First, use a borehole TV to determine the fracture distribution and the specific location of the uranium-bearing sandstone layer in the borehole, and then use a borehole packer corresponding to the borehole diameter for sealing the hole; the packer can be a commonly used packer based on the rubber expansion principle or a packer based on the mechanical expansion principle. The hole sealing effect of these packers and the passing through and connection methods of the corresponding pipelines are already relatively mature common technical equipment in the field of reservoir permeability enhancement.

[0074] At the hole sealing position, for the case where no significant primary fractures are found in the borehole, seal the hole at the upper and lower water isolation layer positions of the uranium ore reservoir ( Figure 1 ): First, move the hole sealing device 4 to the interface between the upper water isolation layer and the sandstone uranium ore reservoir, and then the hole sealing pressure is provided by the hole sealing pressure source 9 and conducted to the packer through the hole sealing pressure transmission pipeline 6, so that the hole sealing device 4 acts according to its design principle to achieve hole sealing.

[0075] The water used for enhancing permeability has no special requirements in essence, and plain water is fine. Its source generally comes from uranium mines. At the construction site, water supply is usually provided, which may be surface water, or water taken from a drilling well, or water supply achieved through transportation from other places.

[0076] IV: In-situ leaching uranium stage.

[0077] The leaching solution in the in-situ leaching uranium mine is liquid water containing ions, which is convenient to use and has low cost. The leaching solution is formed by formation water or other relatively clean water sources mixed with certain chemical components such as acids or alkalis. The steps of in-situ leaching uranium in the present invention are prior art. The present invention only emphasizes that before the water replenishment step, microcrack permeability enhancement should be carried out to address the problem of poor reservoir permeability.

[0078] Example II

[0079] The method for enhancing the matrix permeability of a water-bearing low-permeability sandstone uranium ore reservoir by using low-pressure hydraulic pulses is based on a method for enhancing the matrix permeability of a low-permeability sandstone uranium ore reservoir based on microcracks.

[0080] Different from Example I, constant displacement fracturing can also be regarded as a special case where the pulse frequency is 0. The key of the invention is the pore pressure gradient. In Example I, because it is a hydrophobic reservoir and the initial pore water pressure is 0, a pore water pressure gradient can be directly formed by constant displacement pumping. In Example I, only the water pressure range needs to be controlled. In Example II, since it is a water-bearing reservoir with an initial pore pressure inside, pulses are therefore selected to form an oscillating wave with fluctuating pressure values. The slope of these pulse waves is the pore pressure gradient; the key difference between the two examples lies here. Correspondingly, under different action modes, the parameters to be controlled are also different. For constant displacement pumping, the water pressure range is looked at, and for pulse pumping, not only the range but also the frequency factor is considered.

[0081] There is confined water in most sandstone uranium ore reservoirs, and the initial pore pressure gradient in the reservoir is greater than 0. It is difficult to form a pore pressure gradient by conventional constant displacement pumping; for this situation, the form of pulse action is adopted, which is more likely to form a local pore water pressure gradient. In order to only form microcracks and not form macroscopic hydraulic fractures, the pore water pressure gradient range needs to be controlled between higher than the critical pore water pressure gradient for forming microcracks and lower than the critical pore water pressure gradient for forming macroscopic fractures. This range is lower than the conventional high-pressure pulse fracturing / cracking range, so it belongs to low-pressure permeability enhancement. Since the present invention controls the water pressure range and will not form macroscopic fractures to damage the wellbore, construction can be carried out using the existing boreholes for in-situ leaching uranium, without the need for additional construction boreholes or only a small number of additional boreholes need to be supplemented according to specific working conditions. Generally speaking, the specific action form for forming microcracks in a low-permeability sandstone uranium ore reservoir is low-pressure hydraulic pulses, so as to achieve the purpose of forming microcracks and enhancing the matrix permeability of the reservoir.

[0082] Example 2 further determines the water pressure gradient range on the basis of the water pressure range, so as to further determine the pulse parameters. Example 2 is an additional step generated by the initial pore pressure and the characteristics of the pulse action, such as Figure 4 as shown.

[0083] According to p max2 、p min1 and the parameters in Step 1, calculate the pulse action parameters;

[0084] (1) Calculate the pore water pressure gradient k max ;

[0085]

[0086] (2) Calculate the critical pore water pressure gradient k min ;

[0087]

[0088] In the formula, a and b are correction coefficients used to compensate for the errors caused by the differences between the on-site complex conditions and the theoretical assumption conditions. Usually, a = 1 and b = 1. Empirical adjustments can be further made based on tests or construction effects (mainly to deal with the situation where the on-site conditions have large discreteness while the theoretical assumptions are single. Without adding coefficients, the on-site conditions cannot be completely consistent with the theory, which is likely to weaken the scope of application of the theory) to improve the accuracy of the theoretical value;

[0089] The pore pressure gradient range k during the low-pressure hydraulic pulse action is k min ~k max , and the range of the pore pressure gradient is specifically reflected in the frequency f of the pulse action, the peak pulse pressure p peak , and the valley pulse pressure p vall parameters. Among them, during the construction process, the range of p peak is p min1 ~p max2 ;

[0090] During the actual construction process, the peak pulse pressure p peak and the valley pulse pressure p vall are affected by the discreteness of rock properties and the factor that the fluid resistance increases with the increase of the expansion distance, and are variable values. During the construction process, they are taken in real time according to the monitored pulse water pressure fluctuation curve;

[0091] p peak and p vall are both obtained by monitoring, but the range of p peak is p min1 ~p max2 , p vallThere is no such requirement.

[0092] In the second embodiment, the pore pressure gradient requirement for only forming microcracks without forming macroscopic hydraulic fractures cannot be ensured to be automatically satisfied. Therefore, it is necessary to not only control the water pressure range but also adjust the pulse frequency in real time according to the feedback pressure.

[0093] Specifically, during the actual construction process, in order to form microcracks and suppress the generation of macroscopic fractures, it is necessary to control the output pressure p pump of the water pressure source for enhanced seepage to adjust the water pressure range in the reservoir enhanced seepage section, that is, the peak pulse pressure p peak ~the valley pulse pressure p vall ; at the same time, it is also necessary to adjust the pore pressure gradient range k in the surrounding rock; the adjustment method of the pore pressure gradient range k is to control the output frequency f of the water pressure source for enhanced seepage;

[0094] The relationship between the output pressure p pump of the water pressure source for enhanced seepage and the bottom hole water pressure p bore is:

[0095] p bore = p pump +ρgh 1

[0096] In the above formula, ρ is the density of the leaching solution, and the method for measuring the solution density is an existing technology in the industry. g is the acceleration due to gravity;

[0097] The detection method of the peak pulse pressure p peak and the valley pulse pressure p vall is: A bottom hole water pressure sensor 16 is arranged in the reservoir enhanced seepage section 3 of the borehole to detect the bottom hole water pressure, and the bottom hole water pressure is transmitted through the bottom hole water pressure signal transmission line 18 to the bottom hole water pressure signal acquisition device 17 to obtain the bottom hole water pressure p bore , and all the bottom hole water pressures p gap collected within a certain time interval t bore are compared. The maximum value among them is the peak pulse pressure p peak , and the minimum value among them is the pressure valley value p vall ;

[0098] In the experimental method, a cylindrical core with a length of L is loaded in the column leaching test device, an initial pore pressure is applied, a sufficiently strong pressure fluctuation is generated at one end of the column leaching device, and then the interval time t 0 when the pressure fluctuation arrives is synchronously detected at the other end of the column leaching device. The pulse wave propagation speed v = L / t 0 , and the frequency f is based on the peak pulse pressure p gap monitored within the time period t peak , the valley pulse pressure p vallAdjust in real time to determine that these three parameters should satisfy the following relationship to ensure that k is within the range "k min ~k max ". Determine the pulse frequency parameter f at different pulse pressures as follows:

[0099] According to Figure 4 In the steps, the calculation process of the frequency f is as follows: During construction, the water pressure data is collected in real time through the bottom-hole water pressure signal acquisition device 17. Every time the time interval t gap The collected bottom-hole water pressure data set [p bore is obtained and used as input data to participate in Figure 4 In the calculation of the frequency f, the bottom-hole water pressure data set [p bore is collected in real time. Every time the time interval t gap Input, so during the construction process, the bottom-hole water pressure data set [p bore is continuously input and updated. After receiving the start calculation instruction, manually input the initial value of the pulse frequency f, the pulse wave propagation speed v, the initial value of the gradient k, the upper limit value k of the pore water pressure gradient max And the lower limit value k of the pore water pressure gradient min . Then take the maximum water pressure value in the data set [p bore to obtain the pulse pressure peak p peak , which can be obtained using the maximum value function in the calculation, that is, p peak =max[p bore ; Take the minimum water pressure value in the data set [p bore to obtain the pulse pressure valley value p vall , which can be obtained using the minimum value function in the calculation, that is, p peak =min[p bore . On this basis, refresh the assignment of the frequency f and the pulse wave propagation speed v, that is, f = f, v = v. On this basis, use the following function to calculate the gradient k:

[0100]

[0101] Then compare the calculated gradient k with the upper limit value k of the pore water pressure gradient max . If k < k max Does not hold, then execute the calculation f = f - 1, and then repeat the previous calculation and comparison steps of the gradient k; If if k < k max Holds, then compare the calculated gradient k with the upper limit value k of the pore water pressure gradient min ; If k > k min Does not hold, then execute the calculation f = f + 1, and then repeat the previous calculation and comparison steps of k; If k > k minIf the calculated f value is established, the calculated f value is output, which is the calculated pulse frequency parameter f. Outputting the calculated f value completes a calculation process; after completing a calculation process, if an end instruction is received, the calculation ends; if no end instruction is received, the calculation ends after waiting for the time interval t gap Then from the new data set [p bore ] to calculate the pulse pressure peak p peak , pulse pressure valley value p vall , and continue to calculate the pulse frequency parameter f according to the above steps to achieve continuous output of the pulse frequency parameter f.

[0102] The permeation water pressure source 8 adjusts the output frequency of the pulse wave according to the calculated pulse frequency parameter f. Specifically, the time interval t gap It is set manually and is related to the pulse frequency adjustment range of the device used by the infiltration water pressure source 8. The principle followed by the setting is the time interval t gap The time interval should be greater than the 2 / f value calculated when the frequency f takes the minimum value. For example, if the minimum pumping frequency is 1Hz, the time interval should be greater than 2s. Specifically, the calculation of the frequency f can be followed Figure 4 In the flowchart, the initial pulse frequency input is the minimum value of the adjustable pulse frequency, and the initial gradient value is set to 0.

[0103] In summary, under the conditions of water-bearing sandstone uranium reservoirs, the water pressure range and pulse action parameters are used as the requirements for permeability enhancement construction:

[0104] (1) Low-pressure constant-displacement fracturing is used to increase reservoir permeability. The pressure range of the low-pressure water pressure source 8 is p min1 ~p max2 between.

[0105] (2) The reservoir is permeated by low-pressure hydraulic pulses. The permeation water pressure source 8 is in the form of hydraulic pulses, and the water pressure range needs to be controlled within p min1 ~p max2 The pulse action parameters are based on the monitored bottom water pressure p bore The frequency f is calculated according to the pulse action parameter calculation method and controlled in real time.

[0106] Embodiment 3

[0107] When the leaching liquid is used as the permeability-increasing medium and the permeability-increasing construction is carried out through the injection well, if the flow rate of the leaching liquid pumped in the injection well due to the permeability-increasing is less than or equal to the flow rate of the leaching liquid extracted from the in-situ leaching wells around the injection well, step 4 and step 5 are carried out simultaneously to form a permeability-in-situ leaching combined construction process.

[0108] Specifically, under the condition that the leaching solution injected into the injection well can be completely extracted by the pumping wells around the injection well, ensuring that the injected leaching solution does not diffuse along the formation outside the "injection well - pumping well" coverage area, the leaching solution can be used as an osmotic medium enhancer to carry out combined osmotic enhancement - in - situ leaching construction through the injection well. At the same time, the pumping wells around the injection well are responsible for extracting formation fluids, and the pumping rate of the pumping wells is greater than or equal to the injection rate of the injection well;

[0109] Under this condition, the leaching solution physically enhances the permeability of the reservoir and chemically leaches the uranium - containing minerals in the reservoir, that is, combined osmotic enhancement - in - situ leaching construction.

[0110] When the condition that the injected leaching solution does not diffuse along the formation outside the "injection well - pumping well" coverage area cannot be met, it is necessary to first carry out osmotic enhancement construction according to the construction requirements, and then carry out in - situ leaching construction according to the original in - situ leaching construction parameters; however, after integrating the osmotic enhancement equipment and the in - situ leaching equipment by using the Figure 2 shown combined osmotic enhancement - in - situ leaching construction method, only by switching the valves can different - purpose construction be carried out, without the need to frequently replace the equipment.

[0111] Specifically, in the case of low - pressure hydraulic osmotic enhancement on one side and in - situ leaching construction on the other side, if the acid - method or alkali - method in - situ leaching process is used for uranium extraction, the leaching solution can be directly injected into the sandstone uranium ore reservoir 1 through the low - pressure water pressure transmission pipeline 7 and the low - pressure water pressure source 8.

[0112] Specifically, the osmotic enhancement construction and the injection construction should be adjusted at intervals. When carrying out osmotic enhancement construction, close the control valve 12 of the leaching solution delivery pipeline, open the control valve 13 of the osmotic enhancement water pressure transmission pipeline and the control valve 14 of the hole - sealing pressure transmission pipeline, and carry out osmotic enhancement construction; when carrying out in - situ leaching construction, close the control valve 13 of the osmotic enhancement water pressure transmission pipeline, open the control valve 12 of the leaching solution delivery pipeline and the control valve 14 of the hole - sealing pressure transmission pipeline, and carry out in - situ leaching construction.

[0113] Specifically, in the case of low - pressure hydraulic osmotic enhancement on one side and in - situ leaching construction on the other side, if the " 2 CO 2 +O Figure 2 in - situ leaching process" is used for uranium extraction, only one additional pipeline needs to be added in the injection borehole for injecting the leaching solution into the sandstone uranium ore reservoir 1 ( ); the leaching solution is provided by the leaching solution injection pumping station 11 and enters the sandstone uranium ore reservoir 1 through the leaching solution delivery pipeline 15 to achieve in - situ leaching construction. Specifically, the osmotic enhancement construction and the injection construction should be carried out at intervals, that is, when carrying out osmotic enhancement construction, close the control valve 12 of the leaching solution delivery pipeline, open the control valve 13 of the osmotic enhancement water pressure transmission pipeline and the control valve 14 of the hole - sealing pressure transmission pipeline, and carry out osmotic enhancement construction; when carrying out in - situ leaching construction, close the control valve 13 of the osmotic enhancement water pressure transmission pipeline, open the control valve 12 of the leaching solution delivery pipeline and the control valve 14 of the hole - sealing pressure transmission pipeline, and carry out in - situ leaching construction.

[0114] In the first to third embodiments of the present invention, the determination of the time for permeability enhancement:

[0115] 1. Chloride ions can be added to water, and then the chloride ion concentration can be monitored in adjacent boreholes to plot the chloride ion penetration curve, and the growth of the permeability coefficient of the reservoir can be evaluated based on the time when the chloride ion concentration increases. Both chloride ion concentration monitoring and chloride ion penetration curve plotting are relatively mature existing technologies.

[0116] 2. At the same time, the pumping time can also be determined according to the actual formation fluid pumping volume and the uranium concentration in the leachate: stop when the uranium concentration in the leachate increases significantly or when the uranium concentration in the leachate reaches the normal level designed for the mine.

[0117] 3. Under the condition of need, low-pressure hydraulic permeability enhancement can be carried out on the reservoir multiple times.

[0118] In the first to third embodiments of the present invention, regarding the situation where there are many primary fractures in the reservoir permeability enhancement section, as Figure 3 shown, for the formation with primary fractures in the borehole, the sealing position should avoid the position of the primary fractures, and multiple sealing and permeability enhancement operations should be carried out to maximize the permeability of the reservoir matrix and avoid large "leaching dead zones" during the leaching stage due to poor permeability enhancement effect around the fractures. Specifically, first use one sealing device 4 to seal the lower reservoir permeability enhancement section 3, then carry out permeability enhancement according to the above method, and then use two sealing devices 4 to seal the upper reservoir permeability enhancement section 3 and carry out permeability enhancement again. During the multiple permeability enhancement processes, the permeability enhancement water pressure conduction pipeline 7 changes positions correspondingly to conduct the permeability enhancement water pressure to the corresponding reservoir permeability enhancement section 3. During the multiple permeability enhancement processes, the sealing pressure conduction pipeline 6 changes positions correspondingly and increases the number of pipelines enough to conduct the sealing pressure to the corresponding sealing device 4. Then carry out permeability enhancement construction and determine the time and process arrangement of the permeability enhancement construction according to the construction requirements.

[0119] Since the present invention is pore permeability enhancement and no preferential seepage channels are formed in the formation, under the above-mentioned sealing method conditions, the fracturing fluid can only enter the unsealed section and primary fractures in the form of pore seepage, and the leakage mode of these fracturing fluids has little impact on the construction. This sealing method can operate independently or cooperate with the in-situ leaching uranium process.

[0120] It should be noted that it is also completely feasible to carry out permeability enhancement directly in the primary fracture section, but the later in-situ leaching uranium effect will be affected. Therefore, this embodiment only provides a construction condition for actively avoiding primary fractures.

[0121] In summary, the core idea of the present invention is as follows: stress disturbances are formed in the pores of rocks through pore water media, and then microcracks are formed in the rocks without forming macroscopic cracks / fissures. Here, the microcracks refer to cracks that occur locally between rock mineral grains and do not connect to form a macroscopic planar structure. The principle to achieve this goal is to form a pore water pressure gradient at the scale of mineral grains. The gradient pore pressure causes stress disturbances to the rock mineral grains, and the stress disturbances change the original stress state of the rock mineral grains. When the stress of the mineral grains exceeds the tensile or shear strength of the mineral grains, the mineral grains undergo local rupture to form microcracks. The method to achieve this goal is to control the pore water pressure gradient in the pore water medium to be higher than the critical pore water pressure gradient for forming microcracks and lower than the pore water pressure gradient for forming macroscopic cracks. Among them, the pore water pressure gradient is related to the local pore water pressure difference; more specifically, for the case where the fluid medium acts on the rock to achieve enhanced pore permeability, the pressure of the fluid medium is higher than the critical pressure for forming microcracks and lower than the critical pressure for forming macroscopic fissures, which is also the unique low-pressure feature of the present invention.

[0122] As mentioned above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A method for improving the matrix permeability of a low-permeability sandstone uranium reservoir based on microcracks, characterized in that: The following steps are involved: Step 1: Obtain the formation stress field parameters, hydrogeological condition parameters, and rock physical and mechanical property parameters of the target sandstone uranium reservoir; Step 2: Based on the parameters in step 1, calculate the micro-fracture starting pressure of the hydraulic fracture surface required for fracturing the sandstone uranium reservoir. The starting pressure is the upper limit of the water pressure range p max2 ; Step 3: Use the test method to determine the lower limit of the water pressure range p min1 , then p max2 -p min1 It is the water pressure range used to form micro cracks during the later permeability enhancement construction; Step 4: If the target sandstone uranium reservoir is a geological condition containing confined water, the hydraulic fracturing action of low-pressure hydraulic pulses needs to be used in the later stage of permeability enhancement construction. max2 、p min1 and the parameters in step 1, calculate and obtain the pulse action parameters; Step 5: Implement sandstone uranium reservoir permeability enhancement construction; under the conditions of hydrophobic sandstone uranium reservoir, the water pressure range is used as the construction requirement; under the conditions of water-bearing sandstone uranium reservoir, the water pressure range and pulse action parameters are used as the construction requirements.

2. The method for improving the matrix permeability of a low-permeability sandstone uranium reservoir based on microcracks according to claim 1, characterized in that: In step 1, the formation stress field parameters include maximum principal stress σ1, intermediate principal stress σ2, and minimum principal stress σ3; The hydrogeological condition parameters include the burial depth of the sandstone of the uranium-bearing aquifer h1 and the initial pore water pressure p0; The physical and mechanical properties of rock include tensile strength T0 and average sandstone particle size r0.

3. The method for improving the matrix permeability of a low-permeability sandstone uranium reservoir based on microcracks according to claim 2 is characterized in that: In step 2, the micro-fracture initiation pressure p of the hydraulic fracture surface is calculated based on the parameters in step 1. max2 , the formula is:

4. The method for improving the matrix permeability of a low-permeability sandstone uranium reservoir based on microcracks according to claim 2, characterized in that: In step 3, for the lower limit of the water pressure range p min1 The determination is carried out by experimental method: Take the core of the target sandstone uranium reservoir, and apply the formation stress field parameters σ1, σ2, σ3 and initial pore water pressure p0 as boundary conditions on the core in the laboratory. Then drill a hole in the core, and gradually load and increase the water pressure in the borehole through the fracturing fluid containing microcrack fluorescent tracer. According to experience, set multiple loading water pressure values, and load them separately. Each loading time is 5 to 10 seconds. After each loading, observe the surrounding rock on the inner wall of the borehole. When no hydraulic fracture surface is generated and microcracks marked by fluorescent agent appear under ultraviolet light, the water pressure value loaded this time is the lower limit value p of the water pressure range measured in the experiment. min1 .

5. The method for improving the matrix permeability of a low-permeability sandstone uranium reservoir based on microcracks according to claim 4, characterized in that: In step 4, the pulse action parameters are calculated as follows: (1) Calculation of the pore water pressure gradient k that forms the macroscopic cracks max ; (2) Calculation of the critical pore water pressure gradient k for the formation of microcracks min ; Where a and b are correction coefficients, which are used to compensate for the error caused by the difference between the complex conditions on site and the theoretical assumptions. Usually a=1 and b=1 are taken. On this basis, further empirical adjustments can be made according to the test or construction results to improve the accuracy of the theoretical value. The pore pressure gradient range k during low-pressure hydraulic pulse action is k min ~k max The range of pore pressure gradient is specifically reflected in the frequency f of pulse action and the peak value p of pulse pressure. peak , pulse pressure valley value p vall Parameters, among which, during construction, p peak The range is p min1 ~p max2 ; The peak value of pulse pressure p during actual construction process peak , pulse pressure valley value p vall Due to the influence of the discreteness of rock properties and the increase of fluid resistance with the extension distance, it is a variable value. During the construction process, the value is taken in real time according to the pulse water pressure fluctuation curve monitored. In the actual construction process, in order to form micro cracks and suppress the generation of macro cracks, it is necessary to control the output pressure p of the seepage water pressure source. pump To adjust the water pressure range in the reservoir permeability section, that is, the pulse pressure peak p peak ~Pulse pressure valley value p vall ; At the same time, the pore pressure gradient range k in the surrounding rock should be adjusted; the pore pressure gradient range k is adjusted by controlling the output frequency f of the seepage water pressure source; Output pressure p of the infiltration water pressure source pump and the bottom water pressure p bore The relationship is: p bore =p pump +ρgh1 In the above formula, ρ is the density of the leaching liquid, and g is the acceleration due to gravity; Pulse pressure peak p peak and pulse pressure valley value p vall The detection method is as follows: a bottom hole water pressure sensor is arranged in the reservoir permeability section of the borehole for detection, and the bottom hole water pressure is transmitted to the bottom hole water pressure signal acquisition device through the bottom hole water pressure signal transmission line to obtain the bottom hole water pressure p bore , comparing a certain time interval t gap All the bottom water pressures p collected in bore , where the maximum value is the pulse pressure peak p peak , the minimum value is the pressure valley value p vall ; In the test method, a cylindrical core with a length of L is loaded into the column immersion test device, and the initial pore pressure is applied to generate a sufficiently strong pressure fluctuation at one end of the column immersion device. Then, the interval time t0 of the pressure fluctuation arrival is synchronously detected at the other end of the column immersion device. The pulse wave propagation speed v = L / t0; the frequency f is based on the time period t gap The peak value of the pulse pressure p monitored inside peak , pulse pressure valley value p vall Real-time adjustment is performed to determine whether these three parameters should satisfy the following relationship, so as to ensure that k is within the range of "k min ~k max ", the pulse frequency parameter f under different pulse pressures is determined as follows: The infiltration water pressure source adjusts the output frequency of the pulse wave according to the calculated output pulse frequency parameter f, and the time interval t gap It is set manually and is related to the pulse frequency adjustment range of the equipment used for the infiltration water pressure source. The principle followed in setting is the time interval t gap Greater than the 2 / f value calculated when the frequency f takes its minimum value.

6. A method for improving the matrix permeability of a low-permeability sandstone uranium reservoir based on microcracks according to claim 1 or 5, characterized in that: In step five, the permeability enhancement construction process is as follows: first use the borehole television to determine the distribution of cracks in the uranium-containing sandstone layer in the borehole and the specific location of the rock layer, and then use the borehole sealer corresponding to the borehole diameter to seal the hole; at the sealing position, if no significant primary cracks are found in the borehole, seal the hole at the upper and lower impermeable layers of the uranium reservoir. First, move the sealing device to the interface between the impermeable layer and the sandstone uranium reservoir in the upper part, and then the sealing pressure is provided by the sealing pressure source, and transmitted to the sealer by the sealing pressure transmission pipeline, so that the sealing device acts according to its design principle to achieve sealing.

7. The method for improving the matrix permeability of a low-permeability sandstone uranium reservoir based on microcracks according to claim 6, characterized in that: In the permeability enhancement construction of sandstone uranium reservoirs containing pressurized water: (1) Low-pressure constant-displacement fracturing is used to increase reservoir permeability. The pressure range of the low-pressure water pressure source is p min1 ~p max2 between; (2) Low-pressure hydraulic pulses are used to increase the permeability of the reservoir. The permeability-increasing water pressure source is in the form of hydraulic pulses, and the water pressure range needs to be controlled within p min1 ~p max2 The pulse action parameters are based on the monitored bottom water pressure p bore The frequency f is calculated according to the pulse action parameter calculation method and controlled in real time.

8. The method for improving the matrix permeability of a low-permeability sandstone uranium reservoir based on microcracks according to claim 7, characterized in that: When it is necessary to use leaching liquid as a permeability-enhancing medium and to perform permeability-enhancing construction through injection wells, if the flow rate of leaching liquid pumped into the injection well due to permeability enhancement is less than or equal to the flow rate of leaching liquid extracted by the in-situ leaching pumping wells provided around the injection well, and the leaching liquid injected into the injection well is completely extracted by the pumping wells around the injection well, thereby ensuring that the injected leaching liquid does not diffuse along the formation to areas outside the coverage area of ​​the "injection well-pumping well", steps four and five are performed simultaneously to form a permeability-in-situ leaching combined construction process to chemically leach uranium-containing minerals in the reservoir.

9. The method for improving the matrix permeability of a low-permeability sandstone uranium reservoir based on microcracks according to claim 8, characterized in that: Determination of the time for increasing permeability: The pumping time is determined based on the actual amount of formation fluid pumped and the uranium concentration of the leachate; the pumping can be stopped when the uranium concentration of the leachate increases significantly or reaches the normal level designed for the mine.

10. The method for improving the matrix permeability of a low-permeability sandstone uranium reservoir based on microcracks according to claim 7, characterized in that: For formations containing native fractures in the borehole, the sealing location should avoid the location of the native fractures, and multiple sealing and permeability enhancement operations should be carried out.

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