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16 pages, 3954 KiB

Open AccessArticle

Mechanical Characterization of the Frozen and Thawed States of Coal after the Action of LN₂ at In Situ Formation Pressure

by Lei Qin, Pengfei Liu, Hui Wang, Botao Li, Ruizhe Wang, Jiawei Li, Rongwei Luo and Shiyin Lv

Processes 2024, 12(2), 299; https://doi.org/10.3390/pr12020299 - 30 Jan 2024

Cited by 1 | Viewed by 924

Abstract

Coal penetration enhancement technology is the key to increase the production of coalbed methane. Coal bodies are subjected to different peripheral pressures in the in situ strata, and the study of the changes in the mechanical strength of coal bodies under different peripheral [...] Read more.

Coal penetration enhancement technology is the key to increase the production of coalbed methane. Coal bodies are subjected to different peripheral pressures in the in situ strata, and the study of the changes in the mechanical strength of coal bodies under different peripheral pressures after the action of liquid nitrogen is crucial for the penetration enhancement of liquid nitrogen (LN₂)-fractured coal. In this paper, an MTS universal testing machine was utilized to carry out experiments to obtain the stress–strain curves of the coal under different freezing times under 1 MPa surrounding pressure and different surrounding pressures after 50 min of LN₂ action. The experimental results showed the following: (1) the uniaxial compressive strength and peak strain of coal samples in a frozen state are positively correlated under two conditions. The modulus of elasticity decreased before 100 min at different times of LN₂ action, and the modulus of elasticity was maximum at 5 MPa at different peripheral pressure actions; (2) the uniaxial compressive strength and peak strain of the frozen-thawed coal samples decreased before 100 min of LN₂ action at different times, and the modulus of elasticity continued to decrease. The uniaxial compressive strength and modulus of elasticity of coal samples in freeze–thaw state under different peripheral pressures were the largest at 5 MPa, and the peak strain was negatively correlated. (3) The elastic strain energy of the frozen coal samples under the action of LN₂ at different times was positively correlated with the freezing time before 80 min, and negatively correlated after 80 min. The elastic strain energy of the frozen coal samples was positively correlated with the freezing time. The elastic strain energy and freezing time of the two coal samples under different circumferential pressures were positively correlated before 5 MPa and negatively correlated after 5 MPa, with opposite dissipation energies. (4) The water–ice phase transition and temperature–thermal stresses on the internal structure of the coal in the presence of LN₂ cause significant damage. The degradation of coal samples in the freeze–thaw state is even higher under in situ ground pressure. Full article

(This article belongs to the Special Issue Towards Green Development: Heat Transfer and Advanced Technologies in Unconventional Oil and Gas Exploitation)

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20 pages, 8251 KiB

Open AccessArticle

Expansion Characteristics and Creep Test of New Curing Expansion Material for Gas Extraction Boreholes

by Lijuan Jiang, Ruoyu Bao and Changkui Lei

Processes 2024, 12(2), 293; https://doi.org/10.3390/pr12020293 - 29 Jan 2024

Cited by 2 | Viewed by 956

Abstract

In order to find the optimal expansion effect of a new curing expansion material so that it can better meet the requirements of the efficient sealing of drilled holes, the expansion and creep characteristics of the new curing expansion material were studied. Based [...] Read more.

In order to find the optimal expansion effect of a new curing expansion material so that it can better meet the requirements of the efficient sealing of drilled holes, the expansion and creep characteristics of the new curing expansion material were studied. Based on the creep results of graded loading, the Kelvin–Volgt model was selected to analyze its mechanical parameters, and a new “concentric ring” reinforcement sealing method was proposed. Numerical simulation was employed to analyze and discuss the reinforcement radius and depth of the “protective wall rock hole ring” in the “concentric ring” model, and on-site application experiments were carried out in a soft coal seam. The results show that the “concentric ring” reinforcement sealing method can effectively solve the problems of easy collapse and stress concentration instability in the sealing section of soft coal seams, ensuring long-term and efficient sealing of gas extraction boreholes in soft coal seams. When the diameter of the extraction drilling hole is 100 mm, the optimal reinforcement radius for the “protective wall rock hole ring” is 0.16–0.18 m. A reasonable reinforcement depth of the “protective wall rock hole ring” for drilling in soft coal seams is about 0.8–1 times the width of the roadway. In the on-site application process, experimental boreholes using “concentric ring” reinforcement sealing technology did not show any collapse phenomena, and the volume fraction of extracted gas remained above 30% for the first 30 days. Moreover, the gas volume fraction on the 30th and 60th days was 2.5 times and more than 3 times that of bag sealing boreholes using expanded cement, further proving that the sealing quality of boreholes using “concentric ring” reinforcement sealing is higher. Full article

(This article belongs to the Special Issue Towards Green Development: Heat Transfer and Advanced Technologies in Unconventional Oil and Gas Exploitation)

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25 pages, 15496 KiB

Open AccessArticle

Microstructure Imaging and Characterization of Rocks Subjected to Liquid Nitrogen Cooling

by Xiaoguang Wu, Wenchao Zou, Kun Li, Zikang Wang, Zhongwei Huang, Pengpeng Huang, Ruimin Gao and Xinyu Qin

Processes 2024, 12(1), 127; https://doi.org/10.3390/pr12010127 - 3 Jan 2024

Cited by 2 | Viewed by 1027

Abstract

Liquid nitrogen (LN₂) fracturing is a potential stimulation method in unconventional hydrocarbon recovery, showing its merits in being water free, creating low formation damage and being environmentally friendly. The microstructure evolution of rocks subjected to LN₂ cooling is a fundamental [...] Read more.

Liquid nitrogen (LN₂) fracturing is a potential stimulation method in unconventional hydrocarbon recovery, showing its merits in being water free, creating low formation damage and being environmentally friendly. The microstructure evolution of rocks subjected to LN₂ cooling is a fundamental concern for the engineering application of LN₂ fracturing. In this paper, pore-scale imaging and characterization were performed on two rocks, i.e., tight sandstone and coal specimens subjected to LN₂ cooling using computed tomography scanning. The digital core technique was employed to reconstruct the microstructures of rocks and give a quantitative analysis of the pore structure evolution of both dry and water-saturated rocks. The results indicate that LN₂ cooling has a great effect on the pores’ morphology and their spatial distribution, leading to a great improvement in pore diameter and aspect ratio. When compared to the sandstone, coal is more sensitive to LN₂ cooling and thermal stresses, having a more noticeable growth in pore–throat size. The porosity growth of coal is 291% higher than that of sandstone. There is a growing trend in the irregularity and complexity of pore structures. After LN₂ cooling, the fractal dimensions of the pores of sandstone and coal grow by 11.7% and 0.87%, respectively, and the proportion of pores with a shape factor > 100 increases. More bundle-like and strip-shape pores with multiple branches are generated, which causes a significant growth in the throat size and the proportion of connected pores with a coordination number ≥ 1, enhancing the complexity and connectivity of pore structures dramatically. Additionally, pore water plays an important role in aggravating rock damage during LN₂ cooling, enhancing the pore space and connectivity. The porosities of the saturated sandstone and coal samples grow by 22.6% and 490.4%, respectively, after LN₂ cooling, which are 5.6% and 186.6% higher than dry samples. The generation of macropores ≥ 70 μm is the primary contributor to porosity growth during LN₂ cooling, although such pores account for only a small proportion of the total. These findings contribute to our understanding of the microscopic mechanism of LN₂ cooling on rock damage and may provide some guidance for the engineering application of LN₂ fracturing. Full article

(This article belongs to the Special Issue Towards Green Development: Heat Transfer and Advanced Technologies in Unconventional Oil and Gas Exploitation)

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15 pages, 6140 KiB

Open AccessArticle

Numerical Investigation of the Heat and Mass Transfer during the In Situ Pyrolysis Process of Oil-Rich Coal

by Fu Yang, Xiangqiang Cheng, Mingjie Li, Jinjia Wei, Zhonghui Duan and Li Ma

Processes 2023, 11(11), 3226; https://doi.org/10.3390/pr11113226 - 14 Nov 2023

Cited by 2 | Viewed by 1144

Abstract

A multi-physics numerical method coupling fluid flow, heat transfer, and a chemical reaction was used to determine the temperature distribution and the conversion rate of a coal seam during underground pyrolysis. The coal seam was fractured to enhance the heat and mass transfer. [...] Read more.

A multi-physics numerical method coupling fluid flow, heat transfer, and a chemical reaction was used to determine the temperature distribution and the conversion rate of a coal seam during underground pyrolysis. The coal seam was fractured to enhance the heat and mass transfer. The influences of the pyrolysis pressure on the heat transfer, oil and gas production, and pyrolysis time were also analyzed. When the injection gauge pressure was increased to 14 MPa, the conversion rate on the 120th day was 98.8% and the promotion was not obvious any more at further higher pressures for the model without a fracture. For the model with a fracture, the pyrolysis was completed in only 90 days at the much lower pressure of 4 MPa, which is beneficial for both reducing the heating period and enabling the rapid harvesting of oil. Then, the fractured zone was designed and optimized by investigating different radii of the fractured zone at both the inlet and the outlet of the domain. The dead zones around the two corners at the right side of the computational domain near the outlet well were reduced effectively with an increase in the diameter of the fractured region. The heat and mass transfer were enhanced with a larger area of the fractured region at the outlet well for the reason that the flowing dead zones experienced a longer effective heating time. Full article

(This article belongs to the Special Issue Towards Green Development: Heat Transfer and Advanced Technologies in Unconventional Oil and Gas Exploitation)

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14 pages, 9124 KiB

Open AccessArticle

Proppant Migration Law Considering Complex Fractures

by Cuilong Kong, Liyong Yang, Xinhui Guo, Fuchun Tian and Yuwei Li

Processes 2023, 11(10), 2921; https://doi.org/10.3390/pr11102921 - 7 Oct 2023

Cited by 1 | Viewed by 1010

Abstract

The placement of proppant within fractures is critical to the effectiveness of hydraulic fracturing. To elucidate the migration and placement patterns of proppant within multi-branched fractures during hydraulic fracturing, we conducted simulation experiments under both single-fracture and multi-branched-fracture conditions, varying injection rates and [...] Read more.

The placement of proppant within fractures is critical to the effectiveness of hydraulic fracturing. To elucidate the migration and placement patterns of proppant within multi-branched fractures during hydraulic fracturing, we conducted simulation experiments under both single-fracture and multi-branched-fracture conditions, varying injection rates and proppant sizes. The results of the research indicate that increasing the injection rate effectively increases the magnitude of vortex formation at the leading edge of sandbars and the drag forces acting on the proppant particles, resulting in increased particle migration distances. However, effective proppant packing near the wellbore entrance is not achieved at higher injection rates, leaving the fractures susceptible to closure under in situ stress, thereby reducing overall fracture conductivity. In addition, increasing the proppant size results in higher settling velocities and weakens the vortex’s ability to entrain the proppant particles. This results in shorter proppant placement distances, and the proppant cannot effectively reach the distant branched fractures. In addition, the diversionary effect of the branched fractures gradually reduces the flow rate in the distant branches, resulting in poorer proppant placement efficiency. Based on these findings, we recommend an approach that initially increases injection rates while reducing proppant size to ensure proppant placement in distant wellbore fractures and branched fracture networks. Subsequently, larger proppants can be used to effectively fill fractures close to the wellbore. Full article

(This article belongs to the Special Issue Towards Green Development: Heat Transfer and Advanced Technologies in Unconventional Oil and Gas Exploitation)

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29 pages, 17084 KiB

Open AccessArticle

Complex Flow Mechanism and Pressurization Effect of Liquid Nitrogen Jet Fracturing Formation Perforation Tunnel

by Zengxin Zou, Chengzheng Cai, Bo Wang, Yanan Gao, Zhixiang Tao and Yinrong Feng

Processes 2023, 11(10), 2878; https://doi.org/10.3390/pr11102878 - 29 Sep 2023

Viewed by 970

Abstract

As an anhydrous fracturing method, liquid nitrogen jet fracturing technology is expected to become an efficient development method for shale gas resources. In order to explore the influence of the pressurization effect in the liquid nitrogen jet channel, the flow field in the [...] Read more.

As an anhydrous fracturing method, liquid nitrogen jet fracturing technology is expected to become an efficient development method for shale gas resources. In order to explore the influence of the pressurization effect in the liquid nitrogen jet channel, the flow field in the perforation tunnel during the liquid nitrogen jet fracturing process was simulated by computational fluid dynamics, and the complex flow mechanism of liquid nitrogen in the perforation tunnel was analyzed. The pressurization effect of liquid nitrogen jet and water jet fracturing was compared, and the influence of various parameters on the pressurization effect of liquid nitrogen jet fracturing was studied. The research results indicate that under the same conditions, liquid nitrogen jets have a pressurization effect comparable to water jets, and the difference between the pressurization values of the liquid nitrogen jet and the water jet in the perforation tunnel is not more than 0.4 MPa under different nozzle pressure drop conditions. The larger the nozzle pressure drop and nozzle diameter, the greater the pressure increase value in the perforation tunnel of liquid nitrogen jet fracturing, which decreases with the increase in casing hole diameter. Further analysis shows that the pressurization effect is most affected by the two parameters of casing hole diameter and nozzle diameter. The essential reason for its influence on the pressurization value is the squeezing effect of the jet on the perforation tunnel fluid and the sealing effect of the shrinking part of the perforation tunnel on the backflow. The ambient pressure, the temperature of liquid nitrogen, and the diameter of the wellbore have no obvious effect on the pressurization effect. Therefore, through the reasonable combination of casing hole diameter and nozzle diameter, the sealing effect of the contraction part of the perforation tunnel on the fluid and the squeezing effect on the fluid in the perforation tunnel will be affected, which will significantly improve the pressurization effect of the liquid nitrogen jet in the perforation tunnel. Full article

(This article belongs to the Special Issue Towards Green Development: Heat Transfer and Advanced Technologies in Unconventional Oil and Gas Exploitation)

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13 pages, 2785 KiB

Open AccessArticle

Research and Development of Anti-High-Pressure Sealing Material and Its Bonding Performance

by Shigang Hao, Xianzhong Li, Tao Wu, Weilong Zhou and Jinhao Zhang

Processes 2023, 11(8), 2270; https://doi.org/10.3390/pr11082270 - 28 Jul 2023

Cited by 1 | Viewed by 1196

Abstract

To solve the problem of the field application of downhole hydraulic fracturing technology due to the difficulty in sealing holes, this study analyzes the influence of special cement, expansion agents, stabilizers, and fiber material on basic properties, such as the setting time, fluidity, [...] Read more.

To solve the problem of the field application of downhole hydraulic fracturing technology due to the difficulty in sealing holes, this study analyzes the influence of special cement, expansion agents, stabilizers, and fiber material on basic properties, such as the setting time, fluidity, and compressive strength of high-pressure sealing materials through systematic tests based on a summary of conventional sealing materials. It was determined that with 20–30% special cement and 4% expansion agent added, and a fiber material length of 8 mm and volume of 1%, the high-pressure sealing material had high fluidity and a large expansion rate, demonstrating early strength. The bond performance of the high-pressure sealing material was tested through the variable-angle shear test. The relationship between the fractal dimension of the coal-rock mass around the borehole and the bond performance of the high-pressure sealing material was also explored. Full article

(This article belongs to the Special Issue Towards Green Development: Heat Transfer and Advanced Technologies in Unconventional Oil and Gas Exploitation)

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19 pages, 6839 KiB

Open AccessArticle

Research and Test on the Device of Downhole Near-Bit Temperature and Pressure Measurement While Drilling

by Ming Lu, Hualin Liao, Huajian Wang, Yuhang He, Jiansheng Liu, Yifan Wang and Wenlong Niu

Processes 2023, 11(8), 2238; https://doi.org/10.3390/pr11082238 - 25 Jul 2023

Viewed by 1840

Abstract

The accurate acquisition of downhole engineering parameters, such as real-time pressure and temperature measurements, plays a crucial role in mitigating drilling risks and preventing accidents. In this study, we present the design of a real-time data acquisition and transmission system for drilling operations. [...] Read more.

The accurate acquisition of downhole engineering parameters, such as real-time pressure and temperature measurements, plays a crucial role in mitigating drilling risks and preventing accidents. In this study, we present the design of a real-time data acquisition and transmission system for drilling operations. The system utilizes a near-bit measurement method to simultaneously measure downhole parameters, including mud pressure and temperature. By analyzing the pressure and temperature frequencies obtained from a quartz crystal pressure gauge and compensating for temperature effects, accurate pressure values are obtained. The resistance value of a PT1000 sensor is measured, and a second-order fitting is performed using laboratory scale coefficients to determine the temperature values. The data acquisition system employs an advanced microcontroller as the main control chip, along with an A/D conversion chip. Additionally, signal amplification, data storage modules, data transmission modules, and relevant peripheral circuits are designed. The field tests were conducted in the 4605~4620 m well section of well Qing 2-76 in the Yumen Oilfield. The results demonstrate stable transmission signals and accurate decoding, enabling the real-time monitoring of pressure and temperature. The tests yielded favorable outcomes, providing a tangible means to analyze the actual operating conditions of the downhole drill string. Full article

(This article belongs to the Special Issue Towards Green Development: Heat Transfer and Advanced Technologies in Unconventional Oil and Gas Exploitation)

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19 pages, 12553 KiB

Open AccessArticle

Study on the Mechanism of High-Efficiency Rock Breaking by Hydraulic Jet Based on Explicit Dynamics

by Gang Bi, Xin Wang, Fei Han, Jiemin Wu, Peijie Yuan, Shuaishuai Fu and Ying Ma

Processes 2023, 11(7), 2165; https://doi.org/10.3390/pr11072165 - 20 Jul 2023

Cited by 3 | Viewed by 1408

Abstract

High-efficiency rock breaking by hydraulic jetting is the key to radial horizontal drilling technology. In order to improve the drilling efficiency of hydraulic jet rock breaking in radial horizontal wells, based on LS-Dyna display dynamics, a numerical simulation model of single-nozzle jet rock [...] Read more.

High-efficiency rock breaking by hydraulic jetting is the key to radial horizontal drilling technology. In order to improve the drilling efficiency of hydraulic jet rock breaking in radial horizontal wells, based on LS-Dyna display dynamics, a numerical simulation model of single-nozzle jet rock breaking was established to analyze the influence of different nozzle parameters on the rock-breaking effect. Then, the numerical simulation model of the spin multi-nozzle jet bit was established, and the influence of different rotation speeds on the rock-breaking effect of the jet bit was analyzed. Finally, the rock-breaking drilling characteristics of the spin multi-nozzle jet bit and the conventional multi-nozzle jet bit were compared and analyzed. The results show that when the jet impacts the rock surface, the larger the inclination angle is, the larger the rock-breaking width formed by the jet is. The smaller the dip angle, the greater the rock-breaking depth. When the inclination angle is greater than 60°, it is difficult to meet the needs of reaming. The width and depth of the nozzle gradually increase with the increase of the diameter. When the nozzle diameter is greater than 1.3 mm, the growth rate of rock-breaking depth begins to decrease. The optimum nozzle diameter is 1.3 mm. When v = 50 m/s, the damage caused by the jet to the rock surface is very small, because the condition of rock fracture is not reached with this velocity. This shows that there is a critical value of the water jet impact velocity, and only when the velocity is reached, will the rock break. When the velocity is v = 150 m/s, v = 200 m/s, v = 250 m/s, v = 300 m/s, the rock breaks. At the same time, the higher the speed, the higher the degree of rock fracture, the greater the fracture depth, the greater the fracture area, and the better the fracture effect. The tangential and radial velocity of the jet increases the shear and tensile failure rate of the sample, and improves the rock-breaking efficiency of the jet, which has a certain guiding significance for improving the rock-breaking drilling efficiency of radial horizontal well drilling. Full article

(This article belongs to the Special Issue Towards Green Development: Heat Transfer and Advanced Technologies in Unconventional Oil and Gas Exploitation)

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17 pages, 4789 KiB

Open AccessArticle

Fracture Patterns of Rocks Observed under Cryogenic Conditions Using Cryo-Scanning Electron Microscopy

by Qi An, Chunyang Hong and Haitao Wen

Processes 2023, 11(7), 2038; https://doi.org/10.3390/pr11072038 - 7 Jul 2023

Cited by 3 | Viewed by 1499

Abstract

Cryogenic fracturing, which uses liquid nitrogen (LN₂) as a fracturing fluid, is a waterless fracturing method. However, previous attempts to investigate the fracture morphology of rocks after LN₂ quenching have been mainly based on standard scanning electron microscopy (SEM) analysis [...] Read more.

Cryogenic fracturing, which uses liquid nitrogen (LN₂) as a fracturing fluid, is a waterless fracturing method. However, previous attempts to investigate the fracture morphology of rocks after LN₂ quenching have been mainly based on standard scanning electron microscopy (SEM) analysis at room temperature. This can be problematic since thermally-induced fractures created by temperature difference tend to close as a sample warms and thermal stress relaxes. To address this issue, we established a novel approach employing Cryo-scanning electron microscopy (Cryo-SEM) to investigate the fracture patterns induced by liquid nitrogen quenching under cryogenic conditions. This method can achieve in-situ visualization of fractures and pores with a nano-scale resolution at −190 °C. X-ray computed tomography (CT) is also employed to illustrate the fracture distribution inside samples. Cryo-SEM and standard SEM are compared, and statistical assessments are conducted to quantify fracture aperture size and closure scale. The results demonstrate that Cryo-SEM can more accurately preserve native fracture morphology and provide a more accurate means of evaluating fracture scales generated during LN₂ quenching, particularly at higher temperature differences between rock and liquid nitrogen. Distinct fracture patterns and fracture width are observed for various rock types (i.e., coal, sandstone, shale, granite) by using these methods. More prominently, the maximum fracture width of coal, sandstone, shale and granite were 89.17 µm, 1.29 µm, 0.028 µm and 2.12 µm when the temperature difference between LN₂ and rock samples were 296 °C. LN₂ is shown to exhibit superior fracturing efficiency on coal and granite, characterized by complex fracture networks with branched fractures. This research contributes to our understanding of liquid nitrogen fracturing mechanisms and may offer effective approaches for unconventional reservoirs stimulation. Full article

(This article belongs to the Special Issue Towards Green Development: Heat Transfer and Advanced Technologies in Unconventional Oil and Gas Exploitation)

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27 pages, 7414 KiB

Open AccessArticle

Experimental Study on the Damage and Failure Characteristics of High-Temperature Granite after Liquid-Nitrogen Cooling

by Chengzheng Cai, Bo Wang, Zengxin Zou, Yinrong Feng and Zhixiang Tao

Processes 2023, 11(6), 1818; https://doi.org/10.3390/pr11061818 - 15 Jun 2023

Cited by 1 | Viewed by 1202

Abstract

To analyze the influence of liquid-nitrogen cooling on the damage and failure of high-temperature granite, granite samples were heated to 150~600 °C for natural cooling and liquid-nitrogen cooling treatment. Brazilian splitting tests were carried out as the samples returned to room temperature, and [...] Read more.

To analyze the influence of liquid-nitrogen cooling on the damage and failure of high-temperature granite, granite samples were heated to 150~600 °C for natural cooling and liquid-nitrogen cooling treatment. Brazilian splitting tests were carried out as the samples returned to room temperature, and basic tensile and energy evolution parameters were obtained. Acoustic emission signal parameters during loading were recorded. The experimental results showed that the heating process caused damage to the granite samples, and liquid-nitrogen cooling further increased the degree of damage. Specifically, the ultrasonic velocity of liquid-nitrogen-cooled samples was lower than that of naturally cooled samples at each heating temperature. With an increase in heating temperature, the AE ring-down counts of liquid-nitrogen-cooled samples were higher than that of naturally cooled samples. At the same heating temperature, the dissipated energy of naturally cooled samples was greater than that of liquid-nitrogen-cooled samples. Liquid-nitrogen cooling could effectively promote the propagation of microcracks inside high-temperature granite and result in a reduction in the mechanical strength of granite, which could be conducive to the efficient fracture of high-temperature rock during fracturing. Full article

(This article belongs to the Special Issue Towards Green Development: Heat Transfer and Advanced Technologies in Unconventional Oil and Gas Exploitation)

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16 pages, 4703 KiB

Open AccessArticle

The Influence of Interlayer on the Development of Steam Chamber in Steam Stimulation during Heavy Oil Recovery

by Hongjun Fan, Tingen Fan, Junhui Deng, Lijun Zhang, Wei Zheng, Lifeng Chen, Zunzeng Ge, Haojun Xie and Xu Liang

Processes 2023, 11(6), 1742; https://doi.org/10.3390/pr11061742 - 7 Jun 2023

Cited by 3 | Viewed by 1144

Abstract

Cyclic steam stimulation is an effective thermal recovery method for heavy oil recovery. The key potential mechanism is the growth of the steam chamber after steam injection. Taking the LD5X heavy oil reservoir as an example, besides the interlayer developed in this area, [...] Read more.

Cyclic steam stimulation is an effective thermal recovery method for heavy oil recovery. The key potential mechanism is the growth of the steam chamber after steam injection. Taking the LD5X heavy oil reservoir as an example, besides the interlayer developed in this area, the top water and bottom water distribute above and below the interlayer. These factors may have adverse effects on the development of the steam chamber, thus affecting the final heavy oil exploitation. In this work, our goal is to study the effects of interlayer permeability and well–interlayer distance on CSS performance (in the presence of top and bottom water). We developed a high-temperature-resistant interlayer. Based on the simulated interlayer, the field scale model was converted into a laboratory element model through the similarity criterion. In order to quantitatively evaluate the performance of steam stimulation, a thermal detector was used to measure the dynamic growth of the steam chamber and record the production data. The experimental results show that the self-made interlayer has high-temperature resistance, adjustable permeability, and little difference between the physical parameters and the target interlayer. During the cyclic steam stimulation process, the steam chamber presents two different stages in the presence of the top water area, namely the normal production stage and the top water discharge stage. The bottom water has little effect on the growth of the steam chamber. The small interlayer permeability, the increase in horizontal well–interlayer distance, and the existence of the interlayer will delay the top water leakage during steam stimulation. This study has reference significance for us to develop heavy oil resources with a top water barrier when implementing steam stimulation technology. Full article

(This article belongs to the Special Issue Towards Green Development: Heat Transfer and Advanced Technologies in Unconventional Oil and Gas Exploitation)

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20 pages, 8870 KiB

Open AccessArticle

Effects of Coal Permeability Anisotropy on Gas Extraction Performance

by Futian Nian, Feng Ju, Chunshan Zheng, Haifei Wu and Xiaoyu Cheng

Processes 2023, 11(5), 1408; https://doi.org/10.3390/pr11051408 - 6 May 2023

Cited by 3 | Viewed by 1438

Abstract

To investigate gas flow characteristics in coal seams with strong anisotropy, a coupled anisotropic dual-porosity model was established. Effects of permeability anisotropy on variations in gas pressure, gas extraction volume and effective extraction areas were analyzed. Furthermore, mechanisms of crustal stress, initial gas [...] Read more.

To investigate gas flow characteristics in coal seams with strong anisotropy, a coupled anisotropic dual-porosity model was established. Effects of permeability anisotropy on variations in gas pressure, gas extraction volume and effective extraction areas were analyzed. Furthermore, mechanisms of crustal stress, initial gas pressure, ultimate adsorption strain and Langmuir volume constant on permeability anisotropy and extraction amount were studied. Results show that permeability anisotropy could result in an elliptical pressure drop zone around production boreholes. Changes in effective gas extraction areas are divided into three stages: slow growth in an elliptical shape, rapid growth with a superposition effect and steady growth in a funnel shape. Permeability isotropy enables faster reaching of stage III than the anisotropy case. As the vertical stress increases, gas pressure distribution around boreholes gradually changes from an ellipse with horizontal direction as long axis to a circle. Larger initial gas pressure could bring consistently higher gas production in the initial and middle extraction stages, and a faster decrease in the late phase. When gas pressure is 2.5 MPa, the peak daily gas production in initial extraction stage is about three times higher than that in the late phase. Ultimate adsorption strain is positively correlated with permeability change. This relationship becomes more significant with a longer extraction time. In contrast, permeability variation is inversely proportional to the Langmuir volume constant in the initial extraction stage. However, these factors are directly proportional in the late stage. The order of significance of each factor’s effect on permeability is crustal stress > ultimate adsorption strain > initial gas pressure > Langmuir volume constant. Moreover, initial gas pressure has the most significant effect on gas extraction volume, while Langmuir volume constant has the least significant impact. Results could provide a theoretical reference for extraction borehole design and drainage parameter setting to improve extraction performance. Full article

(This article belongs to the Special Issue Towards Green Development: Heat Transfer and Advanced Technologies in Unconventional Oil and Gas Exploitation)

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13 pages, 7114 KiB

Open AccessArticle

Study of the Jet Output Characteristics under Multi−Source Coupling

by Wenlong Niu, Hualin Liao, Huajian Wang, Jun Wei, Jiansheng Liu, Jilei Niu and Yucai Shi

Processes 2023, 11(3), 900; https://doi.org/10.3390/pr11030900 - 16 Mar 2023

Viewed by 1344

Abstract

The challenges posed by elevated rock hardness, deficient drillability, excessive friction torque, and significant underpressure in extended−reach horizontal wells are the primary factors that contribute to low ROP (Rate of Penetration) and limited horizontal reach during the drilling operation. Reducing drag and friction [...] Read more.

The challenges posed by elevated rock hardness, deficient drillability, excessive friction torque, and significant underpressure in extended−reach horizontal wells are the primary factors that contribute to low ROP (Rate of Penetration) and limited horizontal reach during the drilling operation. Reducing drag and friction is one of the primary methods of addressing the aforementioned challenges. To augment the pulse output characteristics of the oscillating jet and bolster the energy of the hydrodynamic impact load, we developed and designed a multi−source impact oscillation speed−increasing tool coupled with blade rotation disturbance and multi−order oscillation cavity self−excitation. We utilized fluid dynamics software to model and conduct numerical analysis on the multi−source pulsed jet generator. Furthermore, we constructed a prototype and subjected it to testing. This paper examines the impact of dimensionless structural parameters on the pressure output characteristics of the multi−source pulse−jet generator. Specifically, we used three dimensionless quantities (cavity length ratios, cavity diameter ratios, and inner wall collision angle ratios) to study this effect. The findings indicate that the multi−source impact oscillation speed−increasing tool is capable of augmenting the pulse oscillation amplitude, and the frequency of pulse oscillation can be adjusted within the range of 5 Hz to 15 Hz. During the study, we determined that the optimal oscillation output characteristics can be achieved when the cavity diameter ratio is 0.8, the cavity length ratio is 1.0, and the inner wall collision angle ratio is 1.5. These findings present a novel approach for the development of downhole hydraulic impact oscillation speed−increasing tools. Full article

(This article belongs to the Special Issue Towards Green Development: Heat Transfer and Advanced Technologies in Unconventional Oil and Gas Exploitation)

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15 pages, 6867 KiB

Open AccessArticle

A Combined Gated Recurrent Unit and Multi-Layer Perception Neural Network Model for Predicting Shale Gas Production

by Xiaozhou Qin, Xiaohu Hu, Hua Liu, Weiyi Shi and Jiashuo Cui

Processes 2023, 11(3), 806; https://doi.org/10.3390/pr11030806 - 8 Mar 2023

Cited by 7 | Viewed by 2466

Abstract

Shale gas plays an important role in supplementing energy demand and reducing carbon footprint. A precise and effective prediction of shale gas production is important for optimizing completion parameters. This paper established a gated recurrent unit and multilayer perceptron combined neural network (GRU-MLP [...] Read more.

Shale gas plays an important role in supplementing energy demand and reducing carbon footprint. A precise and effective prediction of shale gas production is important for optimizing completion parameters. This paper established a gated recurrent unit and multilayer perceptron combined neural network (GRU-MLP model) to forecast multistage fractured horizontal shale gas well production. A nondominated sorting genetic algorithm II (NSGA II) was introduced into the model to enable its automatic architectural optimization. In addition, embedded discrete fracture models (EDFM) and a reservoir simulator were used to generate training datasets. Meanwhile, a sensitivity analysis was carried out to find the variable’s importance and support the history matching. The results illustrated that the GRU-MLP model can precisely and efficiently predict the productivity of multistage fractured horizontal shale gas in a rapid and effective manner. Additionally, the model fits better at peak values of shale gas production. The GRU-MLP hybrid model has a higher accuracy within an acceptable computational time range compared to recurrent neural networks (RNN), long short-term memory (LSTM), and GRU models. The mean absolute percentage error (MAPE) and root mean square percentage error (RMSPE) for shale gas production generated by GRU-MLP model were 3.90% and 3.93%, respectively, values 84.87% and 84.88% smaller than those of the GRU model. Consequently, compared with a purely data-driven method, the physics-constrained data-driven method behaved better. The main results of the study will hopefully contribute to the intelligent development of shale gas production prediction. Full article

(This article belongs to the Special Issue Towards Green Development: Heat Transfer and Advanced Technologies in Unconventional Oil and Gas Exploitation)

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