bluuebunny/crossref_metadata_2025 huggingface dataset:
Rockbursts Characterization in the Merensky Reef: A Case Study in Siphumelele Platinum Mine, South Africa
Authors: Masethe R. T. , Durapraj S.
Published: September 2023

Rockbursts have remained one of the most serious and least understood problems facing deep mining operations, claiming the lives of thousands of mine workers. Despite many technical advances, rockburst continues to pose a significant risk in deep platinum mines of South Africa as they damage excavations, mining equipment and infrastructures, delay production and cause injuries or even deaths of mining personnel. We analyzed the source mechanisms of large mining-related seismic events (ML1.0 − 2.5) that caused damage to stopes in Siphumelele Platinum Mine. This study attempts to mitigate the risk of rockburst by integrating rock mass complexities (high stress, complex structural geology, mining elements, etc.) with the source mechanisms of mining-induced earthquakes to understand better the main drivers of seismicity within the Merensky Reef. The energy ratio (Es/Ep) was used as a discriminator to define two classes of seismic events. Shear (Es/Ep >10, 22 events), located between 1226 and 1470 m depths and non-shear (Es/Ep <10, 51 events), concentrated from 907 to 1460 m below and above the Merensky Reef. About 76% of these seismic events were related to elements of the mining geometry (pillars, abutments, and back-areas); while 24% were located near known geological structures (faults, dykes).

INTRODUCTION

As the depth of underground mining increases, the stresses in the rock mass increase, and as a result, the level of induced seismicity usually increases. Mine seismicity is a risk to mine personnel and infrastructure. It has become a major operational issue and a problematic planning factor for most underground mines worldwide, particularly at depths greater than 1000 m. As a result, the characterization of rockbursts in the Merensky Reef is critical to understanding the true nature of seismicity and developing mitigation strategies. Given the mine's increased seismicity and risks to production, infrastructure, and mine personnel safety, it is critical to comprehend the rock masses’ behaviour.
Seepage and Stress Analysis of High-Pressure Bifurcated Pipes in a Pumped Storage Power Station
Authors: Fan Bowen , Wang Tao , Wu Hegao , Yang Kai , Wang Suifeng , Liu Songcheng
Published: September 2023

The filling and drainage process of high-pressure bifurcated reinforced concrete pipes in pumped storage power stations (PSPS) can significantly affect the propagation of cracks in the reinforced concrete lining, which in turn impacts the structural safety and long-term stress state of the reinforced concrete lining. Specifically, we study the reinforced concrete bifurcated pipes of a PSPS in China. We use the finite difference method to simulate the fluid-structure interaction and analyze the critical penetration pressure and propagation of cracks in the lining during the water filling and drainage process. Additionally, we calculate the seepage field of the lining and the long-term stress state after the formation of stable seepage, and analyze the structural stability of the lining under the condition of graded drainage. We investigate the influence of structural elements such as rebars and bolts on the propagation of lining cracks, and propose an optimization scheme for the restricted crack design.

INTRODUCTION

PSPS are essential to ensure the safe and stable operation of power systems (Huang et al., 2018). They are considered to be the most environmentally friendly, efficient, and economical means of developing large-scale energy storage facilities. Therefore, the construction of such power stations is highly valued by countries worldwide (Dennehy et al., 2015; Sun, 2018; Yang, 2014). Bifurcated pipes, as the connection area between the main pipe and the branch pipe, are a crucial component of the hydraulic building diversion system, and their design is evolving to accommodate longer lines, larger diameters, and deeper burial depths. Consequently, the surrounding rock and bifurcation areas must withstand high-pressure heads (Hu et al., 2011).

With the increasing development of water resources and hydropower engineering, a considerable number of high-pressure and large-diameter bifurcated pipes are now used in PSPS projects. For instance, the Yangjiang PSPS's high-pressure bifurcated pipe can withstand a static head of 799 m and a maximum dynamic head of 1108 m (Liu et al., 2021). Similarly, the Tianhuangping PSPS's high-pressure bifurcated pipe can withstand a static head of 680 m and a maximum dynamic head of 800 m (Zhang, 2001), while the Guangzhou PSPS's high-pressure bifurcated pipe can withstand a static head of over 600 m (Ye, 2001).
A New Post-Drilling Evaluation Method for Formation Pore Pressure
Authors: Yang H. W. , Li J. , Huang H. L. , Zhang G. , An J. T. , Li J. M. , Li W. T. , Zhang X. J.
Published: September 2023

Eaton and Bowers model are two commonly used methods for formation pore pressure evaluation methods. However, both of them belong to univariate model, which takes few factors into consideration, is subject to many conditions, and has large error. Therefore, combining the results of previous laboratory experiments and field logging data, the correlation between shale content, density, porosity, effective stress and p-wave velocity was analyzed. The function form of each factor term was optimized, and a new p-wave velocity model was established by using multivariate nonlinear regression. Based on the effective stress theorem, a new post-drilling evaluation method for formation pore pressure was proposed. The results show that the density, porosity and effective stress are highly correlated with the p-wave velocity, while the shale content is relatively low. The optimal function forms of their correlation with p-wave velocity are linear, "linear + exponential" combination form, power function form, and linear form, respectively. The accuracy of the developed model is more than 99%, which is much higher than the Eaton and Bowers model. The research results have important reference significance for improving the evaluation accuracy of formation pore pressure, and provide a basis for rational casing design, determination of mud density and adjustment of production technology.

INRTUDUCTION

Formation pore pressure refers to the fluid pressure in the pores of formation. The establishment of a reasonable pore pressure profile is the basis for the reasonable casing design, the mud density determination and the production technology adjustment (Fan, 2006). The logging information can reflect the compaction law of formation and the lithology and physical property of underground rock, and the data amount is very large, which is the most ideal data for evaluating pore pressure. Therefore, using logging data to evaluate pore pressure after drilling is the one of most effective methods (Wang and Guo, 2015). At present, almost all formation pore pressure evaluation methods are indirect estimation based on p-wave velocity, resistivity, density, porosity and other logging parameters as well as effective stress. The evaluation methods mainly fall into two categories: one is based on the normal compaction trend line (Foster, 1966; Ham, 1966; Eaton, 1972, 1975); the other is based on the effective stress theorem (Bellotti, 1978; Bowers, 1995, 2001; Bryant 1989; Alixant, 1991). The above models are univariate models with few factors, more constraints and large errors.
Pre-Drilling Prediction of 3D Geomechanical Parameters Based on Seismic Data: A Case Study of Tarim Oilfield
Authors: Zhou Bo , Zhang Xin , Zhao Li , Zhou Bao , Chen Long , Lu Yunhu
Published: September 2023

A pre-drill prediction method of 3D geomechanical parameters based on seismic data is proposed. Firstly, the wave impedance parameters are predicted in the target area by the logging-constrained method, which mainly uses post-stack seismic data and logged data from drilled wells. The density and velocity data are obtained by separating the wave impedance data. Then, the density and velocity data are used as input to calculate 3D geomechanical parameters in the region, including elasticity parameters, strength parameters, and stress parameters. In particular, experimental data are used to correct the accuracy of the model. The results accurately reflect the geological complexity and non-homogeneity of the region by evaluating the elastic properties, mechanical properties, and stress magnitude of each point. This method can greatly improve the longitudinal resolution of the inversion results by fully exploiting a priori information from the logs and involving them in the seismic inversion process. Pre-drill parameters prediction of a complex field in the Tyuritag of the Tarim Basin is carried out.

INTRODUCTION

A growing number of oil and gas field development projects are facing the challenge of safe, rapid, and efficient development, such as offshore projects like Hibernia and the Gulf of Mexico in Canada, and onshore projects in tectonically active areas like the Cusiana field in Colombia and the Tarim Basin in China. However, as drilling depths continue to deepen, the geological environment encountered in oil and gas development is becoming increasingly complex. The difficulty of engineering problems related to geomechanics is also increasing. On the one hand, there are more and more complex accidents in various wells, such as well wall instability, well leakage, and sand production. Underground accidents seriously increase the time and cost of construction operations. It is estimated that at least 10% of the average well budget is used for unplanned operations due to wellbore instability (Sheng, 2006; Wei, 2012). On the other hand, the inaccuracy of geomechanical modeling makes geomechanics-related engineering measures unable to achieve the expected goals. In shale oil and gas development, about 30-50% of fracturing clusters do not contribute to product improvement. The root cause is poorly designed hydraulic fracturing strategies due to the lack of accurate geomechanical data (Zhang, 2018; Parshall, 2015).
Field-Scale Modeling of Fracturing with Slickwater, N2, CO2 and Foams – A Fundamental Investigation
Authors: Gala Deepen , AlTammar Murtadha J. , Sharma Mukul M.
Published: September 2023

Hydraulic fracturing is typically done with water-based, incompressible fracturing fluids. However, other fluids such as pure gases or foams are also used as driven by logistics or well productivity optimization. There are differences in fracture growth behavior amongst various fracturing fluids due to variability in properties such as viscosity, density, compressibility, leakoff, etc. Several laboratory experiments have recently been performed which indicated differences in breakdown pressure, fracture growth rate, complexity of the created fractures and amount of fracturing fluid leaked off into the formation. However, the laboratory results cannot be directly applied to the field without proper upscaling. In this work, we perform a field scale modeling of different fracturing fluids to provide more insights on how to design a fracturing job using non-water based fluids. We systematically study the role of wellbore volume, viscosity, compressibility, reservoir permeability, poroelasticity and magnitude of minimum horizontal stress on the fracture propagation behavior. It was found that poroelasticity effects are quite important for low viscosity fluids in micro-Darcy reservoirs. Also, when wellbore storage effects are considered, breakdown time is higher and breakdown pressure is lower for higher compressibility fluids. In low permeability reservoirs, an increase in fluid viscosity reduces the fracture length and increases width. In higher permeability reservoirs, an increase in viscosity reduces leakoff and thus increases both length and width. Low stress environments behave differently than high stress environments due to differences in fluid compressibility and stress/tensile strength ratio. A multi-cluster study of a single stage in a horizontal well is also performed for slickwater, gases (CO2 and N2) and foams (with different quality). The injection period and shut-in are both modeled and compared among the different fluid injection cases.

INTRODUCTION

Hydraulic fracturing treatments of oil and gas formations are mostly performed using slickwater, gelled water and hybrid fluids (Dejam et al. 2018). Many field applications, however, require minimizing the amount of water used in fracturing treatments due to water scarcity, environmental issues, and/or local regulations. In addition, using less water in fracturing can improve well productivity by reducing gel damage, relative hydrocarbon permeability damage, clay swelling and fines migration, and proppant embedment (AlTammar 2014). Alternatives to water-based fluids such as nitrogen, CO2, and foams are promising candidates for use as fracturing fluids.
Induced Stress in Reservoirs Under Dual Boundary Conditions of Deformation and Seepage
Authors: Pei Xuehao , Liu Yuetian , Xue Liang
Published: September 2023

Stress sensitivity is a vital factor affecting the seepage mechanism in oil and gas reservoirs. The accurate simulation of reservoir development must comprehensively consider the mechanical properties of fluid and rock. However, the description of boundary conditions in fluid–solid coupling calculations of oil and gas reservoirs mainly adopts a constant overburden stress and uniaxial deformation assumption or involves artificial boundary conditions of stress and displacement; these methods produce results that do not accurately represent the actual situation of the reservoir. In this study, under the condition that the specified compressive stress is positive, the reservoir stress and strain are completely defined, the reservoir induced stress model is constructed, the deformation-seepage dual boundary is proposed, and the semi-analytical solution method of the model under dual boundary conditions is examined. The study shows that the mechanical law followed by the skeleton stress change in the process of oil and gas reservoir development is equivalent to the continuum stress change under the action of certain body and boundary forces. The seepage boundary acts as a boundary force in the deformation model. The induced stress model can be solved by convolution according to the superposition principle using the help of basic solution of the semi-infinite body under the action of concentrated force. The case study of radial flow in infinite formations shows that the radial and vertical strains are in the same order of magnitude near the wellbore, and there is a large error in the assumption of uniaxial deformation and constant overburden stress. The radial deformation of the reservoir has a triple structure, consisting of the compression, micro-tension, and undeformed zones. Vertically, all the reservoirs are compressive and deformed; however, the vertical skeleton stress has a triple structure consisting of falling, rising, and unchanged zones. The proposed solution method lays the foundation for studying the stress sensitivity of oil and gas reservoirs and the numerical simulation of fluid–solid coupling.
Numerical Simulation of Landslide Acoustic Emission Characteristics Using Waveguide Techniques
Authors: Chen Y. , Pan R. , Yuan H. Y. , Chen J. G. , Sun Z. H. , Zhang M. Z. , Huang L. D. , Deng L. Z.
Published: September 2023

Numerous landslide accidents lead to thousands of casualties each year and pose great threats to residents nearby in China. Landslide monitoring and early warning are of great significance. As a deep deformation monitoring method, acoustic emission (AE) monitoring technology is expected to realize the goals of early warning and cost saving. To uncover the mechanisms of AE waveguide, this paper chooses a representative element and establishes a series of models by the discrete element method (DEM) to simulate the reaction between the waveguide and landslide. The AE and mechanical parameters are recorded simultaneously. For the landslide geological characteristics, the mass mechanical properties and the surface structure parameters are considered. The roughness of the sliding surface is simulated by changing the angle and quantity of the convex. Moreover, the impacts of backfill particles are investigated through the particle stiffness, strength, dimension or distribution mode. To improve the performance of AE monitoring, the applicable monitoring parameters in different simulated conditions are determined. For the backfill particles, it can promote the ability of AE monitoring by reducing the strength or dimension, enhancing the stiffness, and utilizing better gradation.

INTRODUCTION

Landslide is a kind of slope rock mass deformation failure process and phenomenon under the action of gravity and external factors (such as rainfall, earthquake, human activities, etc.). As a geologic disaster, landslide is characterized by its high frequency, wide distribution and severe loss, seriously threatening the safety of human life and property and major facilities (Petley, 2012). China is one of the heaviest exposed countries to landslide in Asia and even in the world. Especially since the reform and opening up, land use is progressively expanding to areas at high risk of landslide disasters, leading to an annual increment in landslide disasters (Persichillo et al., 2017). To achieve landslide prevention and mitigation, in addition to landslide treatment, landslide monitoring and early warning are particularly important.
Towards Ultra-Deep Exploration in the Moon: Modeling and Implementation of a Mole-Type Burrowing System
Authors: Yuan Zihao , Zhao Haifeng
Published: September 2023

Effective scientific exploration of extraterrestrial locations requires reaching subsurface destinations and obtaining geology samples of high scientific value. One of the most widely used techniques for geological sampling is drilling, but there is still a need for investigation to achieve greater depth and efficiency. This paper proposes a mole-type autonomous burrowing robotic system for drilling, steering, and accessing scientific samples from the deep subsurface of the Moon. The paper describes the robotic locomotion and operational loads of the self-burrowing robot. The self-burrowing robot with dual-screw configuration is designed and a mathematical model is developed to simulate its excavating capacities. Finally, the paper discusses the robot's performance and compares it with conventional drilling methods using the specific energy method.

INTRODUCTION

The core of near-earth exploration missions, such as those to the Moon, Mars, or asteroids, is extraterrestrial subsurface drilling and sampling (Gorevan et al., 2003). The primary tools for gaining insights into the evolutionary history of the solar system are subsurface exploration equipment, such as coring machines or robots. To achieve scientific objectives, it is necessary to reach the subsurface destination and obtain geological samples of high scientific value (Glass et al., 2020). Typically, the lunar subsurface within about 10 meters in depth consists of igneous regolith and disturbed materials from fine granular particles to chunky rocks along the depth direction (Slyuta, 2014). Drilling is one of most widely used techniques in geological sampling for sand or soil. These have been implemented in extraterrestrial exploration, in missions such as Luna, Apollo and Chang’e (Prissel & Prissel, 2021).

Towards the deep exploration and samples collection in subsurface, there are proposed the conceptual designs or prototypes. This recent research focused on the new technical system to achieve deeper and more efficient soil movement (Lopez-Arreguin & Montenegro, 2020), which imitates locomotion mechanisms of animals and insects such as crawling, swimming, and burrowing in granular mediums. Among these developed bio-inspired robot, typical prototypes, the inchworm robots, such as IDDS (Gorevan et al., 2000) and IBR (Zhang et al., 2018), operate sequentially combining the actions of anchoring and drilling. The wood wasp robots (Cerkvenik et al., 2019) mimic a reciprocating motion of two halves saw-toothed bits to shear and stick into the soil.
Experimental Investigations on the Effect of High Temperature and Pressure on the Mechanical Properties and Drillability of Granite
Authors: Fu Xinkang , Huang Zhongwei , Wu Hongzhi , Shi Huaizhong , Zhang Jiawei , Ji Guodong
Published: September 2023

Hot Dry Rock (HDR) is an important clean energy resource. However, there are many problems in the exploration of HDR, which are closely related to the geological environment and properties of HDR. The representative lithology of HDR is granite. Granite has the characteristics of poor drillability, high hardness and strong abrasive property in underground high-temperature and high-pressure environment. Therefore, the effect of temperature and pressure on physical and mechanical properties and drillability of granite was explored with deep water pore pressure servo system and rock drillability tester. The result shows that Young's modulus and compressive strength increase with the increase of confining pressure. High temperature weakens the mechanical properties of granite under the same confining pressure. The specific manifestation is that density, mass, longitudinal wave velocity and drillability grade value decrease with the increase of temperature, while mass loss rate decreases by 2.2‰ and longitudinal wave velocity decreases by nearly 74%. The drillability grade value of granite increases with the increase of confining pressure, especially at room temperature. This study has certain guiding significance for revealing the mechanical properties of granite after heating under high pressure and efficient drilling in the exploration of HDR.

INTRODUCTION

At present, HDR is a new clean energy, which is a reliable energy resource (Goldstein et al., 2008). HDR is a dense high-temperature rock mass with a temperature between 150 °C and 650 °C, and buried at 3-10 km underground, with little or no liquid (Ma et al., 2022). The most typical reservoir rock of hot and dry rock is granite (H. Liu et al., 2020). However, there are many problems during drilling, such as high confining pressure, high rock hardness and poor drillability (Rossi et al., 2020). The physical and mechanical properties of granite have changed considerably under the influence of high temperature and high pressure (S. Liu & Xu, 2015). Therefore, it makes sense to study the effect of high temperature and pressure on the mechanical properties and drillability of granite.

Lau et al. (1995) heated the granite from 75 °C to 125 °C, and found that the Young's modulus decreased slightly, and the decrease amplitude increased under low confining pressure. In addition, temperature seems to have no effect on Poisson's ratio. Dwivedi et al. (2008) explored various thermodynamic properties of Indian granite at temperatures ranging from 30 to 160 °C, mainly including Poisson's ratio, uniaxial compressive strength, Young's modulus and creep behavior, and scanned micro-cracks generated in the rock due to high temperature by scanning electron microscope (SEM).
Development of a Low Cost Environmentally Friendly Proppant with High Buoyancy for Hydraulic Fracturing Operations
Authors: Haydar Raz Rzgar , Fakher Sherif
Published: September 2023

Proppants are one of the main components/ingredients used in hydraulic fracturing for reservoir stimulation in order for fractures to have conductivity and maintain it. In hydraulic fracturing, usually when dealing with high parting pressure or harsh environment, high strength durable proppants are used that are expensive and require more expensive fracture fluids. Thus, the idea of developing a new type of proppant that has high compressive strength, high durability, resistant to corrosion and erosion, and economical became the focus of this research. Fly ash, a by-product from any combustion process, and a very prominent by-product from cement production, was used to develop a new type of proppant that is durable, is environmentally friendly. Sodium metasilicate and water were used in the mix designs. The samples were subjected to high temperature, pressure, acidic, and alkaline environments to test their durability. The samples showed high durability and minimum erosion, with no corrosion in all of the environments that were subjected to. 20% binder mix design showed the best results having minimum to no deterioration of the samples.

INTRODUCTION

As the industry of petroleum engineering is developing and more technologies are being introduced to optimize the production, stimulating the reservoirs has been an area of development and research that is gaining more attention and attraction, especially with the rise of unconventional reservoirs. The global production ratio of conventional to unconventional reservoirs is 2:8, and in unconventional reservoirs, stimulation is a default practice (Lan et al., 2020). One way to stimulate the reservoir is by hydraulic fracturing, in which proppants are used where the rock is ductile, meaning there is high clay content, closing the fractures that are made. Proppants come in different shapes and sizes being angular, such as natural sand, spherical or rods (Ba Geri et al., 2019). The shape of the proppant is connected to the way it will be placed and arranged inside of the fractures, which the better placement the proppant has the better conductivity the fracture will have, thus better and higher production rate for a long period of time (Wang et al., 2022; Li, 2021).
A Microscale Thermo-Hydro-Mechanical (THM) Model for Thermal Recovery of Shale Gas
Authors: Gao Qi , Han Songcai , Shi Xian , Cheng Yuanfang , Yan Chuanliang , Han Zhongying
Published: September 2023

Studies have shown that up to 85% of total shale gas-in-place could be adsorbed gas. Thus, how much more adsorbed gas can be extracted will significantly impact the ultimate gas recovery. In recent years, the concept of using thermal stimulation to enhance shale gas recovery has been proposed as more gas desorbs under the higher temperature conditions. In this paper, a fully coupled THM model is developed to characterize gas transport and extraction in shale matrix from the microscopic perspective during thermal treatment. A set of partial differential equations are defined to model the processes involved: (1) geomechanical deformation of heterogenous shale matrix; (2) gas sorption and flow in heterogenous shale matrix; and (3) thermal transport in heterogenous shale matrix. All these processes are linked together through the porosity and apparent permeability models. This microscale THM model is verified against an analytical solution available in the literature. The verified model is then applied to investigate rock and fluid responses in shale matrix during thermal treatment and the impacts of operational and rock physical parameters on gas recovery. Simulation results indicate that a greater thermal treatment temperature enhances ultimate gas recovery; and that shale thermal properties and matrix permeability impact initial gas recovery but does not impact ultimate gas recovery.

INTRODUCTION

Gas shale is naturally tight and fine-grained sedimentary rock with methane trapped in its nanopores. Commercial extraction of gas in shale requires the application of horizontal drilling and hydraulic fracturing techniques (Kumar and Ghassemi, 2018; Gao et al., 2019). When hydraulically fractured, shale gas reservoirs can be divided into two sections. One section is the stimulated zone where massive hydraulic fractures are created with natural fractures being activated. The other section is unstimulated zone which mainly consists of unactivated natural fractures and matrixes. Once the production initiates, gas in hydraulic fractures will first flow out into the wellbore. Then, gas in natural fractures will migrate into hydraulic fractures. Finally, gas in matrix will transfer into natural fractures to sustain the production (Zhang et al., 2017). Although fracturing technique has been widely applied, the overall shale gas recovery rate still remains at a low level around 20% (Neil et al., 2020). The main reason is that up to 85% of shale gas-in-place could be adsorbed gas (Darishchev et al., 2013; Zhou et al., 2022) and most of the adsorbed gas is still unattainable after fracturing. Thus, stimulation techniques that can alter gas desorption behavior have the great potential to enhance shale gas recovery.
Geomechanics Analysis of the Phosphate Ore Mining Using the Hoek-Brown Model
Authors: Wang Suifeng , Wang Tao , Fan Bowen , Hu Suoao
Published: September 2023

Phosphate rock is an essential non-renewable resource for both food production and phosphorus chemical production. Located in Yichang City, China, the Houping Phosphate Mine (HPM) poses significant challenges due to its complex topography and geological structures. In this study, we conducted a geomechanical analysis of the mining layer at HPM utilizing the Hoek-Brown model. First, we calibrate the Hoek-Brown parameters through uniaxial compression tests in FLAC3D. Then, we calculate the stress distribution of the rock mass around the stope, the subsidence and displacement law of the roof and floor, and the plastic zone distribution. We find that the shallow-hole room-pillar method with anchor roof protection has poor pillar stability, while the filling method is more stable, lastly. Our results offer valuable insights into efficient phosphate ore mining practices and provide technical support through numerical calculations.

INTRODUCTION

Phosphate rock is not only an important chemical mineral material but also a non-renewable and irreplaceable resource. With much mining in recent years, the shallow phosphate resources have been gradually exhausted, and the mining of underground phosphate layers with larger buried depths has become the focus of research, one of the biggest problems is the mining research of gently inclined medium-thick ore bodies underground. Underground mining will form goaf, goaf destroys the initial stress balance of the mine, redistributes its internal stress, affects the stability of slope rock mass, and cause a series of engineering geological disasters, such as surface subsidence, caving, landslide, etc. In 1980, unreasonable mining of the Yanchihe phosphate Mine in Yuan’an County, Hubei Province led to the collapse of the mountain, which destroyed and buried the entire mining area, resulting in 284 deaths and heavy losses (Li et al., 2016). In order to prevent the occurrence of similar accidents, we should do the safety analysis of mining in advance to ensure the safety of people's lives and property.
Delaying of Bottom-Water-Coning Oriented Hydraulic Fracturing Design and Optimization: Numerical Simulation and Field Case Study
Authors: Jv Liu , Hui Liu , Hongtao Liu , Hongqiang Zhang , Wenjing Lv , Dengfeng Ren
Published: September 2023

Is usually used hydraulic fracturing to enhance the productivity of tight gas sandstone formations. If basal water layers were connected to the upper gas formation via hydraulic fractures, the gas productivity of the stimulated wells would be reduced drastically. It is crucial to postpone the bottom-water-coning effect by meticulous hydraulic fracturing design and operation parameters optimization. Temporary plugging could be a potential solution for controlling hydraulic fracture extension in the vertical direction. This paper proposed a basal water-avoiding hydraulic fracturing design and optimization methodology and procedures to solve this problem. The geological and geo-mechanical models were built based on the characteristics of the gas layer, natural fracture, and basal water layer analysis. Hydraulic fracture propagation simulation conducted pump rate, Hydraulic fracture propagation simulation considered pump rate, frac-fluid volume, frac-fluid viscosity, temporary plugging material volume, proppant concentration, and proppant volume. Hydraulic fracture vertical height and distance to the basal water layer were used as the primary indicators to optimize the frac-fluid volume, pump rate, and temporary plugging material volume. Then simulated fracture area and fracture propped area were used as significant parameters to identify the optimal frac-fluid viscosity, proppant concentration, and proppant volume. KS field is an ultra-deep tight gas sandstone formation with basal aquafers. The fracture propagation model of the KS-X well was established to delay bottom-water-coning-oriented hydraulic fracturing design and optimization. Results showed that the optimal frac-fluid volume, pump displacement, and temporary plugging material quality are 950 m3, 4.5 m3/min, and 300 kg, respectively. The optimal proppant volumes of 70/140 mesh, 40/70 mesh, and 30/50 mesh ceramic proppant are 6 m3, 38 m3, and 9 m3, respectively. After hydraulic fracturing, the gas production rate of the KS-X well is as high as 290,000 m3/day without any water production for one month, indicating the effectiveness of the proposed basal water-avoiding hydraulic fracturing design and optimization methodology. The proposed design and optimization procedures can be further used in other basal aquifer gas fields.
Deep Coal Seam In-Situ Stress Evaluation Through the Integration of Sonic Logging and Micro-Indentation Methods
Authors: Yang Qi , Li Jianchuan , Li Liang , Zhou Libo , Mei Wenbo , Wu Jian , Jiang Yao , Lv Wenjing , Li Ben , Li Hui
Published: September 2023

The porosity and permeability of deep coal seams are usually as low as 5% and 0.1mD, respectively, thus requiring hydraulic fracturing to obtain an economic coalbed methane production rate. In-situ stress evaluation is fundamental to the hydraulic fracturing design. However, the conventional in-situ stress calculation methods could not be used directly due to the specific structure and rock mechanic features of deep coal seams. The in-situ stress of deep coal seam should be interpreted with full consideration of deep coal geology, logging, coal petrology, and elastic mechanics. This paper proposed a modified in-situ stress interpretation method that integrated sonic logging and micro-indentation methods. Sonic logging provides the compressive and shear velocity of the coal seam, and micro-indentation provides the compressibility coefficient of the coal cleats, coal bedding, and principal minerals that are used to identify the effective stress coefficient. Firstly, the dynamic Young's modulus and dynamic Poisson's ratio are calculated by acoustic logging and density logging data, and the correlations of dynamic - static Young's modulus and dynamic - static Poisson's ratio are obtained in combination with indoor core mechanic experiments. Then, the minimum horizontal principal stress estimated from 9 wells of hydraulic fracturing operation data (LX field China) is used to figure out the maximum and minimum horizontal structural coefficients. The micro-indentation of the deep coal seam is used to calculate the effective stress coefficient modifier. Results showed that the Poisson's ratio of the up and bottom layers is slightly smaller than that of the coal seam, and Young's modulus of the up and bottom layers is 6.15 times larger than that of the coal seam. Indicating that there are significant differences in the mechanical properties of the coal seam and the up and bottom layers. In terms of stress prediction results, the LX coal seam has a large interlayer stress difference with the up and bottom layers. The vertical stress is the maximum in the three-dimensional stress, which belongs to the normal fault type in-situ stress type. The proposed method can be used to evaluate the in-situ stress and mechanical properties of the coal seam and can be further used for other coal seams’ in-situ stress and mechanical property evaluation.
Experimental Investigation on the Threshold Transportable Concentration of Temporary Plugging Materials of Different Sizes of Slide Sleeves
Authors: Long Wang , Xiaotong Xie , Xiong Zhang , Bing Zhao , Tunhao Chen , Chunyue Li , Wenjing Lv , Yu Xia , Hui Li , Ben Li
Published: September 2023

The uncased horizontal wellbore is widely used in high-strength formation, especially in low porosity and low permeability carbonate reservoirs to enlarge the drainage area around the whole horizontal section. Multi-staged fracturing and temporary plugging technology are usually used to create complex fracture networks for enhancing well productivity. However, due to the complex geological environments in hydraulic fracturing operations, the sliding sleeve cannot be always fully opened. It is crucial to figure out the threshold concentration of temporary plugging materials at which the temporary plugging materials can be transported through different sizes of slide sleeves. This paper provides an innovative experiment apparatus and experimental procedures to evaluate the transportability of various temporary plugging mixtures concentrations. The proposed sliding sleeve transportability device consists of a 3D migration simulation system, a sliding sleeve simulation device, and a video recording device. The sizes of the sliding sleeve determined by the similarity criterion (the same Reynolds number) are 60mm × 14mm, 45mm × 14mm, and 30mm × 14mm, which can be used to simulate the different degrees of opening the sliding sleeve. Similar criteria that convert filed operation parameters such as pump rate and flow regime to indoor experimental conditions were also proposed. SH-1 well, an uncased horizontal well in the S carbonate reservoir, in China, was used as an example to explore the upper limits concentration of temporary plugging mixtures. The filed temporary plugging displacement is 3m3/min and the carrying fluid viscosity is 12mPa.s. Serial and rigorous experiments were designed to explore the transportability threshold of different sizes of sliding sleeve sizes under different hydraulic fracturing conditions. Results show that the threshold transportability concentration of the temporary mixtures for 60mm×14mm, 45mm×14mm, and 30mm×14mm slide sleeve sizes are 3.2% 4-6mm fiber +2.4% 1-2mm particle, 2.4% 4-6mm fiber +2.0% 1-2mm particle, and 2.0% 4-6mm fiber +1.6% 1-2mm particle, respectively. The proposed experimental apparatus and procedures can be further used to explore the threshold concentrations of temporary plugging materials for other uncased horizontal wells and can provide a theoretical basis for the design of temporary plugging displacement and carrying fluid viscosity.
Experimental Investigation of Methods for Measuring the Permeability of Dry and Water-Saturated Ultra-Deep Tight Sandstones
Authors: Zebo Yuan , Shengxian Pu , Jueyong Feng , Xiwu Yang , Jiangyu Liu , Yesong Li , Jiang Jing , Qiang Wang , Ben Li , Hui Li
Published: September 2023

Ultra-deep tight sandstone reservoirs have extremely low permeability and porosity due to extremely deep burial depth, and extremely high in-situ stress. Therefore, hydraulic fracturing is widely used to create diversion fractures to improve oil well productivity. Incompatible fracturing fluids can severely damage the permeability and fracture surface of the tight sandstone matrix. Rigorous evaluation of formation sensitivity and fracturing fluid compatibility is critical before hydraulic fracturing operations. There are three types of permeability experimental evaluation methods: steady-state permeability method, pressure pulse decay method, and pressure transmission method. In this study, a series of comparative experiments were designed to accurately evaluate the sensitivity and compatibility of injected fluids in ultra-deep tight sandstones. CT scanning and 3D reconstruction techniques were used to obtain digital data on pore space and pore-throat connections of downhole cores. Through statistical regression analysis, a modified correlation between the pressure pulse decay method and the pressure transmission method is proposed. The proposed experimental and regression methods can also be used to validate permeability measurements in other types of reservoirs.

INTRODUCTION

With the development of oil exploration, people pay more and more attention on deep and ultra-deep strata. Since the 21st century, China has made a series of breakthroughs in deep oil and gas exploration, especially in the central and western basins (Li et al., 2023). Unlike conventional reservoirs, ultra-deep tight sandstone reservoirs are characterized by large buried depth, complex structure, tight matrix, and strong heterogeneity. Rocks with extremely low permeability are more affected by stress than those with high permeability (Jones., 1997). Due to the extremely low permeability and porosity (Li et al., 2019; Li et al., 2020), hydraulic fracturing is widely used to create diversion fractures to increase well productivity of tight reservoirs (Li et al., 2018). The fracturing fluid used in hydraulic fracturing can significantly alter some formation properties. Due to the high temperature and pressure, tight reservoirs are susceptible to stress, flow rate, and output, especially in the case of deep and ultra-deep tight sandstonereservoirs (Gilicz., 1991). Therefore, it is critical to evaluate formation sensitivity and fracturing fluid compatibility before hydraulic fracturing (Zhang et al., 2019).
Measuring Poromechanical Properties of Berea Sandstone Relevant to Underground Hydrogen Storage
Authors: K C B. , Frash L. P. , Meng M. , Iyare U. , Madenova Y. , Neil C. , Carey J. W. , Gross M.
Published: September 2023

Seasonal fluctuation in electricity generation is a major set-back for the integration of renewable energy sources such as solar and wind into a national grid. Temporary storage of ‘green’ hydrogen in underground porous reservoirs could be a cost-effective solution to balance renewable energy fluctuations to stabilize the energy grid. However, due to the novelty of Underground Hydrogen Storage (UHS) in deep porous reservoirs, our knowledge about the interaction between hydrogen and host reservoir rock is limited. It is crucial to develop the fundamental understanding of these interactions and their impact on the reservoir rock for successful deployment of UHS. In this study, we measure the poromechanical properties, such as bulk compressibility, in-situ porosity, Biot's effective stress coefficient, and P-wave velocity of Berea sandstone specimen at in-situ reservoir stress condition i.e., depth of ∼ 1.25 km. Results showed decrease in bulk compressibility, porosity, and Biot's coefficient due to increase in effective stress. Considered together, results from this study infer change in stress regime in UHS reservoir due to multiple injection/extraction cycles could alter the reservoir capacity and transport properties. In addition, P-wave velocity increased with the effective stress. However, it remained insensitive to different gas (i.e., air and Argon) saturated pores at same effective stress.

INTRODUCTION

Renewable energy is a focal point in our effort to achieve global net zero emission target by 2050. However, seasonal fluctuation in electricity generation is a major set-back for the integration of renewable energy sources such as solar and wind into national grid. As such, surplus energy produced from renewable sources during the period of low demand can be used to produce ‘green’ hydrogen, which can be stored for future consumption to stabilize the grid when the demand is higher. Hydrogen is an ideal energy storage option due to its low carbon footprint and versatility to be used in different sectors such as transportation, industry, residential, and others (e.g., IEA, 2019). Hydrogen has higher specific energy capacity compared to other gases such as methane but, due to its low density very large volume is required to store energy at the scale of GWhr to TWhr needed to balance seasonal fluctuations. Such large-scale volume is available in underground geological formation such as salt caverns, saline aquifer, and depleted oil and gas reservoir (e.g., Heinemann et al., 2021; Zivar et al., 2021; Chen et al., 2022).
Designing a Reliable Weak Bonded Interface for Fracture Caging Laboratory Validation
Authors: Meng M. , Frash L. P. , K C B. , Madenova Y. , Carey J. W. , Li W.
Published: September 2023

Fracture caging is a proposed approach to geothermal energy extraction that involves using one injection well and multiple boundary wells for continuous fluid injection at high rates and pressures while controlling induced seismicity. To validate this concept, a solid block with a weak layer and injection/production wells will be used to simulate injection induced shear events. Creating a reliable and repeatable weak layer with the necessary bonding strength for shearing is a key challenge. Plaster was selected as the best option due to its light weight, ease of drilling holes, and flexibility in shape. Through experimentation, the optimal interface was found to be between an aluminum surface roughened by 120 grit sandpaper and cured plaster, which provided consistent strength with a friction angle of 42.2 degrees and cohesion of 0.18 MPa. This work helps validate the concept of fracture caging and also has broader implications for civil engineering by providing a reliable method for achieving a weak bonding layer with consistent strength.

INTRODUCTION

The global shift towards renewable energy sources has brought about a renewed focus on the exploration and development of geothermal energy as a sustainable alternative to traditional fossil fuels. Geothermal energy involves harnessing the natural heat stored beneath the Earth's surface to generate electricity or heat, making it a clean and reliable source of energy with a much lower carbon footprint than traditional energy sources.

Despite its great benefits, geothermal energy extraction poses several challenges. One of the primary concerns is the potential for induced seismicity, which can occur when fluids are injected into the subsurface fractured systems and cause shear slip of natural faults. Another challenge facing geothermal energy is its economic viability. The power it generates currently cannot cover the initial capital investment or the return-on-investment period is too long.

To explore geothermal systems in a safe and economically viable manner, a new design approach is needed. One proposed method is fracture caging, which involves using multiple wells for continuous fluid injection and production at high rates and pressure, without causing injection induced seismicity [1-5]. The high flow rate and high pressure hydraulically propping the fracture apertures and promotes the economical profits. This approach is currently being developed and validated from a scientific perspective. One critical step is to experimentally validate the benefits of using multiple boundary wells for a single injection well.