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New Stimulation Methods for Recovery of Energy and Minerals from Ultra-low-permeability Rock Formations

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "H: Geo-Energy".

Deadline for manuscript submissions: closed (15 March 2019) | Viewed by 38930

Special Issue Editors

Prof. Dr. Ranjith Pathegama Gamage

E-Mail Website1 Website2
Guest Editor
Department of Civil Engineering, Monash University, Clayton, VIC 3800, Australia
Interests: carbon sequestration; mine waste recycling; geothermal energy; coal seam gas; shale gas; hydrogen fuel; deep mining; natural gas hydrates
Special Issues, Collections and Topics in MDPI journals
Prof. Liang Weiguo

E-Mail
Guest Editor
1. College of Mining Engineering, Taiyuan University of Technology, Taiyuan 030024, China
2. Key Laboratory of In-situ Property-improving Mining of Ministry of Education, Taiyuan University of Technology, Taiyuan 030024, China
Interests: CO2 sequestration; unconventional gas recovery; THMC coupled behaviour of rock masses and porous rock materials; development of unconventional geo-resources and geo-energy; rock mechanics and testing technique at high temperature and high pressure

Special Issue Information

Dear Colleagues,

Global consumption of minerals and energy has greatly stimulated their extraction, putting unrelenting pressure on the more accessible resources. Demand for raw materials and energy will continue to rise along with steady global economic growth and increased population­s. Rates of consumption and limited reserves make planning for stable and sustainable long-term supply extremely problematic; so it becomes urgent to press forward toward new science—supporting technologies for extracting minerals and fossil fuels from deeper formations in sustainable and economical manner.

In recent years research has shifted to focus on the harvesting of huge unconventional resources with environment sustainability. The greatest challenge comes from very low recovery rates due to ultra-low permeability in these deep reservoirs, limiting the opportunities for commercial and large-scale exploitation. Many industries have been using hydro-fracturing for extractions of oil and gas, as well as for the emergent geothermal industry. However, conventional fracturing has its limitations, demanding vast quantities of water for example. Innovative variants of existing exploration and production methods—such as new stimulation technologies to create complex fracture networks—have potential to release vast quantities of energy from highly impermeable formations. However, attempts to realise these benefits have typically failed on some front or other, whether technical, environmental, or economic.

We call for papers exploring the science and technology of enhancing the recovery of minerals, unconventional oil and gas, and geothermal energy. We will especially welcome submissions on the following topics:

  • Constitutive modelling and numerical methods
  • Coupled thermo-hydro-chemical-mechanical processes
  • Analysis and modelling of hydraulic fracture initiation and propagation
  • Reservoir geomechanics, and wellbore and drilling mechanics
  • Flow in porous and fractured media
  • Geothermal energy extraction
  • Unconventional oil and gas extraction
  • Thermo-hydro-mechanical numerical modelling
  • Case studies of international interest
  • Thermal stimulations
  • Permeability and diffusions
  • Fragmentations theoretical developments

In situ leaching for mineral recoveries

Prof. Ranjith Pathegama Gamage
Prof. Liang Weiguo
Guest Editors

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. Energies is an international peer-reviewed open access semimonthly 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 2600 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 oil/gas
  • shale oil/gas
  • coal seams gas
  • tight oil/gas
  • geomechanics
  • hot dry rocks
  • geothermal energy
  • deep geothermal
  • stimulations
  • gas hydrates
  • insitu mining

Published Papers (13 papers)

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Research

24 pages, 2395 KiB  
Article
A Study on the Mechanical Mechanism of Injection Heat to Increase Production of Gas in Low-Permeability Coal Seam
by Hongmei Cheng, Ning Zhang, Yugui Yang, Weihong Peng and Heng Chen
Energies 2019, 12(12), 2332; https://doi.org/10.3390/en12122332 - 18 Jun 2019
Cited by 12 | Viewed by 2106
Abstract
This paper puts forward a new mathematical model, which is a coal damage-heat-fluid-solid multi-field coupling theory, in order to reveal the mechanical mechanism of the increase of coal-bed methane recovery through thermal stimulation, and to evaluate its effect. The strain field is introduced [...] Read more.
This paper puts forward a new mathematical model, which is a coal damage-heat-fluid-solid multi-field coupling theory, in order to reveal the mechanical mechanism of the increase of coal-bed methane recovery through thermal stimulation, and to evaluate its effect. The strain field is introduced to define the damage of coal by considering of the effects of temperature, gas pressure, and mining stress of the coal seam. It is used to quantitatively describe the degree of coal rupture and damage. Additionally, the elastic and damage constitutive equation of coal and rock mass, the governing equation of the temperature field, and the coupling equation of gas diffusion and seepage are established. Based on these equations, the finite element source program is redeveloped by using the FORTRAN language, and a multi-field coupling analysis program is compiled. This program takes the temperature, the gas seepage, and the damage and deformation of coal and rock mass into consideration. The effect of heat injection temperature on gas production efficiency, gas pressure distribution, and effective extraction radius during coal-bed methane mining process is analyzed. The results show that the injection of heat can significantly improve the desorption and diffusion of gas, as well as the gas production rate and the production efficiency of coal-bed methane. Full article
(This article belongs to the Special Issue New Stimulation Methods for Recovery of Energy and Minerals from Ultra-low-permeability Rock Formations)
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17 pages, 7932 KiB  
Article
Characterization of Pore Throat Size Distribution in Tight Sandstones with Nuclear Magnetic Resonance and High-Pressure Mercury Intrusion
by Hongjun Xu, Yiren Fan, Falong Hu, Changxi Li, Jun Yu, Zhichao Liu and Fuyong Wang
Energies 2019, 12(8), 1528; https://doi.org/10.3390/en12081528 - 23 Apr 2019
Cited by 33 | Viewed by 3233
Abstract
Characterization of pore throat size distribution (PTSD) in tight sandstones is of substantial significance for tight sandstone reservoirs evaluation. High-pressure mercury intrusion (HPMI) and nuclear magnetic resonance (NMR) are the effective methods for characterizing PTSD of reservoirs. NMR T2 spectra is usually [...] Read more.
Characterization of pore throat size distribution (PTSD) in tight sandstones is of substantial significance for tight sandstone reservoirs evaluation. High-pressure mercury intrusion (HPMI) and nuclear magnetic resonance (NMR) are the effective methods for characterizing PTSD of reservoirs. NMR T2 spectra is usually converted to mercury intrusion capillary pressure for PTSD characterization. However, the conversion is challenging in tight sandstones due to tiny pore throat sizes. In this paper, the linear conversion method and the nonlinear conversion method are investigated, and the error minimization method and the least square method are proposed to calculate the conversion coefficients of the linear conversion method and the nonlinear conversion method, respectively. Finally, the advantages and disadvantages of these two different conversion methods are discussed and compared with field case study. The research results show that the average linear conversion coefficients of the 20 tight sandstone core plugs collected from Yanchang Formation, Ordos Basin of China is 0.0133 μm/ms; the average nonlinear conversion coefficient is 0.0093 μm/ms and the average nonlinear conversion exponent is 0.725. Although PTSD converted from NMR spectra by the nonlinear conversion method is wider than that obtained from linear conversion method, the nonlinear conversion method can retain the characteristic of bi-modal distribution in PTSD. Full article
(This article belongs to the Special Issue New Stimulation Methods for Recovery of Energy and Minerals from Ultra-low-permeability Rock Formations)
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31 pages, 6858 KiB  
Article
Uncertainty Evaluation of Safe Mud Weight Window Utilizing the Reliability Assessment Method
by Tianshou Ma, Tao Tang, Ping Chen and Chunhe Yang
Energies 2019, 12(5), 942; https://doi.org/10.3390/en12050942 - 12 Mar 2019
Cited by 22 | Viewed by 3976
Abstract
Due to the uncertainty of formation properties and improper wellbore stability analysis methods, the input parameters are often uncertain and the required mud weight to prevent wellbore collapse is too large, which might cause an incorrect result. However, the uncertainty evaluation of input [...] Read more.
Due to the uncertainty of formation properties and improper wellbore stability analysis methods, the input parameters are often uncertain and the required mud weight to prevent wellbore collapse is too large, which might cause an incorrect result. However, the uncertainty evaluation of input parameters and their influence on safe mud weight window (SMWW) is seldom investigated. Therefore, the present paper aims to propose an uncertain evaluation method to evaluate the uncertainty of SMWW. The reliability assessment theory was introduced, and the uncertain SMWW model was proposed by involving the tolerable breakout, the Mogi-Coulomb (MG-C) criterion and the reliability assessment theory. The influence of uncertain parameters on wellbore collapse, wellbore fracture and SMWW were systematically simulated and investigated by utilizing Monte Carlo simulation. Finally, the field observation of well SC-101X was reported and discussed. The results indicated that the MG-C criterion and tolerable breakout is recommended for wellbore stability analysis. The higher the coefficient of variance is, the higher the level of uncertainty is, the larger the impact on SMWW will be, and the higher the risk of well kick, wellbore collapse and fracture will be. The uncertainty of basic parameters has a very significant impact on SMWW, and it cannot be ignored. For well SC-101X, the SMWW predicted by analytical solution is 0.9921–1.6020 g/cm3, compared to the SMWW estimated by the reliability assessment method, the reliability assessment method tends to give a very narrow SMWW of 1.0756–1.0935 g/cm3 and its probability is only 80%, and the field observation for well kick and wellbore fracture verified the analysis results. For narrow SMWW formation drilling, some kinds of advanced technology, such as the underbalanced drilling (UBD), managed pressure drilling (MPD), micro-flow drilling (MFD) and wider the SMWW, can be utilized to maintain drilling safety. Full article
(This article belongs to the Special Issue New Stimulation Methods for Recovery of Energy and Minerals from Ultra-low-permeability Rock Formations)
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20 pages, 4203 KiB  
Article
A Thermo-Hydro-Mechanical-Chemical Coupling Model and Its Application in Acid Fracturing Enhanced Coalbed Methane Recovery Simulation
by Chaojun Fan, Mingkun Luo, Sheng Li, Haohao Zhang, Zhenhua Yang and Zheng Liu
Energies 2019, 12(4), 626; https://doi.org/10.3390/en12040626 - 15 Feb 2019
Cited by 64 | Viewed by 4392
Abstract
The reservoir permeability dominates the transport of gas and water in coal seam. However, coal seams rich in gas usually contain various pores and fractures blocked by a large amount of minerals, which leads to an ultra-low permeability and gas extraction rate, and [...] Read more.
The reservoir permeability dominates the transport of gas and water in coal seam. However, coal seams rich in gas usually contain various pores and fractures blocked by a large amount of minerals, which leads to an ultra-low permeability and gas extraction rate, and thus an increase of drilling workload. We first propose a thermo-hydro-mechanical-chemical coupled model (THMC) for the acid fracturing enhanced coalbed methane recovery (AF-ECBM). Then, this model is applied to simulate the variation of key parameters during AF-ECBM using a 2D geometry. The effect of different extraction schedules are comparatively analyzed to give an insight into these complex coupling responses in coal seam. Result confirms that the AF-ECBM is an effective way to increase the reservoir permeability and improve the gas production using the proposed model. The range of permeability increment zone increases most dramatically in the way of acid fracturing, followed by none-acid fracturing and acidizing over time. The gas production in order is: acid fracturing (AF-ECBM) > fracturing (F-ECBM) > acidification (A-ECBM)> direct extraction (D-CBM). Full article
(This article belongs to the Special Issue New Stimulation Methods for Recovery of Energy and Minerals from Ultra-low-permeability Rock Formations)
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18 pages, 5961 KiB  
Article
Influences of Fracturing Fluid Injection on Mechanical Integrity of Cement Sheath under Four Failure Modes
by Honglin Xu, Tianshou Ma, Nian Peng and Bin Yang
Energies 2018, 11(12), 3534; https://doi.org/10.3390/en11123534 - 19 Dec 2018
Cited by 20 | Viewed by 3217
Abstract
The significant decreased wellbore temperature and increased casing pressure during fracturing fluid injection present a big challenge for the mechanical integrity of cement sheath in fracturing wells. Based on the theories of elastic mechanics, thermodynamics, and a multi-layer composed thick-wall cylinder, this paper [...] Read more.
The significant decreased wellbore temperature and increased casing pressure during fracturing fluid injection present a big challenge for the mechanical integrity of cement sheath in fracturing wells. Based on the theories of elastic mechanics, thermodynamics, and a multi-layer composed thick-wall cylinder, this paper proposed a new mechanical model of cement sheath for fracturing wells, coupling pressure, and thermal loads, which consider the failure modes of de-bonding, radial cracking, disking, and shear failure. The radial nonuniform temperature change and the continuous radial stress and radial displacement at two interfaces have been considered. With the proposed model, the radial distributions of failure stress and the corresponding safety factor for cement sheath during fracturing fluid injection have been analyzed and compared under four failure modes. Results show that the decreased wellbore temperature will produce significant tri-axial tensile stress and induce cement failure of de-bonding, radial cracking, and disking. The increased casing pressure will significantly lower the risk of de-bonding but also aggravate radial cracking and shear failure. For integrity protection of cement sheath, increasing the injected fluid temperature, maintaining higher circulation pumping pressures, and adopting cement sheath with a low elasticity modulus have been suggested for fracturing wells. Full article
(This article belongs to the Special Issue New Stimulation Methods for Recovery of Energy and Minerals from Ultra-low-permeability Rock Formations)
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15 pages, 7068 KiB  
Article
Field Investigation of Hydraulic Fracturing in Coal Seams and Its Enhancement for Methane Extraction in the Southeast Sichuan Basin, China
by Zuxun Zhang, Hongtu Wang, Bozhi Deng, Minghui Li and Dongming Zhang
Energies 2018, 11(12), 3451; https://doi.org/10.3390/en11123451 - 10 Dec 2018
Cited by 14 | Viewed by 2594
Abstract
Hydraulic fracturing is an effective technology for enhancing the extraction of reservoir methane, as proved by field experience and laboratory experiments. However, unlike conventional reservoirs, coal seams had high stress sensitivity and high anisotropy. Therefore, the efficiency of hydraulic fracturing in coal seams [...] Read more.
Hydraulic fracturing is an effective technology for enhancing the extraction of reservoir methane, as proved by field experience and laboratory experiments. However, unlike conventional reservoirs, coal seams had high stress sensitivity and high anisotropy. Therefore, the efficiency of hydraulic fracturing in coal seams needs to be investigated. In this study, hydraulic fracturing was performed at Nantong mine in the southeast Sichuan basin, China. The field investigation indicated that the hydraulic fracturing could significantly enhance the methane extraction rate of boreholes ten times higher than that of normal boreholes in one of the minable coal seams (named #5 coal seam). The performance of hydraulic fracturing in three districts revealed that compared with south flank, the fluid pressure was higher and the injection rate was lower in north flank. The methane extraction rate of south flank was inferior to that of north flank. It indicated hydraulic fracturing had less effect on #5 coal seam in south flank. Moreover, the injection of high-pressure water in coal seams could also drive methane away from boreholes. The methane extraction rate of the test boreholes demonstrated the existence of methane enrichment circles after hydraulic fracturing. It indicated that hydraulic fracturing did act on #5 coal seam in south flank. However, due to the high stress sensitivity of coal seams and the high geo-stress of south flank, the induced artificial fractures in #5 coal seam might close with the decline of the fluid pressure that led to a sharp decline of the methane extraction rate. Full article
(This article belongs to the Special Issue New Stimulation Methods for Recovery of Energy and Minerals from Ultra-low-permeability Rock Formations)
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18 pages, 8371 KiB  
Article
Effective Exploitation Potential of Shale Gas from Lower Cambrian Niutitang Formation, Northwestern Hunan, China
by Han Cao, Tianyi Wang, Ting Bao, Pinghe Sun, Zheng Zhang and Jingjing Wu
Energies 2018, 11(12), 3373; https://doi.org/10.3390/en11123373 - 02 Dec 2018
Cited by 8 | Viewed by 2545
Abstract
The marine shale in the Lower Cambrian Niutitang Formation is the dominant shale-gas reservoir in northwestern Hunan, which accounts for more than 70% of unconventional energy in Hunan province. Accurately evaluating the shale-gas exploitation potential is a key to determining whether commercial exploitation [...] Read more.
The marine shale in the Lower Cambrian Niutitang Formation is the dominant shale-gas reservoir in northwestern Hunan, which accounts for more than 70% of unconventional energy in Hunan province. Accurately evaluating the shale-gas exploitation potential is a key to determining whether commercial exploitation standards can be met. In the literature, most existing studies have focused on evaluating the shale-gas exploitation potential based on either accumulation conditions or the shale fracability, which will lead to a gap between the real production and proven gas reserves due to the characteristics of the shale’s low permeability and low porosity. Therefore, further studies are needed to evaluate the effective shale-gas exploitation potential. To address this need, the outcrop shale samples in the Niutitang Formation were collected from the target regions, and the geological characteristics, mechanics behavior, and microstructure performance were discussed via both field data and laboratory tests. The results revealed that the shale-gas exploitation potential in the Niutitang Formation was indicated to be comparable to that of five validated shale-gas exploitation regions in the United States. To further illustrate the effective shale-gas exploitation potential, this study suggested using a comprehensive evaluation framework for this purpose, in which both accumulation condition and the shale fracability are simultaneously considered. Therefore, the shale gas reservoir in the Niutitang Formation has highly effective shale-gas exploitation potential by considering both the accumulation conditions and the shale fracability. Full article
(This article belongs to the Special Issue New Stimulation Methods for Recovery of Energy and Minerals from Ultra-low-permeability Rock Formations)
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19 pages, 5921 KiB  
Article
Numerical Investigation on the Influence of Areal Flow on EGS Thermal Exploitation Based on the 3-D T-H Single Fracture Model
by Chi Yao, Yulong Shao and Jianhua Yang
Energies 2018, 11(11), 3026; https://doi.org/10.3390/en11113026 - 04 Nov 2018
Cited by 16 | Viewed by 3780
Abstract
The research on the factors of heat recovery performance of Enhanced Geothermal Systems (EGS) is an important issue, especially in the well position optimization in EGS, because it can maximize the economic benefits of EGS. Based on the three-dimensional thermo and hydro (TH) [...] Read more.
The research on the factors of heat recovery performance of Enhanced Geothermal Systems (EGS) is an important issue, especially in the well position optimization in EGS, because it can maximize the economic benefits of EGS. Based on the three-dimensional thermo and hydro (TH) single-fracture model, a flow field in the EGS is added to the model, the thermal energy mining of the EGS thermal reservoir is realized through the double well and better study of the impact of regional flow on EGS well placement. To verify the reliability of the three-dimensional numerical model, the comparison between the two-dimensional single fracture model and the single fracture analytical model is performed under the same conditions, and it is found that there is a good agreement between the numerical and the analytical solutions. The influence of the direction of regional flow on the thermal recovery performance of EGS is studied, and the operating lifetime, power generation and heat production rate of the system are used as the evaluation indicators. It is found that there are two stagnation points in the flow field under regional flow conditions, and the stagnation point position changes regularly with regional flow direction. The direction of regional flow has a great influence on the heat extraction ratio and service lifetime of the geothermal system, the layout of the double well must take into account the regional flow. When only considered the influence of regional flow on EGS, after 50 years of EGS operation, the production well temperature and system operating lifetime increase with the increase of β (the angle between the direction of the regional flow and the line connecting the centers of the two wells). When it has regional flow, the greater the well spacing, the greater the temperature of the production well, but when the well spacing increases to a certain value, the well spacing will not affect the temperature of the production well. Full article
(This article belongs to the Special Issue New Stimulation Methods for Recovery of Energy and Minerals from Ultra-low-permeability Rock Formations)
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25 pages, 5459 KiB  
Article
Effects of Coal Deformation on Different-Phase CO2 Permeability in Sub-Bituminous Coal: An Experimental Investigation
by Beining Zhang, Weiguo Liang, Pathegama Gamage Ranjith, Wei He, Zhigang Li and Xiaogang Zhang
Energies 2018, 11(11), 2926; https://doi.org/10.3390/en11112926 - 26 Oct 2018
Cited by 7 | Viewed by 2313
Abstract
Coal deformation is one of the leading problems for carbon dioxide (CO2) sequestration in coal seams especially with respect to different-phase CO2 injection. In this paper, a series of core flooding tests were conducted under different confining stresses (8–20 MPa), [...] Read more.
Coal deformation is one of the leading problems for carbon dioxide (CO2) sequestration in coal seams especially with respect to different-phase CO2 injection. In this paper, a series of core flooding tests were conducted under different confining stresses (8–20 MPa), injection pressures (1–15 MPa), and downstream pressures (0.1–10 MPa) at 50 °C temperature to investigate the effects of coal deformation induced by adsorption and effective stress on sub-critical, super-critical, and mixed-phase CO2 permeability. Due to the linear relationship between the mean flow rate and the pressure gradient, Darcy Law was applied on different-phase CO2 flow. Experimental results indicate that: (1) Under the same effective stress, sub-critical CO2 permeability > mixed-phase CO2 permeability > super-critical CO2 permeability. (2) For sub-critical CO2 flow, the initial volumetric strain is mainly attributed to adsorption-induced swelling. A temporary drop in permeability was observed. (3) For super-critical CO2 flow, when the injection pressure is over 10 MPa, effective-stress-generated deformation is dominant over the adsorption-induced strain and mainly contributes to the volumetric strain change. Thus, there is a linear increase of the volumetric strain with mean pore pressure and super-critical CO2 permeability increased with volumetric strain. (4) For mixed-phase CO2 flow, coupling effects of adsorption-induced swelling and effective stress on the volumetric strain were observed but effective stress made more of a contribution. CO2 permeability consistently increased with the volumetric strain. This paper reveals the swelling mechanism of different-phase CO2 injections and its effect on coal permeability. Full article
(This article belongs to the Special Issue New Stimulation Methods for Recovery of Energy and Minerals from Ultra-low-permeability Rock Formations)
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12 pages, 4532 KiB  
Article
Mechanism Analysis of Liquid Carbon Dioxide Phase Transition for Fracturing Rock Masses
by Feng Gao, Leihu Tang, Keping Zhou, Yanan Zhang and Bo Ke
Energies 2018, 11(11), 2909; https://doi.org/10.3390/en11112909 - 25 Oct 2018
Cited by 32 | Viewed by 2516
Abstract
The technique of breaking rocks using carbon dioxide phase transition technology is being widely applied in current research. This article combines theoretical and practical methods to analyze the mechanism by which high-pressure gas breaks rock at different stages. Using the observation that liquid [...] Read more.
The technique of breaking rocks using carbon dioxide phase transition technology is being widely applied in current research. This article combines theoretical and practical methods to analyze the mechanism by which high-pressure gas breaks rock at different stages. Using the observation that liquid carbon dioxide forms a high-pressure jet from release holes at the moment of release, a formula for calculating the initial pressure on the wall in the direction of release was obtained, and the pattern of initial crack formation on the borehole wall under different initial stress conditions was examined. An experiment using carbon dioxide phase transition technology to fracture rock without an initial stress field was conducted. The mechanism of generation and expansion of subsequent cracks under stress waves and high-pressure gas was analyzed, and the formula for calculating crack propagation radius under stress waves was obtained. The results suggested that under the quasi-static action of high-pressure gas, cracks begin to develop when the stress intensity factor KI at the crack tip is equal to or greater than the fracture toughness KIC of the rock. Full article
(This article belongs to the Special Issue New Stimulation Methods for Recovery of Energy and Minerals from Ultra-low-permeability Rock Formations)
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11 pages, 3884 KiB  
Article
Effect of Intermediate Principal Stress on the Strength, Deformation, and Permeability of Sandstone
by Zhenlong Song, Minghui Li, Guangzhi Yin, Pathegama Gamage Ranjith, Dongming Zhang and Chao Liu
Energies 2018, 11(10), 2694; https://doi.org/10.3390/en11102694 - 10 Oct 2018
Cited by 10 | Viewed by 2524
Abstract
Although the mechanical behaviors and flow aspects of sandstone have been previously investigated, studies of the effect of the intermediate principal stress (σ2) on the strength, deformation, and permeability of sandstone are lacking. In this work, the mechanical behaviors and [...] Read more.
Although the mechanical behaviors and flow aspects of sandstone have been previously investigated, studies of the effect of the intermediate principal stress (σ2) on the strength, deformation, and permeability of sandstone are lacking. In this work, the mechanical behaviors and permeability of sandstone under true triaxial stress conditions were investigated using a newly developed true triaxial geophysical apparatus. The experimental results showed that with increasing σ2, the peak strength, octahedral effective normal stress, and octahedral effective shear stress of the sandstone increased, and the rate of increase decreased. This is because a larger intermediate principal stress coefficient b has an inhibitory effect on rock strength. In our study, as the ratio of σ2/σ3 increased, the specimen entered compressive strain in the σ2 direction during the first stress drop. The stress and strain path deviations occur during rock failure. The amount of deviation increased as the σ2 increased before the peak stress. This phenomenon indicates that elastic mechanics are not suitable for understanding this sandstone rock during its failure. The permeability evolution of the sandstone under true triaxial stress conditions was measured and analyzed to investigate the effect of σ2. During the complete true triaxial stress-strain experiments, the variation we found in gas seepage velocity could be divided into two stages. Before the first pressure drop, the gas seepage velocity was mainly affected by volume strain. After the first pressure drop, the seepage velocity was affected by the deviator strain, which can change the seepage channels. Full article
(This article belongs to the Special Issue New Stimulation Methods for Recovery of Energy and Minerals from Ultra-low-permeability Rock Formations)
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28 pages, 4179 KiB  
Article
A Novel Model Incorporating Geomechanics for a Horizontal Well in a Naturally Fractured Reservoir
by Mingxian Wang, Guoqiang Xing, Zifei Fan, Wenqi Zhao, Lun Zhao and Heng Song
Energies 2018, 11(10), 2584; https://doi.org/10.3390/en11102584 - 28 Sep 2018
Cited by 1 | Viewed by 2259
Abstract
Fracture aperture of a fractured reservoir can be affected by both matrix elasticity and fracture compressibility when the reservoir pressure decreases, namely stress sensitivity. An elasticity parameter coupling Young’s modulus and Poisson’s ratio was introduced to reflect this geomechanical behavior, and a new [...] Read more.
Fracture aperture of a fractured reservoir can be affected by both matrix elasticity and fracture compressibility when the reservoir pressure decreases, namely stress sensitivity. An elasticity parameter coupling Young’s modulus and Poisson’s ratio was introduced to reflect this geomechanical behavior, and a new model incorporating geomechanics was developed to analyze the flow behavior of a horizontal well in a naturally fractured reservoir. Pressure solutions for two cases—uniform-flux and infinite-conductivity—were derived, respectively. For the uniform-flux case, the effect of dimensionless elasticity parameter on the pressure-drop profile becomes stronger with continuing production, and the profile may be like a bow. Nine flow regimes can be observed on the transient response of the infinite-conductivity case. Stress sensitivity mainly affects the late-flow period and a larger dimensionless elasticity parameter causes a greater pressure drop. Due to stress sensitivity, the pressure derivative curve exhibits an upward tendency in the pseudo-radial flow regime, and the slope is greater than “1” in the pseudo-steady flow regime. For KT-I formation in the North Truva field, its elasticity parameter decreases with the increase of Young’s modulus or Poisson’s ratio and ranges from 8 × 10−8 Pa−1 to 1.1 × 10−7 Pa−1. Meanwhile, the transient response of H519 has a slight negative correlation with Young’s modulus and Poisson’s ratio in the pseudo-steady flow regime. Full article
(This article belongs to the Special Issue New Stimulation Methods for Recovery of Energy and Minerals from Ultra-low-permeability Rock Formations)
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17 pages, 3612 KiB  
Article
Methane Desorption Characteristics of Coal at Different Water Injection Pressures Based on Pore Size Distribution Law
by Dong Zhao, Tao Gao, Yulin Ma and Zengchao Feng
Energies 2018, 11(9), 2345; https://doi.org/10.3390/en11092345 - 05 Sep 2018
Cited by 13 | Viewed by 2830
Abstract
Methane desorption characteristics of coal under definite water pressure comprises a complex two-phase flow process. A series of mercury intrusion porosimetry (MIP) and desorption experiments at different water injection pressures are reported in this study. Three lumpy coal samples were used in desorption [...] Read more.
Methane desorption characteristics of coal under definite water pressure comprises a complex two-phase flow process. A series of mercury intrusion porosimetry (MIP) and desorption experiments at different water injection pressures are reported in this study. Three lumpy coal samples were used in desorption experiments at three different water injection pressures and at natural desorption for comparison. Samples comprising two ranks of coal were used for MIP measurements including the distribution of porosity and pore sizes. The results of this study enable the establishment of a new model that encompasses a critical theoretical pore size that is most effective for water injection into coalbeds and that can be related to water injection pressure, the length of residual water, and gas adsorption capacity. Data show that the use of different water injection pressures leads to different gas desorption capacities as well as variable time effects and degree of gas desorption. Critical pore size is therefore proposed as a new parameter that can be employed to describe high pressure water effects in the context of gas desorption and can be calculated using pore size and the volume distribution law, as well as via the moisture ratio that remains after experiments and the permanent desorption percentage. Full article
(This article belongs to the Special Issue New Stimulation Methods for Recovery of Energy and Minerals from Ultra-low-permeability Rock Formations)
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