Mechanical Properties Of Shale Research Articles

Weakening Effect of Water on Mechanical Properties of Brittle Shale under Triaxial Compression

Abstract The mechanical properties of rock materials are remarkably affected by water. To reveal the effect of water on the mechanical properties of shale, the conventional triaxial compression tests were implemented for shale with the five kinds of water saturation coefficient. According to the test results, the influence of the saturation coefficient on strength and deformation parameters was analyzed. Based on the fitting result of the Mohr-Coulomb criterion, the relationship between the strength parameters and the water saturation coefficient was analyzed. The softening effect of water on shale is mainly due to the decrease of cohesion and internal friction coefficient with increasing of water saturation coefficient. The strength criterion considering the influence of water weakening was established according to the function relationship between the fitting parameters and the water saturation coefficient. In addition, three kinds of brittleness indexes were selected to quantitatively analyze the influence of the saturation coefficient on shale brittleness. The results indicated that the brittleness indexes all decreased with the increase of the saturation coefficient, and the brittleness of shale is weakened after water absorption. The research results can provide a reference for the evaluation of saturated shale brittleness.

Effect of supercritical CO2-water-shale interaction on mechanical properties of shale and its implication for carbon sequestration

The mechanical behaviors of shale are important parameters influencing the CO2 storage security in shale reservoirs. Thus, understanding the mechanical properties alteration of shale induced by the injected CO2 is essential for evaluating the stability of shale reservoir rock and caprock. In this study, the impact of supercritical CO2(ScCO2)-water soak pressure and temperature (P = 0, 10, 15, 20 MPa, T = 308, 323, 338, 353 K) on the mechanical properties of shale were investigated. Mineral, pore and mechanical alterations in shale triggered by ScCO2-water soak were obtained by multiple characterization methods. The results indicated that ScCO2-water soak caused the decrease in clay and carbonate mineral contents, and the increase in macropore volume and porosity. Then, the average triaxial compressive strength and elastic modulus of shale decreased from 286.65 MPa to 156.90–247.20 MPa, and 13.62 GPa to 10.52–12.99 GPa, respectively, while Poisson's ratio v in shale increased from 0.1147 to 0.1179–0.1780. ScCO2-water soak induced mechanical weakening in shale is positively correlated with the soak pressure and negatively associated with soak temperature. The dissipated energy ratio decreased first and then increased during the stress loading process in all the tested shales, ScCO2-water soaked shale has a larger proportion of energy dissipation in each stage of stress loading. The results inferred that ScCO2-water soak caused an enhanced plastic deformation behavior in shale. The mechanical degradation in shale may increase the failure risk of reservoir rock or caprock, which should be concerned in CO2 geological storage engineering.

超临界CO<sub>2</sub>渗流的流-固-热多场耦合机理研究

<p indent="0mm">Clay swelling and dispersion easily occur when encountering water for shale formation, resulting in problems related to wellbore collapse when using water-based fluids, such as drilling fluid or poor fracturing stimulation when using water-based fluids as the fracturing fluid. Supercritical carbon dioxide (ScCO₂) can effectively protect the clay from hydration and avoid formation damage. Based on this, basic research studies have been performed by researchers regarding the exploitation of shale oil and gas resources using ScCO₂. The multi-physics coupling model describing the water seepage process cannot explain the ScCO₂ seepage because of a great variation in the physical properties of CO₂ with temperature and pressure. To construct multi-physics coupling models capable of reflecting the ScCO₂ seepage process when developing oil and gas resources using ScCO₂, the thermal-hydro-mechanical coupling models are established in this study based on the transport and thermodynamic properties of ScCO₂, combined with the law of effect of ScCO₂ dissolution on the mechanical properties of shale. The finite element method is used to study the distribution of formation temperature, pore pressure, and stress with time and location of ScCO₂ seepage, and the comparison of multi-physics fields is performed between ScCO₂ and water seepage. The results indicate that the compared with water seepage, the formation temperature variation of ScCO₂ seepage is greater, the pore pressure is lower, the stress difference near the wellbore in the direction of minimum <italic>in</italic>-<italic>situ</italic> stress is bigger, and the tangential stress in the direction of maximum <italic>in</italic>-<italic>situ</italic> stress is lower. This study can provide theoretical basis for wellbore stability analysis when using ScCO₂ as the drilling fluid and fracturing design and evaluation when using ScCO₂ as the fracturing fluid.

NANOINDENTATION EXPERIMENTS TO STUDY THE MICROMECHANICAL PROPERTIES OF STRATIFIED SHALE

The micromechanical properties of stratified shale are critical for understanding wellbore stability and hydraulic fracture extension patterns. Based on nanoindentation experiments and data analysis, the mechanical parameters of shale specimens from two laminar directions of the Jimsar Lucaogou Formation in Xinjiang are measured from a microscopic perspective in this paper. The mechanical parameters of multiple indentation points are obtained using grid indentation. The mineral composition of the samples is quantified using field emission scanning electron microscopy (SEM) and XRD ray diffraction. The results show that the shale mechanical parameters have a good linear relationship with each other at the nanoscale. However, the relationship between horizontal bedding and vertical bedding is quite different. The average elastic modulus, average hardness, and average fracture toughness of the parallel laminated specimens are 22.94 GPa, 1.04 GPa, and 1.19 MPa&amp;#183;m&lt;sup&gt;1/2&lt;/sup&gt;, respectively. The average elastic modulus, average hardness, and average fracture toughness of the vertical laminated specimens are 35.23 GPa, 3.47 GPa, and 1.32 MPa&amp;#183;m&lt;sup&gt;1/2&lt;/sup&gt;, respectively. The shale mechanical parameters in the vertical bedding direction are higher than those in the horizontal laminae. The mechanical parameters at the nanoscale are related to the orientation of the laminae. The shale is anisotropic at the nanoscale and the anisotropy of different mechanical parameters behaves differently. The microscopic elastic modulus, hardness, and fracture toughness of shale conform to Weibull distribution. The dispersion of hardness is the highest. The results can help analyze the relationship between shale mechanical properties and laminar orientation.

Study on rock mechanics characteristics of deep shale in Luzhou block and the influence on reservoir fracturing

AbstractThis paper aims to study the influence of deep formation conditions on the mechanical properties of shale, which is of great significance for the engineering application of efficient development of deep shale gas. In this study, a real‐time high‐temperature (25°C–170°C) triaxial compression experiment was first carried out on shale samples. Then, based on the analysis results of rock mineral components and discrete element numerical simulation technology, a thermo‐mechanical coupling model (TMCM) was constructed, and the accuracy of the numerical model was verified. Finally, based on the micromechanical parameters, a numerical fracturing mechanism model considering the influence of temperature, natural fracture density, and fracture length was established, and the influence of current reservoir conditions on hydraulic fracturing was discussed. The results show that confining pressure has a greater effect on rock mechanics than temperature. When the temperature exceeds 110°C, the plasticity of rock samples increases, and the fracture morphology becomes complex. In addition, the increase in temperature promotes the fracture of microcracks to a certain extent. The research results are expected to provide a sufficient theoretical basis for the development and utilization of deep shale gas resources.

Shale Formation Damage during Fracturing Fluid Imbibition and Flowback Process Considering Adsorbed Methane

Hydraulic fracturing of shale gas reservoirs is characterized by large fracturing fluid consumption, long working cycle and low flowback efficiency. Huge amounts of fracturing fluid retained in shale reservoirs for a long time would definitely cause formation damage and reduce the gas production efficiency. In this work, a pressure decay method was conducted in order to measure the amount of fracturing fluid imbibition and sample permeability under the conditions of formation temperature, pressure and adsorbed methane in real time. Experimental results show that (1) the mass of imbibed fracturing fluid per unit mass of shale sample is 0.00021–0.00439 g/g considering the in-situ pressure, temperature and adsorbed methane. (2) The imbibition and flowback behavior of fracturing fluid are affected by the imbibition or flowback pressure difference, pore structure, pore surface properties, mechanical properties of shale and mineral contents. (3) 0.01 mD and 0.001 mD are the critical initial permeability of shales, which could be used to determine the relationship between the formation damage degree and the flowback pressure difference. This work is beneficial for a real experimental evaluation of shale formation damage induced by fracturing fluid.

Investigation of the Temperature Dependence of the Chemical-Mechanical Properties of the Wufeng-Longmaxi Shale.

Shale rocks have been widely investigated to evaluate the productivity of oil/gas. The high temperature generated by the explosive fracturing to stimulate the gas reservoir has a significant impact on the chemical-mechanical properties of shale rocks. Pioneering works have been carried out at temperatures below 500 °C, but little has been done to quantify the correlation between the chemical and mechanical properties of shale at temperatures above 500 °C. Therefore, an experimental study on the effect of temperature on the chemical-mechanical properties of shale rocks is presented in this paper. The temperatures used in our experiments are between 0 and 800 °C. Results indicate that there exist strong chemical reactions leading to a big reduction in the sample's weight and mechanical strength for a temperature over 500 °C. Thermogravimetric analysis data demonstrates that the weight of shale powders has little change below 400 °C and largely decreases after 600 °C. It shows that the chemical reaction rate corresponding to shale compositions varies with temperature. X-ray diffraction and Fourier transform infrared are integrated to quantify the occurrence of contained reactions including the decomposition of kerogen, carbonates, and quartz transition. This can provide a temperature range for all possible reactions. Changes in the compositional information of shale samples have been proven to significantly influence the mechanical properties. A 25% decrease in dynamic Young's modulus emerges as the temperature approaches 700 °C. As the brittle minerals, for instance, carbonates, decrease with temperature, a brittle-ductile transition happens in shale. This work provides very meaningful results different from that at low temperatures to help people better understand the effects of high temperatures in many fields, such as explosive fracturing and radioactive waste disposal.

The investigation of impact of temperature on mixed-mode fracture toughness of shale by semi-circular bend test

Unconventional oil and gas resources are important and have recently attracted attention. High temperature stimulation can effectively release the damage of water phase trapping, which was caused during the drilling and completion of hydraulic fracturing of shale gas reservoirs. The changes of physical and mechanical properties of shale under high temperature is of significance to the safety and efficiency of hydraulic fracturing. This study investigated the effect of temperature on seismic velocity, porosity, permeability, and mixed-mode fracture toughness of shale. Shale samples are separated into two groups, one group of 12 samples to test porosity, permeability and velocity, and the second group of 12 samples to test the fracture toughness of shale. The results showed that as the temperature increased, the color of the shale sample lightened, and seismic velocity decreased while the permeability and porosity increased. The results also revealed that as the temperature was raised to 400 °C–600 °C, seismic velocity, shale permeability, and porosity all increased. Furthermore, the mixed-mode fracture toughness was reduced, indicating that the threshold temperature of the shale was around 400 °C. The threshold value obtained can provide a basis for field evaluation and the potential application of high-temperature treatment. A numerical model was developed to simulate fracture propagation in SCB (semi-circular bend) samples subjected to thermal treatment. The numerical simulation agreed with the experimental results, indicating that the high temperature promoted fracture propagation and had a higher stress concentration at the fracture tip.

Review of the Generation of Fractures and Change of Permeability due to Water-Shale Interaction in Shales

In shale development, water-based liquids are injected into the formations. In this process, water can interact with shales, especially with clay content. The interaction can lead to some phenomena, including clay swelling, reduction of mechanical properties of shales and fractures, generation and propagation of fractures, particle detachment, and permeability change. All the phenomena can impact productivity during the development, thereby impacting our investment and return on investment (ROI). So far, many researchers have put their time and efforts into this topic, and many articles have been published. However, some discrepancies still exist in shale reservoirs regarding the role of the interaction between water and shale, especially the impact of clay swelling. Some believe that clay swelling causes formation damage, mainly impairing shale permeability. Others state that fractures can be induced because of clay swelling, leading to the enhancement of shale permeability. So far, few articles have reviewed the various views on this interaction. Additionally, the relationship between each phenomenon is not discussed. In this paper, we try to draw a clear picture of water-shale interaction by reviewing the published studies, mainly focusing on experimental methodology and experimental results. Based on the review, we summarized the influencing factors as well as the mechanisms about the formation of fractures and change of permeability due to water-shale interaction. In water-shale interaction, the induced fractures are generated by the combined effects from clay swelling, reduction of mechanical properties of shales and fractures, and stress anisotropy. Shale permeability can be enhanced if the generated fractures can form an effective flow channel. However, if the generated fractures cannot serve as an effective flow channel, shale permeability will be impaired by clay swelling, water blocking, stress-sensitive, etc.

Time-Sensitive Characteristics of Bedding Shale Deterioration under the Action of Drilling Fluid

Abstract Fractures continuously extend and expand along bedding shale formations under the action of drilling fluid and eventually form a complex fracture network, which greatly reduces the strength of the rock. To determine the effect of the drilling fluid action time on the physical and mechanical properties of shale, nuclear magnetic resonance tests are carried out on shale soaked in oil-based drilling fluid for different soaking times. The fluid absorption rate of shale takes the form of a power function. The equations relating the shale mass, porosity, and permeability to soaking time are established. Then, in a sonic time-difference test, the change in the dynamic elastic parameters with the immersion time are observed. According to a triaxial strength test, the failure form and the deterioration degrees of the layered shale in different loading directions with immersion time are analyzed. Numerical simulation of the deterioration degree of shale under different water content conditions is carried out. When the water content increases, the collapse density of the surrounding rock of the well wall increases significantly. Finally, considering the anisotropy of bedding shale, the inclination angle, azimuth angle, and drilling fluid immersion time are substituted into the rock mechanics parameter deterioration model, the three pressure profiles of the formation are corrected, and the safe drilling fluid density window of the target interval is given.

Experimental Study on the Mechanical Properties of Shale After Long-term of Immersion in Fracturing Fluids with Different pH

Experimental Study on the Mechanical Properties of Shale After Long-term of Immersion in Fracturing Fluids with Different pH

Determination of shale macroscale modulus based on microscale measurement: A case study concerning multiscale mechanical characteristics

Shale mechanical properties are important for shale gas production, but the magnitudes are difficult to estimate, standard size cores are hard to sample, and secondary interstice generation is inevitable. This paper proposes a method for determining shale macroscale modulus, which is determined at a hierarchy of scales from the nano-to macro-scales. Microscale measurements are upscaled to estimate the corresponding magnitudes at the macroscale. A case study is conducted with Silurian shale samples, using the hierarchy scales, gridding nanoindentation, atomic force microscopy (AFM), mineral liberation analysis (MLA), X-ray diffraction (XRD), and uniaxial compression tests. The mineral compositions are analyzed using MLA and XRD, and the shale composition is described in terms of clay minerals, organic matter, and siliceous and carbonate contents. The variation in the Young's modulus is analyzed based on the recorded indentation depth curves and modulus distributions. The nanoindentation and AFM results are upscaled to the centimeter scale through the Mori–Tanaka method. The upscaled results exhibit satisfactory fitting with the conventional uniaxial compression results, although the fitting of the upscaled AFM results is better than nanoindentation. The proposed approach can be applied to promptly and comprehensively predict the shale mechanical parameters during shale gas exploration.

Water influence on micro and homogenized modulus of shale

By using the outcrop shale of Longmaxi-3, a series of experiments including in-situ AFM Force Map, SEM-EDS before and after water vapor saturation and uniaxial/triaxial compression tests are conducted to discover the changing pattern of shale mechanical properties from micro and macro level. The current research first measures the micro elastic modulus distribution changes of shale under water condition, also verifying the water-softening effects. Expectation Maximization algorithm programmed by C language is utilized to define Gaussian Mixture Model of micro elastic modulus under different moisture. Self-Consistent Scheme by C program and Mori-Tanaka Scheme is adopted to upscale the micro modulus based on the results of EM. In the comparison with compression test results, M-T scheme behaves better on estimating modulus of originally dry shale core than SC scheme, however, the homogenization technique cannot achieve the accurate estimation of core sample modulus based on micro modulus. The combination of AFM morphology and SEM-EDS verifies the component CaSO4 of newborn particles when moisture is low. Due to strong heterogeneity of shale, the relationship between elastic modulus and water saturation is negative and non-linear, homogenization technique is not proper to upscale micro modulus of sample processed by water or other factors.

Nanoscale mechanical property variations concerning mineral composition and contact of marine shale

Mechanical properties of shales are key parameters influencing hydrocarbon production – impacting borehole stability, hydraulic fracture extension and microscale variations in in situ stress. We use Ordovician shale (Sichuan Basin, China) as a type-example to characterize variations in mineral particle properties at microscale including particle morphology, form of contact and spatial distribution via mineral liberation analysis (MLA) and scanning electron microscopy (SEM). Deformation-based constitutive models are then built using finite element methods to define the impact of various architectures of fracture and mineral distributions at nanometer scale on the deformation characteristics at macroscale. Relative compositions of siliceous, calcareous and clay mineral particles are shown to be the key factors influencing brittleness. Shales with similar mineral composition show a spectrum of equivalent medium mechanical properties due to differing particle morphology and mineral heterogeneity. The predominance of small particles and/or point-point contacts are conducive to brittle failure, in general, and especially so when quartz-rich. Fracture morphology, length and extent of filling all influence shale deformability. High aspect-ratio fractures concentrate stress at fracture tips and are conducive to extension, as when part-filled by carbonate minerals. As fracture spacing increases, stress transfer between adjacent fractures weakens, stress concentrations are amplified and fracture extension is favored. The higher the fractal dimension of the fracture and heterogeneity of the host the more pervasive the fractures. Moreover, when fractures extend, their potential for intersection and interconnection contributes to a reduction in strength and the promotion of brittle failure. Thus, these results provide important theoretical insights into the role of heterogeneity on the deformability and strength of shale reservoirs with practical implications for their stimulation and in the recovery of hydrocarbons from them.

On the consequences of shale desaturation: physicochemical and mechanical perspectives

Adsorption of water by desaturated shale could be misinterpreted as osmotic swelling. If the saturation state of shale is not known, one should not presume that osmosis is responsible for water adsorption and resultant swelling. Such presumption may overlook the fact that spontaneous imbibition could be responsible for most water adsorption and apparent swelling in desaturated shale. This work examines mechanisms responsible for water adsorption by desaturated shale and proposes a superimposing technique that separate water adsorption by imbibition from that by chemical and diffusion osmosis. Also, this work investigates the impact of desaturation on physicochemical and mechanical properties of shale using gravimetric measurements, ASTM methods., X-ray diffraction and pore fluid’s chemical composition analysis. Results show that water transport in desaturated shale is falsely attributed to osmotic swelling and that spontaneous imbibition is the main force driving water transport. In the absence of diffusion osmosis and hydraulic flow, amount of water adsorbed via spontaneous imbibition is 2–3 times higher than that adsorbed by chemical osmosis. For desaturated shale, results revealed that reduction in water activity is non- linearly proportional to desaturation (drying) time. Results also showed that compressive strength and Young’s modulus increased non-linearly as moisture content decreased.

Investigation on Hydration and Deformation Characteristics of Shale Using X-ray Computed Tomography

The physical and mechanical properties of shale are significant for completion engineering and fracturing design for shale oil and gas production. To further study the water effect and the deformation characteristics of shale, some cylindrical specimens were soaked at three periods (0, 20, and 60 days), the in situ uniaxial compression tests were conducted, and the CT technique was used at different hydration and loading stages. Based on the CT results, the image gray variance value in each hydration specimen was extracted; the evolution results show that the water imbibition has a significant influence on the structure of shale in the early soaking stage, and the influence degree is more evident in the external region. Moreover, the water influence on the mechanical property of shale was analyzed by comparing the failure characteristics of specimens with and without hydration; the CT results show that the hydration treatment affects the failure mode of shale. In addition, a new method based on the CT image was proposed to calculate the lateral strain; the evolution of the axial stress-strain curve reveals that the expansion phenomena exist before failure, and the evolution process includes four stages. At last, the differences in the deformation degree were discussed by analyzing the volumetric strain at different CT scanning layers; the results reflect the expansion or compression degree along with the specimen height. Those conclusions can help us further understand the water effect and the deformation characteristics of shale oil and gas reservoirs.

Effects of supercritical CO₂/water imbibition under dynamic pressures on shale mechanics and acoustic emission characteristics

During exploitation of shale gas and geological sequestration of CO2 in shale gas reservoirs, the temperature and pressure of shale are increased with depth, whereas the reservoir pressure is gradually decreased with depth as exploitation proceeds. Therefore, it is important to investigate the effects of CO2 and water on the mechanical properties of shale under dynamic pressure conditions. In this study, we have investigated the effects of supercritical CO2 and water immersion on the mechanical properties of shale under different dynamic pressures (pressure 1: 20–8 MPa; pressure 2: 40–28 MPa), respectively. The test results indicate that after soaking in supercritical CO2 and water, the uniaxial compressive strength (UCS) of shale is decreased by 51.05% and 58.36% (pressure 1), and by 35.98% and 36.84% (pressure 2), respectively. The strength and Young's modulus of shale are decreased more significantly after water immersion compared to supercritical CO2 immersion. Due to the matrix compression effects, the mechanical properties of shale are changed more significant under lower imbibition pressures. Supercritical CO2 immersion leads to increase in the Poisson's ratio along with more complex fracture patterns, whereas water immersion results in slight decrease in the Poisson's ratio along with shear fractures only. The acoustic emission (AE) signals have obvious stage characteristics during the compressional deformation of samples, and the AE energy is mainly generated in the unstable crack propagation stage. Supercritical CO2 immersion plays an important role in crack generation, whereas water immersion is dominated by the alteration of pore structure. Compared with the constant pressure imbibition, the dynamic pressure imbibition changes the microstructure of shale and weakens its mechanical properties more significantly. The results of this study may help to better evaluate the effects of CO2 and water on the mechanical properties of shale during exploitation of shale gas.

Chemical-mechanical coupling effects on the permeability of shale subjected to supercritical CO2-water exposure

The permeability of shale reservoir rock and caprock is the key parameters influencing the shale gas production and the storage security of CO2. During the CO2 enhanced shale gas recovery, the issue of how the coupled chemical-mechanical process control the evolution of porosity and permeability in shale remains undetermined. In this study, multiple tests were conducted to obtained the shale properties alteration induced by ScCO2-water exposure, including the mineral compositions measured by XRD, XRF and ICP-OES, the mechanical properties measured by uniaxial compression test, the pore structure and permeability of shale measured using nuclear magnetic resonance (NMR) at different confining stresses over a range of injection pressures. After ScCO2-water exposure, the contents of carbonate and clay minerals decreased, while the contents of quartz and feldspar increased. The geochemical reaction altered the pore structure and mechanical properties of shale, resulting in the enlargement of pore, the decrease in uniaxial compressive strength and elastic modulus of shale, which in turn impact the porosity and permeability evolution in shale. At the unstressed state, the pore in shale was enlarged by the pure chemical reaction, leading to the increase in porosity and the initial permeability of shale. At the stressed condition, the porosity and permeability of shale is controlled by the chemical-mechanical coupling effects, the permeability of CO2-water treated shale sample is lower than that of the untreated shale sample, which can be explained by the increase in stress sensitivity of shale permeability induced by the mechanical weakening, as the compressibility Cf and permeability change rate Δkc were increased after ScCO2-water exposure. In addition, the stress sensitivity of permeability in shale is stress-dependent, for both untreated and ScCO2-water treated shale samples, the Cf and Δkc of shale shown a negative relation with effective stress. At a higher effective stress condition, the change in the permeability of ScCO2-water treated shale is more significantly enhanced. The results demonstrated that the ScCO2-water-shale interaction induced chemical-mechanical effect may decrease the permeability of shale at in-situ stress condition, and hence adversely affecting the efficiency of gas recovery and CO2 sequestration in shale formation.

Study on Mechanical Properties of Shale Under Different Loading Rates

In the process of shale gas development, different drilling, hydro-fracturing, and pumping speeds will produce different productivity effects. This reflects the effect of the loading rate of rock mechanics. Therefore, it is of great scientific significance to study the deformation and failure characteristics of shale under different loading rates. In order to reveal the loading rate effect of the Longmaxi shale, a series of laboratory experiments were carried out, including scanning electron microscope, XRD, and uniaxial compression tests at different loading rates. The results show that 1) the peak strength and elastic modulus of shale increase with the increase in the loading rate, but Poisson’s ratio has no obvious rule with the increase in the loading rate. In contrast, the loading rate causes the peak strength to vary by about 20%, which is larger than that of the elastic modulus. 2) The loading rate has a significant influence on shale failure. A higher loading rate will lead to severe damage but with simple cracks, whereas a lower loading rate will lead to complex damage of cracks. With the decrease in the strain rate, the length of the failure crack increases greatly. Therefore, a lower strain rate is helpful to form more broken fragments in the shale matrix. 3) By analyzing the relationship between elastic strain energy/dissipated energy and the loading rate, it is found that the elastic strain rate has a preliminary increasing and then a decreasing trend with the loading rate, but the dissipated energy has a decreasing trend with the loading rate. A higher loading rate is helpful to increase the brittleness of the shale, but a lower loading rate is beneficial to forming more cracks and a greater degree of fracture in the shale matrix. The effect of the loading rate on the mechanical properties and fracture properties of the shale is discussed. It is suggested that the lower hydro-fracturing rate is useful for generating more complex crack networks in the shale reservoirs.

Mechanical Properties of Shale After CO2 and CO2-Based Fluids Imbibition: Experimental and Modeling Study

Mechanical Properties of Shale After CO2 and CO2-Based Fluids Imbibition: Experimental and Modeling Study