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 5940

Special Issue Editors


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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

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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
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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

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Keywords

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

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Published Papers (6 papers)

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Research

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22 pages, 9333 KiB  
Article
Refractured Well Hydraulic Fractures Optimization in Tight Sandstone Gas Reservoirs: Application in Linxing Gas Field
by Zhengrong Chen, Yantao Xu, Bumin Guo, Zhihong Zhao, Haozeng Jin, Wei Liu and Ran Zhang
Processes 2024, 12(9), 2033; https://doi.org/10.3390/pr12092033 - 21 Sep 2024
Viewed by 601
Abstract
Poorly producing wells in sandstone gas reservoirs are often refractured to enhance production. Considering the mutual interference of initial/refractured fractures, conductivity dynamic evolution, non-uniform inflow, and variable mass flow in the fracture comprehensively, a semi-analytical reservoir-fracture coupled production model fusing spatial and time [...] Read more.
Poorly producing wells in sandstone gas reservoirs are often refractured to enhance production. Considering the mutual interference of initial/refractured fractures, conductivity dynamic evolution, non-uniform inflow, and variable mass flow in the fracture comprehensively, a semi-analytical reservoir-fracture coupled production model fusing spatial and time separation methods is introduced to model refractured well performance. The proposed model is verified by CMG. The field applications indicate that the refracture job should be carried out when production is lower than the desired value. Restoring the Cf-ini and constructing the Cf-ref can increase productivity, which increases over 8 D•cm. The production growth rate just obtained a slight improvement. The production increased significantly with Lf-ini increasing from 120~270 m and Lf-ref increasing from 100~150 m. Hence, it is essential to extend the Lf-ini under engineering conditions. The ks/km = 10 can obviously increase production, but further enlarging ks does not contribute to well performance. Conversely, further producing larger bs is vital to enhancing production. Subsequently, the optimal parameter combinations (ds > Lf-ini > Lf-ref > Cf-ini > ks > Cf-ref) for well(X1) are carried out by orthogonal experiments. This work proposes a novel method to simulate refractured vertical well performance in tight gas reservoirs for refracture optimization. Full article
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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
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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
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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 793
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
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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
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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
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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 999
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
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Review

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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 1150
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
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