A deep shale dessert evaluation method based on high temperature and high pressure rheological experiment

Abstract

The application discloses a deep shale dessert evaluation method based on high-temperature and high-pressure rheological experiment, and relates to the technical field of oil and natural gas exploration and development.The application provides a new idea about deep dessert evaluation: under the condition of simulating high-temperature and high-pressure of deep strata, macro and micro scales before and after shale rheology are compared and analyzed, and pore size distribution, adsorption and desorption characteristics and microstructure characteristics before and after high-temperature and high-pressure rheological experiment of shale are analyzed.Pore structure evolution characteristics in the deformation process are approximately dynamically analyzed, so that a deep shale dessert evaluation model is preliminarily established.The application develops the deep shale characteristics of "dessert", evaluates the "source" and "reservoir" of shale gas richness and the percolation mechanism of fracturing reconstruction under high-temperature and high-pressure "flow", that is, in the shale dessert evaluation, attention is paid to the reservoir comprehensive evaluation before development or whether complex cracks are formed after shale fracturing.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas exploration and development, in particular to the technical field of shale compressibility evaluation, and more particularly to a deep shale dessert evaluation method based on high temperature and high pressure rheology. BACKGROUND

[0002] Shale gas is a natural gas resource that can be mined from shale layers, and the recoverable reserves of shale gas in China are large. The deep shale gas reserves with a burial depth greater than 3500 m are abundant, but due to the characteristics of high temperature, ultra-high pressure, dense matrix, complex reservoir space and structure, and strong heterogeneity, the exploitation is difficult, and large-scale fracturing modification is necessary to realize effective development. Therefore, obtaining shale compressibility evaluation parameters and quantitatively evaluating the compressibility of shale gas horizontal wells are of great significance to the efficient and economic development of shale gas fields.

[0003] At present, there are various evaluation indexes for shale compressibility, and the main evaluation indexes mainly focus on the calculation of brittleness index. However, only brittleness index cannot comprehensively evaluate the compressibility of shale. Li Qinghui (2012) proposed that the brittleness characteristics of shale are related to its type, coring depth, coring direction, and loading conditions. When evaluating its mechanical properties, it is suggested to conduct research for specific regions, and the test should be simulated under the underground mechanical environment, so as to obtain more accurate results. Lai Fqiang (2018) used parameters such as brittleness coefficient (BIe), brittleness mineral content (BM), organic carbon content (TOC), clay mineral content (CL), fracture toughness (KC), and horizontal stress difference coefficient (Kh) to quantitatively analyze the weight of each parameter using the analytic hierarchy process to evaluate the fracturing property of shale gas reservoirs. Liu Yaowen (2022) proposed a new method for evaluating compressibility based on the angles of crack rupture, extension, and filling: selecting key evaluation parameters: brittleness index, ground stress characteristic parameters, and construction parameters to perform stress inversion, and based on each parameter, a comprehensive compressibility index is obtained to establish a new model for interpreting mechanical parameters.

[0004] Deep shale reservoirs mainly develop micropores and mesopores with a pore size less than 50 nm. In the high temperature and high pressure environment of deep shale (the pressure is generally higher than 70 MPa, and the average formation temperature is about 130 ℃). After fracturing under high temperature and high pressure, it is difficult to form a complex fracture network, and it is difficult for the crack to initiate and extend, and it is relatively difficult to inject proppants compared with shallow layers, which makes it difficult to obtain fractures with high conductivity. The flow and production of gas in micro-pore fractures in shale reservoirs are the key to the development of shale gas fracturing.

[0005] After consulting relevant literature, it is found that the current compressibility evaluation method is not perfect, especially the research on deep shale compressibility is insufficient, and the existing compressibility evaluation mainly has the following deficiencies:

[0006] (1) Existing compressibility evaluation is relatively macroscopic, and shale macroscopic characteristics and microscopic characteristics cannot be combined;

[0007] (2) The changes of pore and fracture structure, organic matter and mineral structure cannot be reflected;

[0008] (3) The pore and fracture evolution process of shale rheology under high temperature and high pressure is not clear;

[0009] (4) The analysis condition is relatively static, and the changes of shale pore and fracture structure and adsorption and desorption before and after transformation are not analyzed. SUMMARY

[0010] In order to overcome the defects and deficiencies existing in the prior art, the present application provides a deep shale sweet spot evaluation method based on high temperature and high pressure rheology, and the purpose of the present application is to solve the problems existing in the shale compressibility evaluation in the prior art. The present application provides a new idea for deep sweet spot evaluation: under the condition of simulating deep formation high temperature and high pressure, the macro and micro scales before and after shale rheology are compared and analyzed, and the pore size distribution, adsorption and desorption characteristics and microstructure characteristics before and after the high temperature and high pressure rheology experiment of shale are analyzed. The pore structure evolution characteristics in the deformation process are approximately dynamically analyzed, so as to preliminarily establish a deep shale sweet spot evaluation model. The present application develops the deep shale characteristics of "sweet spot", evaluates the "source", "storage" of shale gas and the percolation mechanism of fracturing reconstruction under high temperature and high pressure "flow", that is, in the shale gas sweet spot evaluation, the comprehensive evaluation of reservoir before development or whether complex fractures are formed after shale fracturing is paid more attention.

[0011] In order to solve the problems existing in the prior art, the present application is realized by the following technical scheme.

[0012] The present application provides a deep shale sweet spot evaluation method based on high temperature and high pressure rheology, which comprises the following steps:

[0013] S1, coring the shale gas well to be evaluated to prepare shale samples to be evaluated;

[0014] S2, cutting the prepared shale samples to be evaluated according to the experimental requirements of various experimental samples;

[0015] S3, performing basic experiments on the upper part of the cut sample, and performing high temperature and high pressure rheology experiments on the lower part of the cut sample;

[0016] S4, the sample after high temperature and high pressure rheological experiment is cut and processed, the fresh end face is selected for scanning electron microscope observation, the microstructure characteristics of the sample after high temperature and high pressure rheological experiment are analyzed, and at the same time, the low temperature CO2 and low temperature N2 adsorption experiments of the sample after high temperature and high pressure rheological experiment are carried out, and the pore size distribution characteristics of the sample after high temperature and high pressure rheological experiment are analyzed;

[0017] S5, the microstructure characteristics after high temperature and high pressure rheological experiment are compared and analyzed with the microstructure characteristics obtained by the basic experiment, and the scanning electron microscope, low temperature CO2 adsorption and low temperature N2 adsorption experiment results before and after high temperature and high pressure rheological experiment are combined, and the change characteristics of shale after high temperature and high pressure rheological experiment are analyzed;

[0018] S6, the experimental results after high temperature and high pressure rheological experiment are comprehensively sorted with the basic experimental results, and the deep shale mineability evaluation index is formed;

[0019] S7, according to the enrichment condition evaluation index of deep shale and the mineability evaluation index of deep shale, according to the analysis structure of the target layer, the condition layer and the parameter layer, the deep shale sweet spot evaluation is carried out by using the analytic hierarchy process.

[0020] Further preferably, in the step S7, the analysis structure of the target layer, the condition layer and the parameter layer is that the condition layer is a first index, and the parameter layer is a second index; the deep shale sweet spot is the target layer, the enrichment condition of deep shale and the mineability of deep shale are the condition layer, and the specific parameter index is the parameter layer.

[0021] More preferably, in the step S7, under the first index of the enrichment condition of deep shale, the second index includes TOC content, effective thickness of reservoir, porosity and gas content; under the first index of the mineability of deep shale, the second index includes brittle mineral content, reservoir burial depth, horizontal stress difference and change of pore and fracture after rheological.

[0022] Further preferably, in the step S3, the lower part of the cut sample is subjected to high temperature and high pressure rheological experiment, and the specific steps are as follows:

[0023] The end face of the lower part of the cut sample is ground on a flat glass surface with diamond sand to ensure that the end face is smooth and parallel to each other, and the high temperature and high pressure rheological experiment sample is obtained;

[0024] Before the sample is loaded, it is placed in a drying oven at 120 DEG C for 24 hours to dry and dehydrate, and is uniformly placed in a dry bottle for storage;

[0025] The prepared experimental sample is placed into the core chamber of the experimental equipment;

[0026] After the experimental sample is installed, vacuum is first drawn for 30 minutes, and then axial pressure and confining pressure are synchronously applied at a certain ratio, displacement control is switched to pressure control when the confining pressure reaches the set value, and then heating is started after stabilization.

[0027] When the temperature and confining pressure reach the pre-set values, friction correction is performed, and then high-temperature and high-pressure rheological experiment is performed, and displacement rate loading mode is used during loading, and the experiment is stopped after loading to failure.

[0028] Further preferably, in the S3 step, a high-temperature and high-pressure experimental device using a gas medium is used to perform a high-temperature and high-pressure rheological experiment on the lower part of the split sample core, and the high-temperature and high-pressure conditions are determined according to the actual depth of the formation, and the size of the lower part of the split sample core is specified according to the size of the core chamber of the high-temperature and high-pressure experimental device.

[0029] More preferably, the size of the lower part of the split sample core is a Φ20mm x 40mm columnar core.

[0030] Further preferably, the basic experiment includes any one or a combination of multiple of XRD experiment, TOC experiment, RO experiment, rock pyrolysis experiment, SEM electron microscope experiment, low-temperature liquid nitrogen adsorption experiment, and low-temperature carbon dioxide adsorption experiment.

[0031] More preferably, the S6 step specifically comprises: comprehensively sorting the experimental results after the high-temperature and high-pressure rheological experiment, the XRD experiment results of the shale, and the TOC content analysis results, to form the deep shale mineability evaluation index.

[0032] More preferably, according to the X-ray diffraction analysis method for clay minerals and common non-clay minerals in sedimentary rocks (SY / T 5163-2018), a Japanese Rigaku TTR III multifunctional X-ray diffractometer is used to carry out the shale XRD experiment, and the non-clay mineral composition and clay mineral composition of the studied shale are analyzed.

[0033] More preferably, according to the method for determination of total organic carbon in sedimentary rocks (GB / T 19145-2003), organic carbon analysis is performed, and a LECO CS-230 carbon and sulfur analyzer is used to carry out pyrolysis experiment on the studied shale, and the TOC content of the shale is analyzed.

[0034] More preferably, according to the scanning electron microscope analysis method for rock samples (SY / T 5162-1997), a Zeiss Sigma500 field emission scanning electron microscope is used to observe the microstructure of the shale, and the microstructure of the pores and fractures of the shale is analyzed.

[0035] Further preferably, according to the analysis method of GB / T 21650.3-2011 mercury injection method and gas adsorption method for determining the pore size distribution and porosity of solid materials, part 3, gas adsorption method for analyzing micropores, low-temperature CO2 and N2 adsorption experiments of shale are carried out by using ASAP 2460 surface area and porosity analyzer and the matching MicroActive software, and the pore distribution level adsorption characteristics of shale are analyzed.

[0036] Compared with the prior art, the beneficial technical effects brought by the present application are as follows:

[0037] The evaluation of the microstructure of shale is focused on systematization, which reduces the influence of heterogeneity on experimental results, and the comprehensive experiment of the microstructure of the same piece of shale is carried out, the research content is more systematic, and the pertinence is stronger; the rheological experiment is carried out to evaluate the microstructure characteristics of shale, on the one hand, the in-situ conditions of underground shale are restored, and on the other hand, the pore structure evolution characteristics after fracturing or geological structure movement can be analyzed, the static microstructure is changed to dynamic evaluation, and then the shale source, storage and flow are comprehensively evaluated, which is beneficial to guide the industrial development of shale gas. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 It is a flowchart of the shale sweet spot evaluation method based on high-temperature and high-pressure rheological experiment;

[0039] Figure 2 It is a sample cutting schematic diagram in the embodiment;

[0040] Figure 3 It is a structure schematic diagram of high-temperature and high-pressure rheological experiment device;

[0041] Figure 4 It is a core chamber schematic diagram of high-temperature and high-pressure rheological experiment;

[0042] Figure 5 It is a structure diagram of analytic hierarchy process sweet spot evaluation;

[0043] Figure 6 It is a relationship diagram between the calculated sweet spot evaluation comprehensive index and the gas production in the example. DETAILED DESCRIPTION

[0044] In order for those skilled in the art to better understand the technical solutions in the specification, the technical solutions in the specification will be described clearly and completely in the specification below in combination with the drawings in the specification. Obviously, the described embodiments are only part of the embodiments of the specification, not all the embodiments. Based on the embodiments in the specification, all other embodiments obtained by those skilled in the art without creative labor should belong to the protection scope of the specification.

[0045] Embodiment 1

[0046] As a preferred embodiment of the present application, referring to the accompanying drawings of the specification Figure 1 The present embodiment discloses a deep shale dessert evaluation method based on high temperature and high pressure rheology, which comprises the following steps:

[0047] S1, coring the shale gas well to be evaluated to make shale samples to be evaluated;

[0048] S2, cutting the made shale samples to be evaluated according to the experimental requirements of various category experimental samples;

[0049] S3, performing basic experiments on the upper part of the cut sample and high temperature and high pressure rheology experiments on the lower part of the cut sample;

[0050] S4, performing sectioning treatment on the sample after the high temperature and high pressure rheology experiment, selecting a fresh end face for scanning electron microscope observation, analyzing the microstructure characteristics of the sample after the high temperature and high pressure rheology experiment, and at the same time, performing low temperature CO2 and low temperature N2 adsorption experiments on the sample after the high temperature and high pressure rheology experiment to analyze the pore size distribution characteristics of the sample after the high temperature and high pressure rheology experiment;

[0051] S5, comparing and analyzing the microstructure characteristics after the high temperature and high pressure rheology experiment with the microstructure characteristics obtained by the basic experiment, and combining the scanning electron microscope, low temperature CO2 adsorption and low temperature N2 adsorption experimental results before and after the high temperature and high pressure rheology experiment, to analyze the change characteristics of the shale after the high temperature and high pressure rheology experiment;

[0052] S6, comprehensively arranging the experimental results after the high temperature and high pressure rheology experiment and the basic experimental results to form deep shale mineability evaluation indexes;

[0053] S7, according to the enrichment condition evaluation indexes of the deep shale and the deep shale mineability evaluation indexes, according to the analysis structure of the target layer, the condition layer and the parameter layer, using the analytic hierarchy process to evaluate the deep shale dessert.

[0054] As an implementation manner of the present embodiment, referring to the accompanying drawings of the specification Figure 5 In the S7 step, the analysis structure of the target layer, the condition layer and the parameter layer is specifically that the condition layer is a first index and the parameter layer is a second index; the deep shale dessert is the target layer, the enrichment condition of the deep shale and the mineability of the deep shale are the condition layer, and the specific parameter indexes are the parameter layer.

[0055] Furthermore, in the S7 step, under the first index of the enrichment condition of the deep shale, the second indexes include TOC content, effective thickness of the reservoir, porosity and gas content; and under the first index of the mineability of the deep shale, the second indexes include brittle mineral content, reservoir burial depth, horizontal stress difference and change of pore and fracture after rheology.

[0056] Embodiment 2

[0057] As another preferred embodiment of the present application, the embodiment is further detailed supplement and elaboration to the technical solution of the present application on the basis of the above-mentioned embodiment 1. In the embodiment, referring to the drawings in the description Figure 3 As shown in the drawings, the gas medium high temperature and high pressure experimental equipment is used for high temperature and high pressure rheological experiment on the lower part of the split sample core, and the high temperature and high pressure conditions are determined according to the depth of the actual formation, and the size of the lower part of the split sample core is specified according to the size of the core chamber of the high temperature and high pressure experimental equipment.

[0058] As an example, the size of the lower part of the split sample core is Φ20mm*40mm columnar core.

[0059] The high temperature and high pressure rheological experiment is performed on the lower part of the split sample core, and the specific steps are as follows:

[0060] The end face of the lower part of the split sample core is ground on a flat glass surface with diamond sand to ensure that the end face is smooth and parallel to each other, and a high temperature and high pressure rheological experiment sample is obtained.

[0061] Before the sample is loaded, it is placed in a drying oven at 120℃ for 24 hours of dehydration, and is uniformly placed in a drying bottle for storage.

[0062] The prepared experimental sample is placed in the core chamber of the experimental equipment;

[0063] After the experimental sample is installed, vacuum is first drawn for 30min, then axial pressure and confining pressure are synchronously applied at a certain ratio, displacement control is switched to pressure control when the confining pressure reaches the set value, and then the temperature is increased after stabilization;

[0064] After the temperature and confining pressure reach the pre-set values, friction correction is performed, and then high temperature and high pressure rheological experiment is performed, and displacement rate loading mode is used during loading, and the experiment is stopped after loading to failure. After the experiment is completed, the sample is unloaded, photographed and described.

[0065] Embodiment 3

[0066] As another preferred embodiment of the present application, the embodiment is further detailed supplement and elaboration to the technical solution of the present application on the basis of the above-mentioned embodiment 1 or embodiment 2. In the embodiment, the basic experiment includes any one or a combination of multiple of XRD experiment, TOC experiment, RO experiment, rock pyrolysis experiment, SEM electron microscope experiment, low temperature liquid nitrogen adsorption experiment and low temperature carbon dioxide adsorption experiment.

[0067] Further, the step S6 is specifically, the experimental results after the high temperature and high pressure rheological experiment are comprehensively arranged with the shale XRD experimental results, TOC content analysis results, and deep shale mineability evaluation indexes are formed.

[0068] As an example, according to the X-ray diffraction analysis method of clay minerals and common non-clay minerals in sedimentary rocks in SY / T5163-2018, the Japanese science TTR III multifunctional X-ray diffractometer is used to carry out shale XRD experiment, and the non-clay mineral composition and clay mineral composition of the studied shale are analyzed.

[0069] As another example, according to the method for determination of total organic carbon in sedimentary rocks in GB / T19145-2003, the organic carbon analysis is carried out, the LECO CS-230 carbon and sulfur analyzer is used for pyrolysis experiment of the studied shale, and the TOC content of the shale is analyzed.

[0070] As another example, according to the method for determination of total organic carbon in sedimentary rocks in GB / T19145-2003, the organic carbon analysis is carried out, the LECO CS-230 carbon and sulfur analyzer is used for pyrolysis experiment of the studied shale, and the TOC content of the shale is analyzed.

[0071] As another example, according to the method for determination of total organic carbon in sedimentary rocks in GB / T19145-2003, the organic carbon analysis is carried out, the LECO CS-230 carbon and sulfur analyzer is used for pyrolysis experiment of the studied shale, and the TOC content of the shale is analyzed.

[0072] Embodiment 4

[0073] As another preferred embodiment of the present application, referring to the shale sweet spot evaluation method based on high temperature and high pressure rheology shown in the accompanying drawings of the specification, Figure 1 The embodiment discloses a deep shale sweet spot evaluation method based on high temperature and high pressure rheology, which comprises the following steps:

[0074] The whole shale sample evaluation is made: the shale on the same small layer of the full diameter core of the deep shale gas well is taken by using the wire cutting coring technology.

[0075] As shown in the accompanying drawings of the specification, Figure 2 The obtained long core is designed according to the experimental requirements of various category experimental samples, and as an example, the cutting ratio can be 2:8.

[0076] The XRD experiment, TOC experiment, Ro experiment, rock pyrolysis experiment, SEM electron microscope experiment, low temperature liquid nitrogen adsorption experiment and low temperature carbon dioxide adsorption experiment of the upper part of the cutting sample are carried out.

[0077] The cut lower part core is subjected to high temperature and high pressure deformation experiment, and then high temperature and high pressure rheological experiment is carried out by using high temperature and high pressure pseudo triaxial experiment equipment; the microstructure characterization experiment of the sample after the rheological experiment is carried out, the pore structure characterization experiment is carried out after the sample is cut; finally, the microstructure of the shale before and after deformation is compared, and the source, storage and flow characteristics of the shale are analyzed.

[0078] Further, as shown in the description accompanying drawings Figure 3 Further, as shown in the description accompanying drawings

[0079] The end face of the prepared core sample is ground on a flat glass surface with diamond sand to ensure smooth and parallel end faces. The experimental sample is dried and dehydrated in a drying oven at 120°C for 24 hours before being loaded, and is uniformly stored in a drying bottle. The prepared core is placed in the core chamber of the experimental equipment. After the sample is installed, vacuum is drawn for 30 minutes, then the axial pressure and confining pressure are applied simultaneously at a certain ratio, and when the confining pressure reaches the set value, the displacement control is switched to pressure control, and after stabilization, the temperature is raised. Constant pressure control can ensure that the sample expansion does not change the pressure during temperature rise, ensuring that the sample is in a static rock pressure state during temperature rise. After the temperature and confining pressure reach the pre-set values, friction correction is performed, then high temperature and high pressure rheological experiment is performed, and displacement rate loading mode is used during loading. After loading to failure, the experiment is stopped. After the experiment is completed, the sample is unloaded, photographed and described.

[0080] After the high temperature and high pressure experiment, the sample is further cut and processed, the fresh end face is observed by scanning electron microscope, the microstructure characteristics after high temperature and high pressure deformation are analyzed, and at the same time, low temperature CO2 and low temperature N2 adsorption experiments are carried out on part of the samples to analyze the pore size distribution characteristics after high temperature and high pressure rheological experiment.

[0081] Further, the microstructure of the shale before and after the well high temperature and high pressure rheological experiment is compared and analyzed, and the results of scanning electron microscope, low temperature CO2 adsorption and low temperature N2 adsorption experiments before and after the experiment are combined to analyze the change characteristics of the shale under high temperature and high pressure.

[0082] Further, the experimental results under high temperature and high pressure are combined with the XRD results of the shale, the TOC content analysis results, and the deep shale mineability evaluation index is formed.

[0083] Furthermore, by combining basic experimental data with high-temperature and high-pressure rheological experimental data, the analytic hierarchy process (AHP) was used to obtain the sweet spot evaluation index for deep shale.

[0084] Example 5

[0085] Considering that existing evaluations of deep shale sweet spots are limited to the macroscopic mechanical and mineral characteristics of shale, and most evaluations are based on static parameters under normal temperature and pressure, lacking consideration of in-situ high-temperature and high-pressure conditions in deep shale and the evolution of pore and fracture characteristics under high temperature and pressure, this method provides a new approach to the evaluation of deep shale sweet spots: under simulated deep strata high-temperature and high-pressure conditions, a comparative analysis of the macro- and micro-scale changes in shale rheology before and after is conducted, analyzing the pore size distribution, adsorption and desorption characteristics, and microstructural features before and after the high-temperature and high-pressure rheological experiment. The evolution of pore structure during deformation under high temperature and pressure is analyzed approximately dynamically to establish a deep shale sweet spot evaluation model. The evaluation of deep shale sweet spots focuses on two aspects: the "source" and "reservoir" characteristics that characterize shale gas abundance, and the "flow" mechanism of fracturing and permeability enhancement under high temperature and pressure. In other words, the evaluation of shale gas sweet spots focuses on the comprehensive reservoir evaluation before development, or pays considerable attention to whether shale fracturing creates channels conducive to shale gas flow.

[0086] Furthermore, according to Figure 1 A method for evaluating sweet spots in deep shale based on high-temperature and high-pressure rheological experiments was developed. First, the research samples were prepared and then subjected to... Figure 2 The samples were cut and then subjected to basic experiments and high-temperature and high-pressure rheological experiments.

[0087] Furthermore, following the X-ray diffraction analysis method for clay minerals and common non-clay minerals in sedimentary rocks (SY / T5163-2018), XRD experiments were conducted on shale using a Rigaku TTRⅢ multi-functional X-ray diffractometer to analyze the non-clay mineral and clay mineral components of the studied shale.

[0088] Furthermore, in accordance with the method for determination of total organic carbon in sedimentary rocks (GB / T19145-2003), organic carbon analysis was performed. The pyrolysis experiment of the studied shale was conducted using a LECO CS-230 carbon-sulfur analyzer to analyze the TOC content of the shale.

[0089] Furthermore, referring to the analysis method of scanning electron microscopy for rock samples in SY / T 5162-1997, the microstructure of shale was observed using a Zeiss Sigma 500 field emission scanning electron microscope, and the microstructure of shale pores and fractures was analyzed.

[0090] Further, according to GB / T 21650.3-2011 Mercury Intrusion Porosimetry and Gas Adsorption Method for Determining Pore Size Distribution and Porosity of Solid Materials, Part 3: Gas Adsorption Method for Analysis of Micropores, low-temperature CO2 and N2 adsorption experiments of shale are carried out by using an ASAP 2460 surface area and porosity analyzer and a matching MicroActive software, and pore distribution level adsorption characteristics of shale are analyzed.

[0091] Further, high-temperature and high-pressure experiments of shale are carried out by using a gas medium high-temperature and high-pressure experimental equipment, and a schematic diagram of the experimental equipment is as shown in Figure 3 The high-temperature and high-pressure conditions are determined according to the actual depth of the formation. The core for the high-temperature and high-pressure experiment is prepared according to the size of the core chamber of the high-temperature and high-pressure experimental equipment, and the size of the sample is a columnar core of Φ20mm*40mm. The sample for the high-temperature and high-pressure experiment is prepared to minimize the influence of sample heterogeneity on the experiment, and to ensure that the characteristics of the sample, such as pore structure, mineral content and organic matter, are as same as possible.

[0092] Further, the end faces of the prepared core sample are ground on a flat glass surface with diamond sand to ensure that the end faces are smooth and parallel to each other. The experimental sample is dried and dehydrated in a drying oven at 120°C for 24 hours before being loaded, and is uniformly stored in a dry bottle. The prepared core is placed in the core chamber of the experimental equipment, and the structure of the core chamber is as shown in Figure 4 After the sample is installed, vacuum is first drawn for 30 minutes, and then axial pressure and confining pressure are synchronously applied at a certain ratio. When the confining pressure reaches the set value, displacement control is switched to pressure control, and after stabilization, heating is started. Constant pressure control can ensure that the expansion of the sample during heating does not change the pressure, and the sample is in a static rock pressure state during heating. After the temperature and confining pressure reach the pre-set values, friction correction is carried out, and then high-temperature and high-pressure rheology is carried out. The loading mode is displacement rate loading during loading, and the experiment is stopped after loading to failure. After the experiment is completed, the sample is unloaded, photographed and described.

[0093] After the high-temperature and high-pressure experiment is completed, further, the sample after the experiment is cut and processed, and a fresh end face is selected for scanning electron microscope observation to analyze the microstructure characteristics after high-temperature and high-pressure deformation. At the same time, low-temperature CO2 and low-pressure N2 adsorption experiments are carried out on part of the samples to analyze the pore size distribution characteristics after the high-temperature and high-pressure rheological experiment.

[0094] Further, the microstructure of shale before and after the high-temperature and high-pressure rheological experiment is compared and analyzed, and the results of scanning electron microscope, low-temperature CO2 adsorption and low-temperature N2 adsorption experiments before and after the experiment are combined to analyze the change characteristics of shale under high temperature and high pressure.

[0095] Further, the experimental results under high temperature and high pressure are combined with XRD results of shale, TOC content analysis results to form deep shale mineability evaluation index.

[0096] Finally, according to the "source" and "reservoir" characteristics of deep shale and the shale gas "flow" characteristics representing shale mineability, the deep shale gas sweet spot is evaluated according to the following formula: Figure 5 The evaluation results are used as a reference for deep shale development and guide the economic and efficient development of deep shale gas.

[0097] Further, the hierarchical structure is composed of the geological characteristics and mineability characteristics of shale gas reservoirs, which reflect the characteristics of shale gas generation, migration and enrichment, and the complex relationship between the numerous factors. Through summary and analysis, the factors affecting the quality of shale gas reservoirs are divided into two evaluation indexes: shale reservoir geological characteristics and shale gas mining mineability characteristics. Each evaluation index is determined by a plurality of secondary factors affecting the quality of shale gas reservoirs. According to the characteristics of each parameter and the nature of the evaluation index, the deep shale gas sweet spot area is selected as the target layer, and the reservoir geological conditions and reservoir mineability are set as the first index according to the "source", "reservoir" characteristics and "flow characteristics" representing the shale gas reservoir. The reservoir geological conditions include TOC content, effective thickness, porosity and gas content parameters, and the reservoir mineability includes shale reservoir burial depth, brittleness index, horizontal stress difference and pore volume change before and after rheological. Further, different hierarchical structures are formed, and the elements at the same level dominate the elements at the next level, while being dominated by the elements at the previous level. This top-down domination relationship forms a hierarchical structure, the topmost level is the result of sweet spot area selection, the middle level is the condition layer, and the lowest level is the evaluation parameter of sweet spot evaluation area.

[0098] After establishing the hierarchical structure, the membership relationship between the upper and lower layers is determined. According to the hierarchical structure relationship, the target layer, condition layer and parameter are coded and weighted.

[0099] Table 1 Deep shale evaluation index

[0100]

[0101] The weight assignment uses the 1-9 scale method for pairwise comparison to assign weights to each element. The meaning of the scale is shown in Table 2.

[0102] Table 2 Meaning of scale

[0103]

[0104] The weight of each evaluation element is quantitatively calculated by using the Delphi method. The basic idea is that the influence degree of factor Bi on target factor A is different, and then factor Bi is used to form a pairwise comparison matrix C:

[0105] ;

[0106] wherein C satisfies: a, C ii = 1; b, C ij = 1 / C ji ;

[0107] The weight of all elements in target A can be obtained by solving the eigenvalue of the judgment function C. The matrix is tested for consistency by using the random consistency ratio C.R. proposed by T.L. Saaty. Wherein, , n is the order of the matrix, and λ Max is the maximum eigenvalue. When C.R. < 10%, it is considered that the inconsistency of the judgment matrix is acceptable, and when C.R. > 10%, it needs to be revalued and calculated until C.R. < 10%.

[0108] Table 3 R.I. Value Table

[0109]

[0110] By using the above method, the characteristic vector and the maximum eigenvalue of each element in the high-yield area of coalbed methane in the study area are calculated by using Matlab software, and the reasonable weight value is obtained through consistency test. Among them, the importance scale of two factors in the judgment factor is valued according to the following table 4.

[0111] Table 4 Comparison matrix of each layer and parameter value

[0112]

[0113] Through the calculation of matrix and consistency test, the weight of each parameter for the optimization of deep shale gas sweet spot area is obtained, and the calculation results of weight are shown in the following table 5:

[0114] Table 5 Calculation results of weight of each parameter

[0115]

[0116] From the weight calculation results, it can be found that the proportion of TOC in the reservoir geological conditions is the highest, reaching 0.3, and the porosity is the lowest, being 0.17. The proportion of brittle mineral content (brittle index) in the reservoir recoverability condition representing the flowable reservoir fluid is the highest, reaching 0.42, and the burial depth is the lowest, being 0.12.

[0117] In the parameter layer, each parameter is different in different shale gas wells and blocks. According to the characteristics of the shale gas block, the parameters of the shale gas target area are divided into three levels of good, medium and poor, which are represented by I, II and III respectively. Each level is assigned a value of 70-100 points, 30-70 points and 0-30 points respectively (Table 8-2). According to the scoring type, the parameters of different shale gas wells or blocks are normalized, and finally the comprehensive evaluation index is calculated by combining the weight of each parameter in the shale gas sweet spot evaluation. According to the index, the shale gas reservoir development well layer is optimized.

[0118] Table 6 Index system and grade scoring table of shale gas "sweet spot area"

[0119]

[0120] Therefore, according to the research, the comprehensive evaluation index of the deep shale gas sweet spot area can be expressed as:

[0121] The comprehensive recoverable index = 0.215*NI(TOC) + 0.181*NI(H effective thickness) + 0.112*NI(porosity) + 0.163*NI(gas content) + 0.139*NI(brittle index) + 0.041*NI(buried depth) + 0.055*NI(horizontal stress difference) + 0.095*NI(pore volume increase multiple).

[0122] This study establishes an evaluation method system for optimizing the favorable area, and optimizes the favorable blocks of shale gas distribution. The optimization of the shale gas "sweet spot area" is related to the geological and reservoir recoverability conditions. Based on the geological and recoverability, the sweet spot area is optimized and evaluated in three levels. The three progressive levels from top to bottom are target layer, condition layer and parameter layer. The shale gas target area is a relatively favorable sweet spot area optimized by various parameters. The first level index of the condition layer refers to the geological conditions and recoverability of shale, which corresponds to the resource basis of "source" and "reservoir" of shale and the reservoir recoverability of "flow". First, good shale reservoir gas content is the basis of high yield of shale reservoir; second, high shale brittleness and good compressibility are important factors for shale gas resources to be produced. According to the main controlling factors of shale gas enrichment described in the parameter calculation model, the important factors are organic matter content, shale thickness, porosity, pore development degree, brittle mineral, buried depth, horizontal stress difference and pore fracture volume increase multiple. The shale gas wells in Weiyuan area of Sichuan Basin are comprehensively evaluated. Referring to the evaluation index weight table and index system and grade scoring table of the favorable area, each parameter of the known well is scored and summed to get the total score of each mineralized area. The higher the score, the greater the shale gas exploration and development potential, and the more favorable the block. The evaluation results are shown in Table 7.

[0123] Table 7 Comprehensive evaluation results

[0124]

[0125] The evaluation results show that the comprehensive evaluation index of the wells in the study area is located in 58.4-87.58, and the overall evaluation index is good. In order to verify the relationship between the evaluation index and the development effect, the relationship between the comprehensive evaluation index and the test gas production is established, and the results are shown in Figure 6

[0126] The results show that the comprehensive evaluation index and the test gas production have a good positive correlation. With the increase of the comprehensive index, the test gas production increases, and the linear correlation between them is high, R2=0.9166, indicating that the evaluation model has good applicability in the area.​

Claims

1. A method for deep shale dessert evaluation based on high temperature and high pressure rheological experiment, characterized in that: The evaluation method comprises the following steps: S1, coring the shale gas well to be evaluated to produce shale samples to be evaluated; S2, cutting the produced shale samples to be evaluated according to the experimental requirements of various category experimental samples; S3, performing basic experiments on the upper part of the cut sample, and performing high temperature and high pressure rheological experiments on the lower part of the cut sample; the basic experiments include any one or more combinations of XRD experiments, TOC experiments, RO experiments, rock pyrolysis experiments, SEM electron microscope experiments, low temperature liquid nitrogen adsorption experiments and low temperature carbon dioxide adsorption experiments; S4, performing sectioning treatment on the sample after the high temperature and high pressure rheological experiment, selecting a fresh end face for scanning electron microscope observation, analyzing the microstructure characteristics of the sample after the high temperature and high pressure rheological experiment, and at the same time, performing low temperature CO2 and low temperature N2 adsorption experiments on the sample after the high temperature and high pressure rheological experiment, and analyzing the pore size distribution characteristics of the sample after the high temperature and high pressure rheological experiment; S5, comparing and analyzing the microstructure characteristics after the high temperature and high pressure rheological experiment with the microstructure characteristics obtained by the basic experiments, and combining the scanning electron microscope, low temperature CO2 adsorption and low temperature N2 adsorption experiment results before and after the high temperature and high pressure rheological experiment, to analyze the change characteristics of the shale after the high temperature and high pressure rheological experiment; S6, comprehensively arranging the experimental results after the high temperature and high pressure rheological experiment and the basic experimental results, to form deep shale mineability evaluation indexes; S7, according to the deep shale enrichment condition evaluation indexes and the deep shale mineability evaluation indexes, and according to the analysis structure of the target layer, the condition layer and the parameter layer, using the analytic hierarchy process to evaluate the deep shale sweet spot.

2. The method for deep shale sweet spot evaluation based on high temperature and high pressure rheological experiment of claim 1, wherein: In the S7 step, the analysis structure of the target layer, the condition layer and the parameter layer is specifically that the condition layer is a first level index, and the parameter layer is a second level index; the deep shale sweet spot is the target layer, the enrichment condition of the deep shale and the mineability of the deep shale are the condition layer, and the specific parameter indexes are the parameter layer.

3. The method of claim 2, wherein: In the S7 step, under the first level index of the enrichment condition of the deep shale, the second level indexes include TOC content, effective thickness of the reservoir, porosity and gas content; under the first level index of the mineability of the deep shale, the second level indexes include brittle mineral content, reservoir burial depth, horizontal stress difference and change of pores and fractures after rheology.

4. The method of deep shale sweet spot evaluation based on high temperature and high pressure rheological experiment according to any one of claims 1-3, characterized in that: In the S3 step, the lower part of the cut sample is subjected to high temperature and high pressure rheological experiment, and the specific steps are as follows: Grind the end face of the lower part of the cut sample on a flat glass surface with diamond sand to ensure that the end face is smooth and parallel to each other to obtain a high temperature and high pressure rheological experimental sample; Before loading the experimental sample, place it in a drying oven at 120 DEG C for 24 hours to dry and dehydrate, and uniformly place it in a drying bottle for storage; Place the prepared experimental sample into the core chamber of the experimental equipment; After the experimental sample is installed, first perform vacuum pumping for 30 minutes, then apply axial pressure and confining pressure simultaneously at a certain ratio, switch from displacement control to pressure control when the confining pressure reaches the set value, and start heating after stabilization; After the temperature and confining pressure reach the pre-set values, perform friction correction, then perform high temperature and high pressure rheological experiment, and load at a constant displacement rate during loading, stop the experiment after loading to failure.

5. A method for deep shale sweet spot evaluation based on high temperature and high pressure rheological experiment according to any one of claims 1-3, characterized in that: In S3, the gas medium high temperature and high pressure experimental equipment is used to perform high temperature and high pressure rheological experiment on the lower part of the split sample core, the high temperature and high pressure condition is determined according to the actual formation depth, and the size of the lower part of the split sample core is specified according to the size of the core chamber of the high temperature and high pressure experimental equipment.

6. The method for deep shale sweet spot evaluation based on high temperature and high pressure rheological experiment of claim 5, wherein: The size of the lower part of the split sample core is Φ20mm*40mm columnar core.

7. A method for deep shale sweet spot evaluation based on high temperature and high pressure rheological experiment according to any one of claims 1-3, characterized in that: In S6, the experimental results after the high temperature and high pressure rheological experiment are comprehensively sorted with the shale XRD experimental results and TOC content analysis results to form the deep shale mineability evaluation index.

8. A method for deep shale sweet spot evaluation based on high temperature and high pressure rheological experiment according to any one of claims 1-3, characterized in that: According to the X-ray diffraction analysis method for clay minerals and common non-clay minerals in sedimentary rocks (SY / T 5163-2018), the Japanese TTR III multifunctional X-ray diffractometer is used to carry out shale XRD experiment, and the non-clay mineral composition and clay mineral composition of the studied shale are analyzed.

9. A method for deep shale sweet spot evaluation based on high temperature and high pressure rheological experiment according to any one of claims 1-3, characterized in that: According to the determination method for total organic carbon in sedimentary rocks (GB / T 19145-2003), the organic carbon analysis is performed, the LECO CS-230 carbon and sulfur analyzer is used to perform pyrolysis experiment on the studied shale, and the TOC content of the shale is analyzed.

10. A method for deep shale sweet spot evaluation based on high temperature and high pressure rheological experiment according to any one of claims 1-3, characterized in that: According to the scanning electron microscope analysis method for rock samples (SY / T 5162-1997), the Zeiss Sigma500 field emission scanning electron microscope is used to observe the microstructure of the shale, and the pore and fracture microstructure of the shale is analyzed.

11. A method for deep shale sweet spot evaluation based on high temperature and high pressure rheological experiment according to any one of claims 1-3, characterized in that: According to the analysis method for analyzing micropores by gas adsorption method in GB / T 21650.3-2011, the ASAP 2460 surface area and porosity analyzer and the matching MicroActive software are used to perform low temperature CO2 and N2 adsorption experiment on the shale, and the pore distribution level adsorption characteristics of the shale are analyzed.

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