Dynamic evaluation method for repeated reconstruction of shale gas fractured well

Abstract

The invention relates to the technical field of shale gas storage development and yield increase, in particular to a shale gas fractured well repeated transformation dynamic evaluation method which comprises the steps that a hydraulic pulse unblocking device is adopted to conduct repeated transformation on a well section, with repeated transformation potential, of a target shaft, and a pulse pressure curve of the hydraulic pulse unblocking device is collected in real time; and in response to the change of the pulse pressure curve waveform from the first waveform to the second waveform, determining that the repeated transformation of the shale gas fractured well is completed, otherwise, determining that the repeated transformation of the shale gas fractured well is not completed. According to the method, the repeated transformation completion degree can be dynamically evaluated in real time, so that the efficient, real-time and coherent repeated transformation process is achieved, shale gas resources are fully and repeatedly developed and utilized, the gas well productivity is excavated to a greater extent, and the resource recovery rate is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of shale gas storage development and production increase, and in particular to a dynamic evaluation method for repeated transformation of a shale gas fracturing well. Background Art

[0002] With the development of the global economy, energy demand continues to rise. As an important unconventional natural gas resource, the large-scale development of shale gas can significantly increase the natural gas production of a country or region, thereby reducing dependence on imported natural gas and other traditional fossil energy, effectively improving energy self-sufficiency, and ensuring the stability and security of energy supply.

[0003] The geological structure of shale gas reservoirs is complex, and initial fracturing and other mining measures often make it difficult to fully exploit the shale gas resources therein, and a considerable portion of the remaining reserves will remain in the formation. Through repeated transformation, the natural fracture network in the formation can be further connected, the gas leakage area can be expanded, and the remaining shale gas that was not effectively exploited can be produced, thereby improving the resource recovery rate of the entire shale gas well and achieving more effective utilization of shale gas resources. Since the original fracture failure in the shale gas mining process mainly includes blockage caused by chemical scaling and deposition, blockage caused by particle migration, etc., unblocking shale gas wells is an important part of repeated transformation.

[0004] The existing repeated transformation is difficult to achieve ideal results, mainly for two reasons. First, it is difficult to accurately grasp the selection of repeated transformation sections and the selection of repeated transformation timing, and the changes in engineering and geological conditions during the dynamic construction process of repeated transformation are not considered, resulting in the lag of engineering practice. Secondly, during the repeated transformation process, there is no real-time and quantitative evaluation of whether the repeated transformation of a certain section is completed. If the transformation time is insufficient, it is difficult to form effective cracks, and if the transformation time is too long, it may cause the wellbore to collapse and deform. Therefore, it is necessary to conduct a dynamic evaluation of repeated transformation and a real-time evaluation of the completion of each repeated transformation.

[0005] At present, the selection of repeated transformation sections is determined only according to the well logging curve and the previous fracturing construction curve, and the re-evaluation and transformation after the repeated transformation construction are not involved; the existing methods for unblocking repeated transformation wells include ordinary acid washing, hydraulic vibration method, electro-hydraulic pulse method, etc., but these methods have certain limitations, such as small cleaning range, poor unblocking effect, high difficulty in operation, high operating cost, and easy to cause environmental pollution. In addition, the existing technology mainly relies on pre-designed test plans or single flow changes to determine whether the repeated transformation process is completed, which has a certain lag. Summary of the invention

[0006] The purpose of the present invention is to provide a dynamic evaluation method for repeated transformation of shale gas fracturing wells, which can perform real-time dynamic evaluation on the completion of repeated transformation, so as to realize an efficient, real-time and coherent repeated transformation process, so that shale gas resources can be fully and repeatedly developed and utilized, and the gas well production capacity can be exploited to the maximum extent, and the resource recovery rate can be improved.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] The present invention provides a dynamic evaluation method for repeated transformation of a shale gas fracturing well, which comprises: using a hydraulic pulse unblocking device to repeatedly transform a well section with repeated transformation potential in a target wellbore, and collecting a pulse pressure curve of the hydraulic pulse unblocking device in real time; in response to a change in the waveform of the pulse pressure curve from a first waveform to a second waveform, determining that the repeated transformation of the shale gas fracturing well is completed, otherwise determining that the repeated transformation of the shale gas fracturing well is not completed.

[0009] Furthermore, the first waveform is an irregular sine wave, and the second waveform is a regular sine wave.

[0010] Furthermore, the method for determining the waveform of the pulse pressure curve is as follows: obtaining three peak values ​​P1, P2, and P3 near the end of the pulse pressure curve and time points t1, t2, and t3 corresponding to the three peak values, respectively; in response to P1=P2=P3, and t3-t2=t2-t1, determining that the waveform of the pulse pressure curve is the second waveform, i.e., a regular sine wave; otherwise, determining that the waveform of the pulse pressure curve is the first waveform, i.e., an irregular sine wave.

[0011] Furthermore, based on the early well logging curves and fracturing construction curves of the target wellbore, the well sections with the potential for repeated transformation of the target wellbore are determined; the well logging curves include resistivity curves, acoustic wave time difference curves, density curves, porosity curves and natural gamma curves; the fracturing construction curves include construction pressure curves, displacement curves, sand ratio curves, net pressure curves and microseismic monitoring curves.

[0012] Furthermore, determining the well section of the target wellbore with the potential for repeated transformation specifically includes: dividing the target wellbore into a number of well sections according to a preset length, evaluating whether the wellbore integrity, formation reserves, and remaining production of the well section meet the preset requirements, and in response to the wellbore integrity, formation reserves, and remaining production all meeting the preset requirements, determining that the well section has the potential for repeated transformation, otherwise determining that the well section does not have the potential for repeated transformation.

[0013] The wellbore integrity assessment includes: using a resistivity curve to judge whether there is corrosion or cracks in the casing wall of the wellbore, using a natural gamma curve to measure the change in the casing wall thickness of the wellbore, using an acoustic wave time difference curve to detect the cement ring bonding quality of the wellbore and whether there is channeling, and using an image acquisition device to observe the surface morphology of the wellbore; in response to the resistivity curve, the natural gamma curve, the acoustic wave time difference curve and the wellbore surface morphology all meeting the preset requirements, it is determined that the wellbore integrity meets the preset requirements, otherwise it is determined that the wellbore integrity does not meet the preset requirements.

[0014] The formation reserve assessment includes: conducting formation reserve assessment based on the volumetric method, calculating the reserves by reservoir geometric volume, porosity, and fluid saturation, that is, reserves = reservoir geometric volume × porosity × fluid saturation; in response to the formation reserves not being lower than a preset threshold, it is determined that the formation reserves meet the preset requirements, otherwise it is determined that the formation reserves do not meet the preset requirements.

[0015] The remaining production evaluation includes: evaluating the remaining production based on the fracturing operation curve, and in response to the remaining production being not less than a preset threshold, determining that the remaining production meets the preset requirement, otherwise determining that the remaining production does not meet the preset requirement.

[0016] Furthermore, after obtaining the evaluation results of wellbore integrity, formation reserves and remaining production, the wellbore integrity, formation reserves and remaining production are judged one by one, and the repeated transformation potential of each section is scored and ranked according to the average value of the three indicators to obtain the position of the repeated transformation section; the scores of all well sections with repeated transformation potential are added together and the average score is calculated to determine the repeated transformation potential of the entire wellbore.

[0017] Furthermore, the use of a hydraulic pulse unblocking device to repeatedly transform a well section with the potential for repeated transformation of a target wellbore includes: ground equipment layout: arranging a continuous tubing pressure operation system and a fracturing pump truck, cleaning the wellbore and detecting the integrity of the wellbore; installing a hydraulic pulse tool: installing a hydraulic pulse tool and a positioning and sealing pipe string, sending the positioning and sealing pipe string under pressure to a set position, and achieving an upper and lower sealing closed environment through a pulse tool; pulse hydraulic injection unblocking: setting a positive pressure difference in the annulus, and pulse hydraulic injection unblocking.

[0018] Furthermore, the process parameters of pulse hydraulic injection plugging removal include: pulse frequency is set to 0.05-50 Hz, pulse pressure is set to 0.01-120 MPa, pulse waveform is sine wave or rectangular wave, displacement is set to 0.01-2 m 3 / min; the action time is set to 10 to 20 minutes.

[0019] Furthermore, in response to the completion of repeated transformation of the shale gas fracturing well, fracturing construction and production are carried out, and the repeated transformation potential of the shale gas fracturing well is evaluated again. If the shale gas fracturing well has transformation potential, the wellbore continues to be transformed until it is evaluated as having no transformation potential.

[0020] The present invention has the following unexpected beneficial effects: the present invention collects the pulse pressure curve of the hydraulic pulse unblocking device in real time, and dynamically determines whether the repeated transformation of the shale gas fracturing well is completed according to the waveform change of the pulse pressure curve, thereby being able to conduct real-time dynamic evaluation of the completion degree of the repeated transformation of the shale gas fracturing well, realizing an efficient, real-time and coherent repeated transformation process of the shale gas fracturing well, so that shale gas resources can be fully and repeatedly developed and utilized, thereby maximizing the gas well production capacity and improving the resource recovery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic flow chart of the dynamic evaluation method for repeated transformation of shale gas fracturing wells according to the present invention is shown.

[0022] Figure 2 A schematic flow chart of the method for determining the pulse pressure curve waveform of the present invention is shown.

[0023] Figure 3 A schematic flow chart of the peak value determination method of the pulse pressure curve of the present invention is shown. DETAILED DESCRIPTION

[0024] The following will describe the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention, not for limiting the scope of protection of the present invention.

[0025] In one embodiment, see Figure 1 As shown, the present invention provides a dynamic evaluation method for repeated transformation of shale gas fracturing wells, which includes: using a hydraulic pulse unblocking device to repeatedly transform a well section with repeated transformation potential in a target wellbore, and collecting a pulse pressure curve of the hydraulic pulse unblocking device in real time; in response to the change of the pulse pressure curve waveform from a first waveform to a second waveform, determining that the repeated transformation of the shale gas fracturing well is completed, otherwise determining that the repeated transformation of the shale gas fracturing well is not completed. Exemplarily, the first waveform is an irregular sine wave, and the second waveform is a regular sine wave.

[0026] This evaluation method uses the change in the waveform of the pulse pressure curve during the repeated transformation of the shale gas fracturing well by the hydraulic pulse unblocking device to determine whether the transformation is completed. The horizontal axis of the pulse pressure curve is time, and the vertical axis is the hydraulic pulse pressure of the hydraulic pulse unblocking device. In the initial stage, when the shale gas well section is blocked and needs to be transformed, the pulse pressure curve presents the first waveform, i.e., an irregular sine wave, which means that the fluid flow state and formation stress state in the well are in a relatively complex and unstable state. The irregular pressure transmission may be caused by the blockage of formation pores, the closure of original fractures, or the poor flow of fluids. As the hydraulic pulse unblocking device continues to work, it unblocks the formation, opens new cracks, and optimizes seepage channels. When the pulse pressure curve waveform changes to a second waveform (such as a regular sine wave), it means that the pressure transmission downhole has become regular and stable, the fluid flow state in the formation has tended to be stable, and the original problems that hindered the fluid flow and affected the gas well production capacity have been effectively solved. Therefore, it is determined that the repeated transformation of the shale gas fracturing well has been completed; conversely, if the waveform has not changed to a regular state, it is determined that the transformation has not been completed, which means that it is necessary to continue the transformation operation to further optimize the formation conditions.

[0027] The present invention can grasp the downhole situation at any time during the transformation process by collecting the pulse pressure curve in real time, and the operator can make timely decisions based on the changes in the waveform. For example, if the waveform has not changed for a long time, the working parameters of the hydraulic pulse unblocking device, such as pulse frequency, pressure, etc., can be adjusted in time to better adapt to the formation conditions, improve the transformation efficiency, and avoid ineffective operations and waste of resources. In addition, the present invention focuses on well sections with the potential for repeated transformation, avoiding indiscriminate operations on the entire wellbore, accurately processing key parts that may increase the production capacity of the gas well, and using the changes in the waveform of the pulse pressure curve as an objective criterion, so that the evaluation results are more scientific and targeted, which helps to accurately tap the production capacity potential of shale gas wells and increase the production of shale gas.

[0028] In a preferred embodiment, see Figure 2 As shown, the method for judging the pulse pressure curve waveform is: obtaining three peak values ​​P1, P2, P3 near the end of the pulse pressure curve and time points t1, t2, t3 corresponding to the three peak values, respectively; in response to P1=P2=P3, and t3-t2=t2-t1, judging that the pulse pressure curve waveform is the second waveform, i.e., a regular sine wave, indicating that the repeated transformation has been completed and the process has stopped; otherwise, judging that the pulse pressure curve waveform is the first waveform, i.e., an irregular sine wave, indicating that the repeated transformation has not been completed, and hydraulic pulse unblocking continues, and pulse pressure curve data is continuously collected for judgment.

[0029] For a regular sine wave, its characteristics are periodicity and equal amplitude. When P1=P2=P3, it means that the amplitude of the waveform is equal, satisfying the equal amplitude; when t3-t2=t2-t1, it means that the waveform is equally spaced in time, satisfying the periodicity. Only when these two conditions are met at the same time can the pulse pressure curve waveform be determined to be a regular sine wave (second waveform), otherwise the pulse pressure curve waveform is determined to be an irregular sine wave (first waveform).

[0030] Further, see Figure 3 As shown, the peak value judgment method of the pulse pressure curve is: set a pressure threshold value P for the pulse pressure curve n Capture the pressure value of each point on the pulse pressure curve, and set the pressure value at a certain time point as P m , the pressure value of its left adjacent point is P m-1 , the pressure value of the right adjacent point is P m+1 When P m-1 <P m <P m+1 With P m ≥P n When both conditions are met at the same time, it is determined that the pulse pressure curve has reached its peak value.

[0031] In a preferred embodiment, the section of the target wellbore with the potential for repeated transformation is determined based on the previous well logging curve and fracturing construction curve of the target wellbore; the well logging curve includes a resistivity curve, an acoustic wave time difference curve, a density curve, a porosity curve and a natural gamma curve; the fracturing construction curve includes a construction pressure curve, a displacement curve, a sand ratio curve, a net pressure curve and a microseismic monitoring curve.

[0032] The resistivity curve is obtained by resistivity logging, which is a method based on electrical principles and uses power supply electrodes and measuring electrodes arranged at different positions in a borehole to measure the resistivity of rocks (including the fluid therein).

[0033] When current is applied to the power supply electrode in the borehole, the current forms an electric field in the surrounding rock medium. Due to the different conductivity of different rocks and the fluids therein, the resistivity of the rock is calculated by measuring the voltage and current through the measuring electrode according to Ohm's law.

[0034] For example, for rocks with good conductivity (such as sandstone containing a large amount of formation water), at the same current intensity, the voltage measured by the measuring electrode is relatively low, and the calculated resistivity is also low; while for rocks with poor conductivity (such as dense limestone or oil-bearing sandstone), the voltage is higher at the same current and the resistivity is higher.

[0035] Generally speaking, there are many forms of arrangement of power supply electrodes and measuring electrodes. In ordinary resistivity logging, the electrodes are arranged along the well axis, and there are different modes such as monopole power supply-monopole measurement and bipole power supply-bipole measurement. For example, the monopole power supply-monopole measurement mode uses one electrode to supply power in the well and another electrode to measure the electric field strength at another location. This arrangement is simple, but it is easily disturbed by the environment around the wellbore.

[0036] The acoustic time difference curve is a logging curve that reflects the characteristics of the formation by measuring the propagation time of the sound wave in the formation. During the logging process, the downhole instrument sends out an acoustic pulse, which propagates in the rock and the fluid therein, and is then received by the receiving device. The instrument records the time difference from the emission to the reception of the sound wave, and then calculates the acoustic time difference per unit length of the formation. For example, in dense rocks, the propagation speed of sound waves is fast and the acoustic time difference is small; while in rocks with larger porosity, the propagation path of sound waves in rock particles and pore fluids is more complex, the propagation speed is slow, and the acoustic time difference is large.

[0037] The logging density curve obtains formation density information by measuring the interaction between gamma rays and the formation. The logging instrument usually contains a gamma ray source and a detector. The gamma ray source emits gamma rays to the well wall formation, and these gamma rays undergo Compton scattering with electrons in the formation. According to the principle of Compton scattering, the energy of the scattered gamma rays will decrease, and the detector measures the intensity of the scattered gamma rays. The higher the formation density, the more electrons there are in a unit volume, the greater the probability of gamma rays being scattered, and the lower the intensity of the scattered gamma rays received by the detector. Through preset calibration and calculation, the received gamma ray intensity can be converted into formation density, and then a density curve can be obtained.

[0038] The porosity curve is indirectly measured based on various physical principles and is used to reflect the porosity of the formation. For example, according to the Willy time-average formula To calculate the porosity, v is the speed of sound waves in the rock, v f is the speed of sound waves in the pore fluid, v m is the speed of sound waves in the rock skeleton, is the porosity. Or by calculating To calculate the porosity, ρ b is the formation density, is the porosity, ρ m is the rock skeleton density, ρ f is the pore fluid density.

[0039] Natural gamma logging is a logging method that measures the natural radioactivity intensity of formations. Radioactive elements in formations (such as the decay series of potassium-40, uranium-238, and thorium-232) emit gamma rays. The gamma-ray detector in the logging instrument measures the intensity of these naturally emitted gamma rays to obtain a natural gamma curve. Different formations contain different types and quantities of radioactive elements, resulting in different natural gamma ray intensities.

[0040] The construction pressure curve records the change of wellhead pressure over time during the fracturing operation. In the fracturing operation, high-pressure liquid is injected into the well to break the formation rock and form cracks. The construction pressure is mainly affected by factors such as the flow rate of the injected liquid, the stress state of the formation, the mechanical properties of the rock, and the expansion of the cracks. For example, when the injection liquid flow rate increases, the construction pressure usually rises; when the formation rock begins to break and form cracks, the construction pressure will drop significantly. This is because the formation of cracks provides new flow channels for the liquid and the pressure is released.

[0041] The displacement curve reflects the change of the flow rate of the injected liquid over time during the fracturing construction process. The displacement is adjusted by controlling the working state of the ground equipment (such as the fracturing pump). The size of the displacement directly affects the expansion speed and range of the cracks. A higher displacement can provide greater energy, causing the cracks to extend and expand faster, but it will also bring higher pressure to the formation and equipment.

[0042] The sand ratio curve shows the change of the concentration of proppant (sand) in the fracturing fluid over time. The function of the proppant is to form support in the cracks formed by fracturing, prevent the cracks from closing, and thus maintain the permeability of the formation. The size of the sand ratio is determined according to factors such as the nature of the formation and the width of the cracks. In the early stage of construction, a liquid with a low sand ratio may be injected first to prop open the cracks. As the cracks gradually stabilize and expand, the sand ratio is gradually increased to fill the cracks.

[0043] Net pressure refers to the difference between bottom hole pressure and the minimum principal stress of the formation. The net pressure curve reflects the change of this difference over time. Net pressure has a key influence on the initiation, extension and diversion of fractures. When the net pressure reaches the fracture pressure of the rock, the formation rock begins to fracture; during the extension of the fracture, the magnitude of the net pressure determines the expansion direction and shape of the fracture.

[0044] Microseismic monitoring is to monitor the tiny earthquake events caused by rock fracture during fracturing by placing seismic detectors around the well or on the ground. The microseismic monitoring curve records the energy, frequency, occurrence time and location of these microseismic events. When the fracturing fluid propels the formation rock to form cracks, the rock fracture will generate microseismic signals, which can be monitored and analyzed.

[0045] In a preferred embodiment, determining the target wellbore section with the potential for repeated transformation specifically includes: dividing the target wellbore into several sections according to a preset length, evaluating whether the wellbore integrity, formation reserves, and remaining production of the well section meet the preset requirements, and when the wellbore integrity, formation reserves, and remaining production all meet the preset requirements, determining that the well section has the potential for repeated transformation, otherwise determining that the well section does not have the potential for repeated transformation. This arrangement can more scientifically and systematically screen out the well sections in the target wellbore that are suitable for repeated transformation, providing a basis for subsequent related transformation decisions and project implementation.

[0046] The present invention uses a variety of different measurement methods and curve analysis to examine the relevant conditions of the wellbore from multiple dimensions, and then determines whether it meets the preset integrity requirements. Specifically, the wellbore integrity assessment includes:

[0047] The resistivity curve is used to judge whether there is corrosion or cracks in the casing wall of the wellbore. Resistivity is an electrical property of a material. Different materials and different structural states inside the material (such as the presence or absence of corrosion, medium changes caused by cracks, etc.) will cause the resistivity to present different values ​​or change patterns. By analyzing the changing characteristics of the resistivity curve, professionals can infer whether there is corrosion in the casing wall or whether cracks have occurred, which serves as an important basis for evaluating the integrity of the wellbore.

[0048] The natural gamma curve is used to measure the change of casing wall thickness in the wellbore. The intensity of natural gamma rays is related to the radioactivity of formation rocks and casing materials, and the change of casing wall thickness will affect the absorption and attenuation of natural gamma rays, which is then reflected in the natural gamma curve. Through accurate measurement and analysis of the curve, it is possible to obtain information on the change of casing wall thickness. If the casing wall thickness changes abnormally, it may mean that the integrity of the wellbore is affected, such as the presence of local damage.

[0049] The acoustic time difference curve is used to detect the cement sheath bonding quality and whether there is channeling in the wellbore. The propagation speed of the acoustic wave in different media is different, and when propagating in cement sheaths with good bonding and channeling, the time difference of the acoustic wave will be significantly different. By monitoring and analyzing the acoustic time difference curve, the quality of the cement sheath bonding can be accurately judged. If there is a bad situation such as channeling, the acoustic time difference curve will show corresponding characteristic changes, thereby helping to determine the integrity of the wellbore in this regard.

[0050] The most intuitive way to observe the wellbore surface morphology is to use image acquisition equipment. It can clearly see whether there are any abnormal morphology visible to the naked eye, such as potholes, damage, deformation, etc. on the wellbore surface, providing intuitive image evidence for evaluating the integrity of the wellbore.

[0051] In response to the resistivity curve, natural gamma curve, acoustic time difference curve and wellbore surface morphology all meeting the preset requirements, it is determined that the wellbore integrity meets the preset requirements; conversely, as long as any one of the indicators does not meet the preset requirements, it is determined that the wellbore integrity does not meet the preset requirements.

[0052] Through such a comprehensive and multi-dimensional evaluation method and rigorous judgment logic, the integrity of the wellbore can be measured more accurately, providing key basic data support for subsequent decisions such as determining whether the well section has the potential for repeated transformation.

[0053] The formation reserve assessment includes: conducting formation reserve assessment based on the volumetric method, and calculating the reserves through the reservoir geometric volume, porosity, and fluid saturation, that is, reserves = reservoir geometric volume × porosity × fluid saturation.

[0054] The volumetric method is a classic method commonly used in the field of petroleum geology to calculate formation reserves. Its basic idea is to regard the reservoir as a container with a certain geometric shape, and to comprehensively determine the recoverable reserves contained therein by analyzing the geometric volume, porosity and fluid saturation of the reservoir. Simply put, the geometric volume of the reservoir determines the size range of the entire "container", the porosity reflects the proportion of space available for fluid storage inside the reservoir rock, and the fluid saturation reflects the degree to which these pore spaces are occupied by fluids such as oil and gas. By multiplying these three factors, we can roughly estimate the reserves contained in the formation.

[0055] Reservoir geometry: This requires the use of geological exploration, logging and other methods to determine the distribution range of the reservoir underground and its approximate shape, and then calculate the corresponding volume value. For example, for layered reservoirs, the volume can be accurately calculated based on its lateral extension and longitudinal thickness; for irregularly shaped reservoirs, more complex geological modeling and other methods may be needed to reasonably estimate its volume.

[0056] Porosity: It is an important indicator to measure the reservoir performance of rocks, usually obtained through laboratory core analysis, logging interpretation and other methods. It represents the ratio of the pore volume in the rock to the total volume of the rock. Different types of rocks, different sedimentary environments and other factors will lead to large differences in porosity, and the size of the porosity directly affects the amount of fluid that can be accommodated in the formation.

[0057] Fluid saturation: It mainly reflects the proportion of oil, gas and other fluids in the pore space, and is often determined by special logging technology and reservoir engineering analysis. For example, in an oil reservoir, oil saturation refers to the proportion of oil in the pore volume. It, together with water saturation, constitutes a related index of fluid saturation and plays a key role in accurately calculating formation reserves.

[0058] When the formation reserve value calculated according to the above-mentioned volumetric method is not lower than the preset threshold value, it is judged that the formation reserves meet the preset requirements, which means that from the perspective of reserves, the well section has a certain mining value and potential for repeated transformation; on the contrary, if the calculated formation reserves are lower than the preset threshold value, it means that the exploitable resources in the formation are relatively limited, and it is judged that the formation reserves do not meet the preset requirements. In this case, when considering repeated transformation of this well section, it is necessary to carefully weigh factors such as its economic benefits.

[0059] The remaining production evaluation includes: evaluating the remaining production based on the fracturing operation curve, and in response to the remaining production being not less than a preset threshold, determining that the remaining production meets the preset requirement, otherwise determining that the remaining production does not meet the preset requirement.

[0060] The fracturing construction curve is a curve chart recorded during the fracturing construction process of oil wells, gas wells, etc., which can reflect many key information. It usually includes the changes in multiple parameters such as construction time, construction pressure, injection fluid volume, sand volume, etc. over time. The changes in these parameters are closely related to the characteristics of the formation, the expansion of the cracks, and the final production performance. Through in-depth analysis of the fracturing construction curve, the current seepage capacity of the formation, the production corresponding to the remaining recoverable reserves, etc. can be indirectly inferred. For example, the changing trend of the construction pressure can reflect the opening and extension of the formation cracks, while the injection fluid volume, sand volume, etc. are related to the scale of the effective fracture network formed, which in turn affects the subsequent fluid production, that is, the production performance.

[0061] In a preferred embodiment, after obtaining the evaluation results of wellbore integrity, formation reserves, and remaining production, the wellbore integrity, formation reserves, and remaining production are judged one by one, and the potential for repeated transformation of each section is scored and ranked according to the average value of the three indicators to obtain the position of the repeated transformation section; the scores of all well sections with repeated transformation potential are added together and averaged to determine the overall repeated transformation potential of the wellbore.

[0062] For example, the assessment results of wellbore integrity, formation reserves, and remaining production of a wellbore section are shown in Table 1.

[0063] Serial number Wellbore Integrity Formation reserves Remaining output average value A1 A1x A1y A1z <![CDATA[A1 ave ]]> A2 A2x A2y A2z <![CDATA[A2 ave ]]> A3 A3x A3 A3z <![CDATA[A3 ave ]]> …… …… …… …… …… An Anx Any Anz <![CDATA[An ave ]]>

[0064] In the table, A1x, A2x, A3x...Anx correspond to the wellbore integrity assessment scores of well section A1, well section A2, well section A3...An, respectively; A1y, A2y, A3y...Any correspond to the formation reserve assessment scores of well section A1, well section A2, well section A3...An, respectively; A1z, A2z, A3z...Anz correspond to the remaining production assessment scores of well section A1, well section A2, well section A3...An, respectively; A1y, A2y, A3y...Any correspond to the formation reserve assessment scores of well section A1, well section A2, well section A3...An, respectively; A1z, A2z, A3z...Anz correspond to the remaining production assessment scores of well section A1, well section A2, well section A3...An, respectively.ave 、A2 ave 、A3 ave ……An ave The summed average values ​​of the wellbore integrity assessment scores, formation reserve assessment scores and remaining production assessment scores corresponding to the A1 section, A2 section, A3 section...An section respectively.

[0065] When judging the potential for repeated transformation, the wellbore integrity, formation reserves, and remaining production are first judged one by one, that is, whether the wellbore integrity assessment score, formation reserve assessment score, and remaining production assessment score of a certain well section meet the preset requirements. In response to the wellbore integrity assessment score, formation reserve assessment score, and remaining production assessment score all meeting the preset requirements, it is determined that the well section has the potential for repeated transformation; otherwise, it is determined that the well section does not have the potential for repeated transformation.

[0066] After the evaluation of all sections of the wellbore is completed, the sequence number of the sections with the potential for repeated transformation can be obtained.

[0067] The summed evaluation values ​​of the assessment scores of the well sections with repeated transformation potential are added together to calculate the average score to obtain the transformation potential score of the wellbore, and the transformation potential score of the wellbore is compared with a preset threshold to determine whether the wellbore as a whole has the potential for repeated transformation.

[0068] In a preferred embodiment, the method of repeatedly reforming a well section with a potential for repeated reforming of a target wellbore by using a hydraulic pulse unblocking device comprises:

[0069] Step 1, ground equipment layout: Arrange the continuous tubing pressure operation system and the fracturing pump truck. The continuous tubing pressure operation system includes a continuous tubing truck, an injection head, a blowout preventer (BOP) system, a control system and a power unit. The continuous tubing pressure operation system can realize various downhole operations under the condition of wellbore pressure, and has the advantages of high operation efficiency and little damage to the formation. The fracturing pump truck provides a powerful power source for subsequent hydraulic pulse injection, including a high-pressure pump, a hydraulic drive system, a control system and a sand mixing equipment. The fluid is injected into the wellbore at a higher pressure through the fracturing pump truck. The two work together to build a basic ground equipment guarantee for the entire transformation operation.

[0070] Before officially carrying out the unblocking and transformation, it is necessary to clean the wellbore first. There may be various impurities, sediments, etc. in the wellbore. Cleaning the wellbore can remove these obstacles that affect subsequent operations and fluid flow, and ensure that the internal environment of the wellbore is relatively clean. At the same time, detecting the integrity of the wellbore can reconfirm the structural condition of the wellbore, such as whether the casing is intact and whether the quality of cement ring bonding meets the requirements, so as to avoid unexpected situations due to hidden dangers in the wellbore itself during subsequent operations, and provide a basis for the safe and smooth progress of the transformation operation. Specifically, select a suitable cleaning fluid, use a pipeline pump to pressurize and inject it, and ensure that the cleaning fluid is fully circulated in the wellbore to remove the blockage. After the cleaning is completed, use the downhole endoscopic camera equipment to send it into the wellbore to observe the condition of the inner wall of the wellbore in real time.

[0071] Step 2, install the hydraulic pulse tool: install the hydraulic pulse tool and the positioning and sealing string, send the positioning and sealing string under pressure to the set position, and use the pulse tool to achieve the upper and lower sealing environment. Connect the hydraulic pulse tool to one end of the oil pipe, and the other end of the oil pipe to the fracturing pump truck. Start the roller device of the continuous tubing truck, send the continuous tubing into the wellbore, and lower it to the predetermined depth and position. When the positioning and sealing string is lowered to the predetermined blocking position, stop the lowering operation of the continuous tubing and use the positioning tool to confirm the specific position of the string.

[0072] The hydraulic pulse tool can generate specific hydraulic pulses, using the energy of the pulses to destroy the blockage structure in the formation and improve the seepage performance of the formation. The positioning and sealing string plays a role in accurate positioning and sealing at a specific location underground to build a closed environment. The two are installed in a matching manner to ensure that the hydraulic pulse tool can be accurately placed at the set position that needs to be unblocked and create good sealing conditions for subsequent pulse effects.

[0073] When the positioning and sealing string reaches the designated position, the hydraulic pulse tool is operated to achieve upper and lower sealing, thereby forming a relatively closed environment underground, so that the subsequently injected pulse hydraulic force can fully play its role in this limited space and concentrate its strength to unblock the surrounding blocked formations.

[0074] Step 3: Pulse hydraulic injection to remove blockage: Set a positive pressure difference in the annulus and use pulse hydraulic injection to remove blockage. Specifically, inject balance fluid into the wellbore to stabilize the pressure, and inject balance fluid into the annulus or adjust the height of the liquid column to form the required positive pressure difference. Use pressure sensors to monitor the pressure changes inside and outside the wellbore in real time, and adjust the pressure control valve of the injection head through the ground control system to ensure stable pressure difference. The whole process is under pressure, which can effectively control the return of sand from the formation.

[0075] The present invention can guide the pulse hydraulic force to flow in the formation in the expected direction and force by reasonably controlling the pressure difference in the annulus, so that the energy of the hydraulic pulse can better act on the blockage and enhance the blockage removal effect. For example, a suitable positive pressure difference can cause the pulse hydraulic force to more effectively impact the blocking particles, colloids and other substances in the pores of the formation, causing them to loosen and disperse, and then be carried out of the formation by the fluid.

[0076] The present invention utilizes ground equipment such as a fracturing pump truck to inject fluid into the wellbore in the form of pulses and act on the formation. With the help of high-frequency vibration, impact and other energies generated by hydraulic pulses, the original blockage structure in the formation is destroyed, such as breaking up rock fragments that block the pores, diluting materials such as colloid asphalt adhering to the pore walls, restoring the seepage channels of the formation, improving the permeability of the formation, and ultimately achieving unblocking and improving the production potential of the well section.

[0077] Furthermore, the process parameters of pulse hydraulic injection plugging removal include: pulse frequency is set to 0.05-50 Hz, pulse pressure is set to 0.01-120 MPa, pulse waveform is sine wave or rectangular wave, displacement is set to 0.01-2 m 3 / min; the action time is set to 10 to 20 minutes.

[0078] In a preferred embodiment, in response to the completion of repeated transformation of the shale gas fracturing well, fracturing construction and exploitation are carried out, and the repeated transformation potential of the shale gas fracturing well is evaluated again. If the shale gas fracturing well has transformation potential, the wellbore will continue to be transformed, aiming to optimize the permeability of the formation and increase production through further measures. This re-transformation process will also follow the corresponding transformation process and technical requirements, and after completion, the new fracturing construction curve will be used as the basis for the next round of repeated transformation potential evaluation. This cycle is repeated until the evaluation results show that the wellbore has no transformation potential, which means that at this time, from a comprehensive consideration of technical, economic and other aspects, continuing the transformation can no longer obtain considerable benefits or effectively improve production conditions.

[0079] The above embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent substitution or change made by a person skilled in the art based on the present invention is within the protection scope of the present invention.

Claims

1. A dynamic evaluation method for repeated transformation of shale gas fracturing wells, characterized in that: include: Use a hydraulic pulse plugging removal device to repeatedly transform the target wellbore section with the potential for repeated transformation, and collect the pulse pressure curve of the hydraulic pulse plugging removal device in real time; In response to the pulse pressure curve waveform changing from the first waveform to the second waveform, it is determined that the repeated transformation of the shale gas fracturing well is completed, otherwise it is determined that the repeated transformation of the shale gas fracturing well is not completed.

2. The method for dynamic evaluation of repeated transformation of shale gas fracturing wells according to claim 1, characterized in that: The first waveform is an irregular sine wave, and the second waveform is a regular sine wave.

3. The dynamic evaluation method for repeated transformation of shale gas fracturing wells according to claim 2, characterized in that: The method for determining the waveform of the pulse pressure curve is as follows: obtaining three peak values ​​P1, P2, and P3 near the end of the pulse pressure curve and time points t1, t2, and t3 corresponding to the three peak values, respectively; in response to P1=P2=P3, and t3-t2=t2-t1, determining that the waveform of the pulse pressure curve is the second waveform, i.e., a regular sine wave; otherwise, determining that the waveform of the pulse pressure curve is the first waveform, i.e., an irregular sine wave.

4. The method for dynamic evaluation of repeated transformation of shale gas fracturing wells according to claim 1, characterized in that: Determine the target wellbore section with the potential for repeated transformation based on the target wellbore's early logging curves and fracturing operation curves; The logging curves include resistivity curves, acoustic time difference curves, density curves, porosity curves and natural gamma curves; The fracturing construction curve includes a construction pressure curve, a displacement curve, a sand ratio curve, a net pressure curve and a microseismic monitoring curve.

5. The method for dynamic evaluation of repeated transformation of shale gas fracturing wells according to claim 4, characterized in that: The well sections with the potential for repeated transformation in the target wellbore include: Divide the target wellbore into several well sections according to a preset length, evaluate whether the wellbore integrity, formation reserves, and remaining production of the well section meet the preset requirements, and when the wellbore integrity, formation reserves, and remaining production all meet the preset requirements, determine that the well section has the potential for repeated reconstruction, otherwise determine that the well section does not have the potential for repeated reconstruction; The wellbore integrity assessment includes: using a resistivity curve to judge whether there is corrosion and cracks in the casing wall of the wellbore, using a natural gamma curve to measure the change of the casing wall thickness of the wellbore, using an acoustic time difference curve to detect the cement ring bonding quality of the wellbore and whether there is channeling, and using an image acquisition device to observe the surface morphology of the wellbore; in response to the resistivity curve, the natural gamma curve, the acoustic time difference curve and the wellbore surface morphology all meeting the preset requirements, it is determined that the wellbore integrity meets the preset requirements, otherwise it is determined that the wellbore integrity does not meet the preset requirements; The formation reserve assessment includes: performing formation reserve assessment based on the volumetric method, calculating the reserves by reservoir geometric volume, porosity, and fluid saturation, that is, reserves = reservoir geometric volume × porosity × fluid saturation; in response to the formation reserves not being lower than a preset threshold, determining that the formation reserves meet the preset requirements, otherwise determining that the formation reserves do not meet the preset requirements; The remaining production evaluation includes: evaluating the remaining production based on the fracturing operation curve, and in response to the remaining production being not less than a preset threshold, determining that the remaining production meets the preset requirement, otherwise determining that the remaining production does not meet the preset requirement.

6. The method for dynamic evaluation of repeated reconstruction of shale gas fracturing wells according to claim 5, characterized in that: After obtaining the evaluation results of wellbore integrity, formation reserves, and remaining production, the wellbore integrity, formation reserves, and remaining production are judged one by one, and the repeat reformation potential of each section is ranked according to the average value of the three indicators to obtain the location of the repeat reformation section; The scores of all well sections with repeatable reformation potential are added together and averaged to determine the repeatable reformation potential of the wellbore as a whole.

7. The method for dynamic evaluation of repeated reconstruction of shale gas fracturing wells according to claim 1, characterized in that: The repeated transformation of the target wellbore section with the potential for repeated transformation by using the hydraulic pulse plugging removal device comprises: Surface equipment layout: layout of coiled tubing pressure operation system and fracturing pump truck, wellbore cleaning and wellbore integrity detection; Install hydraulic pulse tool: Install hydraulic pulse tool and positioning and sealing pipe string, send the positioning and sealing pipe string into the set position under pressure, and realize the upper and lower sealing closed environment through the pulse tool; Pulse hydraulic injection to remove blockage: set positive pressure difference in the annulus, and pulse hydraulic injection to remove blockage.

8. The method for dynamic evaluation of repeated reconstruction of shale gas fracturing wells according to claim 7, characterized in that: The process parameters of pulse hydraulic injection plugging removal include: pulse frequency is set to 0.05~50Hz, pulse pressure is set to 0.01~120MPa, pulse waveform is sine wave or rectangular wave, displacement is set to 0.01~2m 3 / min; the action time is set to 10 to 20 minutes.

9. The method for dynamic evaluation of repeated reconstruction of shale gas fracturing wells according to claim 1, characterized in that: In response to the completion of repeated transformation of the shale gas fracturing well, fracturing construction and production are carried out, and the repeated transformation potential of the shale gas fracturing well is evaluated again. If the shale gas fracturing well has transformation potential, the wellbore continues to be transformed until it is evaluated as having no transformation potential.

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