bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fracture Opening Patterns in Granular Media Subjected to Injection of Non-Newtonian Fluids
Authors: Li Zihao , Song Haofeng , Balhoff Matthew T. , Espinoza D. Nicolas 
Published: September 2022

ABSTRACT:
Fluid injection into sand may initiate fluid-driven fractures. The fluid-sand interaction patterns depend on the injection velocity, fluid viscosity, rheology and stress boundary conditions. However, the extension to non-Newtonian fluids and anisotropic stress conditions, such as in the case of injection of a polymer in the subsurface, is largely unexplored. In this paper, we study the injection of a Newtonian fluid (glycerol aqueous solution) and a shear-thinning fluid (scleroglucan) into a sand-filled Hele-Shaw cell. The experimental results demonstrate complex fracture patterns depending on injection velocity, fluid viscosity, boundary conditions and fluid rheology. The presence of stress-free boundaries causes the fracture opening to be almost perpendicular to the minimum principal stress. The peak injection pressure is also higher compared to the fixed-displacement boundaries. Compared to Newtonian fluid (glycerol), shear thinning polymer (scleroglucan) causes thinner fracture openings and more radial infiltration morphology in sand. The fracturing mechanism in sand is associated with the shear dilation at the tip of fractures and fracture offshoots. This study helps to clarify the basic flow and failure mechanisms of sand when subjected to injection of a non-Newtonian fluid. The insights obtained from these experiments can aid in the prediction of fracture morphology and sweep efficiency for on-site polymer injection.

1. INTRODUCTION
Hydro-mechanical interactions between fluid flow and solids are common in many industries, such as oil and gas exploration, formation damage caused by particle jamming during oil and gas production (Li et al., 2021a), hydraulic fracturing (Zheng et al., 2020; Zheng and Sharma, 2021, Li et al., 2020), spray coating processes in food processing (Hilton et al., 2013) and tablet production in pharmaceuticals (Hemamanjushree and Tippavajhala, 2020). Different fluid infiltration and fracture opening morphologies caused by the injection of Newtonian fluids affect the fluid injectivity (Li et al., 2021b). However, extensions to non-Newtonian fluids and anisotropic stress conditions, such as in the case of injection of polymers in geological formations, are largely unexplored.
A Visualization Study of Fracture Propagation in Tight Sandstone Under Triaxial Loading
Authors: Zang Y. X. , Wang Q. , Tian K. J. , Wang H. Z. , Tian S. C. 
Published: September 2022

ABSTRACT:
Hydraulic fracturing is the key technique in the development of unconventional resources. Many optical experimental studies have been made to qualitatively study the hydraulic fracturing process. However, due to the time of fracture propagation being extremely short (ms), real-time quantitative description of the fracturing process is challenging. To clarify the process of fracture propagation, a novel triaxial optical hydraulic fracturing experimental apparatus is developed which mainly includes an ISCO displacement pump, triaxial servo control devices, high-intensity illumination devices, high-speed camera, and data acquisition systems. The fracturing process could be captured visually in real-time by using a high-resolution camera. This study also proposes an accurate and effective analysis method, Digital Image Correlation (DIC), for characterizing fracture and measuring the strain field. The results show that the pressure-time curve of hydraulic fracturing can be divided into three stages: pressure rise stage, the crack initiation and propagation stage, and the pressure plateau stage; the initiation pressures of water and CO2 fracturing in tight sandstone are 10.1 MPa and 5.2 MPa respectively; hydraulic fractures active the natural fractures, resulting in a complex fracture network structure; hydraulic fractures will turn and gradually become vertical to the minimum principal stress during the extension process. The results of this paper can provide guidance for the field application of hydraulic fracturing in tight sandstone resources.

1. INTRODUCTION
With the rapid development of the economy, the energy demand has increased rapidly, and unconventional oil and gas resources such as tight gas, coalbed methane, and shale gas have become an important guarantee for the national energy strategy1. Hydraulic fracturing technology is an important technology for the exploitation of unconventional oil and gas resources2, among which the geometry of hydraulic fractures is the key to evaluating hydraulic fracturing operations, still needs further research3-7.
Fully Coupled Thermo-Hydro-Mechanical Model for Wellbore Stability Analysis of a CBM Horizontal Well
Authors: Liu Jinhua , Ma Tianshou , Fu Jianhong , Fan Xiangyu , Zhang Qiangui 
Published: September 2022

ABSTRACT:
Due to the influence of drilling disturbance, wellbore collapse frequently occurs in the underbalanced drilling process of coalbed methane (CBM) horizontal wells. In fact, this kind of wellbore collapse problem is influenced and controlled by the thermo-hydro-mechanical (T-H-M) coupling effect and coal shrinkage induced by methane desorption that happened in the underbalanced condition. However, most previous studies ignored the influence of T-H-M coupling and coal shrinkage on wellbore stability. Therefore, a fully coupled T-H-M model with local thermal equilibrium condition was proposed for wellbore stability analysis of a CBM horizontal well, where the coal shrinkage induced by methane desorption was taken into account, and the finite element method was employed to solve the present model. The changes of the time-dependent field variables, such as pore pressure, temperature, and stress components were analyzed with considering different coupling conditions. The failure behaviors of a horizontal wellbore in different coupling conditions were also analyzed and compared with the results of the traditional analyzing method. The results indicated that both T-H-M coupling and coal shrinkage induced by gas desorption have a significant impact on these time-dependent field variables and failure behaviors of horizontal wellbore, in other words, the effect of gas desorption and T-H-M coupling cannot be ignored in CBM underbalanced drilling. Thus, the present model can help us understand the multiple fields coupling behaviors around the CBM horizontal wellbore in underbalanced drilling, and it can also provide the theoretical basis for predicting collapse pressure accurately, optimizing drilling mud density and maintaining wellbore stability.

1. INTRODUCTION
Coalbed methane (CBM) is considered to be a kind of significant unconventional natural gas resource, and a large amount of attention has been paid to it worldwide (Palmer 2010; Moore 2012). Nowadays, underground gas drainage and surface drilling are the two main technologies to develop CBM from coal seam (Shen et al. 2012; Thakur et al. 2014). Depends on the development of drilling technology, CBM surface drilling technology has developed very rapidly in recent years. And the horizontal drilling technology from the surface is now considered to be the most efficient technology for extracting CBM, which has the advantage of much higher safety, economy and much more reservoir stimulation measures (Tao et al. 2019).
Analysis of Low-Pressure Operation Stability of Underground Hydrogen Storage Salt Cavern
Authors: Dong Jingnan , Zhuang Xiaoqian , Gong Danni , Ban Fansheng , Zhang Yingbin 
Published: September 2022

ABSTRACT:
In order to meet today’s increasing fluctuations in energy demand, large-scale underground salt rock gas storage is widely used in the storage of fuels, including natural gas, oil and hydrogen. From the perspective of macroscopic structure and stratigraphic structure, the Jintan salt deposit in China has good sealing properties, and is an ideal solution mining area for the construction of salt rock gas storage. Salt rock has extremely low permeability and self-repairing properties, which greatly increase the sealing performance of the gas storage. Underground salt cavern hydrogen storage has been proved feasible in some area worldwide. The molecular weight of hydrogen is extremely low, so it has high requirements on the sealing performance of hydrogen storage, especially in terms of long-time storage. In this paper, two geo-mechanical models are established as one single-cavern configuration and 4-cavern configuration to analyze the stability of the hydrogen storage in terms of cavity volume shrinkage, stress distribution of rock mass around caverns, and surface subsidence. Through numerical simulation using FLAC3D, the evolution law under long-time low-pressure conditions is investigated. The tightness and stability of the trap conditions of the salt interval are studied, and the reasonable low operating pressure range of the salt rock hydrogen storage is proposed. The study found that under the condition of ensuring the stability of the salt cavity, the gas storage should keep the operating pressure from 8 MPa to 9 MPa at the depth around 800 to 1000 m. The long-term constant pressure operation at lower and higher limit did not see obvious salt cavity tensile stress concentration areas within 30 years, and the salt cavity expansion area was concentrated in the local area. For most salt cavern hydrogen storages of 800 to 1000 meters depth, 8.27 MPa is an acceptable operational pressure. Considering the surface subsidence, it is necessary to pay more attention when multi cavern configuration is applied. An increase in the amount of underground space will lead to large surface subsidence. This study provides guidance for the hydrogen underground salt cavern construction in bedded salt.
Some Attempts on Characterization and Evaluation of Properties of Fracture/Shear Zones
Authors: Aydan Ö. , Kumsar H. , Iwata N. , Ulusay R. 
Published: September 2022

ABSTRACT:
This study is concerned with main causes of fault/shear formation and the utilization of various experimental techniques for their evaluating mechanical properties. In the first part, the results of several experimental studies on the formation of fault/shear zones are presented. Then, some proposals have been done how to characterize the geometry, fracturing, morphology, and internal structure of fault/shear zones and some examples are given using some rock classifications. Then, some direct shear tests were performed on the actual fault gouges and their actual characteristics have been evaluated. The characterization and evaluation of the properties of fault/shear zones using RMQR rock classification method are explored. In addition, the utilization of conventional and modified Needle Penetration Index (NPI) for assessing the characteristics of fault/shear core is investigated. Finally, the presented procedures and techniques are applied to actual fault/shear zones and they are validated.

1. INTRODUCTION
Fault/shear zones commonly exist in Earth’s crust and they may be encountered almost in all engineering projects. They may cause very severe engineering problems such as heavy water in-flow, squeezing, instability. They may be pathways for leakage of radio-active wastes to the environment as shown in Figure 1.
Many fundamental studies on fracture/shear zones have been done by various researchers (e.g., Cloos, 1930, 1968; Tchalenko, 1970; Roth et al. 1981; Tsuneishi, 1978). Hubbert (1951) and Hafner (1951) were first to give the first theoretical treatise of fracture/shear formations in non-cohesive materials. In engineering applications, some studies were concerned how to locate important structures outside the potential rupture zones (e.g. Cole and Lade, 1984a,b; Bray et al. 1992).
Many experimental studies on hydro-mechanical properties of fractures zones and faults in several institutes (e.g. Byerlee 1990, Kutter and Rautenberg, 1979; Lama 1978; Moore et al. 1983; Rutter et al. 1986; Archambault et al. 1990). They tested several types of gouges found in fractured zones and faults under different environmental conditions such a normal pressure, temperature, water content, loading rate.
Evaluation of the Timing of Different Stages of Collaborative Construction of Underground Gas Storage and Natural Gas Flooding
Authors: Fuguo Yin , Shiqing Cheng , Dengke Shi , Penglin Liu , Rui Zhou 
Published: September 2022

ABSTRACT:
An underground gas storage (UGS) rebuilt from oil reservoir is constructed in collaboration with natural gas flooding, which is a new type of UGS developed in recent years and is called collaborative type UGS. The collaborative type UGS aims to improve the recovery of the original reservoir as much as possible while building the UGS. At present, the construction process of cooperative type UGS has been divided into three stages: oil displacement, collaboration and UGS. However, the transition time node of different stages is still fuzzy, which is very important for the construction of collaborative type UGS. Therefore, in order to clarify the starting time nodes of each state of collaborative type UGS construction, a method is proposed to dividing stages of collaborative type UGS construction based on the full research of cases which the UGS were converted form the oil reservoirs. On the basis of this classification method, a new analytical model of injected gas volume in different construction stages is build based on a new type of gas flooding characteristic curve and material balance method. Finally, we confirmed that our model is well suited for collaborative type UGS. The predicted production of our model is very close compared to the actual production data, and thus the methodology should be attractive to the industry. This study extends existing analytical model methodology for collaborative type UGS and is relatively easy for reservoir engineers to understand.

1. INTRODUCTION
Underground gas storage (UGS) is a kind of artificial gas field or gas reservoir formed by injecting commercial natural gas transported by long distance pipeline into underground space. It has important functions such as regulating gas supply in different seasons, strategic energy reserve and obtaining economic benefits. According to statistics from the latest World Natural Gas Congress (GIOUSE, 2018), a total of 689 underground gas storage facilities have been built around the world, with the total working gas volume accounting for 11.8% of the total annual consumption of natural gas. There are 4 types of reservoirs commonly used for underground gas storage 1) oil reservoir 2) gas reservoir 3) aquifer and 4) salt cavern, each of the storage reservoirs has very specific producing parameters (Ding, 2011; Jiang, 2021;). Figure 1 shows the proportion of working gas in different types of underground gas storage.
Utilization of Impression Creep Tests as Index Testing Technique in Rock Mechanics and Rock Engineering
Authors: Aydan Ö. , Ito T. , Özcan N. T. , Rassouli F. , Özkan Í. 
Published: September 2022

ABSTRACT:
Impression creep devices capable of applying a tip pressure up to 134 MPa for an indenter of 3 mm in diameter as an index creep testing technique was developed by the authors. In this study, a new monitoring system utilized in the impression creep devices is described and its utilization for evaluating creep responses of rock salt samples from Çankin and Tuzköy in Nevçehir Provinces of Turkey and Oya tuff from Tochigi Prefecture in Japan are presented and discussed. The experimental results obtained from impression creep tests are compared with those from conventional creep tests and the suitability of impression creep tests as an index test is explored. The most critical issue in creep tests is the determination of stress level. This issue is investigated theoretically and experimentally. It is suggested the short-term impression test can be utilized for determination of the stress level in impression creep tests. The experimental results clearly demonstrated that both conventional and index tests could be quite comparable and similar type responses are observed and it is concluded that there is a high possibility for the utilization of the impression creep as an index creep test.

INTRODUCTION
Creep experiments are of paramount importance for assessing the long-term stability of rock engineering structures. ISRM (2007) recognized this issue and a Suggested Method for Creep Test was developed (Aydan et al 2014a). The creep tests have been used in the field of rock mechanics and rock engineering for decades (e.g., Jaeger and Cook 1979; Aydan et al. 2011, 2014a, 2016; Aydan 2016). Apparatuses for creep tests can be of cantilever-type or load/displacement-controlled type. The major issue in creep tests is keeping sustained loading on samples and monitoring of displacement and other parameters throughout experiments without any interruptions.
The authors involved with the methods for creep tests under indirect tensile stress regime of Brazilian test, uniaxial and triaxial compression tests and direct shear tests, to determine the creep characteristics of rocks. Ito et al. (2021) have recently developed a new monitoring system for continuous measurement of displacement, acoustic emissions in addition to environmental parameters and utilized in uniaxial compression, Brazilian tensile and bending tests. It is shown that the new monitoring system can measure long-term responses without requiring any conventional power system.
Impact of Stress Concentration of Pores on Shale Gas Production
Authors: Peng Yan , Shen Liji , Lv Peihong , Wei Shengjie , Wang Xiaohan 
Published: September 2022

ABSTRACT:
Shale gas reservoirs have extreme low permeability which changes with stress variation. Numerical simulation results show that the stress-dependent permeability sharply affects shale gas production. Common permeability model indicates that the stress-dependent behavior of permeability results from pore volume change which is calculated by the equation for rock solid phase. Generally, pores are void inside rocks and the stress concentration should be generated around pores but the common model fails to consider this impact. In this paper, the permeability model with impact of stress concentration is used in the flow-geomechanics coupled numerical simulation for shale gas production. This numerical simulation model is validated by field data. After that, several factors affecting shale gas production are analyzed. The results show that (a) the error of shale gas production rate between prediction result and field data within 10%; (2) the difference between production rates predicted through the new model can be over 67% because the stress alternation behavior in real reservoir is different to the one in laboratory; (3) the impact of stress orientation on shale gas production is few and the difference of accumulative production is only 4.3% when the stress orientation changes from 0 ° to 40°. Those results indicate that (1) the model with impact of stress concentration is valid for shale gas production; (2) if the alternations of stress components are different, stress concentration significantly affects shale gas production.

1. INTRODUCTION
Unconventional oil and gas resources have become essential parts of the global oil and gas supply. Global unconventional oil and gas production is expected to account for more than 20% of the total output in 2030 (Zou et al., 2013). The successful development of shale gas reservoir benefits from horizontal well and large-scale hydraulic fracturing (HF)technology, making shale gas exploitation become an essential direction of unconventional natural gas development(Ding et al., 2014; Du et al., 2017).
Numerical Simulation on Characteristics of Hydraulic Fracture Initiation Induced by Circle Pumping Method
Authors: Peng Yan , Wei Shengjie , Lv Peihong 
Published: September 2022

ABSTRACT:
Hydraulic fracturing is an important treatment for tight reservoirs, however, it may induce high initiation pressure of fracture or generate a hydraulic fracture with simple shape. In order to increase hydraulic fracture efficiency, recently, the fatigue hydraulic fracturing method is proposed by several scholars. Experimental data show that this method can generate complicated hydraulic fractures, reduce initiation pressure, reduce magnitude of seismicity and increase permeability. Using the circle pumping schedule is a method to generate the fatigue loading inside hydraulic fractures. In this paper, a flow-geomechanics coupled numerical simulation model is first built. This coupled model has two governing equations. The first governing equation is the transient flow model (TFM) which is used to describe the flow behavior of fluid inside hydraulic fractures. The second governing equation is the rock deformation equation which is used to calculate the stress solution of rocks. The maximum tensile criterion is used to judge whether the hydraulic fracture can be generated. Several factors affecting fluid flow and hydraulic fracture initiation are analyzed by this numerical simulation model. The results show that (1) The circle pumping schedule can initiate new fractures around the hydraulic fracture. This pumping schedule induces heterogeneous distribution of fracture pressure and further induces tensile stress in several locations. This tensile stress initiates new fracture. (2) input pressure amplitude, frequency, roughness and viscosity affect hydraulic fracture initiation.

1. INTRODUCTION
The success of unconventional reservoir development is the benefits of hydraulic fracturing and horizontal wells (Rong et al.,2004; Karacan et al., 2011; Dong et al., 2019; Nguyen et al., 2020; Wang et al., 2020; Zhang et al., 2020;). The production rate of the unconventional reservoirs increases with stimulated reservoir volume (SRV) induced by hydraulic fracturing. In order to reduce initiation pressure and magnitude of seismicity but increase the SRV, the circle pumping hydraulic fracturing method (CPHFM) has been proposed and investigated. The HFST results show that the production rate of shale oil reservoir is increased by 10% when the CPHFM is used (Ciezobka et al., 2018). The borehole pressure generated by the CPHFM is higher than the one by ordinary method so the extra hydraulic fractures is initiated around perforations(Ciezobka et al., 2018).