Method for determining crack initiation position of hydraulic fracturing crack by applying continuous stress waves

Abstract

The invention relates to the technical field of hydraulic fracturing, in particular to a method for determining the crack initiation position of a hydraulic fracturing crack by using continuous stress waves, which comprises the following steps of: identifying a water hammer wave and two adjacent shock waves continuously appearing subsequently in stress wave data of a descending section in a pump stop pressure drop process, distinguishing the characteristics of the water hammer wave and the shock waves, and determining the crack initiation position of the hydraulic fracturing crack. And the shock wave propagation distance is calculated according to the wave velocity and the interval time of two adjacent shock wave data, and then the perforation cluster crack initiation position can be determined. The method is suitable for all hydraulic fracturing construction operations, and can realize identification of the crack initiation position with the precision at the m level. The method is different from inversion identification of the crack initiation position by using test data to perform test data signal processing, belongs to a direct measurement method, has higher precision and resolution, and can realize accurate identification of the crack initiation position.

Description

Technical Field

[0001] This invention relates to the field of hydraulic fracturing technology, and is a method for determining the fracture initiation location in hydraulic fracturing using continuous stress waves. Background Technology

[0002] Hydraulic fracturing is a technique commonly used to stimulate unconventional oil and gas reservoirs and increase well production. It involves injecting high-pressure fluid into underground rock formations, causing them to fracture and increasing permeability. Determining the fracture initiation location is crucial for evaluating fracturing effectiveness, optimizing fracturing design, and improving well production efficiency. This is especially true in multi-stage fracturing of horizontal wells, where knowing the specific location of fluid injection from the perforation stage allows for real-time optimization of the hydraulic fracturing process, significantly increasing the production of unconventional oil and gas.

[0003] Currently, methods for determining fracture initiation locations mainly include distributed fiber optic acoustic monitoring, microseismic monitoring, electromagnetic monitoring, and high-frequency pressure monitoring. These methods infer fracture formation and propagation by analyzing changes in physical signals generated during fracturing of underground rocks. However, each of these existing technologies has limitations. For example, distributed fiber optic acoustic monitoring can provide information on fracture development direction and length, but cannot pinpoint the specific fracture initiation location within a perforation segment, primarily due to its resolution limitations in deep or complex geological structures. Microseismic monitoring can provide information on fracture distribution in three-dimensional space, but it suffers from high equipment costs, complex data processing, and cannot identify the initial fracture initiation location. Electromagnetic monitoring is significantly affected by geological conditions and cannot determine the fracture initiation location at perforation clusters. High-frequency pressure monitoring utilizes high-frequency pressure data, but it identifies the initiation location through spectral analysis, which involves mathematically processing and inverting the data to derive the fracture initiation location, rather than directly providing the location from fluid data.

[0004] While the methods described above can help locate fractures to some extent, they are insufficient in accurately identifying the initial location of fracture initiation. Accurately determining the initial location of fracture initiation is crucial for optimizing fracturing design, improving fracturing efficiency, and reducing environmental impact. Furthermore, existing technologies often require expensive equipment and complex data processing, increasing the cost and difficulty of oil and gas development.

[0005] To address the limitations of existing technologies, a method for determining the fracture initiation location in hydraulic fracturing using continuous stress wave data is proposed. This method analyzes the continuous stress wave signals generated during hydraulic fracturing, utilizing the characteristics that distinguish between water hammer waves and shock waves within the stress waves to accurately identify the initial location of fracture initiation. Compared to existing technologies, this method provides more accurate fracture initiation locations while reducing equipment costs and operational complexity. The method of determining the fracture initiation location in hydraulic fracturing using continuous stress wave data not only overcomes the limitations of existing technologies but also provides more precise and efficient technical support for oil and gas well fracturing operations. This new method is expected to bring about significant changes in the oil and gas development field. Summary of the Invention

[0006] This invention provides a method for determining the initiation location of hydraulic fracturing fractures using continuous stress waves, which overcomes the shortcomings of the prior art and can accurately identify the initial location of fracture initiation.

[0007] The technical solution of this invention is achieved through the following measures: a method for determining the initiation location of hydraulic fracturing fractures using continuous stress waves, comprising:

[0008] 1) Stress wave pressure sensor placement and data acquisition

[0009] Stress wave pressure sensor placement: Before the start of hydraulic fracturing operations, stress wave pressure sensors are placed at predetermined monitoring locations; these sensors should be able to accurately capture fluid stress wave data caused by hydraulic fracturing.

[0010] Data acquisition: Throughout the hydraulic fracturing process, stress wave data of the fluid is continuously acquired. The stress wave data includes stress wave data during the initial stage of fracturing fluid injection, the injection process, and the pressure drop process after pump shutdown.

[0011] 2) Determine the fluid wave velocity

[0012] Based on the provided perforation scheme, determine the specific location of each perforation cluster within the perforation section and the distance between each perforation cluster and the wellhead; calculate the fluid wave velocity range V based on the distance between the location of each perforation cluster and the wellhead, as well as the wave propagation time.

[0013] 3) Determine the location where the cracks begin to crack.

[0014] Stress wave data during the pump shutdown pressure drop process is collected. The stress wave data during the descending segment of the pump shutdown pressure drop process is locally magnified to identify water hammer waves and shock waves (water hammer waves are characterized by high amplitude and long period, while shock waves exhibit abrupt, jump-like changes). Two consecutive shock waves following the water hammer wave are selected as the basis for calculation. The time of the first shock wave's appearance is defined as T1, and the distance between a certain cluster of perforations and the wellhead is defined as L1. The wave velocity V1 is calculated as V1 = L1 / T1. When V1 falls within the wave velocity range V, the time of the second shock wave's appearance is defined as T2. The fracture initiation location A is determined using V1 and the difference between T2 and T1.

[0015] If the calculated wave velocity V1 does not fall within the wave velocity range V, the water hammer wave and shock wave data are searched and identified again.

[0016] 4) Verification of the location of crack initiation

[0017] If the fracture initiation location determined by the instantaneous pressure drop data during the initial stage and process of fracturing fluid injection is the same as the fracture initiation location obtained by the stress wave data during the pressure drop phase after pump shutdown, then the fracture initiation location determined by the pressure drop phase after pump shutdown is accurate.

[0018] Only after these three factors are mutually verified regarding the crack initiation location can it be confirmed that the crack initiation location determined during the pump shutdown pressure drop process is accurate.

[0019] The following are further optimizations and / or improvements to the above-mentioned technical solution:

[0020] The location A where the crack begins is calculated using the following formula:

[0021] S1=V1 xΔT

[0022] In the formula, S1 is the crack initiation location A, ΔT is the difference between T2 and T1, and V1 is the wave velocity.

[0023] The specific verification of the crack initiation location is as follows:

[0024] The instantaneous pressure drop data of the stress wave at the initial stage of fracturing fluid injection is collected. This instantaneous pressure drop data is locally magnified to identify the shock wave. Two consecutively occurring shock waves are selected as the basis for calculation. The time of the first shock wave's occurrence is defined as T1', and the distance between a certain cluster of perforations and the wellhead is defined as L1'. The wave velocity V1' is calculated as V1' = L1' / T1'. When V1' falls within the wave velocity range V, the time of the second shock wave's occurrence is defined as T2'. The fracture initiation location B is determined using V1' and the difference between T2' and T1'.

[0025] S1'=V1'xΔT'

[0026] In the formula, S1' is the crack initiation location B, ΔT' is the difference between T2' and T1', and V1' is the wave velocity;

[0027] The instantaneous pressure drop data of the stress wave during the fracturing fluid injection process is collected. The instantaneous pressure drop data is locally magnified to identify the shock wave. Two consecutively occurring shock waves are selected as the basis for calculation. The time of the first shock wave is T1”, and the distance between a certain cluster of perforations and the wellhead is L1”. The wave velocity V1” is calculated as V1” = L1” / T1”. The time of the second shock wave is T2”. When V1” falls within the wave velocity range V, the fracture initiation location C is determined by V1” and the difference between T2” and T1”.

[0028] S1”=V1”xΔT”

[0029] In the formula, S1” is the crack initiation location C, ΔT” is the difference between T2” and T1”, and V1” is the wave velocity;

[0030] If the crack initiation location B and the crack initiation location C are the same as or similar to the crack initiation location, then the crack initiation location A is accurate; otherwise, it is inaccurate.

[0031] When the crack initiation locations B and C are within 10 meters of crack initiation location A, then crack initiation locations B and C are approximately the same as crack initiation location A.

[0032] This invention provides a method for determining the fracture initiation location in hydraulic fracturing using continuous stress wave data. Applicable to all hydraulic fracturing operations, it achieves fracture initiation location identification with an accuracy at the m-level. Unlike inversion-based identification of fracture initiation locations using test data signal processing, this method is a direct measurement approach, offering higher accuracy and resolution, enabling precise identification of fracture initiation locations.

[0033] This invention directly analyzes the monitored data, reducing the difficulty and complexity of technical implementation, improving work efficiency, and reducing reliance on specialized technical personnel. Compared to traditional fracture location monitoring technologies (such as distributed acoustic monitoring and microseismic monitoring), this invention reduces required equipment and operating costs. The accurate fracture initiation location information obtained through this invention allows for on-site monitoring of fracture propagation behavior and optimization of fracturing design.

[0034] Overall, this invention provides a more accurate, cost-effective, and easy-to-operate solution to improve the determination of fracture initiation location during hydraulic fracturing, which has a positive impact on the oil and gas development field.

[0035] The key technical point of this invention is to identify three consecutive waveforms in the stress wave data during the pressure drop phase of the pump shutdown process: the water hammer wave and the two adjacent shock waves that follow it. By distinguishing the characteristics of the water hammer wave and the shock wave, and calculating the propagation distance of the shock wave based on the wave velocity and the time interval between the two adjacent shock wave data, the location of the perforation cluster initiation can be determined.

[0036] This invention is particularly applicable to determining the fracture initiation location after multiple perforations within a hydraulically fractured perforated section in a horizontal well, and can directly provide the specific location of the fluid-injecting perforation cluster within the perforated section of the horizontal well. Attached Figure Description

[0037] Appendix Figure 1 This is stress wave data from the hydraulic fracturing process.

[0038] Appendix Figure 2 For the appendix Figure 1 A magnified view of the pressure drop process during pump shutdown. Detailed Implementation

[0039] The present invention is not limited to the following embodiments, and the specific implementation can be determined according to the technical solution of the present invention and the actual situation.

[0040] The present invention will be further described below with reference to embodiments:

[0041] Example 1: This method for determining the initiation location of hydraulic fracturing fractures using continuous stress waves includes:

[0042] 1) Stress wave pressure sensor placement and data acquisition

[0043] Stress wave pressure sensor placement: Before the start of hydraulic fracturing operations, stress wave pressure sensors (using pressure gauges with a frequency of 1 kHz or higher) are placed at the predetermined monitoring location (wellhead); these sensors should be able to accurately capture fluid stress wave data caused by hydraulic fracturing.

[0044] Data Acquisition: Throughout the hydraulic fracturing process, stress wave data of the fluid is continuously acquired. This stress wave data includes data from the initial stage of fracturing fluid injection, the injection process, and after pump shutdown (i.e., the pressure drop process after pump shutdown). (See...) Figure 1 );

[0045] 2) Determine the fluid wave velocity

[0046] Based on the provided perforation scheme, determine the specific location of each perforation cluster within the perforation section and the distance between each perforation cluster and the wellhead; calculate the fluid wave velocity range V based on the distance between each perforation cluster and the wellhead and the wave propagation time. The wave velocity range V is 1200m / s to 1450m / s (based on existing hydraulic fracturing operations, the specific location of each perforation cluster within the perforation section and the distance between each perforation cluster and the wellhead are common, and the wave velocity range V is generally 1200m / s to 1450m / s).

[0047] 3) Determine the location where the cracks begin to crack.

[0048] Take stress wave data during the pump shutdown pressure drop process (see) Figure 2 The stress wave data of the pressure drop segment during the pump shutdown process is magnified locally to identify water hammer waves and shock waves (water hammer waves are characterized by high amplitude and long period, while shock waves have abrupt, jump-like characteristics). Two consecutive shock waves following the water hammer wave are selected as the basis for calculation. The time of the first shock wave is T1, and the distance between a certain perforation location and the bridge plug is L1. The wave velocity V1 is calculated as V1 = L1 / T1. When V1 falls within the wave velocity range V, the time of the second shock wave is T2. The crack initiation location A is determined by V1 and the difference between T2 and T1.

[0049] S1=V1 xΔT

[0050] In the formula, S1 is the crack initiation location A, ΔT is the difference between T2 and T1, and V1 is the wave velocity;

[0051] Principle Explanation: Throughout the hydraulic fracturing process, the water hammer wave continuously moves within the casing. When the water hammer wave impacts downwards and reflects off the bridge plug, it increases the fluid pressure near the bridge plug, resulting in a high-pressure state at most perforation cluster locations. As the fluid wave front moves towards the wellhead and away from the bridge plug, the fluid near the perforation locations near the bridge plug is under relative negative pressure. Due to the high-pressure state of the fluid within the fracture at the fracture initiation point, a significant pressure difference exists between the inside and outside of the casing, forming a new loading wave (i.e., the first shock wave formed after the water hammer wave). This loading wave propagates towards the wellhead and also towards the bridge plug. The pressure wave propagating towards the bridge plug impacts the bridge plug, forming a reflected wave (i.e., the second shock wave formed after the water hammer wave) that propagates towards the wellhead. The pressure sensor at the wellhead detects these two pressure waves, and the corresponding distance, i.e., the fracture initiation location of the perforation cluster, can be calculated based on the wave velocity and the time difference between them.

[0052] Since the time between the first and second shock waves is relatively short, and the fluid in the well is clear water after the pump stops, the wave velocity is stable. Therefore, the wave velocities of the first and second shock waves are basically the same. Thus, only the wave velocity V1 is calculated.

[0053] 4) Verification of the location of crack initiation

[0054] The instantaneous pressure drop data of the stress wave at the initial stage of fracturing fluid injection is collected. This instantaneous pressure drop data is locally magnified to identify the shock wave. Two consecutively occurring shock waves are selected as the basis for calculation. The time of the first shock wave's occurrence is defined as T1', and the distance between a certain cluster of perforations and the wellhead is defined as L1'. The wave velocity V1' is calculated as V1' = L1' / T1'. When V1' falls within the wave velocity range V, the time of the second shock wave's occurrence is defined as T2'. The fracture initiation location B is determined using V1' and the difference between T2' and T1'.

[0055] S1'=V1'xΔT'

[0056] In the formula, S1' is the crack initiation location B, ΔT' is the difference between T2' and T1', and V1' is the wave velocity;

[0057] The instantaneous pressure drop data of the stress wave during the fracturing fluid injection process is collected. The instantaneous pressure drop data is locally magnified to identify the shock wave. Two consecutively occurring shock waves are selected as the basis for calculation. The time of the first shock wave is T1”, and the distance between a certain cluster of perforations and the wellhead is L1”. The wave velocity V1” is calculated as V1” = L1” / T1”. The time of the second shock wave is T2”. When V1” falls within the wave velocity range V, the fracture initiation location C is determined by V1” and the difference between T2” and T1”.

[0058] S1”=V1”xΔT”

[0059] In the formula, S1” is the crack initiation location C, ΔT” is the difference between T2” and T1”, and V1” is the wave velocity;

[0060] If the crack initiation location B and the crack initiation location C are the same as or similar to the crack initiation location, then the crack initiation location A is accurate; otherwise, it is inaccurate.

[0061] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A method for determining the initiation location of hydraulic fracturing fractures using continuous stress waves, characterized in that, include: Stress wave pressure sensor placement and data acquisition Stress wave pressure sensor placement: Stress wave pressure sensors are placed at predetermined monitoring locations before the start of hydraulic fracturing operations. Data acquisition: Throughout the hydraulic fracturing process, stress wave data of the fluid is continuously acquired. The stress wave data includes stress wave data during the initial stage of fracturing fluid injection, the injection process, and the pressure drop process after pump shutdown. Determine fluid wave velocity Based on the provided perforation scheme, determine the specific location of each perforation cluster within the perforation section and the distance between each perforation cluster and the wellhead; calculate the fluid wave velocity range V based on the distance between each perforation cluster location and the wellhead, and the wave propagation time; determine the fracture initiation location. Take the stress wave data during the pump shutdown pressure drop process, locally magnify the stress wave data during the descending segment of the pump shutdown pressure drop process, identify water hammer waves and shock waves, select two consecutive shock waves that appear after the water hammer wave as the basis for calculation, take the time when the first shock wave appears as T1, take the distance between a certain cluster of perforations and the wellhead as L1, calculate the wave velocity V1, V1 = L1 / T1, when V1 falls into the wave velocity range V, take the time when the second shock wave appears as T2, and use V1 and the difference between T2 and T1 to determine the fracture initiation location A.

2. The method for determining the fracture initiation location in hydraulic fracturing using continuous stress waves according to claim 1, characterized in that... The crack initiation location A is calculated using the following formula: S1=V1xΔT In the formula, S1 is the crack initiation location A, ΔT is the difference between T2 and T1, and V1 is the wave velocity.

3. The method for determining the initiation location of hydraulic fracturing fractures using continuous stress waves according to claim 1 or 2, characterized in that... This also includes: verification of the location of crack initiation. If the fracture initiation location determined by the instantaneous pressure drop data during the initial stage and process of fracturing fluid injection is the same as the fracture initiation location obtained by the stress wave data during the pressure drop phase after pump shutdown, then the fracture initiation location determined by the pressure drop phase after pump shutdown is accurate.

4. The method for determining the fracture initiation location of hydraulic fracturing using continuous stress waves according to claim 3, characterized in that... The location of the crack initiation was definitively verified as follows: The instantaneous pressure drop data of the stress wave data at the initial stage of fracturing fluid injection is taken, and the instantaneous pressure drop data is magnified locally to identify the shock wave. Two consecutive shock waves are selected as the basis for calculation. The time of the first shock wave is T1', and the distance between a certain cluster of perforations and the wellhead is L1'. The wave velocity V1' is calculated, V1' = L1' / T1'. When V1' falls into the wave velocity range V, the time of the second shock wave is T2'. The fracture initiation position B is determined by V1' and the difference between T2' and T1'. The instantaneous pressure drop data of the stress wave during the fracturing fluid injection process is collected, and the instantaneous pressure drop data is locally magnified to identify the shock wave. Two consecutively occurring shock waves are selected as the basis for calculation. The time of the first shock wave is T1”, and the distance between a certain cluster of perforations and the wellhead is L1”. The wave velocity V1” is calculated as V1” = L1” / T1”. The time of the second shock wave is T2”. When V1” falls into the wave velocity range V, the fracture initiation position C is determined by V1” and the difference between T2” and T1”. If the crack initiation location B and the crack initiation location C are the same as or similar to the crack initiation location, then the crack initiation location A is accurate; otherwise, it is inaccurate.

5. The method for determining the initiation location of hydraulic fracturing fractures using continuous stress waves according to claim 4, characterized in that... When the crack initiation locations B and C are within 10 meters of crack initiation location A, then crack initiation locations B and C are approximately the same as crack initiation location A.

6. The method for determining the initiation location of hydraulic fracturing fractures using continuous stress waves according to claim 4 or 5, characterized in that... The crack initiation location B is calculated using the following formula: S1'=V1'xΔT' In the formula, S1' is the crack initiation location B, ΔT' is the difference between T2' and T1', and V1' is the wave velocity.

7. The method for determining the initiation location of hydraulic fracturing fractures using continuous stress waves according to claim 4 or 5, characterized in that... The crack initiation location C is calculated using the following formula. S1”=V1”xΔT” In the formula, S1” is the crack initiation position C, ΔT” is the difference between T2” and T1”, and V1” is the wave velocity.

8. The method for determining the initiation location of hydraulic fracturing fractures using continuous stress waves according to claim 6, characterized in that... The crack initiation location C is calculated using the following formula. S1”=V1”xΔT” In the formula, S1” is the crack initiation position C, ΔT” is the difference between T2” and T1”, and V1” is the wave velocity.

9. The method for determining the initiation location of hydraulic fracturing fractures using continuous stress waves according to claim 1, 2, 3, 4, 5, or 8, characterized in that... The stress wave pressure sensor uses a pressure gauge with a frequency of 1KHz or higher.

10. The method for determining the initiation location of hydraulic fracturing fractures using continuous stress waves according to claim 7, characterized in that... The stress wave pressure sensor uses a pressure gauge with a frequency of 1KHz or higher.

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