Simulation method for stress wall effect of three-dimensional well pattern based on optical fiber monitoring

Abstract

The invention belongs to the technical field of oil and gas field development, and discloses a three-dimensional well pattern stress wall effect simulation method based on optical fiber monitoring, which comprises the following steps of: arranging simulation horizontal wells into a rock block, longitudinally and alternately distributing and transversely arranging the simulation horizontal wells into N well groups at intervals, mutually staggering holes in any two adjacent simulation horizontal wells, arranging optical fibers and pressure gauges in wellbores, the interior of the rock is not layered or is vertically separated by at least one interlayer; placing the rock block into a true triaxial confining pressure system, and pressurizing the rock block according to each set confining pressure; after the system is stable, fracturing the well group according to different fracturing sequences and different stratigraphic dip angles, monitoring the crack propagation form by adopting an optical fiber, and monitoring the change condition of the pressure of the well group along with time by adopting a pressure meter; and analyzing and evaluating the effectiveness of the stress wall effect according to an experimental result. According to the method, the three-dimensional well pattern stress wall effect can be explored in a laboratory, and the effectiveness and multi-parameter influence mechanism of the three-dimensional well pattern stress wall partition effect under different influence factor conditions can be analyzed.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas field development, and particularly relates to a simulation method for stress wall effect based on fiber optic monitoring of a three-dimensional well pattern. Background Art

[0002] Tight conglomerate reservoirs often exhibit complex lithology, strong heterogeneity, and complex fracture networks. In the development process, the three-dimensional well pattern large-scale hydraulic fracturing technology is widely used. Among them, the local stress increase caused by the induced stress of the first fractured well will cause the fractures of the later fractured well to extend to the local stress increase area of the first fractured well, resulting in the phenomenon that the fracture stops propagating forward and turns to form a complex fracture network or fracture arrest, which is called the stress wall effect. Making full use of the stress wall effect can control the shape of the fracture network through stress, and assist in forming a fracture network with a simple near-well zone and a complex far-well zone. In the development process of horizontal wells, by using the shielding effect of the stress wall effect, it is possible to simultaneously achieve development, fracturing, and drilling, improving the production and development efficiency. Therefore, the stress wall effect plays an important positive role in the development of the three-dimensional well pattern and is one of the key technical means for the development of the three-dimensional well pattern.

[0003] At present, the mechanism and main controlling factors of the stress wall effect on fracture propagation are not clear, which restricts the popularization and application of this technology in the field. Therefore, studying the parameter optimization in the development process of the three-dimensional well pattern by the stress wall effect plays an important guiding role in subsequent engineering development.

[0004] The invention patent CN111609967A discloses a test device and method for a distributed fiber optic monitoring device, belonging to the field of oil and gas well testing instruments; the test device includes: a casing, a tubing, an optical fiber, a gas source, and a liquid source. Both ends of the casing are closed ends. The casing is sleeved on the tubing, and an annulus is formed between the casing and the tubing. An inlet and outlet liquid pipe is provided on the casing for communicating with the liquid source. Both ends of the tubing are closed ends. At least one leakage point is provided on the tubing, and the tubing communicates with the annulus through the leakage point. The tubing is used to communicate with the gas source. The optical fiber is inserted into the tubing. The optical fiber includes a first end for connecting with a distributed fiber optic monitoring device, and both the first end and the second end of the optical fiber are arranged outside the casing and the tubing. This invention patent can verify the feasibility of using the distributed fiber optic monitoring technology to monitor the leakage of the gas storage wellbore and the reliability of the detection results. However, the method of this patent only monitors the wellbore leakage and does not involve the stress wall effect; moreover, it does not study the influence of well pattern deployment, fracturing sequence, etc. on the detection results. Summary of the Invention

[0005] The present invention aims to solve the technical problems existing in the background art, and provides a simulation method for the stress wall effect of a three-dimensional well pattern based on optical fiber monitoring, which can explore the stress wall effect of the three-dimensional well pattern in the laboratory, explore the influence of the stress wall effect of the three-dimensional well pattern on the propagation direction of the crack tip of the post-pressure well, and the influence of the stress wall effect of the three-dimensional well pattern on the "cross-wall" flow process of the fracturing fluid of the post-pressure well, and analyze the effectiveness of the stress wall partition effect and the multi-parameter influence mechanism of the three-dimensional well pattern under different influencing factor conditions.

[0006] To achieve the above technical objectives, the present invention adopts the following technical solutions:

[0007] A simulation method for the stress wall effect of a three-dimensional well pattern based on optical fiber monitoring, the method comprising the following steps:

[0008] Step S1: Arrange a plurality of simulated horizontal wells into the rock block, and ensure that the simulated horizontal wells are longitudinally staggered and horizontally spaced into N well groups in the three-dimensional space. At the same time, the holes arranged on the well walls of any two adjacent simulated horizontal wells are staggered in the three-dimensional space, and an optical fiber and a pressure gauge are arranged in the wellbore of each simulated horizontal well; if exploring the interaction mechanism of stress walls between different strata of the three-dimensional well pattern, at least 1 interlayer is provided inside the rock block to separate the rock block and the simulated horizontal wells into upper and lower layers; if exploring the stress interference between wells in the same stratum, no interlayer is provided inside the rock block;

[0009] Step S2: Place the rock block into the true triaxial confining pressure system, start the true triaxial confining pressure system, and pressurize the rock block according to the set confining pressures.

[0010] Step S3: After the system is stable, fracture multiple well groups in different fracturing sequences to generate fractures. Monitor the fracture propagation morphology of the well groups through the optical fiber, and monitor the change of the well group pressure with time through the pressure gauge, and conduct simulation experiments on the stress wall effect under different fracturing pressurization parameters and different fracturing sequences;

[0011] Step S4: Deflect the experimental device by a set angle to conduct fracturing simulation of the stress wall effect under different formation dips;

[0012] Step S5: According to the experimental results, analyze and evaluate the effectiveness of the stress wall effect, including the analysis of the effectiveness of the stress wall partition effect under different fracturing pressurization parameters, different fracturing sequences, and different dips, and complete the mechanism analysis and evaluation of the simulation experiment of the stress wall effect of the three-dimensional well pattern.

[0013] Further, the optical fiber monitoring adopts a DAS distributed optical fiber acoustic wave monitoring device or a DTS distributed optical fiber temperature monitoring device.

[0014] Further, in the step S3, fracturing the well groups in different fracturing sequences to generate fractures specifically includes:

[0015] The unidirectional fracturing sequence is used to explore the influence of the stress wall effect of the three-dimensional well pattern with unidirectional sequential fracturing on the propagation direction of the crack tip of the later-fractured well;

[0016] The synchronous zipper-type fracturing sequence is used to explore the influence of the stress wall effect of the three-dimensional well pattern with synchronous zipper-type sequential fracturing on the propagation direction of the crack tip of the later-fractured well;

[0017] Different fracturing schemes are implemented for the simulated horizontal wells in the upper and lower rock blocks of the interlayer to explore the blocking effect of the stress walls in different layers.

[0018] Furthermore, 3 well groups are arranged in the rock block, 1 interlayer is arranged in the middle of the rock block, and the fiber optic monitoring adopts a DAS distributed fiber optic acoustic monitoring device;

[0019] In the step S3, to explore the influence of the stress wall effect of the three-dimensional well pattern with unidirectional sequential fracturing on the propagation direction of the crack tip of the later-fractured well, it specifically includes:

[0020] Step S311: First, fracture the first well group. After the fracturing of the first well group is completed, do not relieve the pressure, keep the pore pressure of the well group unchanged and wait statically;

[0021] Step S312: After the waiting time t1, start to fracture the second well group; after the fracturing of the second well group is completed, do not relieve the pressure, keep the pore pressure of the well group unchanged and wait statically;

[0022] Step S313: After the waiting time t1, start to fracture the third well group. Obtain the fracture distribution of the rock sample through the distributed fiber optic acoustic monitoring device, observe the change of the crack response of the later-fractured well, and at the same time observe and record the change of the pressure gauge of the first well group over time; after the fracturing and recording are completed, relieve the pressure of all well groups and pump out the fluid in the well groups outward.

[0023] Furthermore, 3 well groups are arranged in the rock block, 1 interlayer is arranged in the middle of the rock block, and the fiber optic monitoring adopts a DAS distributed fiber optic acoustic monitoring device;

[0024] In the step S3, to explore the influence of the stress wall effect of the three-dimensional well pattern with synchronous zipper-type sequential fracturing on the propagation direction of the crack tip of the later-fractured well, it specifically includes:

[0025] Step S321: First, fracture the first well group. After the fracturing of the first well group is completed, do not relieve the pressure, keep the pore pressure of the well group unchanged and wait statically;

[0026] Step S322: After the waiting time t2, start to fracture the third well group; after the fracturing of the third well group is completed, do not relieve the pressure, keep the pore pressures of the first well group and the third well group unchanged and wait statically;

[0027] Step S323: After waiting for time t2, start fracturing the second well group. Meanwhile, record the changes in fracture morphology and pressure over time within the horizontal well length range monitored by the DAS distributed fiber optic acoustic monitoring devices of the first well group and the third well group. After the fracturing and recording are completed, relieve the pressure on all well groups and pump out the fluid inside the well groups.

[0028] Further, there are 3 well groups arranged within the rock mass, and there is 1 interlayer arranged in the middle of the rock mass. The fiber optic monitoring uses DAS distributed fiber optic acoustic monitoring devices.

[0029] In step S3, different fracturing schemes are implemented for the simulated horizontal wells in the upper and lower parts of the interlayer to explore the blocking effect of stress walls in different horizons, specifically including:

[0030] Step S331: First, fracture the lower well group of the first well group. After the fracturing is completed, do not relieve the pressure, keep the pore pressure of the lower well group of the first well group unchanged and wait statically.

[0031] Step S332: After waiting for time t3, start fracturing the upper and lower well groups of the third well group. Meanwhile, relieve the pressure on the lower well group of the first well group and pump out the fluid inside the lower well group of the first well group. After the fracturing, keep the pore pressure of the upper and lower well groups of the third well group unchanged and wait statically.

[0032] Step S333: After waiting for time t3, fracture the lower well group of the second well group. After the fracturing, keep the pore pressure of the lower well group of the second well group unchanged and wait statically.

[0033] Step S334: After waiting for time t3, record the changes in fractures and pressure over time for the upper and lower well groups of the first well group and the third well group respectively. After the recording is completed, relieve the pressure on all well groups and pump out the fluid inside the well groups.

[0034] Further, there are 3 well groups arranged within the rock mass, and there is 1 interlayer arranged in the middle of the rock mass. The fiber optic monitoring uses DTS distributed fiber optic temperature monitoring devices.

[0035] In step S3, explore the influence of the stress wall effect of the one-way sequential fracturing three-dimensional well pattern on the propagation direction of the crack tip of the later fractured well, specifically including:

[0036] Step S311: First, conduct cold hydraulic fracturing on the first well group. After the fracturing is completed, do not relieve the pressure, keep the pore pressure of the first well group unchanged and wait statically.

[0037] Step S312: After waiting for a time t4, start the thermal hydraulic fracturing of the second well group. Meanwhile, obtain the fracture distribution of the rock samples in the first well group through distributed optical fiber monitoring, observe the temperature change response of the post-pressured well fractures on the DTS distributed optical fiber temperature monitoring device of the first well group, and simultaneously observe and record the change of the pressure in the first well group over time. After the fracturing and recording are completed, depressurize all well groups and pump out the fluid in the well groups outward.

[0038] Further, there are 3 well groups arranged in the rock block, and there is 1 interlayer in the middle of the rock block. The optical fiber monitoring uses a DTS distributed optical fiber temperature monitoring device.

[0039] In step S3, explore the influence of the stress wall effect of the synchronous zipper-type sequential fracturing three-dimensional well pattern on the propagation direction of the tip of the post-pressured well fractures, specifically including:

[0040] Step S321: First, perform cold hydraulic fracturing on the first well group. After the fracturing is completed, do not depressurize, keep the pore pressure of the first well group unchanged and wait statically.

[0041] Step S322: After waiting for a time t5, start the cold hydraulic fracturing of the third well group. After the fracturing is completed, do not depressurize, keep the pore pressures of the first well group and the third well group unchanged and wait statically.

[0042] Step S323: After waiting for a time t5, start the thermal hydraulic fracturing of the second well group, record the temperature change response of the fractures over time within the horizontal well length range monitored in the first well group and the third well group, as well as the pressure changes in the first well group and the third well group. After the fracturing and recording are completed, depressurize all well groups and pump out the fluid in the well groups outward.

[0043] Further, there are 3 well groups arranged in the rock block, and there is 1 interlayer in the middle of the rock block. The optical fiber monitoring uses a DTS distributed optical fiber temperature monitoring device.

[0044] In step S3, implement different fracturing schemes for the simulated horizontal wells in the upper and lower parts of the interlayer to explore the blocking effect of the stress walls in different layers, specifically including:

[0045] Step S331: First, perform cold hydraulic fracturing on the lower well group of the first well group. After the fracturing is completed, do not depressurize, keep the pore pressure of the lower well group of the first well group unchanged and wait statically.

[0046] Step S332: After waiting for a time t6, start the cold hydraulic fracturing of the upper and lower well groups of the third well group. Meanwhile, depressurize the lower well group of the first well group and pump out the fluid in the lower well group of the first well group outward. After the fracturing, maintain the pore pressures of the upper and lower well groups of the third well group unchanged and wait statically.

[0047] Step S333: After waiting for time t6, conduct thermal hydraulic fracturing on the lower well group of the second well group. After fracturing, maintain the pore pressure of the lower well group of the second well group unchanged and wait statically;

[0048] Step S334: After waiting for time t6, record the crack temperature change response and pressure change of the upper and lower well groups of the first well group and the third well group over time respectively; Depressurize all well groups and pump out the fluid in the well groups outward.

[0049] Further, in step S5, analyze and evaluate the effectiveness of the stress wall effect, specifically including:

[0050] Step S501: Standardize the optical fiber detection signal to obtain the standardized optical fiber detection signal data. The standardized data processing formula is as follows:

[0051]

[0052] In the above formula, x is the standardized optical fiber detection signal data, x * is the original optical fiber detection signal data, μ is the mean of the original optical fiber detection signal data, and σ is the variance of the original optical fiber detection signal data;

[0053] Standardize the pressure data in the same way to obtain the standardized pressure data p;

[0054] Step S502: The optical fiber detection signal data is continuous data. Subtract the standardized optical fiber detection signal data x at time t + 1 from that at time t. After removing the signal noise, according to the denoised standardized detection signal data x, divide the detection signal response μ V (x) into grades as follows:

[0055]

[0056] In the above formula, μ V (x) is the optical fiber detection signal response corresponding to the denoised standardized optical fiber detection signal data x, and its values 0, 1, and 2 represent low, medium, and high detection signal responses respectively;

[0057] The pressure data is non - continuous data and can be directly processed in segments. According to the standardized pressure data p, divide the pressure response μ S (p) into grades as follows:

[0058]

[0059] In the above formula, μ S (p) is the pressure response corresponding to the standardized pressure data p, and its values 0, 1, and 2 represent small, medium, and large pressure responses respectively;

[0060] Step S503: According to expert experience, determine the relationship between the fiber optic detection signal response, the pressure response, and the stress wall effect, and construct the stress wall effect function μ W (x, p) as follows:

[0061]

[0062] In the above formula, ε(x, p) is the step function, is the value range function related to the fiber optic detection signal response μ V (x) and the pressure response μ S (p), and the expression is as follows:

[0063]

[0064]

[0065] Among them, μ W (x, p) is the stress wall effect function corresponding to the standardized fiber optic detection signal data x and the standardized pressure data p. When its value is -2, the data is abnormal. When its values are 0, 1, 2, 3, and 4, they respectively correspond to the five levels of the stress wall effect: weak, relatively weak, medium, relatively strong, and strong.

[0066] Compared with the prior art, the beneficial effects produced by the present invention are as follows:

[0067] The method of the present invention has universality and can analyze the influence of various parameters on the stress wall partition effect of the three-dimensional well pattern. By changing parameters such as the stress state of the true triaxial confining pressure system, the formation dip angle, the type of perforation, the well spacing distribution of the well pattern, the combination of longitudinal rock layers, the viscosity of the fracturing fluid, the waiting time, the multi-well fracturing sequence, the environmental temperature, and the fracturing displacement, the effectiveness of the stress wall partition effect of the three-dimensional well pattern under different influencing factor conditions and the multi-parameter influence mechanism can be analyzed. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 is a schematic structural diagram of the stress wall effect simulation device in Embodiment 1 of the present invention;

[0069] Figure 2 is a schematic cross-sectional view of the stress wall effect simulation device in Embodiment 1 of the present invention;

[0070] Figure 3 is a schematic diagram of the well layout position of the stress wall effect simulation device in Embodiment 1 of the present invention;

[0071] Figure 4 is a schematic cross-sectional view of the stress wall effect simulation device with a formation dip angle rotation system in Embodiment 1 of the present invention;

[0072] Figure 5 is a flow chart of the stress wall effect simulation method in Embodiment 1 of the present invention;

[0073] Figure 6 Schematic diagram of well layout positions of the stress wall effect simulation device for Embodiment 3 of the present invention;

[0074] Figure 7 Monitoring result graph of acoustic wave signal response for Embodiment 3 of the present invention;

[0075] Figure 8 Schematic diagram of well layout positions of the stress wall effect simulation device for Embodiment 5 of the present invention;

[0076] Figure 9 Monitoring result graph of temperature signal response for Embodiment 5 of the present invention. Detailed implementation manners

[0077] 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. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0078] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "coaxial", "bottom", "one end", "top", "middle", "the other end", "upper", "one side", "top", "inner", "front", "center", "both ends", etc. are based on the orientation or positional relationships shown in the accompanying drawings. These are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention.

[0079] In the present invention, unless otherwise clearly defined and limited, the terms "installed", "set", "connected", "fixed", "swivelly connected", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two elements or the interaction relationship between two elements. Unless otherwise clearly limited, for those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0080] Embodiment 1

[0081] Embodiment 1 of the present invention provides a method for simulating the stress wall effect of a three-dimensional well pattern based on optical fiber monitoring, which is implemented based on the following experimental device.

[0082] As Figures 1-3As shown, the experimental device includes a monitoring system, a true triaxial confining pressure system 1, and a pumping and pressurizing system; the monitoring system includes a distributed optical fiber monitoring device 16 and an interpretation module 15, and the pumping and pressurizing system includes a valve system 9, a pumping system 10, a pressurizing system 11, and a liquid storage tank 12.

[0083] The true triaxial confining pressure system 1 is fixedly arranged on the base 8, and the true triaxial confining pressure system 1 is used to apply true triaxial confining pressure to the rock block inside; the rock blocks are separated layer by layer up and down through a partition layer 5, and the number of the partition layers 5 can be specifically set according to the experimental needs. In the embodiment of the present invention, the rock block is separated into an upper formation rock block 2 and a lower formation rock block 6 by a partition layer 5.

[0084] In some other embodiments, there may be multiple partition layers 5 to explore the interaction mechanism of stress walls between multi-layer formations; if exploring the stress interference between wells in the same formation, there is no need to set partition layers inside the rock block.

[0085] There are 3 well groups arranged in the rock block, as Figure 3 shown, which are the first well group 301, the second well group 302, and the third well group 303 respectively; there are two simulated horizontal wells 4 arranged above each well group and three simulated horizontal wells 4 arranged below, and a total of 15 simulated horizontal wells 4 are arranged in 3 well groups. The 15 simulated horizontal wells 4 are longitudinally staggered and horizontally spaced.

[0086] In some other embodiments, the number of the well groups, the number of the simulated horizontal wells 4 in each well group, and the spacing can be flexibly adjusted according to the experimental requirements.

[0087] A fiber optic pipeline 13 is also arranged in the wellbore where each simulated horizontal well 4 is located. An optical fiber 3 is lowered into the fiber optic pipeline 13. The optical fiber 3 is connected to the interpretation module 15 and is used to transmit detection signals to the interpretation module 15 in real time; the interpretation module 15 is connected to the distributed optical fiber monitoring device 16 and is used to compile and interpret signals and transmit them to the distributed optical fiber monitoring device 16 to observe the expansion change of the crack morphology in the pre-pressed horizontal well; through holes 7 are penetrated through the well wall of each simulated horizontal well 4 for simulating well fracture experiments; a pressure gauge 14 is installed at the end of the wellbore of each simulated horizontal well 4 for real-time monitoring of the change of the fracturing fluid pressure in the wellbore, and together with the distributed optical fiber monitoring device 16, it quantifies the stress wall effect and realizes the mechanism analysis and evaluation of the stress wall effect simulation experiment of the three-dimensional well pattern.

[0088] The simulation horizontal wells 4 of three well groups are each connected with a valve system 9 through pipelines. The valve systems 9 are respectively connected with a pumping and discharging system 10 and a pressurizing system 11. Both the pumping and discharging system 10 and the pressurizing system 11 are connected with a liquid storage tank 12 through pipelines. The liquid storage tank 12 stores fracturing fluid (high-temperature fracturing fluid or low-temperature fracturing fluid). The pumping and discharging system 10 is used to pump the fracturing fluid in the well group outwards into the liquid storage tank 12, and the pressurizing system 11 is used to pressurize and extract the fracturing fluid in the liquid storage tank 12 to the well group for carrying out a simulation experiment on the stress wall effect generated by cross-well fracturing in a three-dimensional well pattern.

[0089] In some other embodiments, the holes 7 on any two adjacent simulation horizontal wells 4 are arranged staggeredly. The shape of the holes 7 is one or a combination of shapes such as round holes, vertical slots 701 or horizontal slots 702, etc.

[0090] In some other embodiments, the simulation horizontal wells 4 of the three well groups are correspondingly connected with three valve systems 9 through pipelines. Two pumping and discharging systems 10 are connected in series between the three valve systems 9, which can reduce the number of required pumping and discharging systems and simplify the system structure.

[0091] As a further improvement, as Figure 4 shown, in the embodiment of the present invention, a housing 18 and a motor drive device 17 are further arranged outside the true triaxial confining pressure system 1 and the base 8. The two sides of the bottom of the housing 18 are meshed with the motor drive device 17 to form a formation dip rotation system, so as to realize the analysis and evaluation of the simulation experiment mechanism of the stress wall effect of the three-dimensional well pattern under different dips.

[0092] Specifically, rotating teeth are arranged on both sides of the bottom of the housing 18. The motor drive device 17 includes a driving device and a gear. The driving device is drivingly connected with the gear. The gear is meshed with the rotating teeth on both sides of the bottom plate of the housing 18, and drives the housing 18 to drive the whole device to deflect at a set angle under the drive of the driving device.

[0093] The optical fiber in the embodiment of the present invention can adopt either DAS optical fiber or DTS optical fiber.

[0094] A simulation method for the stress wall effect of a three-dimensional well pattern based on optical fiber monitoring provided by the embodiment of the present invention, as Figure 5 shown, specifically includes the following steps:

[0095] Step S1: Arrange each simulation horizontal well 4 into the rock block, and ensure that each simulation horizontal well 4 is longitudinally staggered and horizontally spaced in a three-dimensional space to form three well groups (see Figure 3 ). At the same time, the holes 7 arranged on the well walls of any two adjacent simulation horizontal wells are also staggered in a three-dimensional space. There is one interlayer 5 inside the rock block, which divides the rock block and the simulation horizontal wells into upper and lower layers;

[0096] Step S2: placing the rock block into the true triaxial confining pressure system 1, starting the true triaxial confining pressure system 1, and pressurizing the rock block according to the set confining pressures;

[0097] Step S3: After the system is stable, multiple well groups are fractured in different fracturing sequences to generate cracks, the crack extension morphology of the well group is monitored by optical fiber, the change of the well group pressure over time is monitored by a pressure gauge, and a simulation experiment of stress wall effect generated by inter-well fracturing in a three-dimensional well network is conducted;

[0098] Step S4: deflecting the experimental device to a set angle to achieve stress wall effect fracturing simulation under different formation inclination angles;

[0099] Step S5: Analyze and evaluate the effectiveness of the stress wall effect based on the experimental results, including the influence of different fracturing pressurization parameters, different fracturing sequences (including different fracturing sequences in the same layer wells and different fracturing sequences between wells in different layers), and different inclination angles and other parameters and influencing factors on the effectiveness of the stress wall barrier effect, and complete the mechanism analysis and evaluation of the three-dimensional well network stress wall effect simulation experiment.

[0100] Example 2

[0101] Based on Example 1, the embodiment of the present invention specifically provides a method for simulating stress wall effect of a three-dimensional well network based on DAS optical fiber monitoring, and the method comprises the following steps:

[0102] Step S1: Arrange each simulated horizontal well 4 into the rock block, and ensure that each simulated horizontal well 4 is staggered vertically in the three-dimensional space and arranged horizontally in intervals to form three well groups (see Figure 3 ), at the same time, the holes 7 arranged on the walls of different simulated horizontal wells are also staggered in three-dimensional space; a partition 5 is provided inside the rock block, which separates the rock block and the simulated horizontal well into two layers, the upper layer and the lower layer;

[0103] Step S2: placing the rock block into the true triaxial confining pressure system 1, starting the true triaxial confining pressure system 1, and pressurizing the rock block according to the set confining pressures;

[0104] Step S3: After the system is stable, the three well groups ( Figure 3 The first well group 301, the second well group 302 and the third well group 303) are subjected to fracturing in different fracturing sequences to generate cracks, the crack extension morphology of the well group is monitored by optical fiber, the change of the well group pressure over time is monitored by a pressure gauge, and the stress wall effect simulation experiment is conducted under different fracturing pressure parameters and different fracturing sequences;

[0105] Step S4: driving the experimental device to deflect to a set angle through the motor transmission device 17 in the formation inclination rotation system to achieve stress wall effect fracturing simulation at different inclination angles;

[0106] Step S5: Analyze and evaluate the effectiveness of the stress wall effect based on the experimental results, including the analysis of the effectiveness of the stress wall partitioning effect under different fracturing pressurization parameters, different fracturing sequences (including different fracturing sequences of wells in the same horizon and different fracturing sequences between wells in different horizons), and different dip angles and other parameters and influencing factors, and complete the mechanism analysis and evaluation of the stress wall effect simulation experiment of the three-dimensional well pattern.

[0107] The method of the embodiment of the present invention is universal and can analyze the influence of various parameters on the stress wall partitioning effect. By changing parameters such as the stress state of the true triaxial confining pressure system, the type of perforation, the distribution of well pattern well spacing, the combination of longitudinal rock formation interlayers, the viscosity of the fracturing fluid, the waiting time, the multi-well fracturing sequence, the environmental temperature, and the fracturing displacement, repeating steps S1 - S5 can achieve the analysis of the effectiveness of the stress wall partitioning effect and the multi-parameter influence mechanism under different influencing factor conditions.

[0108] Among them, in the step S3, fracturing is performed on three well groups in different fracturing sequences to generate fractures, specifically including:

[0109] A. Unidirectional fracturing sequence to explore the influence of the stress wall effect of the three-dimensional well pattern with unidirectional sequence fracturing on the crack tip propagation direction of the later fractured well, specifically including:

[0110] Step S311: First, fracture the first well group 301. After the fracturing of the first well group 301 is completed, do not relieve the pressure. Keep the pore pressure of the well group unchanged through the pressurization system 11 and wait statically.

[0111] Step S312: After the waiting time t1, start fracturing the second well group 302; after the fracturing of the second well group 302 is completed, do not relieve the pressure. Keep the pressure in the well unchanged through the pressurization system 11 and wait statically.

[0112] Step S313: After the waiting time t1, start fracturing the third well group 303. At the same time, relieve the pressure of the first well group 301 and open the pumping and drainage system 10 to pump out the fluid in the first well group 301; obtain the change in the acoustic wave response of the rock sample fracture of the later fractured well through the distributed optical fiber monitoring device 16 (DAS distributed optical fiber acoustic wave monitoring device), and at the same time observe and record the change of the pressure gauge 14 of the first well group 301 over time; after the fracturing and recording are completed, relieve the pressure of all well groups and open the pumping and drainage system 10 to pump out the fluid in the well groups.

[0113] B. Synchronous zipper - type fracturing sequence to explore whether there is an inhibitory effect during the "cross - wall" flow process of the fracturing fluid of the later fractured well, specifically including:

[0114] Step S321: First, fracture the first well group 301. After the fracturing of the first well group 301 is completed, do not relieve the pressure. Keep the pore pressure of the well group unchanged through the pressurization system 11 and wait statically;

[0115] Step S322: After the waiting time t2, start to fracture the third well group 303; after the fracturing of the third well group 303 is completed, do not relieve the pressure. Keep the pore pressures of the first well group 301 and the third well group 303 unchanged through the pressurization system 11 and wait statically;

[0116] Step S323: After the waiting time t2, start to fracture the second well group 302, and record the change of the fracture morphology with time within the horizontal well length range monitored by the distributed optical fiber monitoring device 16 of the first well group 301 and the third well group 303 and the change of the pressure of the pressure gauge 14; after the fracturing and recording are completed, relieve the pressure of all well groups and pump out the fluid in the well groups outward.

[0117] C. Implement different fracturing schemes for the simulated horizontal wells in the strata blocks above and below the interlayer to explore the blocking effect of stress walls in different horizons, specifically including:

[0118] Step S331: First, fracture the lower well group of the first well group 301. After the fracturing is completed, do not relieve the pressure. Keep the pore pressure of the lower well group of the first well group 301 unchanged through the pressurization system 11 and wait statically;

[0119] Step S332: After the waiting time t3, start to fracture the upper and lower well groups of the third well group 303. At the same time, relieve the pressure of the lower well group of the first well group 301 and open the pumping system 10 to pump out the fluid in the lower well group of the first well group 301 outward; after the fracturing, keep the pore pressures of the upper and lower well groups of the third well group 303 unchanged and wait statically;

[0120] Step S333: After the waiting time t3, fracture the lower well group of the second well group 302. After the fracturing, keep the pore pressure of the lower well group of the second well group 302 unchanged and wait statically;

[0121] Step S334: After the waiting time t3, record the change of the fracture response with time of the upper and lower well groups of the first well group 301 and the third well group 303 and the change of the pressure of the pressure gauge 14 respectively; after the recording is completed, relieve the pressure of all well groups and open the pumping system 10 to pump out the fluid in the well groups outward.

[0122] In the said step S5, analyze and evaluate the effectiveness of the stress wall effect, specifically including:

[0123] Step S501: Standardize the DAS acoustic wave signals to obtain the standardized acoustic wave signal data. The standardized data processing formula is as follows:

[0124]

[0125] In the above formula (1), x1 is the standardized acoustic wave signal data, and x1 * is the original acoustic wave signal data, μ1 is the mean of the original acoustic wave signal data, and σ1 is the variance of the original acoustic wave signal data;

[0126] The pressure data is standardized in the same way to obtain the standardized pressure data p.

[0127] Step S502: The acoustic wave signal response data at a certain moment is continuous data. The standardized acoustic wave signal data x1 at time t + 1 is differentiated from that at time t to remove signal noise. Then, according to the denoised standardized acoustic wave signal data x1, the acoustic wave signal response μ V1 (x1) is classified as follows:

[0128]

[0129] In the above formula (2), μ V1 (x1) is the acoustic wave signal response corresponding to the denoised standardized acoustic wave signal data x1, and its values 0, 1, and 2 represent low, medium, and high acoustic wave signal responses respectively.

[0130] Meanwhile, the pressure data at a certain moment is non - continuous data and can be directly segmented. According to the standardized pressure data p, the pressure response μ S (p) is classified as follows:

[0131]

[0132] In the above formula (3), μ S (p) is the pressure response corresponding to the standardized pressure data p, and its values 0, 1, and 2 represent small, medium, and large pressure responses respectively.

[0133] Step S503: According to expert experience, the relationships between the detection signal response, pressure response, and stress wall effect are determined as follows:

[0134] If the pressure response is small and the acoustic wave signal response is low, the stress wall effect is strong;

[0135] If the pressure response is medium and the acoustic wave signal response is low, or the pressure response is small and the acoustic wave signal response is medium, the stress wall effect is relatively strong;

[0136] If the pressure response is small and the acoustic wave signal response is high, or the pressure response is medium and the acoustic wave signal response is medium, the stress wall effect is medium;

[0137] If the pressure response is large and the acoustic wave signal response is medium, or if the pressure response is medium and the acoustic wave signal response is large, then the stress wall effect is weak;

[0138] If the pressure response is large and the acoustic wave signal response is high, then the stress wall effect is weak;

[0139] If the pressure response is large and the acoustic wave signal response is low, then the data is abnormal.

[0140] According to the above corresponding relationships, applying the acoustic wave grading data and the pressure grading data, construct the stress wall effect function μ W (x1, p) as follows:

[0141]

[0142] In the above formula (4), ε(x1, p) is a step function, is the value range function related to the acoustic wave signal response μ V1 (x1) and the pressure response μ S (p), and the expression is as follows:

[0143]

[0144]

[0145] Among them, μ W (x1, p) is the stress wall effect function corresponding to the standardized acoustic wave signal data x1 and the pressure data p. Its value of -2 indicates data abnormality, and its values of 0, 1, 2, 3, and 4 respectively correspond to the five levels of the stress wall effect: weak, relatively weak, medium, relatively strong, and strong.

[0146] The corresponding relationships between the acoustic wave grading data, the pressure grading data, and the pressure wall effect are shown in Table 1-1 as follows:

[0147] Table 1-1 Corresponding Relationship Table of Acoustic Wave Grading Data, Pressure Grading Data, and Pressure Wall Effect

[0148]

[0149] According to the above corresponding relationships between the acoustic wave grading data, the pressure grading data, and the pressure wall effect, the quantitative evaluation of the stress wall effect for the three fracturing sequences in step S3 can be realized, specifically as follows:

[0150] For A. Unidirectional fracturing sequence:

[0151] If the DAS distributed fiber optic acoustic wave monitoring device of the first well group 301 monitors that the acoustic wave signal response of the fracturing fracture of the second well group 302 is high and the pressure response of the pipeline pressure gauge is large, then the fracture of the second well group 302 penetrates the first well group 301, and the stress wall effect is weak;

[0152] If the DAS distributed fiber optic acoustic monitoring device of the first well group 301 monitors that the acoustic signal response of the fracturing cracks in the second well group 302 is high and the pressure response of the pipeline pressure gauge is medium, or the acoustic signal response is medium and the pressure response is large, then the stress wall effect is weak;

[0153] If the DAS distributed fiber optic acoustic monitoring device of the first well group 301 monitors that the acoustic signal response of the fracturing cracks in the second well group 302 is high and the pressure response of the pipeline pressure gauge is small, or the acoustic signal response is medium and the pressure signal response is medium, then the stress wall effect is medium;

[0154] If the DAS distributed fiber optic acoustic monitoring device of the first well group 301 does not monitor that the acoustic signal response of the fracturing cracks in the second well group 302 is low and the pressure response of the pipeline pressure gauge is small, then the stress wall effect is strong.

[0155] For B. Synchronous zipper - type fracturing sequence:

[0156] If the DAS distributed fiber optic acoustic monitoring devices of the first well group 301 and the third well group 303 monitor that the acoustic signal response of the fracturing cracks in the second well group 302 is high and the pressure response of the pipeline pressure gauge is large, then the cracks in the second well group 302 penetrate the first well group 301 and the third well group 303, and the stress wall effect is weak;

[0157] If the DAS distributed fiber optic acoustic monitoring devices of the first well group 301 and the third well group 303 monitor that the acoustic signal response of the fracturing cracks in the second well group 302 is high and the pressure response of the pipeline pressure gauge is medium, or the acoustic signal response is medium and the pressure response is large, then the stress wall effect is weak;

[0158] If the DAS distributed fiber optic acoustic monitoring devices of the first well group 301 and the third well group 303 monitor that the acoustic signal response of the fracturing cracks in the second well group 302 is high and the pressure response of the pipeline pressure gauge is small, or the acoustic signal response is medium and the pressure response is medium, then the stress wall effect is medium;

[0159] If the DAS distributed fiber optic acoustic monitoring devices of the first well group 301 and the third well group 303 do not monitor that the acoustic signal response of the fracturing cracks in the second well group 302 is low and the pressure response of the pipeline pressure gauge is small, then the stress wall effect is strong.

[0160] For C. Implement different fracturing schemes for the simulated horizontal wells in the upper and lower rock blocks of the interlayer:

[0161] If the DAS distributed fiber optic acoustic monitoring devices in the lower well groups of the first well group 301 and the third well group 303 detect a high response of the acoustic signal of the fracturing cracks in the lower well group of the second well group 302 and a large pressure response of the pipeline pressure gauge, then the fractures in the lower well group of the second well group 302 penetrate the lower well groups of the first well group 301 and the third well group 303, and the stress wall effect is weak;

[0162] If the DAS distributed fiber optic acoustic monitoring devices in the lower well groups of the first well group 301 and the third well group 303 detect a high response of the acoustic signal of the fracturing cracks in the lower well group of the second well group 302 and a medium pressure response of the pipeline pressure gauge, or, a medium response of the acoustic signal and a large pressure response, then the stress wall effect is relatively weak;

[0163] If the DAS distributed fiber optic acoustic monitoring devices in the lower well groups of the first well group 301 and the third well group 303 detect a high response of the fracturing acoustic signal in the lower well group of the second well group 302 and a small pressure response of the pipeline pressure gauge, or, a medium response of the acoustic signal and a medium pressure response, then the stress wall effect is medium.

[0164] If the DAS distributed fiber optic acoustic monitoring devices in the lower well groups of the first well group 301 and the third well group 303 detect a low response of the acoustic signal of the fracturing cracks in the lower well group of the second well group 302 and a small pressure response of the pipeline pressure gauge, then the stress wall effect is strong.

[0165] Embodiment 3

[0166] Based on Embodiment 2, this embodiment of the present invention specifically conducts a simulation experiment on the stress wall effect of a three-dimensional well pattern based on DAS fiber optic monitoring for a certain conglomerate in a certain block.

[0167] As Figure 6 shown in the schematic diagram of the model of the rock block to be experimented, this rock block is processed from the conglomerate rock slab in the target block, and the size of the rock block is 1.2 m in length × 1.2 m in width × 1.2 m in height. Three groups of well patterns are horizontally drilled and deployed on the rock block, labeled as Well Pattern A, Well Pattern B, and Well Pattern C respectively. One well is deployed in each group of well patterns, arranged at equal intervals, and the well spacing is 0.4 m.

[0168] It should be additionally noted that in this embodiment of the present invention, the well pattern is deployed as a single-layer well. For the device of the present invention, both deploying the well pattern as a single-layer well and multiple upper and lower layers of wells can be achieved. The single-layer well is a simplified special case of the multi-layer well.

[0169] The simulated horizontal well and the DAS fiber are placed parallel into the rock block and sealed with cement, and then each device and pipeline are assembled and connected for the experiment. The experimental process is as follows:

[0170] (1) Turn on the true triaxial confining pressure system, apply a maximum horizontal stress of 35 Mpa, a minimum horizontal stress of 25 MPa, and an overburden pressure of 10 MPa, and conduct a fracturing simulation on the sample;

[0171] (2) During the fracturing process, two clusters are opened for each well (fracturing is carried out at two positions, and one main fracture is one cluster), and each well pattern is fractured unidirectionally in the order of one-way sequence C - B - A to explore the stress wall effect under the condition of one-way sequential fracturing. Monitor and record the acoustic signal responses of well pattern C (right) and well pattern A (left) at the end of the fracturing of well pattern B in the middle during fracturing. The results are as Figure 7 shown.

[0172] As can be seen from the following figure, at the end of the fracturing of well pattern B, the acoustic signal responses of the two simulated perforation sections of well pattern B were monitored on well pattern A (the general trend is two wave peaks, and the remaining small wave peaks are signal noise), but there was no obvious acoustic signal response on well pattern C, indicating that the fracture network of well pattern B has monitoring signals on well pattern A and no monitoring signals on well pattern C. Therefore, fracturing well pattern C first generated a stress field, blocking the rightward extension of the fractures in well pattern B.

[0173] Therefore, through the device and method of the embodiment of the present invention, it is possible to monitor the stress wall effect through DAS optical fiber, and by changing parameters, it is possible to analyze the effectiveness of the stress wall blocking effect and the multi-parameter influence mechanism under different influencing factor conditions.

[0174] Example 4

[0175] On the basis of Example 1, the embodiment of the present invention specifically provides a method for simulating the stress wall effect of a three-dimensional well pattern based on DTS optical fiber monitoring, which is implemented using the device in Example 1. The method includes the following steps:

[0176] Step S1: Arrange each simulated horizontal well 4 into the rock block, and ensure that the simulated horizontal wells 4 are longitudinally staggered and horizontally spaced into 3 well groups in the three-dimensional space. At the same time, the holes 7 arranged on the well walls of different simulated horizontal wells are also staggered in the three-dimensional space; there is 1 interlayer 5 inside the rock block, separating the rock block and the simulated horizontal wells into upper and lower layers;

[0177] Step S2: Place the rock block into the true triaxial confining pressure system 1, start the true triaxial confining pressure system 1, and pressurize the rock block according to the set confining pressures;

[0178] Step S3: After the system is stable, fracture multiple well groups in different fracturing sequences to generate fractures. Monitor the fracture propagation morphology of the well groups through optical fiber, and monitor the change of the well group pressure over time through a pressure gauge to conduct a simulation experiment on the stress wall effect under different fracturing pressurization parameters and different fracturing sequences;

[0179] Step S4: Drive the experimental device to deflect by a set angle through the motor drive device 17 in the formation dip rotation system, so as to realize the stress wall effect fracturing simulation at different dips;

[0180] Step S5: According to the experimental results, analyze and evaluate the effectiveness of the stress wall effect, including the analysis of the effectiveness of different fracturing pressurization parameters, different fracturing sequences (including different fracturing sequences of wells in the same formation and different fracturing sequences between wells in different formations), and parameters and influencing factors such as different dips on the effectiveness of the stress wall partition effect, and complete the mechanism analysis and evaluation of the stress wall effect simulation experiment of the three-dimensional well pattern.

[0181] The method of the embodiment of the present invention is universal and can analyze the influence of various parameters on the stress wall partition effect. By changing parameters such as the stress state of the true triaxial confining pressure system, the type of perforation, the distribution of well pattern well spacing, the combination of longitudinal rock formation interlayers, the viscosity of the fracturing fluid, the waiting time, the multi-well fracturing sequence, the ambient temperature, and the fracturing displacement, repeating steps S1 - S5 can realize the analysis of the effectiveness of the stress wall partition effect and the influence mechanism of multiple parameters under different influencing factor conditions.

[0182] Among them, in the step S3, fracturing is carried out on multiple well groups in different fracturing sequences to generate fractures, which specifically includes:

[0183] A. Unidirectional fracturing sequence, to explore the influence of the stress wall effect of the three-dimensional well pattern with unidirectional sequence fracturing on the crack tip propagation direction of the later fractured well, which specifically includes:

[0184] Step S311: First, conduct cold hydraulic fracturing on the first well group 301. After the fracturing is completed, do not relieve the pressure. Keep the pore pressure of the first well group 301 unchanged through the pressurization system 11 and wait statically;

[0185] After the waiting time t4, start to conduct hot hydraulic fracturing on the second well group 302. At the same time, obtain the crack distribution of the rock sample of the first well group 301 through the distributed optical fiber monitoring device 16 (DTS distributed optical fiber temperature monitoring device). Observe the temperature change response of the cracks in the later fractured well on the DTS distributed optical fiber temperature monitoring device of the first well group 301, and at the same time observe and record the change of the pressure gauge 14 of the first well group 301 over time; after the fracturing and recording are completed, relieve the pressure on all well groups and pump out the fluid in the well groups outward.

[0186] B. Synchronous zipper - type fracturing sequence, to explore whether there is an inhibitory effect during the "cross - wall" flow process of the fracturing fluid in the later fractured well, which specifically includes:

[0187] Step S321: First, conduct cold hydraulic fracturing on the first well group 301 and maintain the pore pressure. After the fracturing is completed, do not relieve the pressure. Keep the pore pressure of the first well group 301 unchanged through the pressurization system 11 and wait statically;

[0188] Step S322: After waiting time t5, start cold hydraulic fracturing on the third well group 303; after the fracturing of the third well group 303 is completed, do not relieve the pressure, and keep the pore pressure of the first well group 301 and the third well group 303 unchanged through the pressurization system 11, and then stand by;

[0189] Step S323: After waiting time t5, start hot hydraulic fracturing on the second well group 302, and record the response of the crack temperature change over time within the horizontal well length range of the first well group 301 and the third well group 303 monitored by the distributed optical fiber monitoring device 16, as well as the pressure change of the pressure gauge 14; after the fracturing and recording are completed, relieve the pressure on all well groups and pump out the fluid in the well groups outward.

[0190] C. Implement different fracturing schemes for the simulated horizontal wells in the strata blocks above and below the interlayer to explore the blocking effect of stress walls in different horizons, specifically including:

[0191] Step S331: First, perform cold hydraulic fracturing on the lower well group of the first well group 301. After the fracturing is completed, do not relieve the pressure, and keep the pore pressure of the lower well group of the first well group 301 unchanged through the pressurization system 11, and then stand by;

[0192] Step S332: After waiting time t6, start cold hydraulic fracturing on the upper and lower well groups of the third well group 303. At the same time, relieve the pressure on the lower well group of the first well group 301 and open the pumping system 10 to pump out the fluid in the lower well group of the first well group 301 outward; after the fracturing, keep the pore pressure of the upper and lower well groups of the third well group 303 unchanged, and then stand by;

[0193] Step S333: After waiting time t6, perform hot hydraulic fracturing on the lower well group of the second well group 302. After the fracturing, keep the pore pressure of the simulated horizontal well 4 in the strata block of the lower part of the second well group 302 unchanged, and then stand by;

[0194] Step S334: After waiting time t6, record the temperature change over time of the upper and lower well groups of the first well group 301 and the third well group 303 respectively, as well as the pressure change of the pressure gauge 14; after the recording is completed, relieve the pressure on all well groups and pump out the fluid in the well groups outward.

[0195] In step S5, analyze and evaluate the effectiveness of the stress wall effect, specifically including:

[0196] Step S501: Standardize the DTS temperature signal to obtain the standardized temperature signal data. The processing formula is as follows:

[0197]

[0198] In the above formula (7), x2 is the standardized temperature signal data, x2* Let \(\mu_2\) be the mean of the original temperature signal data and \(\sigma_2\) be the variance of the original temperature signal data;

[0199] Process the pressure data in the same way for standardization to obtain the standardized pressure data \(p\).

[0200] Step S502: The temperature signal response data at a certain moment is continuous data. Take the difference of the standardized temperature signal data \(x_2\) to remove signal noise, and then according to the denoised standardized temperature signal data \(x_2\), divide the temperature signal response \(\mu\) V2 (\(x_2\)) into grades as follows:

[0201]

[0202] In the above formula (8), \(\mu\) V2 (\(x_2\)) is the temperature signal response corresponding to the denoised standardized temperature signal data \(x_2\), and the values 0, 1, and 2 represent low, medium, and high temperature signal responses respectively.

[0203] At the same time, the pressure data at a certain moment is non - continuous data and can be directly processed in segments. According to the standardized pressure data \(p\), divide the pressure response \(\mu\) S (\(p\)) into grades as follows:

[0204]

[0205] In the above formula (9), \(\mu\) S (\(p\)) is the pressure signal corresponding to the standardized temperature signal data \(x_2\), and the values 0, 1, and 2 represent small, medium, and large pressure responses respectively.

[0206] Step S503: According to expert experience, determine the relationship between the pressure response, the acoustic wave signal, and the stress wall effect as follows:

[0207] If the pressure response is small and the temperature signal response is low, then the stress wall effect is strong;

[0208] If the pressure response is medium and the temperature signal response is low, or if the pressure response is small and the temperature signal response is medium, then the stress wall effect is relatively strong;

[0209] If the pressure response is small and the temperature signal response is high, or if the pressure response is medium and the temperature signal response is medium, then the stress wall effect is medium;

[0210] If the pressure response is large and the temperature signal response is medium, or if the pressure response is medium and the temperature signal response is large, then the stress wall effect is relatively weak;

[0211] If the pressure response is large and the temperature signal response is high, then the stress wall effect is weak;

[0212] If the pressure response is large and the temperature signal response is low, the data is abnormal.

[0213] According to the above corresponding relationship, apply the temperature classification data and pressure classification data to construct the stress wall effect function μ W (x2) as follows:

[0214]

[0215] Among them, ε(x2, p) is a step function, which is the value range function related to the temperature signal response μ V2 (x2) and the pressure response μ S (p), and the expression is as follows:

[0216]

[0217]

[0218] In the above equations (11)-(12), μ W (x2, p) is the stress wall effect function corresponding to the standardized temperature signal data x2 and pressure data p. When its value is -2, the data is abnormal. When its values are 0, 1, 2, 3, and 4, they respectively correspond to the five levels of the stress wall effect: weak, relatively weak, medium, relatively strong, and strong.

[0219] The corresponding relationship between the temperature classification data, pressure classification data, and pressure wall effect is shown in Table 1-2 below:

[0220] Table 1-2 Corresponding Relationship Table of Temperature Classification Data, Pressure Classification Data, and Pressure Wall Effect

[0221]

[0222] According to the above corresponding relationship between the temperature classification data, pressure classification data, and pressure wall effect, a quantitative evaluation of the stress wall effect of the three fracturing sequences in step S3 can be realized, specifically as follows:

[0223] For A. Unidirectional fracturing sequence:

[0224] If the DTS distributed optical fiber temperature monitoring device of the first well group 301 monitors that the temperature signal response of the fracturing crack of the second well group 302 is high and the pressure response of the pipeline pressure gauge is large, then the crack of the second well group 302 penetrates the first well group 301, and the stress wall effect is weak;

[0225] If the DTS distributed optical fiber temperature monitoring device of the first well group 301 monitors that the temperature signal response of the fracturing crack of the second well group 302 is high and the pressure response of the pipeline pressure gauge is medium, or the temperature signal response is medium and the pressure response is large, then the stress wall effect is relatively weak;

[0226] If the DTS distributed optical fiber temperature monitoring device of the first well group 301 monitors that the temperature signal response of the fracturing cracks in the second well group 302 is high and the pressure response of the pipeline pressure gauge is small, or the temperature signal response is medium and the pressure signal response is medium, then the stress wall effect is medium;

[0227] If the DTS distributed optical fiber temperature monitoring device of the first well group 301 monitors that the temperature signal response of the fracturing cracks in the second well group 302 is low and the pressure response of the pipeline pressure gauge is small, then the stress wall effect is strong.

[0228] For B. Synchronous zipper - type fracturing sequence:

[0229] If the DTS distributed optical fiber temperature monitoring devices of the first well group 301 and the third well group 303 monitor that the temperature signal response of the fracturing cracks in the second well group 302 is high and the pressure response of the pipeline pressure gauge is large, then the cracks in the second well group 302 penetrate the first well group 301 and the third well group 303, and the stress wall effect is weak;

[0230] If the DTS distributed optical fiber temperature monitoring devices of the first well group 301 and the third well group 303 monitor that the temperature signal response of the fracturing cracks in the second well group 302 is high and the pressure response of the pipeline pressure gauge is medium, or the temperature signal response is medium and the pressure response is large, then the stress wall effect is relatively weak;

[0231] If the DTS distributed optical fiber temperature monitoring devices of the first well group 301 and the third well group 303 monitor that the temperature signal response of the fracturing cracks in the second well group 302 is high and the pressure response of the pipeline pressure gauge is small, or the temperature signal response is medium and the pressure response is medium, then the stress wall effect is medium;

[0232] If the DTS distributed optical fiber temperature monitoring devices of the first well group 301 and the third well group 303 monitor that the temperature signal response of the fracturing cracks in the second well group 302 is low and the pressure response of the pipeline pressure gauge is small, then the stress wall effect is strong.

[0233] For C. Implementing different fracturing schemes for the simulated horizontal wells 4 in the upper and lower rock blocks of the interlayer:

[0234] If the DTS distributed optical fiber temperature monitoring devices of the upper and lower well groups of the first well group 301 and the third well group 303 monitor that the temperature signal response of the fracturing cracks in the lower well group of the second well group 302 is high and the pressure response of the pipeline pressure gauge is large, then the cracks in the lower well group of the second well group 302 penetrate the lower well groups of the first well group 301 and the third well group 303, and the stress wall effect is weak;

[0235] If the DTS distributed optical fiber temperature monitoring device of the lower well groups of the first well group 301 and the third well group 303 monitors that the temperature signal response of the fracturing cracks in the lower well group of the second well group 302 is high and the pressure response of the pipeline pressure gauge is medium, or the temperature signal response is medium and the pressure response is large, then the stress wall effect is weak;

[0236] If the DTS distributed optical fiber temperature monitoring device of the lower well groups of the first well group 301 and the third well group 303 monitors that the temperature signal response of the fracturing cracks in the lower well group of the second well group 302 is high and the pressure response of the pipeline pressure gauge is small, or the temperature signal response is medium and the pressure response is medium, then the stress wall effect is medium;

[0237] If the DTS distributed optical fiber temperature monitoring device of the lower well groups of the first well group 301 and the third well group 303 monitors that the temperature signal response of the fracturing cracks in the lower well group of the second well group 302 is low and the pressure response of the pipeline pressure gauge is small, then the stress wall effect is strong;

[0238] Example 5

[0239] On the basis of Example 4, this embodiment of the present invention specifically conducts a simulation experiment on the stress wall effect of a three-dimensional well pattern based on DTS optical fiber monitoring for a certain conglomerate in a certain block.

[0240] The model schematic diagram of the rock block to be experimented is as Figure 8 shown, with a total size of 1.2 m in length × 1.2 m in width × 1.2 m in height. The rock block is separated into upper and lower layers by a partition in the middle; 3 groups of well patterns are horizontally drilled and deployed on the rock block, labeled as well pattern A, well pattern B, and well pattern C respectively. Each group of well patterns has 2 wells, respectively above and below the partition. Among them, wells A1, B1, and C1 are respectively in the upper rock block, and wells A2, B2, and C2 are respectively in the lower rock block. Each well pattern is arranged at equal intervals, and the well spacing is 0.4 m.

[0241] Place the simulated horizontal well and the DTS optical fiber parallel into the rock block and seal them with cement. Then, assemble and connect the equipment and pipelines for the experiment. The experimental process is as follows:

[0242] (1) Turn on the true triaxial confining pressure system, apply a horizontal maximum stress of 35 Mpa, a horizontal minimum stress of 25 MPa, and an overlying rock pressure of 10 MPa to conduct a fracturing simulation on the sample;

[0243] (2) During the fracturing process, each well is fractured in 2 clusters (fractured at two positions, and one main fracture is a cluster). The two wells in each group of well patterns are fractured simultaneously, and the fracturing is carried out in the one-way sequence of C - B - A to explore the stress wall effect under the condition of one-way sequential fracturing. Monitor and record the DTS responses of well pattern C (right) and well pattern A (left) at the end of the fracturing of well pattern B in the middle during the fracturing. The results are as Figure 9 shown.

[0244] From Figure 9 It can be seen that at the end of the fracturing of Well Pattern B, both Well A1 and Well A2 monitored that the general trend of the hydrothermal temperature response signal injected by Well Pattern B was two peaks (the remaining small peaks were signal noise). The two peaks could show the fracture networks formed by the fracturing of the two perforations on Well B1 and Well B2. However, there was no obvious injected hydrothermal temperature response signal in Well C1 and Well C2, indicating that the hydrothermal fluid injected by Well Pattern B was more likely to contact Well Pattern A through the fracture network formed by fracturing, and it was difficult to directly contact Well Pattern C. Therefore, the stress walls generated by first killing Well C1 and Well C2 blocked the rightward extension of the fractures in Well Pattern B.

[0245] Therefore, through the device and method of the embodiment of the present invention, it is possible to monitor the stress wall effect through DTS optical fiber, and by changing parameters, analyze the effectiveness of the stress wall blocking effect and the multi-parameter influence mechanism under different influencing factor conditions.

[0246] The above are only the embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the scope of the application of the present invention shall be included in the protection scope of the present invention.

Claims

1. A simulation method for the stress wall effect of a three-dimensional well pattern based on optical fiber monitoring, characterized in that, The method includes the following steps: Step S1: Arrange several simulated horizontal wells into the rock block, and ensure that the simulated horizontal wells are longitudinally staggered and laterally spaced into N well groups in the three-dimensional space. At the same time, the holes arranged on the well walls of any two adjacent simulated horizontal wells are staggered in the three-dimensional space. An optical fiber and a pressure gauge are arranged in the wellbore of each simulated horizontal well. If exploring the interaction mechanism of stress walls between different formations of the three-dimensional well pattern, at least one interlayer is provided inside the rock block to separate the rock block and the simulated horizontal wells into upper and lower layers; If exploring the stress interference between wells in the same formation, no interlayer is provided inside the rock block; Step S2: Place the rock block into the true triaxial confining pressure system, start the true triaxial confining pressure system, and pressurize the rock block according to the set confining pressures; Step S3: After the system stabilizes, fracture multiple well groups in different fracturing sequences to generate fractures. Monitor the fracture propagation morphology of the well groups through the optical fiber, and monitor the change of the well group pressure over time through the pressure gauge to conduct simulation experiments on the stress wall effect under different fracturing pressure parameters and different fracturing sequences; Step S5: Rotate the experimental device by a set angle to conduct fracturing simulation of the stress wall effect under different formation dips; Step S6: According to the experimental results, analyze and evaluate the effectiveness of the stress wall effect, including the analysis of the effectiveness of different fracturing pressure parameters, different fracturing sequences, and different dips on the stress wall blocking effect, and complete the mechanism analysis and evaluation of the simulation experiment of the stress wall effect of the three-dimensional well pattern.

2. The method according to claim 1, wherein The optical fiber monitoring uses a DAS distributed optical fiber acoustic wave monitoring device or a DTS distributed optical fiber temperature monitoring device.

3. The method according to claim 1, characterized in that, In the said step S3, when fracturing the well groups in different fracturing sequences to generate fractures, it specifically includes: A. Unidirectional fracturing sequence to explore the influence of the stress wall effect of the three-dimensional well pattern with unidirectional sequence fracturing on the fracture tip propagation direction of the later fractured well; B. Synchronous zipper fracturing sequence to explore the influence of the stress wall effect of the three-dimensional well pattern with synchronous zipper sequence fracturing on the fracture tip propagation direction of the later fractured well; C. Implement different fracturing schemes for the simulated horizontal wells in the upper and lower rock blocks of the interlayer to explore the stress wall blocking effect of different layers.

4. The method according to claim 3, wherein There are 3 well groups arranged in the rock block, and 1 interlayer is arranged in the middle of the rock block. The optical fiber monitoring uses a DAS distributed optical fiber acoustic wave monitoring device; In the said step S3, when exploring the influence of the stress wall effect of the three-dimensional well pattern with unidirectional sequence fracturing on the fracture tip propagation direction of the later fractured well, it specifically includes: Step S311: First, fracture the first well group. After the fracturing of the first well group is completed, do not relieve the pressure, keep the pore pressure of the well group unchanged and wait statically; Step S312: After waiting for time t1, start to fracture the second well group. After the fracturing of the second well group is completed, do not relieve the pressure, keep the pore pressure of the well group unchanged and wait statically; Step S313: After waiting for time t1, start to fracture the third well group. Obtain the fracture distribution of the rock sample through the distributed optical fiber acoustic wave monitoring device, observe the change of the fracture response of the later fractured well, and at the same time observe and record the change of the pressure gauge of the first well group over time. After the fracturing and recording are completed, relieve the pressure of all well groups and pump out the fluid in the well groups outward.

5. The method according to claim 3, characterized in that, There are 3 well groups arranged inside the rock block, and there is 1 interlayer arranged in the middle of the rock block. The fiber optic monitoring uses a DAS distributed fiber optic acoustic wave monitoring device; In step S3, to explore the influence of the stress wall effect of the synchronous zipper-type sequential fracturing three-dimensional well pattern on the propagation direction of the crack tip of the subsequent fractured well, it specifically includes: Step S321: First, fracture the first well group. After the fracturing of the first well group is completed, do not relieve the pressure, keep the pore pressure of the well group unchanged and stand by; Step S322: After the waiting time t2, start to fracture the third well group; after the fracturing of the third well group is completed, do not relieve the pressure, keep the pore pressures of the first well group and the third well group unchanged and stand by; Step S323: After the waiting time t2, start to fracture the second well group. At the same time, record the changes in the fracture morphology and pressure over time within the horizontal well length range monitored by the DAS distributed fiber optic acoustic wave monitoring devices of the first well group and the third well group; after the fracturing and recording are completed, relieve the pressure on all well groups and drain the fluid inside the well groups outward.

6. The method according to claim 3, wherein There are 3 well groups arranged inside the rock block, and there is 1 interlayer arranged in the middle of the rock block. The fiber optic monitoring uses a DAS distributed fiber optic acoustic wave monitoring device; In step S3, different fracturing schemes are implemented for the simulated horizontal wells in the upper and lower parts of the interlayer to explore the blocking effect of the stress walls in different layers, which specifically includes: Step S331: First, fracture the lower well group of the first well group. After the fracturing is completed, do not relieve the pressure, keep the pore pressure of the lower well group of the first well group unchanged and stand by; Step S332: After the waiting time t3, start to fracture the upper and lower well groups of the third well group. At the same time, relieve the pressure on the lower well group of the first well group and drain the fluid inside the lower well group of the first well group outward; after the fracturing, keep the pore pressures of the upper and lower well groups of the third well group unchanged and stand by; Step S333: After the waiting time t3, fracture the lower well group of the second well group. After the fracturing, keep the pore pressure of the lower well group of the second well group unchanged and stand by; Step S334: After the waiting time t3, record the changes in the fractures and pressures of the upper and lower well groups of the first well group and the third well group over time respectively; after the recording is completed, relieve the pressure on all well groups and drain the fluid inside the well groups outward.

7. The method according to claim 3, wherein There are 3 well groups arranged inside the rock block, and there is 1 interlayer arranged in the middle of the rock block. The fiber optic monitoring uses a DTS distributed fiber optic temperature monitoring device; In step S3, to explore the influence of the stress wall effect of the one-way sequential fracturing three-dimensional well pattern on the propagation direction of the crack tip of the subsequent fractured well, it specifically includes: Step S311: First, perform cold hydraulic fracturing on the first well group. After the fracturing is completed, do not relieve the pressure, keep the pore pressure of the first well group unchanged and stand by; Step S312: After the waiting time t4, start to perform hot hydraulic fracturing on the second well group. At the same time, obtain the fracture distribution of the rock samples in the first well group through distributed fiber optic monitoring, observe the temperature change response of the crack of the subsequent fractured well on the DTS distributed fiber optic temperature monitoring device of the first well group, and at the same time observe and record the change in the pressure of the first well group over time; after the fracturing and recording are completed, relieve the pressure on all well groups and drain the fluid inside the well groups outward.

8. The method according to claim 3, wherein There are 3 well groups arranged inside the rock mass, and there is 1 interlayer arranged in the middle of the rock mass. The optical fiber monitoring uses a DTS distributed optical fiber temperature monitoring device; In step S3, to explore the influence of the stress wall effect of the synchronous zipper - type sequential fracturing three - dimensional well pattern on the propagation direction of the crack tip of the later - fractured well, it specifically includes: Step S321: First, cold hydraulic fracturing is carried out on the first well group. After the fracturing is completed, the pressure is not relieved, and the pore pressure of the first well group is kept unchanged and left to stand and wait; Step S322: After the waiting time t5, start cold hydraulic fracturing on the third well group; after the fracturing is completed, the pressure is not relieved, and the pore pressures of the first well group and the third well group are kept unchanged and left to stand and wait; Step S323: After the waiting time t5, start hot hydraulic fracturing on the second well group, and record the response of the crack temperature change over time within the horizontal well length range monitored by the first well group and the third well group, as well as the pressure change situations of the first well group and the third well group; after the fracturing and recording are completed, relieve the pressure on all well groups and pump out the fluid inside the well groups outward.

9. The method according to claim 3, wherein There are 3 well groups arranged inside the rock mass, and there is 1 interlayer arranged in the middle of the rock mass. The optical fiber monitoring uses a DTS distributed optical fiber temperature monitoring device; In step S3, different fracturing schemes are implemented for the simulated horizontal wells in the upper and lower parts of the interlayer to explore the blocking effect of the stress wall in different horizons, which specifically includes: Step S331: First, cold hydraulic fracturing is carried out on the lower well group of the first well group. After the fracturing is completed, the pressure is not relieved, and the pore pressure of the lower well group of the first well group is kept unchanged and left to stand and wait; Step S332: After the waiting time t6, start cold hydraulic fracturing on the upper and lower well groups of the third well group, and at the same time relieve the pressure on the lower well group of the first well group and pump out the fluid inside the lower well group of the first well group; after the fracturing, maintain the pore pressures of the upper and lower well groups of the third well group unchanged and leave to stand and wait; Step S333: After the waiting time t6, carry out hot hydraulic fracturing on the lower well group of the second well group, and maintain the pore pressure of the lower well group of the second well group unchanged and leave to stand and wait after the fracturing; Step S334: After the waiting time t6, record the response of the crack temperature change over time and the pressure change situations of the upper and lower well groups of the first well group and the third well group respectively; relieve the pressure on all well groups and pump out the fluid inside the well groups outward.

10. The method according to any one of claims 1-9, characterized in that In step S5, analyze and evaluate the effectiveness of the stress wall effect, which specifically includes: Step S501: Standardize the optical fiber detection signal to obtain the standardized optical fiber detection signal data. The standardized data processing formula is as follows: In the above formula, x is the standardized optical fiber detection signal data, and x * is the original optical fiber detection signal data, μ is the mean of the original optical fiber detection signal data, and σ is the variance of the original optical fiber detection signal data; Use the same method to standardize the pressure data to obtain the standardized pressure data p; Step S502: The optical fiber detection signal data is continuous data. Subtract the normalized optical fiber detection signal data x at time t + 1 from that at time t. After removing the signal noise, according to the denoised normalized detection signal data x, divide the detection signal response μ V (x) into grades as follows: In the above formula, μ V (x) is the optical fiber detection signal response corresponding to the denoised and normalized optical fiber detection signal data x, and the values 0, 1, and 2 represent low, medium, and high detection signal responses respectively; The pressure data is discontinuous data and can be directly processed in segments. According to the standardized pressure data p, the pressure response μ S (p) is classified as follows: In the above formula, μ S (p) is the pressure response corresponding to the standardized pressure data p, and the values 0, 1, and 2 represent small, medium, and large pressure responses respectively; Step S503: Determine the relationship between the optical fiber detection signal response, the pressure response, and the stress wall effect based on expert experience, and construct the stress wall effect function μ W (x, p) as follows: In the above formula, ε(x, p) is a step function, is the fiber optic detection signal response μ V (x) and the pressure response μ S (p) related value range function, and the expression is as follows: where μ W (x, p) is the stress wall effect function corresponding to the standardized optical fiber detection signal data x and the standardized pressure data p. A value of -2 for it indicates data anomaly, and the values 0, 1, 2, 3, and 4 respectively correspond to the five levels of the stress wall effect: weak, relatively weak, medium, relatively strong, and strong.

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