Indoor physical model experiment method for hydraulic fracturing of shale oil highly-deviated well

Abstract

The invention provides an indoor physical model experiment method for hydraulic fracturing of a shale oil highly-deviated well, which belongs to the technical field of oil production engineering and comprises the following steps: acquiring an underground rock core, and testing physical properties and mechanical parameters of the rock core; stratigraphic stratification and crack characteristics are obtained; preparing a simulation rock sample matched with physical parameters, mechanical parameters and structural characteristics of the underground rock core; setting different well deviations, perforation processes, cluster numbers and cluster intervals in the simulation rock sample; three-dimensional stress is loaded on the simulation rock sample, injection parameters are set, and cracks with different morphological characteristics are obtained; dynamically monitoring the crack initiation and expansion process by using an acoustic emission monitoring system to obtain the internal crack form of the simulated rock sample; and factors influencing crack initiation and expansion of the highly-deviated well are analyzed, and a construction parameter combination for reducing the fracture pressure of the highly-deviated well is determined. According to the method, the physical property, the mechanical property and the structural characteristic of the deep fractured shale oil highly-deviated well can be reflected more truly, and the crack initiation and expansion rule description is more reliable.

Description

Technical Field

[0001] This invention belongs to the field of oil production engineering technology, and in particular relates to an indoor physical model test method for hydraulic fracturing of highly deviated shale oil wells. Background Technology

[0002] Shale oil has become a new front for increasing oil and gas reserves and production. In some areas, deep fractured shale oil has characteristics such as poor matrix properties, well-developed bedding, and well-developed natural fractures. Conventional vertical and horizontal wells have high limitations on fracturing and development effectiveness. At present, exploration tests using highly deviated wells have achieved certain results.

[0003] Shale oil is developed using highly deviated wells, with different well sections traversing multiple reservoirs and bedding structures. The fracture propagation characteristics are complex and cannot be characterized by conventional numerical simulation methods; only physical modeling methods can be used to characterize the fractures.

[0004] Shale oil formations and natural fractures are well-developed and lack outcrops. Conventional artificial cores are mainly homogeneous models, which cannot simultaneously depict the formations and fracture characteristics of deep fractured shale oil. There is an urgent need to establish an experimental method for fracturing artificial cores of deep fractured shale oil in the laboratory. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a laboratory model experimental method for hydraulic fracturing of highly deviated shale oil wells. The technical problem to be solved by this invention is how to establish a laboratory model experimental method for fracturing artificial cores of deep fractured shale oil.

[0006] To address the aforementioned technical problems, this invention provides a laboratory model experimental method for hydraulic fracturing in highly deviated shale oil wells, comprising the following steps:

[0007] Step S1: Obtain downhole core samples and test their physical and mechanical properties;

[0008] Step S2: Perform well logging imaging and lithological observation on the downhole core to obtain stratigraphic bedding and fracture characteristics;

[0009] Step S3: Prepare simulated rock samples that match the physical properties, mechanical parameters, and structural characteristics of the downhole core;

[0010] Step S4: Set different well inclinations, perforation techniques, cluster numbers, and cluster spacing in the simulated rock sample;

[0011] Step S5: Apply triaxial stress to the simulated rock sample, set the injection parameters, and obtain cracks with different morphological characteristics;

[0012] Step S6: Use an acoustic emission monitoring system to dynamically monitor the crack initiation and propagation process and obtain the internal crack morphology of the simulated rock sample;

[0013] Step S7: Analyze the factors affecting fracture initiation and propagation in highly deviated wells, and determine the combination of construction parameters to reduce fracture pressure in highly deviated wells.

[0014] Furthermore, in step S1, a full-diameter downhole core is obtained, and the full-diameter downhole core is processed into a core sample using a waterless wire cutting method.

[0015] Furthermore, in step S1, the core physical properties include porosity and permeability; the mechanical parameters include Young's modulus, Poisson's ratio, and tensile strength.

[0016] Furthermore, in step S2, the interaction between bedding and reservoir, including bedding density, is obtained through imaging logging interpretation results and core observation; the characteristics of natural fractures, including parameters such as natural fracture dip angle, are obtained through imaging logging interpretation results.

[0017] Furthermore, in step S3, the proportions of cement, sand, and water are adjusted differently based on the core physical parameters and mechanical properties measured in step S1, and then artificial samples are cast. Based on the parameters such as bedding density and natural crack dip angle obtained in step S2, A4 paper is inserted during the artificial sample casting process to simulate natural cracks with different bonding strengths by adjusting the number of A4 sheets. Glass slides are inserted to simulate bedding planes.

[0018] Furthermore, in step S3, the physical properties of artificial samples prepared with different proportions of cement, sand, and water are tested, and the ratio that can produce the closest physical properties to the downhole core is selected to prepare a simulated rock sample.

[0019] Furthermore, in step S4, a prefabricated wellbore is embedded in the middle layer of the simulated rock sample. By changing the shape of the wellbore, a high-angle well with different inclination angles is simulated. Prefabricated iron rods are used to connect the prefabricated wellbore to simulate perforation. By changing the number, length, and angle of the iron rods, the number, depth, and phase angle of perforations can be changed.

[0020] Furthermore, in step S5, a true triaxial hydraulic fracturing simulation system is applied to the simulated rock sample to apply triaxial stress, and the injection fluid type, viscosity and displacement are set to induce hydraulic fractures in the simulated rock sample.

[0021] Furthermore, in step S6, the DS5 acoustic emission monitoring system is used to track the cracks in real time based on the P-wave polarity microseismic solution mechanism; based on the simulated rock sample after the CT scan test, the internal crack morphology of the simulated rock sample is obtained non-destructively to clarify the crack initiation and propagation characteristics.

[0022] Furthermore, in step S7, based on the fracture initiation pressure value of a highly deviated well, the main controlling factors affecting fracture rupture pressure are determined. The influence of each factor is ranked according to the magnitude of the change in fracture pressure value, and a combination of construction parameters that can effectively reduce fracture pressure and promote the balanced propagation of multiple fractures is obtained.

[0023] This invention provides a laboratory physical model experimental method for hydraulic fracturing in highly deviated shale oil wells. By acquiring the physical and mechanical parameters, formation bedding, and fracture characteristics of downhole core samples, physical parameter tests are conducted on artificial samples prepared with different cement, sand, and water ratios. The optimal ratio is selected to prepare simulated rock samples that most closely resemble the physical parameters of the downhole core samples. The simulated rock samples prepared in this way can more realistically reflect the physical, mechanical, and structural characteristics of deep fractured highly deviated shale oil wells, and the fracture initiation and propagation laws are more reliably depicted, thus providing more effective guidance for fracturing and stimulation of highly deviated wells. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of an artificial sample prepared using an optimized ratio in an indoor physical model experiment method for hydraulic fracturing of highly deviated shale oil wells according to the present invention.

[0025] Figure 2 This is a schematic diagram of a simulated rock sample after fracturing, based on an indoor physical model experiment method for hydraulic fracturing of highly deviated shale oil wells according to the present invention; in the diagram, σV is the vertical stress, σ h It is the minimum horizontal principal stress, σ H It is the maximum horizontal principal stress.

[0026] Figure 3 This is a schematic diagram of the three-dimensional reconstruction results of the multi-fracture propagation morphology of simulated rock samples from an indoor physical model experiment method for hydraulic fracturing of highly deviated shale oil wells according to the present invention.

[0027] Figure 4 This is a schematic flowchart of an indoor physical model test method for hydraulic fracturing of highly deviated shale oil wells according to the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0030] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0031] To better understand the purpose, structure, and function of this invention, the following detailed description of the indoor physical model experimental method for hydraulic fracturing of highly deviated shale oil wells, in conjunction with the accompanying drawings, is provided.

[0032] Example 1:

[0033] like Figure 4 As shown, the present invention provides a laboratory physical model experimental method for hydraulic fracturing of highly deviated shale oil wells, comprising the following steps:

[0034] Step S1: Obtain downhole core samples and test their physical and mechanical properties;

[0035] Step S2: Perform well logging imaging and lithological observation to obtain stratigraphic bedding and fracture characteristics;

[0036] Step S3: Prepare simulated rock samples that match the physical properties, mechanical parameters, and structural characteristics of the downhole core;

[0037] Step S4: Set different well inclinations, perforation techniques, cluster numbers, and cluster spacing in the simulated rock sample;

[0038] Step S5: Apply triaxial stress to the simulated rock sample, set the injection parameters, and obtain cracks with different morphological characteristics;

[0039] Step S6: Use an acoustic emission monitoring system to dynamically monitor the crack initiation and propagation process and obtain the internal crack morphology of the simulated rock sample;

[0040] Step S7: Analyze the factors affecting fracture initiation and propagation in highly deviated wells, and determine the combination of construction parameters to reduce fracture pressure in highly deviated wells.

[0041] Example 2:

[0042] like Figure 4 As shown, the present invention provides a laboratory physical model experimental method for hydraulic fracturing of highly deviated shale oil wells, comprising the following steps:

[0043] Step S1: Obtain downhole core samples and test their physical and mechanical properties;

[0044] Step S2: Perform well logging imaging and lithological observation to obtain stratigraphic bedding and fracture characteristics;

[0045] Step S3: Prepare simulated rock samples that match the physical properties, mechanical parameters, and structural characteristics of the downhole core;

[0046] Step S4: Set different well inclinations, perforation techniques, cluster numbers, and cluster spacing in the simulated rock sample;

[0047] Step S5: Apply triaxial stress to the simulated rock sample, set the injection parameters, and obtain cracks with different morphological characteristics;

[0048] Step S6: Use an acoustic emission monitoring system to dynamically monitor the crack initiation and propagation process and obtain the internal crack morphology of the simulated rock sample;

[0049] Step S7: Analyze the factors affecting fracture initiation and propagation in highly deviated wells, and determine the combination of construction parameters to reduce fracture pressure in highly deviated wells.

[0050] The difference between this embodiment and the first embodiment is that:

[0051] In step S1, a full-diameter downhole core is obtained, and the full-diameter downhole core is processed into a core sample with a diameter of 25 mm and a height of 50 mm using a waterless wire cutting method.

[0052] In step S1, the core physical properties include porosity and permeability; the mechanical parameters include Young's modulus, Poisson's ratio, and tensile strength.

[0053] In step S2, the interaction between bedding and reservoir, including bedding density, is obtained through imaging logging interpretation results and core observation; the characteristics of natural fractures, including parameters such as natural fracture dip angle, are obtained through imaging logging interpretation results.

[0054] In step S3, the proportions of cement, sand, and water are adjusted differently based on the core physical parameters and mechanical properties measured in step S1, and then artificial samples are cast. Then, based on the parameters such as bedding density and natural crack dip angle obtained in step S2, A4 paper is inserted during the artificial sample casting process. Four sheets of A4 paper are inserted to simulate natural cracks with moderate cementation strength. A 2mm glass slide is inserted to simulate the layers.

[0055] In step S3, the physical properties of artificial samples prepared with different proportions of cement, sand and water are tested, and the ratio that can best match the physical properties of the downhole core is selected to prepare a 300mm×300mm×300mm simulated rock sample.

[0056] In step S4, a prefabricated wellbore is embedded in the middle layer of the simulated rock sample. A high-angle well with a 60° inclination angle is simulated by placing a "7"-shaped wellbore. Prefabricated iron rods are used to connect the prefabricated wellbore to simulate perforation. The number, depth and phase angle of perforation are changed by changing the number, length and angle of the iron rods.

[0057] In step S5, a true triaxial hydraulic fracturing simulation system is used to apply triaxial stress to the simulated rock sample, and the injection fluid type, viscosity and discharge rate are set to induce hydraulic fractures in the simulated rock sample.

[0058] In step S6, the DS5 acoustic emission monitoring system is used to track the cracks in real time based on the P-wave polarity microseismic solution mechanism; based on the simulated rock sample after the CT scan test, the internal crack morphology of the simulated rock sample is obtained non-destructively to clarify the crack initiation and propagation characteristics.

[0059] In step S7, based on the fracture initiation pressure value of a highly deviated well, the main controlling factors affecting fracture rupture pressure are determined. The influence of each factor is ranked according to the magnitude of the change in fracture pressure value, and a combination of construction parameters that can effectively reduce fracture pressure and promote the balanced propagation of multiple fractures is obtained.

[0060] Example 3:

[0061] The specific implementation process of the laboratory physical model test method for hydraulic fracturing of highly deviated shale oil wells according to the present invention in Zone M is as follows:

[0062] The target reservoir is the Fengcheng Formation shale reservoir of Yimahu. A full-diameter core sample of the fractured section with a vertical depth of 4895.2m was obtained. The core samples were processed into 25mm diameter and 50mm high samples using a waterless wire cutting method. The physical properties (porosity, permeability) and mechanical parameters (Young's modulus, Poisson's ratio and tensile strength) of the core samples were tested.

[0063] like Figure 1 As shown, based on the rock physical properties, mechanical properties, and structural characteristics measured in step S1, artificial samples with different cement, sand, and water ratios were prepared. The optimal water-cement ratio, which matches the key physical and mechanical properties of the downhole core, was selected, namely cement:sand:water of 6:1:2 and 4:1:2. Simulated rock samples of 300mm×300mm×300mm were prepared.

[0064] A prefabricated wellbore was embedded in the middle layer of the simulated rock sample. The well inclination angle and perforation angle were changed according to the experimental requirements. The perforations were made by connecting the wellbore model with prefabricated iron rods. By changing the number, length, and angle of the iron rods, the number of perforations, the perforation depth, and the perforation phase angle could be changed.

[0065] The true triaxial hydraulic fracturing simulation system was used to simulate the initiation and propagation process of hydraulic fractures. The maximum effective triaxial loading stress was 30 MPa, the maximum injection flow rate was 300 ml / min, and the maximum injection pressure was 60 MPa.

[0066] The DS5 acoustic emission monitoring system used in this embodiment has a probe receiving frequency of 40-150KHz, an amplifier with adjustable gain of 20 / 40 / 60dB, a sampling rate of 2.5MHz, a sampling accuracy of 400ns, and an A / D resolution greater than 16 bits.

[0067] The cracks generated in this embodiment, such as Figure 2 As shown, the simulated rock samples exhibit two types of fractures: tensile fractures and shear fractures. The number of fractures ranges from 1 to 4, the fracturing pressure ranges from 3.13 to 31.04 MPa, and the fracture height ranges from 5 cm to 30 cm.

[0068] In this embodiment, the results of the acoustic emission monitoring and positioning interpretation of rock samples, and the quantitative analysis of acoustic emission event points, show that the proportions of tensile acoustic emission events and shear acoustic emission times are similar, with an average tensile event ratio of 44.14%, a shear event ratio of 45.26%, and a compression event ratio of 10.6%. The more transverse cuts produced by the sample, the higher the proportion of shear events.

[0069] The three-dimensional reconstruction results of the multi-fracture propagation morphology of the rock sample in this embodiment are as follows: Figure 3 As shown, the results indicate that as the wellbore inclination angle decreases, the angle between the fracture surface and the well axis decreases, making it difficult for multiple fractures to propagate evenly. When the segment spacing is large, the multi-fracture propagation in staged fracturing exhibits strong non-uniformity, with tortuous fracture paths. Directional perforation and increasing perforation depth are beneficial for initiating transverse fractures and penetrating the layer barrier. When the layer is well-developed, it is necessary to increase the fracturing fluid viscosity to overcome the layer barrier. The factors affecting fracture failure pressure are: directional perforation < spiral perforation, deep penetration < shallow perforation, large segment spacing < small segment spacing. Therefore, using a perforation process with directional perforation, deep penetration, and increased segment spacing is beneficial for reducing fracture failure pressure. Using a fracturing process with increased segment spacing, directional perforation, deep penetration, and increased fracturing fluid viscosity is beneficial for forming transverse fractures and promoting the even propagation of multiple fractures.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for shale oil high deviated well hydraulic fracturing indoor physical model experiment, characterized in that, The method comprises the following steps: Step S1: obtaining downhole cores, testing core physical properties and mechanical parameters; Step S2: imaging and observing the lithology of the downhole cores to obtain the characteristics of the formation layering and fractures; Step S3: preparing simulation rock samples matched with the physical parameters, mechanical parameters and structural characteristics of the downhole cores; Step S4: setting different well inclinations, perforation processes, cluster numbers and cluster spacings in the simulation rock samples; Step S5: loading three-directional stress on the simulation rock samples, setting injection parameters to obtain fractures with different morphological characteristics; Step S6: dynamically monitoring the crack initiation and expansion process by using an acoustic emission monitoring system to obtain the internal crack morphology of the simulation rock samples; Step S7: analyzing the factors affecting the crack initiation and expansion of the high-deviation well to determine the construction parameter combination for reducing the breakdown pressure of the high-deviation well.

2. The method of claim 1, wherein the method is a shale oil high- deviated well hydraulic fracturing indoor physical model experiment method, characterized in that, In the step S1, the full-diameter downhole core is obtained, and the full-diameter downhole core is processed into a core sample by using a water-free linear cutting method.

3. The method of claim 2, wherein the method further comprises, In the step S1, the core physical properties include porosity and permeability; and the mechanical parameters include Young's modulus, Poisson's ratio and tensile strength.

4. The method of claim 3, wherein the method further comprises, In the step S2, the layering and reservoir interaction relationship is obtained through imaging logging interpretation results and core observation, including layering density; and the natural fracture characteristics are obtained through imaging logging interpretation results, including natural fracture dip angle and other parameters.

5. The method of claim 4, wherein the method further comprises, In the step S3, first, the proportions of cement, sand and water are differentiated and adjusted according to the core physical parameters and mechanical properties measured in the step S1, and then the artificial sample is cast; according to the layering density and natural fracture dip angle and other parameters obtained in the step S2, paper is inserted during the casting preparation of the artificial sample to simulate natural fractures with different cementing strengths by adjusting the number of papers; and glass sheets are inserted to simulate layering surfaces.

6. The method of claim 5, wherein the method further comprises, In the step S3, the physical parameter test is carried out on the artificial samples prepared with different proportions of cement, sand and water, and the proportion closest to the physical parameters of the downhole core is selected to prepare the simulation rock sample.

7. The method of claim 6, wherein the method further comprises, In the step S4, a prefabricated wellbore is embedded in the middle layer of the simulation rock sample, and different high-deviation wells with different well inclinations are simulated by changing the shape of the wellbore; a prefabricated iron rod is used to connect the prefabricated wellbore to simulate perforation, and the number, length and angle of the iron rod are changed to change the number, depth and phase angle of the perforation.

8. The method of claim 7, wherein the method further comprises, In the step S5, a true triaxial hydraulic fracturing simulation system is applied to apply three-directional stress to the simulation rock sample, and the injection liquid type, viscosity and displacement are set to make the simulation rock sample produce hydraulic fractures.

9. The method of claim 1, wherein the method further comprises, In the step S6, a DS5 acoustic emission monitoring system is used to track the cracks in real time based on the P-wave polarity microseismic mechanism solution, and the internal crack morphology of the simulation rock sample is obtained after CT scanning test to determine the crack initiation and expansion characteristics.

10. The method of claim 1, wherein the high angle deviated well hydraulic fracturing indoor physical model experiment method is characterized in that, In the step S7, the main control factors affecting the crack breakdown pressure are determined according to the crack initiation pressure value of the high-deviation well, the influence degree of each factor is sorted according to the change range of the breakdown pressure value, and the combined construction parameters that can effectively reduce the breakdown pressure and promote the balanced expansion of multiple fractures are obtained.

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