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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "H1: Petroleum Engineering".

Deadline for manuscript submissions: closed (28 April 2023) | Viewed by 12377

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Prof. Dr. Xinpu Shen

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School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, China
Interests: geomechanics; mechanics of string and tubing; continuun damage mechanics; numerical solution of multi-physics problems in petroleum industry
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Dear Colleagues,

Unconventional oil and gas played important roles in the energy industry for many decades. Due to the low-permeability characteristics of unconventional reservoirs, challenges related to the development of unconventional oil and gas have appeared in various academic and technical domains such as geology, geophysics, geochemistry, geomechanics, mechanics of string and tubing, and reservoir stimulation, etc. Many research achievements have been obtained in solving the aforementioned problems as technologies are developed accordingly. Still, there are many other problems existing in the current industrial and academic domains related to the development of unconventional oil and gas. This Special Issue provides a platform for the exchange and exhibition of achievements related to unconventional oil and gas.

The following topics are of major interests for this Special Issue:

Geology and sweet spots;
Hydraulic fracturing;
Geophysics;
Geomechanics;
Geochemistry;
Mechanics of string and tubing;
Cases of best practice of various technical applications.

Solutions and research results achieved by either experimental or numerical as well as analytical and empirical methods are welcome.

Prof. Dr. Xinpu Shen
Guest Editor

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Keywords

geology
geophysics
geomechanics
mechanics of string and tubing
drilling and completion
hydraulic fracturing
geostress
unconventional reservoir
tight sand reservoir
shale gas
heavy oil
multiphysics modeling
porous flow
mud logging
casing deformation

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Related Special Issue

Challenges and Research Trends of Unconventional Oil and Gas II in Energies (1 article)

Published Papers (9 papers)

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Research

14 pages, 7986 KiB

Open AccessArticle

An Overview of the Differential Carbonate Reservoir Characteristic and Exploitation Challenge in the Tarim Basin (NW China)

by Lixin Chen, Zhenxue Jiang, Chong Sun, Bingshan Ma, Zhou Su, Xiaoguo Wan, Jianfa Han and Guanghui Wu

Energies 2023, 16(15), 5586; https://doi.org/10.3390/en16155586 - 25 Jul 2023

Cited by 2 | Viewed by 1120

Abstract

The largest marine carbonate oilfield and gas condensate field in China have been found in the Ordovician limestones in the central Tarim Basin. They are defined as large “layered” reef-shoal and karstic reservoirs. However, low and/or unstable oil/gas production has been a big challenge for effective exploitation in ultra-deep (>6000 m) reservoirs for more than 20 years. Together with the static and dynamic reservoir data, we have a review of the unconventional characteristics of the oil/gas fields in that: (1) the large area tight matrix reservoir (porosity less than 5%, permeability less than 0.2 mD) superimposed with localized fracture-cave reservoir (porosity > 5%, permeability > 2 mD); (2) complicated fluid distribution and unstable production without uniform oil/gas/water interface in an oil/gas field; (3) about 30% wells in fractured reservoirs support more than 80% production; (4) high production decline rate is over 20% per year with low recovery ratio. These data suggest that the “sweet spot” of the fractured reservoir rather than the matrix reservoir is the major drilling target for ultra-deep reservoir development. In the ultra-deep pre-Mesozoic reservoirs, further advances in horizontal drilling and large multiple fracturing techniques are needed for the economic exploitation of the matrix reservoirs, and seismic quantitative descriptions and horizontal drilling techniques across the fault zones are needed for oil/gas efficient development from the deeply fractured reservoirs. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Unconventional Oil and Gas)

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18 pages, 4972 KiB

Open AccessArticle

Study of the Failure Mechanism of an Integrated Injection-Production String in Thermal Recovery Wells for Heavy Oil

by Wei Zhang, Deli Gao, Yigang Liu, Jianhua Bai and Cheng Wang

Energies 2023, 16(7), 3246; https://doi.org/10.3390/en16073246 - 5 Apr 2023

Cited by 1 | Viewed by 1583

Abstract

The integrated injection-production string is the core tool used in thermal recovery wells for heavy oil, the mechanical behavior of which is complex due to the coupling effect of downhole temperature and pressure and the load induced by steam huff and puff operations. In this paper, an analysis model that calculates the temperature and pressure field during steam huff and puff operations has been established based on the basic principles of energy conservation and heat transfer. Then, the force distribution and strength check of the integrated injection-production string were analyzed. The fatigue damage of the string was evaluated by considering dynamic loads during the injection process. The corrosion life of the string was predicted. Finally, the failure mechanism of the integrated injection-production string in thermal recovery wells for heavy oil was illustrated. The results showed that the strength of the string and vibration fatigue are not the main causes of failure, but corrosion is the main reason for string failure. The residual strength of the corroded string was greatly reduced, which is the fundamental reason for the failure of the string. This paper is of guiding significance to the optimization of design and safety evaluations of the integrated injection-production string in thermal recovery wells for heavy oil. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Unconventional Oil and Gas)

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13 pages, 38707 KiB

Open AccessArticle

The Fractured Permian Reservoir and Its Significance in the Gas Exploitation in the Sichuan Basin, China

by Xin Luo, Siqi Chen, Jiawei Liu, Fei Li, Liang Feng, Siyao Li, Yonghong Wu, Guanghui Wu and Bin Luo

Energies 2023, 16(4), 1968; https://doi.org/10.3390/en16041968 - 16 Feb 2023

Cited by 1 | Viewed by 1151

Abstract

Large gas reserves have been found in the Permian platform margin of the Kaijiang-Liangping area of the Sichuan Basin in SW China. They are assumed to be a widely developed reef–shoal reservoir. However, the tight matrix reservoir cannot support high gas production using conventional development technology at deep subsurface. In this contribution, we analyze the fractured reservoirs along the strike-slip fault zones using the compiled data of cores, well logging, and production data, and provide a seismic description. It was shown that the fractures and their dissolution developed along the strike-slip fault zones. The porosity and permeability of the fractured reservoir could increase by more than one and 1–2 orders of magnitude, respectively. The seismic anisotropic energy found in the steerable pyramid process suggests that fractured reservoirs have a strong heterogeneity, with a localized fault damage zone. This fracturing has both positive and negative effects, showing varied reservoir parameters in the fault damage zone. The development pattern should adopt a non-uniform well pattern, in order to target the localized “sweet spot” of the fractures in these deep tight matrix reservoirs. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Unconventional Oil and Gas)

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15 pages, 10147 KiB

Open AccessArticle

Integrated Analysis of the 3D Geostress and 1D Geomechanics of an Exploration Well in a New Gas Field

by Linsheng Wang, Xinpu Shen, Baocheng Wu, Tian Shen and Jiangang Shi

Energies 2023, 16(2), 806; https://doi.org/10.3390/en16020806 - 10 Jan 2023

Viewed by 1447

Abstract

The aim of this study was to propose the workflow for integrated analysis of the 3D geostress and 1D geomechanics of an exploration in a new gas field. This integrated analysis will allow for problems associated with the inaccuracy of 1D geomechanical analysis to be overcome in a region with obvious anticline/syncline structures. The 1D geomechanical analysis of the well in the exploration of a new gas field mainly included the prediction of pore pressure and calculation of the mud weight window for safe drilling. In general, this integrated workflow included both a method for pore pressure prediction and a method for the calculation of the mud weight window, with the numerical solution of 3D geostress plus the interval velocity of formations. The procedure for the calculation of the 3D geostress of a target block was also introduced. Numerical solution of the 3D geostress of the target gas field, as well as solutions of 1D geomechanical analysis, have demonstrated the efficiency and practical use of the proposed theory in the successful drilling of the LT-1 well in the Junggar Basin, Xinjiang, China. For this LT-1 well in the target TS block, there was no logging data to refer to when predicting the pore pressure of undrilled formations. Only 3D geostress could be used to calculate the mud weight window. Influences of anticline structures were considered in the calculation of 3D geostress. Since the accuracy of the numerical solution of 3D geostress is higher than the accuracy of the 1D geostress solution for a single well analysis, the results of pore pressure and the mud weight window are more accurate than those obtained with conventional 1D geostress analysis. Details of the finite element modeling of the 3D geostress field of the TS block is presented along with the solution of the 3D geostress field. With the data of the interval velocity of formations and 3D geostress solution of the TS block, pore pressure prediction was carried out for the 7000 m-deep pilot LT-1 well. Finally, calculations were performed for the values of the mud weight window of the LT-1 well. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Unconventional Oil and Gas)

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13 pages, 15219 KiB

Open AccessArticle

Classification and Assessment of Core Fractures in a Post-Fracturing Conglomerate Reservoir Using the AHP–FCE Method

by Renyan Zhuo, Xinfang Ma, Shicheng Zhang, Junxiu Ma, Yuankai Xiang and Haoran Sun

Energies 2023, 16(1), 418; https://doi.org/10.3390/en16010418 - 29 Dec 2022

Cited by 2 | Viewed by 1242

Abstract

To characterize the hydraulic fracture network of a conglomerate reservoir, a slant core well was drilled aimed to obtain direct information regarding hydraulic fractures through slant core at the conglomerate hydraulic fracturing test site (CHFTS). Core fracture classification was the fundamental issue of the project. In this study, three grade classifications for core fractures were proposed. Comprehensive classification of core fractures was carried out using the analytic hierarchy process (AHP)–fuzzy comprehensive evaluation (FCE) method. Finally, the fracture classification results were validated against numerical simulation. The grade-1 fracture classification included hydraulic fractures, drilling-induced fractures and core cutting-induced fractures. A total of 214 hydraulic fractures were observed. For the grade-2 classification, the hydraulic fractures were divided into 47 tensile fractures and 167 shear fractures. For the grade-3 classification, the shear fractures were subdivided into 45 tensile-shear fractures and 122 compression-shear fractures. Based on the numerical verification of the core fracture classifications, the dataset acquired was applied to analyze the spatial distribution of tensile and shear fractures. Results showed that the tensile fractures were mainly in the near-wellbore area with lateral distances of less than 20–25 m from the wellbore. The shear fractures were mainly in the far-wellbore area with lateral distances of 20–30 m from the wellbore. These results provide a basis for understanding the fracture types, density, and failure mechanisms of post-fracturing conglomerate reservoir. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Unconventional Oil and Gas)

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20 pages, 5837 KiB

Open AccessArticle

Study on the Effect of Fracturing Pump Start and Stop on Tubing Fluid-Structure Interaction Vibration in HPHT Wells via MOC

by Lu Cui, Fanfan Qiao, Meng Li, Yiming Xiao and Jiarui Cheng

Energies 2022, 15(24), 9291; https://doi.org/10.3390/en15249291 - 7 Dec 2022

Cited by 1 | Viewed by 1034

Abstract

The processes of HTHP well fracturing, oil drive, and gas recovery are accompanied by the non-stationary flow of medium in the tubing, which may lead to periodic vibration and cause the failure and fatigue of the tubing, thread leakage, and bending deformation. In this paper, a fluid–structure interaction model with 4-equation was established, which considered the unsteady flow of fluid and the motion state of tubing during the periodic injection, pump start, and shutdown of fluid in the tubing. Further, the discrete solution of MOC was used to obtain the variation of fluid flow rate and pressure, tubing vibration rate, frequency, and additional stress with time. The resonance construction parameters corresponding to different tubing diameters were analyzed by discussing the effects of different start and shutdown times as well as pressure on the tubing vibration parameters. The results show that under the periodic injection condition, increasing the tubing diameter or start inside pressure would lead to a sharp increase in the axial additional stress of the tubing generated by fluid–structure interaction, which is not conducive to the safety protection of the tubing. When the pump was shutdown, excessively short operation times and high pressure in the tubing would lead to excessive transient loads in addition to resonance, which would cause damage to the pipeline. Finally, corresponding to the above analysis results, this paper proposes the optimal injection parameters to avoid the generation of resonance, which provides a theoretical basis and reference range for the safe service conditions of the tubing. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Unconventional Oil and Gas)

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13 pages, 2358 KiB

Open AccessArticle

Strength Failure of CO₂ Injection Tubular Strings Considering CO₂ Phase Transition

by Yanbin Qin, Yinping Cao, Yihua Dou, Wenwen Lin, Jiahao Cao and Luyao Wang

Energies 2022, 15(23), 8932; https://doi.org/10.3390/en15238932 - 25 Nov 2022

Cited by 1 | Viewed by 1312

Abstract

Compared with traditional injection tubular strings, the stresses on CO₂ injection tubular strings are more complex. The results from field applications show that the phase transition of CO₂ fluid in CO₂ injection strings is an important factor in the calculation of temperature distribution and analysis of string mechanics. Therefore, we propose a strength analysis method for CO₂ injection tubular strings that considers the CO₂ phase transition. We selected four CO₂ injection strings in an oil field in China as examples to evaluate their strength and safety. First, we established coupled differential equations for the temperature, pressure, and physical parameters of CO₂ injection strings according to the theory of fluid flow and heat transfer. Then, we used an adaptive fuzzy neural network to construct the model for calculating the CO₂ convection heat transfer coefficient and used this to obtain the high-precision convection heat transfer coefficients of tubular strings under conditions of CO₂ flooding. We analyzed the injection-string deformations that resulted from the piston, spiral bending, expansion, friction and temperature effects according to the stress characteristics of the CO₂ injection strings with packers under different working conditions. Finally, we performed mechanical analyses on the collapse resistance, internal pressure resistance, and tensile and triaxial stresses of the CO₂ injection strings, and the results of these analyses provide a theoretical basis for the strength analysis of CO₂ injection strings. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Unconventional Oil and Gas)

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16 pages, 4426 KiB

Open AccessArticle

Analysis of Energy Dissipation on the Sealing Surface of Premium Connection Based on a Microslip Shear Layer Model

by Yang Yu, Zhan Qu, Yihua Dou and Yinping Cao

Energies 2022, 15(22), 8400; https://doi.org/10.3390/en15228400 - 10 Nov 2022

Cited by 6 | Viewed by 1395

Abstract

In high production gas wells, premium connections are subject to alternating loads and vibration excitation due to the change of fluid pressure exerted on the tubing string. The energy dissipation on the sealing surface of premium connections affects the sealing performance of premium connections. The present study proposes a new energy dissipation analysis method for the sealing performance of premium connections using a microslip shear layer mode, a novel technique to overcome and improve the limitations of existing analysis method of premium connections. In this paper, based on a microslip shear layer model, a vibration equilibrium equation of premium connection was established with the constraints of the taper of the sealing surface, the thread, and the torque shoulder. Then, the control equilibrium equations of the stick and microslip were derived, and the critical microslip tangential force and force–displacement hysteresis curves under different interface parameters were obtained by solving the equilibrium equations. The influence of different interface parameters on the energy dissipation of premium connection was discussed by using a standardized regression coefficient method. It was found that the friction coefficient influenced both the minimum and maximum microslip tangential forces, while the shear layer stiffness influenced only the minimum microslip tangential force. The greater the stiffness of the shear layer, the smaller the minimum microslip tangential force and the relative displacement of the contact surface, which made it easier to generate energy dissipation. The influence of the friction coefficient on energy dissipation was much greater than the stiffness of the shear layer. There was positive correlation between the friction coefficient and energy dissipation. While, there was a negative correlation between the stiffness of shear layer and energy dissipation. The results can provide a theoretical guide for micro sealing failure mechanism of premium connections under dynamic loads and expand the analysis method of metal seals. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Unconventional Oil and Gas)

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10 pages, 2710 KiB

Open AccessArticle

Application Characteristics of Zeolite-Based Stuffing for Nanofluidic Packer Rubber

by Yafei Zhang, Jingwei Liang, Rui Luo, Shiwei Min and Yihua Dou

Energies 2022, 15(21), 7962; https://doi.org/10.3390/en15217962 - 27 Oct 2022

Cited by 3 | Viewed by 1374

Abstract

Aiming at obtaining the application characteristics of more nanofluidic stuffing to enrich the database of nanofluidic packer rubber, three zeolite-based nanofluidic types of stuffing with water, glycerin, and a saturated aqueous solution of KCl (hereinafter referred to as saturated KCl solution) as the functional liquids were studied using experiments. The results showed that all the three zeolite-based nanofluidic stuffing types could be applied as stuffing for nanofluidic packer rubber. The setting pressure ranges for zeolite/water, zeolite/glycerin, and zeolite/saturated KCl solution stuffing were 21.71 to 30.62 MPa, 15.31 to 23.57 MPa, and 27.50 to 38.83 MPa, and the specific deformation quantities of the three stuffing types were 72.76, 102.07, and 77.54 mm³∙g⁻¹, respectively. In zeolite/saturated KCl solution stuffing, the number of liquid molecules retained in the nanochannels was the minimum; thus, this stuffing type was the most stable during application. The order of the equivalent surface tensions of the three zeolite-based stuffing types in the confined nanochannels was consistent with the order of the gas–liquid surface tensions in the bulk phase. The equivalent surface tension, which reflected the interaction between liquid–solid phases, dominated the pressure threshold, the deformation capacity, and the stability of nanofluidic stuffing. This research study provided data support for the application of nanofluidic packer rubber. Full article

(This article belongs to the Special Issue Challenges and Research Trends of Unconventional Oil and Gas)

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