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Processes
Special Issues
Innovations in Hydraulic Fracturing Technology for Unconventional Reservoirs
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Innovations in Hydraulic Fracturing Technology for Unconventional Reservoirs

A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Energy Systems".

Deadline for manuscript submissions: closed (30 July 2024) | Viewed by 3424

Special Issue Editors

Dr. Xiaoguang Wu

E-Mail Website
Guest Editor
College of Carbon Neutral Energy, China University of Petroleum (Beijing), Beijing 102249, China
Interests: hydraulic fracturing; hydra-jet drilling and well completion; geothermal stimulation and development
Dr. Xianwei Dai

E-Mail Website
Guest Editor
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu 610059, China
Interests: PDC bit; rock breaking; hot dry rock; numerical simulation
Special Issues, Collections and Topics in MDPI journals
Dr. Xu Zhang

E-Mail
Guest Editor Assistant
School of Petroleum Engineering, China University of Petroleum (Beijing), Beijing 102249, China
Interests: geothermal energy; hydraulic fracturing; numerical simulation

Special Issue Information

Dear Colleagues,

Unconventional reservoirs, with their vast reserves and extensive distribution, have become key to future energy development. Hydraulic fracturing is a stimulation technique utilized in low-permeability unconventional reservoirs such as tight sandstone, shale, certain coal beds, and geothermal reservoirs. However, there is a pressing need for intensified efforts to advance innovative hydraulic fracturing technologies. These advancements should focus on improving efficiency, ensuring cost-effectiveness, and mitigating environmental impact.

This Special Issue, titled “Innovations in Hydraulic Fracturing Technology for Unconventional Reservoirs”, aims to cover the recent advances in hydraulic fracturing technology in unconventional reservoirs. Topics of interest include, but are not limited to, the following areas:

  • New theories, models, and numerical simulation methods for hydraulic fracturing;
  • Innovative fracturing method and technology in low-permeability oil and gas reservoir (tight oil and gas, shale oil and gas, etc.), coalbed methane, natural gas hydrate, geothermal, etc.;
  • Cross-layer fracturing in laminated reservoirs;
  • Carbonate reservoir acid fracturing;
  • Ultra-deep high-temperature high-pressure reservoir fracturing;
  • CO2 fracturing and CCUS technology;
  • Novel fracturing materials (fracturing fuild, proppant, etc.) and tools;
  • Non-aqueous fracturing technology;
  • Hydraulic fracturing assied by artificial intelligence, internet of things, and big data;
  • Monitoring and evaluation of hydraulic fracturing (fiber-optic cables, etc.);
  • Envoiromental risks and seism reduction.

Dr. Xiaoguang Wu
Dr. Xianwei Dai
Guest Editors

Dr. Xu Zhang
Guest Editor Assistant

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Processes is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • unconventional reservoir
  • hydraulic fracturing
  • coalbed methane
  • natural gas hydrate
  • geothermal reservoir
  • ultra-deep reservoir
  • artificial intelligence
  • CCUS
  • fracturing monitoring techniques
  • novel fracturing materials

Published Papers (5 papers)

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Research

Jump to: Review

26 pages, 9279 KiB  
Article
Fracture Evolution during CO2 Fracturing in Unconventional Formations: A Simulation Study Using the Phase Field Method
by Bing Yang, Qianqian Ren, Hai Huang, Haizhu Wang, Yong Zheng, Liangbin Dou, Yanlong He, Wentong Zhang, Haoyu Chen and Ruihong Qiao
Processes 2024, 12(8), 1682; https://doi.org/10.3390/pr12081682 - 12 Aug 2024
Abstract
With the introduction of China’s “dual carbon” goals, CO2 is increasingly valued as a resource and is being utilized in unconventional oil and gas development. Its application in fracturing operations shows promising prospects, enabling efficient extraction of oil and gas while facilitating [...] Read more.
With the introduction of China’s “dual carbon” goals, CO2 is increasingly valued as a resource and is being utilized in unconventional oil and gas development. Its application in fracturing operations shows promising prospects, enabling efficient extraction of oil and gas while facilitating carbon sequestration. The process of reservoir stimulation using CO2 fracturing is complex, involving coupled phenomena such as temperature variations, fluid behavior, and rock mechanics. Currently, numerous scholars have conducted fracturing experiments to explore the mechanisms of supercritical CO2 (SC-CO2)-induced fractures in relatively deep formations. However, there is relatively limited numerical simulation research on the coupling processes involved in CO2 fracturing. Some simulation studies have simplified reservoir and operational parameters, indicating a need for further exploration into the multi-field coupling mechanisms of CO2 fracturing. In this study, a coupled thermo-hydro-mechanical fracturing model considering the CO2 properties and heat transfer characteristics was developed using the phase field method. The multi-field coupling characteristics of hydraulic fracturing with water and SC-CO2 are compared, and the effects of different geological parameters (such as in situ stress) and engineering parameters (such as the injection rate) on fracturing performance in tight reservoirs were investigated. The simulation results validate the conclusion that CO2, especially in its supercritical state, effectively reduces reservoir breakdown pressures and induces relatively complex fractures compared with water fracturing. During CO2 injection, heat transfer between the fluid and rock creates a thermal transition zone near the wellbore, beyond which the reservoir temperature remains relatively unchanged. Larger temperature differentials between the injected CO2 fluid and the formation result in more complicated fracture patterns due to thermal stress effects. With a CO2 injection, the displacement field of the formation deviated asymmetrically and changed abruptly when the fracture formed. As the in situ stress difference increased, the morphology of the SC-CO2-induced fractures tended to become simpler, and conversely, the fracture presented a complicated distribution. Furthermore, with an increasing injection rate of CO2, the fractures exhibited a greater width and extended over longer distances, which are more conducive to reservoir volumetric enhancement. The findings of this study validate the authenticity of previous experimental results, and it analyzed fracture evolution through the multi-field coupling process of CO2 fracturing, thereby enhancing theoretical understanding and laying a foundational basis for the application of this technology. Full article
(This article belongs to the Special Issue Innovations in Hydraulic Fracturing Technology for Unconventional Reservoirs)
►▼ Show Figures

Figure 1

Figure 1
<p>COMSOL implementation of phase field modeling for fracturing problems.</p> Full article ">Figure 2
<p>Schematic of a cracked square plate under a single-edge notched tension test, where <span class="html-italic">L</span> = 1 mm.</p> Full article ">Figure 3
<p>Validation of 2D single-edge notched square subjected to tension. (<b>a</b>) When <math display="inline"><semantics> <mrow> <msub> <mi>l</mi> <mn>0</mn> </msub> <mo>=</mo> <mn>7.5</mn> <mo>×</mo> <msup> <mrow> <mn>10</mn> </mrow> <mrow> <mo>−</mo> <mn>3</mn> </mrow> </msup> <mi>mm</mi> </mrow> </semantics></math>, the crack extended in a pattern under displacements of <math display="inline"><semantics> <mrow> <mi>u</mi> <mo>=</mo> <mn>5.3</mn> <mo>×</mo> <msup> <mrow> <mn>10</mn> </mrow> <mrow> <mo>−</mo> <mn>3</mn> </mrow> </msup> <mi>mm</mi> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>u</mi> <mo>=</mo> <mn>5.6</mn> <mo>×</mo> <msup> <mrow> <mn>10</mn> </mrow> <mrow> <mo>−</mo> <mn>3</mn> </mrow> </msup> <mi>mm</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>u</mi> <mo>=</mo> <mn>5.9</mn> <mo>×</mo> <msup> <mrow> <mn>10</mn> </mrow> <mrow> <mo>−</mo> <mn>3</mn> </mrow> </msup> <mi>mm</mi> </mrow> </semantics></math>. (<b>b</b>) When <math display="inline"><semantics> <mrow> <msub> <mi>l</mi> <mn>0</mn> </msub> <mo>=</mo> <mn>1.5</mn> <mo>×</mo> <msup> <mrow> <mn>10</mn> </mrow> <mrow> <mo>−</mo> <mn>2</mn> </mrow> </msup> <mi>mm</mi> </mrow> </semantics></math>, the crack extended in a pattern under displacements of <math display="inline"><semantics> <mrow> <mi>u</mi> <mo>=</mo> <mn>5.0</mn> <mo>×</mo> <msup> <mrow> <mn>10</mn> </mrow> <mrow> <mo>−</mo> <mn>3</mn> </mrow> </msup> <mi>mm</mi> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>u</mi> <mo>=</mo> <mn>5.2</mn> <mo>×</mo> <msup> <mrow> <mn>10</mn> </mrow> <mrow> <mo>−</mo> <mn>3</mn> </mrow> </msup> <mi>mm</mi> </mrow> </semantics></math>, and <math display="inline"><semantics> <mrow> <mi>u</mi> <mo>=</mo> <mn>5.4</mn> <mo>×</mo> <msup> <mrow> <mn>10</mn> </mrow> <mrow> <mo>−</mo> <mn>3</mn> </mrow> </msup> <mi>mm</mi> </mrow> </semantics></math>.</p> Full article ">Figure 4
<p>Load–displacement curves of the 2D single-edge notched tension test.</p> Full article ">Figure 5
<p>Geometric model of CO<sub>2</sub> fracturing.</p> Full article ">Figure 6
<p>The main properties of CO<sub>2</sub>: (<b>a</b>) density, (<b>b</b>) viscosity, (<b>c</b>) heat conductivity, and (<b>d</b>) specific heat capacity changing with temperature and pressure. (<b>a</b>) The density varied with the temperature and pressure. (<b>b</b>) The viscosity distribution of CO<sub>2</sub>. (<b>c</b>) The thermal conductivity distribution of CO<sub>2</sub>. (<b>d</b>) The specific heat capacity of CO<sub>2</sub>.</p> Full article ">Figure 7
<p>Main process of water fracturing on tight reservoir.</p> Full article ">Figure 8
<p>Main process of CO<sub>2</sub> fracturing on tight reservoir.</p> Full article ">Figure 9
<p>The pressure at the top of the wellbore during water and SC-CO<sub>2</sub> fracturing.</p> Full article ">Figure 10
<p>Temperature distribution of formation at different times. (<b>a</b>) Formation temperature distribution during water fracturing. (<b>b</b>) Formation temperature distribution during SC-CO<sub>2</sub> fracturing.</p> Full article ">Figure 11
<p>Contour of displacement in SC-CO<sub>2</sub> fracturing process.</p> Full article ">Figure 11 Cont.
<p>Contour of displacement in SC-CO<sub>2</sub> fracturing process.</p> Full article ">Figure 12
<p>Displacement changes with time at top of wellbore.</p> Full article ">Figure 13
<p>Variation characteristics of formation porosity during water and SC-CO<sub>2</sub> fracturing.</p> Full article ">Figure 14
<p>Permeability changes with time at top of wellbore.</p> Full article ">Figure 15
<p>Fracture mode induced by SC-CO<sub>2</sub> under different stress conditions ((<b>a</b>) 12/8 MPa; (<b>b</b>) 12/10 MPa; (<b>c</b>) 12/11 MPa; and (<b>d</b>) 12/12 MPa).</p> Full article ">Figure 16
<p>Porosity of formation fractured by SC-CO<sub>2</sub> under different in situ stress values.</p> Full article ">Figure 17
<p>Permeability of formation fractured by SC-CO<sub>2</sub> under different in situ stress values.</p> Full article ">Figure 18
<p>Fracture mode induced by SC-CO<sub>2</sub> under different temperature conditions.</p> Full article ">Figure 19
<p>Porosity of formation fractured by SC-CO<sub>2</sub> under different temperatures.</p> Full article ">Figure 20
<p>Permeability of formation fractured by SC-CO<sub>2</sub> under different temperatures.</p> Full article ">Figure 21
<p>Fracture mode induced by SC-CO<sub>2</sub> under different injection rates.</p> Full article ">Figure 22
<p>Porosity of formation fractured by SC-CO<sub>2</sub> under different injection rates.</p> Full article ">Figure 23
<p>Permeability of formation fractured by SC-CO<sub>2</sub> under different injection rates.</p> Full article ">
15 pages, 12144 KiB  
Article
Oscillation Times in Water Hammer Signatures: New Insights for the Evaluation of Diversion Effectiveness in Field Cases
by Bingxiao Liu, Wenhan Yue, Yajing Wang, Zhibin Gu, Ran Wen, Yang Qiu, Pukang Yi and Xiaodong Hu
Processes 2024, 12(7), 1312; https://doi.org/10.3390/pr12071312 - 24 Jun 2024
Viewed by 562
Abstract
Diversion is a crucial technique for effectively improving shale reservoir production by creating more complex fracture networks. Evaluating diversion effectiveness is necessary to optimize the parameters in hydraulic fracturing. Water hammer diagnostics, an emerging fracturing diagnosis technique, evaluate diversion effectiveness by analyzing water [...] Read more.
Diversion is a crucial technique for effectively improving shale reservoir production by creating more complex fracture networks. Evaluating diversion effectiveness is necessary to optimize the parameters in hydraulic fracturing. Water hammer diagnostics, an emerging fracturing diagnosis technique, evaluate diversion effectiveness by analyzing water hammer signals. The water hammer attenuation, as indicated by the oscillation time, correlates with the complexity of fracture networks. However, it remains unclear whether the oscillation time is associated with diversion effectiveness. This paper elucidates the relationship between the water hammer oscillation time and diversion effectiveness by taking the probability of diversion and the treating pressure response as the evaluation criteria. Initially, a high-frequency pressure sensor was installed at the wellhead to sample the water hammer signals. Next, the oscillation times were determined using the feature extraction method. Simultaneously, the probability of diversion and the treating pressure response were calculated using the cepstrum error function and treating pressure curve, respectively. Then, the relationship between the oscillation time and diversion effectiveness was analyzed. Finally, a rapid judgment method for evaluating diversion effectiveness based on the water hammer oscillation time was proposed. The results indicated a negative correlation between the probability of diversion and the oscillation time, with higher probabilities resulting in lower oscillation times. The oscillation times exhibited a negative correlation with the treating pressure response, including the treating pressure increases and diversion pressure spikes, wherein a greater pressure differential led to lower oscillation times. Drawing from the statistics of a shale gas horizontal well in Sichuan, a better diversion effectiveness is associated with fewer oscillations, demonstrating a negative correlation between the diversion effectiveness and the oscillation time in water hammer signatures. Finally, a rapid judgment method for evaluating diversion effectiveness was proposed, utilizing the 95% confidence interval of the mean oscillation time. This paper offers useful insights into evaluating diversion performance in field cases. Full article
(This article belongs to the Special Issue Innovations in Hydraulic Fracturing Technology for Unconventional Reservoirs)
►▼ Show Figures

Figure 1

Figure 1
<p>The equipment configuration. A pump truck is used to inject fracturing fluid. The water hammer will be generated when the pump track shuts down. The high-frequency sensor is installed at the wellhead to record the water hammer signal. The data acquisition and analysis system is used to process and analyze the sampled signals.</p> Full article ">Figure 2
<p>The feature extraction procedure of the water hammer oscillation times.</p> Full article ">Figure 3
<p>The processed water hammer signal and schematic diagram of oscillation times, including the defined period and peak-to-peak value.</p> Full article ">Figure 4
<p>The cepstrum of the water hammer signal.</p> Full article ">Figure 5
<p>Reflection depths of diversion and shutdown. The yellow scale is the perforation position (m). The blue square are dissolvable bridge plugs.</p> Full article ">Figure 6
<p>Treating pressure curve and the schematic diagram of the treating pressure increasing and the diverting pressure spike.</p> Full article ">Figure 7
<p>The results statistics of well 1 and well 2: (<b>a</b>) the water hammer oscillation time dataset; (<b>b</b>) the probability of diversion using cepstrum analysis and error function; (<b>c</b>) the treating pressure increasing; (<b>d</b>) the diversion pressure spike.</p> Full article ">Figure 8
<p>The relationship between the oscillation time and the probability of diversion from the cepstrum analysis and error function in well 1 and well 2.</p> Full article ">Figure 9
<p>(1) The relationship between oscillation time and treating pressure increase in well 1 and well 2. (2) The relationship between oscillation time and diversion pressure spike.</p> Full article ">
15 pages, 250734 KiB  
Article
Strategies for Optimizing Shut-In Time: New Insights from Shale Long-Term Hydration Experiments
by Bo Zeng, Enjia Dong, Zhiguang Yao, Yi Song, Zhuang Xiong, Yongzhi Huang, Xiaoyan Gou and Xiaodong Hu
Processes 2024, 12(6), 1096; https://doi.org/10.3390/pr12061096 - 27 May 2024
Viewed by 506
Abstract
In the process of hydraulic fracturing, fracturing fluid invades the formation and reacts with shale. Water-sensitive clay minerals swell when exposed to water. This results in a change in the mechanical properties of shale. However, the influences of a long-term water–shale reaction on [...] Read more.
In the process of hydraulic fracturing, fracturing fluid invades the formation and reacts with shale. Water-sensitive clay minerals swell when exposed to water. This results in a change in the mechanical properties of shale. However, the influences of a long-term water–shale reaction on mechanical properties are still unclear, and an optimization strategy of the shut-in time is required. In this paper, an optimization strategy for the shut-in time based on a shale long-term hydration experiment is proposed. In this paper, the water–shale reaction is simulated by laboratory experiments under normal temperature and pressure. The experiments are performed based on specimens from a shale outcrop. Clay and mineral composition, Young’s modulus, surface hardness, and tensile strength parameters are measured at 30-day intervals for 90 days. A CT scan was performed for 180 days. The experimental results show that the mass fraction of clay increased by 14.719%. In addition, significant argillaceous shedding occurs during the water–shale reaction period of 3–4 months. By testing the tensile strength, uniaxial compression decreases by 90.481% in three months. The Young’s modulus of mineral points decreases to 40% after reaction for three months. The shale has softened. The softening process is nonlinear and there are inflection points. The diffusion behavior of clay minerals and the expansion behavior of new fractures are observed by CT during 3–4 months of water–shale reaction. The results show that the shale softening and pore fracture structure changes are non-linear and heterogeneous, resulting in critical water–shale reaction time. According to the experimental results, the critical water–shale reaction time can be summarized. In this time, the fracture volume increases significantly, which is conducive to increasing oil and gas production. However, the fracture volume is not significantly increased by prolonging the shut-in time. The experimental results can guide the design of hydraulic fracturing shut-in time of shale reservoirs. Full article
(This article belongs to the Special Issue Innovations in Hydraulic Fracturing Technology for Unconventional Reservoirs)
►▼ Show Figures

Figure 1

Figure 1
<p>Shale specimens acquisition process.</p> Full article ">Figure 2
<p>Precision cutting system.</p> Full article ">Figure 3
<p>Shale porosity and permeability test system.</p> Full article ">Figure 4
<p>(<b>a</b>,<b>b</b>) Water–shale reaction vessel.</p> Full article ">Figure 5
<p>XRD test results of #1-S1 shale specimen: (<b>a</b>) mineral spectrum; (<b>b</b>) clay spectrum.</p> Full article ">Figure 6
<p>Typical stress load–displacement curve for nanoindentation experiments.</p> Full article ">Figure 7
<p>Schematic diagram of indenter pressing depth and deformation area.</p> Full article ">Figure 8
<p>(<b>a</b>,<b>b</b>) Tensile strength test picture and shale bedding direction diagram.</p> Full article ">Figure 9
<p>Average mass fraction of each component of shale specimen.</p> Full article ">Figure 10
<p>Change of clay content with water–shale reaction time (<b>a</b>): change of clay mass fraction; (<b>b</b>): clay composition mass fraction change).</p> Full article ">Figure 11
<p>Test results of shale tensile strength.</p> Full article ">Figure 12
<p>Schematic diagram of test points.</p> Full article ">Figure 13
<p>Results of nanoindentation experiment: (<b>a</b>) Young’s modulus at measuring point; (<b>b</b>) surface hardness at measuring point.</p> Full article ">Figure 14
<p>Total fracture volume scanned by CT.</p> Full article ">
22 pages, 8635 KiB  
Article
Study on the Interaction Propagation Mechanism of Inter-Cluster Fractures under Different Fracturing Sequences
by Xiaojun Cai, Weixuan Zhao, Tianbao Hu, Xinwei Du, Haiyang Wang and Xiong Liu
Processes 2024, 12(5), 971; https://doi.org/10.3390/pr12050971 - 10 May 2024
Cited by 1 | Viewed by 794
Abstract
Horizontal-well multi-cluster fracturing is one of the most important techniques for increasing the recovery rate in unconventional oil and gas reservoir development. However, under the influence of complex induced stress fields, the mechanism of interaction and propagation of fractures within each segment remains [...] Read more.
Horizontal-well multi-cluster fracturing is one of the most important techniques for increasing the recovery rate in unconventional oil and gas reservoir development. However, under the influence of complex induced stress fields, the mechanism of interaction and propagation of fractures within each segment remains unclear. In this study, based on rock fracture criteria, combined with the boundary element displacement discontinuity method, a two-dimensional numerical simulation model of hydraulic fracturing crack propagation in a planar plane was established. Using this model, the interaction and propagation process of inter-cluster fractures under different fracturing sequences within horizontal well segments and the mechanism of induced stress field effects were analyzed. The influence mechanism of cluster spacing, fracture design length, and fracture internal pressure on the propagation morphology of inter-cluster fractures was also investigated. The research results indicate that, when using the alternating fracturing method, it is advisable to appropriately increase the cluster spacing to weaken the inhibitory effect of induced stress around the fractures created by prior fracturing on subsequent fracturing. Compared to the alternating fracturing method, the propagation morphology of fractures under the symmetrical fracturing method is more complex. At smaller cluster spacing, fractures created by prior fracturing are more susceptible to being captured by fractures from subsequent fracturing. The findings of this study provide reliable theoretical support for the optimization design of fracturing sequences and fracturing processes in horizontal well segments. Full article
(This article belongs to the Special Issue Innovations in Hydraulic Fracturing Technology for Unconventional Reservoirs)
►▼ Show Figures

Figure 1

Figure 1
<p>Constant displacement discontinuity of crack surface [<a href="#B29-processes-12-00971" class="html-bibr">29</a>].</p> Full article ">Figure 2
<p>(<b>a</b>) Crack element discretization. (<b>b</b>): Stress components in global coordinates <span class="html-italic">x-y</span> and local coordinates s-n [<a href="#B29-processes-12-00971" class="html-bibr">29</a>,<a href="#B30-processes-12-00971" class="html-bibr">30</a>].</p> Full article ">Figure 3
<p>(<b>a</b>) Numerical simulation model of crack growth for alternating fracturing. (<b>b</b>) Numerical simulation model for crack growth for symmetrical fracturing.</p> Full article ">Figure 4
<p>Alternate fracturing fracture propagation patterns under different cluster spacing (fracture internal pressure is 34 MPa).</p> Full article ">Figure 5
<p>Normal stress field in X direction around fractures of alternating fracturing under different cluster spacing.</p> Full article ">Figure 6
<p>Shear stress field around fractures of alternating fracturing under different cluster spacing.</p> Full article ">Figure 7
<p>Fracture growth patterns of alternating fracturing under different intra-fracture pressures (cluster spacing, 25 m).</p> Full article ">Figure 8
<p>Induced stress field around fractures of alternating fracturing under different intra-fracture pressures (cluster spacing 25 m).</p> Full article ">Figure 9
<p>Fracture propagation morphology and corresponding induced stress field of alternating fracturing under different fracture lengths produced by previous fracturing (intra-fracture pressure, 34 MPa; cluster spacing, 25 m).</p> Full article ">Figure 10
<p>The critical length of previously fractured fractures at which subsequent fractures can initiate and expand under different cluster spacing (intra-fracture pressure is 34 MPa).</p> Full article ">Figure 11
<p>Critical intra-fracture pressure at which subsequent fracturing fractures can initiate and propagate under different cluster spacing (previously fracturing fractures 2 and 4 intra-fracture pressure = 31 MPa, previously fracturing fracture 2 length L = 50 m).</p> Full article ">Figure 12
<p>The critical intra-fracture pressure at which subsequent fracturing fractures can initiate and propagate under different previously fractured fracture lengths (previously fractured fractures 2 and 4 intra-fracture pressure = 31 MPa; cluster spacing = 25 m).</p> Full article ">Figure 13
<p>Symmetric fracturing crack growth process.</p> Full article ">Figure 14
<p>Crack deflection angle changes curve with crack length.</p> Full article ">Figure 15
<p>Changes in the induced stress field during the crack propagation process of symmetrical fracturing.</p> Full article ">Figure 16
<p>Fracture propagation morphology and induced stress field distribution of symmetrical fracturing under different cluster spacing.</p> Full article ">Figure 17
<p>Variation curve of fracture 2 deflection angle with length for symmetrical fracturing under different cluster spacing.</p> Full article ">Figure 18
<p>Critical intra-fracture pressure at which subsequent fracturing fractures can initiate and propagate under different cluster spacing (intra-fracture pressure of previously fractured fractures 1 and 5 = 31 MPa).</p> Full article ">Figure 19
<p>Fracture propagation morphology and corresponding induced stress field distribution of symmetrical fracturing under different critical intra-fracture pressures (cluster spacing 15 m).</p> Full article ">

Review

Jump to: Research

22 pages, 6498 KiB  
Review
Review of Shale Oil and Gas Refracturing: Techniques and Field Applications
by Liru Xu, Dajiang Wang, Lizhi Liu, Chen Wang, Haiyan Zhu and Xuanhe Tang
Processes 2024, 12(5), 965; https://doi.org/10.3390/pr12050965 - 9 May 2024
Cited by 1 | Viewed by 781
Abstract
Shale oil and gas wells usually experience a rapid decline in production due to their extremely low permeability and strong heterogeneity. As a crucial technique to harness potential and elevate extraction rates in aged wells (formations), refracturing is increasingly employed within oil and [...] Read more.
Shale oil and gas wells usually experience a rapid decline in production due to their extremely low permeability and strong heterogeneity. As a crucial technique to harness potential and elevate extraction rates in aged wells (formations), refracturing is increasingly employed within oil and gas reservoirs globally. At present, the selection processes for refracturing, both of wells and layers, are somewhat subjective and necessitate considerable field data. However, the status of fracturing technology is difficult to control precisely, and the difference in construction effects is large. In this paper, well selection, formation selection, and the fracturing technology of shale oil and gas refracturing are deeply analyzed, and the technological status and main technical direction of refracturing technology at home and abroad are analyzed and summarized. The applicability, application potential, and main technical challenges of existing technology for different wells are discussed, combined with the field production dynamics. The results show that well and layer selection is the key to the successful application of refracturing technology, and the geological engineering parameters closely related to the remaining reservoir reserves and formation energy should be considered as the screening parameters. General temporary plugging refracturing technology has a low cost and a simple process, but it is difficult to accurately control the location of temporary plugging, and the construction effect is very different. Mechanical isolation refracturing technology permits the exact refurbishment of regions untouched by the initial fracturing. However, it is costly and complex in terms of construction. Consequently, cutting the costs of mechanical isolation refracturing technology stands as a pivotal research direction. Full article
(This article belongs to the Special Issue Innovations in Hydraulic Fracturing Technology for Unconventional Reservoirs)
►▼ Show Figures

Figure 1

Figure 1
<p>Top view of microseismic monitoring event density and sweep characteristics [<a href="#B9-processes-12-00965" class="html-bibr">9</a>].</p> Full article ">Figure 2
<p>Function mechanism of the temporary block agent (Revised from [<a href="#B32-processes-12-00965" class="html-bibr">32</a>,<a href="#B33-processes-12-00965" class="html-bibr">33</a>]).</p> Full article ">Figure 3
<p>Schematic diagram of the “nested casing” wellbore (Revised from [<a href="#B34-processes-12-00965" class="html-bibr">34</a>]).</p> Full article ">Figure 4
<p>Schematic diagram of expansion liner technology (Revised from [<a href="#B37-processes-12-00965" class="html-bibr">37</a>]).</p> Full article ">Figure 5
<p>Pipe string diagram under open-hole completion conditions (Revised from [<a href="#B38-processes-12-00965" class="html-bibr">38</a>]).</p> Full article ">Figure 6
<p>Pipe string diagram under casing completion conditions (Revised from [<a href="#B38-processes-12-00965" class="html-bibr">38</a>]).</p> Full article ">Figure 7
<p>Scraping tool assembly (Revised from [<a href="#B37-processes-12-00965" class="html-bibr">37</a>]).</p> Full article ">Figure 8
<p>Schematic diagram of the expansion process (Revised from [<a href="#B37-processes-12-00965" class="html-bibr">37</a>]).</p> Full article ">Figure 9
<p>Stimulation effect after large-scale refracturing (Revised from [<a href="#B31-processes-12-00965" class="html-bibr">31</a>]).</p> Full article ">Figure 10
<p>Fracturing growth rate under different numbers of temporary plugging balls (Revised from [<a href="#B45-processes-12-00965" class="html-bibr">45</a>]).</p> Full article ">Figure 11
<p>Comparison of gas production before and after refracturing (Revised from [<a href="#B45-processes-12-00965" class="html-bibr">45</a>]).</p> Full article ">Figure 12
<p>F19 refracturing construction curve.</p> Full article ">Figure 13
<p>F39 refracturing construction curve in Fuling shale gas reservoir.</p> Full article ">Figure 14
<p>Refracturing construction curve of F20 in Fuling shale gas reservoir.</p> Full article ">Figure 15
<p>Correlation analysis between refracturing construction parameters and post-productivity in Haynesville shale gas field in the United States (Revised from [<a href="#B48-processes-12-00965" class="html-bibr">48</a>]).</p> Full article ">Figure 16
<p>Comparison of 90-day normalized production before and after refracturing (Revised from [<a href="#B48-processes-12-00965" class="html-bibr">48</a>]).</p> Full article ">Figure 17
<p>Comparison of test data of refracturing wells in Fuling shale gas reservoir. (<b>a</b>) Test pressure comparison of refractured wells. (<b>b</b>) Refractured well test production comparison.</p> Full article ">Figure 18
<p>Production test of expandable liner before and after refracturing (Revised from [<a href="#B49-processes-12-00965" class="html-bibr">49</a>]).</p> Full article ">
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