bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on Matrix Acidizing of Low-Permeability Hybrid Sediment Rocks Using Microemulsion Retarded Acid
Authors: Liu Shiduo , Liu Yong , Xiong Tingsong , Zhang Yang , Shang Litao , Xie Guiqi , Zhang Haining , Sun Xun , Sui Guojie , Zhao Endong , Wang Qing , Zhou Fujian
Published: September 2023

The high reaction rate of hydrochloric acid, the low dissolution rate of organic acids, and the difficulty of injection of highly viscous gelled acids are all unsuitable for the acidification of low-permeability hybrid sediment reservoirs. The lithology of hybrid sediment rock reservoir is complex, and the dissolution rate of single acid is low. In this paper, an oil-in-water (O/W) microemulsion retarded acid is developed, and acidizing performance is studied. The microemulsion can be diluted in the acid system, and the structure of the microemulsion is not destroyed. The average particle size is less than 10 nm. The microemulsion acid can effectively reduce the oil-water interfacial tension, reducing the resistance to enter low-permeability cores. By adding microemulsion to the multi-hydrogen acid system, the dissolution rate is greater than 45 %. The retarded mechanism is that the polyhydric acid gradually releases hydrogen ions, then the microemulsion adsorbs on the rock surface. At the same time, the corrosion rate of microemulsion retarded acid and N80 steel is only 1.07 g/m2 h. Microemulsion retarders can adjust the surfactant composition according to the rock mineral composition to achieve the effect of high acid dissolution and substantial retardation and provide guidance for the stimulation of hybrid sediments rock reservoirs in the field.

INTRODUCTION

The global exploration and development of oil and gas resources have been continuously increasing, leading to significant progress in exploiting clastic and carbonate reservoirs. However, more research must be conducted on another widely distributed sedimentary rock type, hybrid sediment rocks (Feng et al., 2011). Hybrid sediment rock reservoirs share similarities and differences with conventional sandstone or carbonate reservoirs. The most significant difference lies in the mineral composition, lithology complexity, complex pore structure, low permeability, and strong heterogeneity of hybrid sediment rocks (Chen et al., 2015). In western China's northwestern region of the Qaidam Basin, a mixed sedimentary environment consisting of carbonate, mudstone, and fine sandstone has formed (Li et al., 2022). This region has significant oil and gas reserves, but the reservoir's low permeability and complex lithology require stimulation to reduce oil and gas flow resistance and improve production.
Study on the Fracturing Pattern and Damage Characteristics of Deep Shale by Liquid Nitrogen Fracturing
Authors: Qu Hai , Li Zhelun , Liu Ying , Zeng Zhijun , Liu Xu
Published: September 2023

Liquid nitrogen (LN) can undermine the structure of the rock and its mechanical properties. It is also effective in engineering applications of deep resource exploitation. There are few lab experiments that use LN as a fracturing fluid directly. In this work, we have studied LN fracturing performances in deep shales under actual triaxial-confining stresses by a high-pressure LN fracturing device. Microcracks and matrix structures have been analyzed by scanning electron microscopy. The breakdown pressure and fracture morphologies have been compared with hydraulic fracturing. The result demonstrates that LN fracturing can obviously lower fracture initiation pressure and increase fracture complexity. The increase of differential stress ratio does not reduce fracture complexity. Microcracks and pore clusters can be induced on LN fracture surfaces, improving matrix permeability. Curved cracks, branched cracks, and horizontal bedding planes can be thermally induced around the borehole. Low fluid viscosity of LN can facilitate the fracture propagation and network generation during the fracturing process. The longer the bare-hole, the more thermally induced microcracks around the borehole, and the more complex macro fractures. Moreover, LN pretreatment can lower fracture initiation pressure actually. The productive findings obtained in this work are expected to provide an alternative for the sustainable development of deep shales resources.

INTRODUCTION

Deep shale gas resources below 3400 m are widely distributed and have the potential for sustainable natural gas development(Altammar et al., 2019).The deep shale formations have characteristics of low porosity and permeability and characterized by significant in-situ stresses, horizontal stress differences, and high temperature(Carpenter, 2017). Hydraulic fracturing is a traditional measure to stimulate these formations. However, the burden of hydraulic fracturing operations has been a topic of great importance to the energy industry and public alike(Han et al., 2018). Traditional hydraulic fracturing is challenging to generate complex fractures, and the production is usually less than expected (Cong et al., 2021).

Cryogenic liquid nitrogen (LN, −196 °C at atmospheric pressure) fracturing is one possible method of solving these water-related issues(Yang et al., 2019). When LN is injected into the reservoir formation, the sudden heat transfer could cause shrinkage of the rock and exert a sharp thermal gradient that can induce numerous fractures at the surface of the formation rocks (Elwegaa et al., 2019). The significant thermal stress between LN and rock will lower fracture initiation pressure and create complex fractures(Wan et al., 2018). Therefore, LN fracturing will be an effective engineering method to develop high-temperature or deep formation resources(Wan et al., 2019).
Experimental Investigation on Corrosion and Emulsification During CO2 Injection in Heavy Oil Reservoirs
Authors: Luo Chen , Liu Huiqing , Wang Zuochen , Lyu Xiaocong , Huang Yaowei , Peng Chao
Published: September 2023

Carbon dioxide (CO2) injection possesses an immense potential for production improvement in heavy oil reservoirs. The primary interest of this work is to investigate the corrosion effect of carbonated water formed by CO2 and formation water on reservoir rock, and the emulsification of crude oil. This study used the scanning electron microscope and interfacial tension (IFT) setup to research the core micro-structure and oil-water IFT. The results showed that the corrosion ability of carbonated water gradually increased as pressure increased within a certain range of pressure. When the pressure increased from 8MPa to 16MPa, the average corrosion rate increased from 0.45% to 0.66%. Moreover, the injection of CO2 caused the appearance of corrosion pits and cracks, surface particles peeled off and dissolved, and cracks extending as pressure increased. The dynamic IFT between the decyl trimethyl ammonium bromide solution and crude oil changed less and stabilized in less quickly without CO2 injection. The dynamic IFT decreased faster with pressure increase after CO2 injection, which was favorable for crude oil emulsification and emulsion stabilization. There is a positive correlation between Equilibrium IFT and temperature at the condition of low temperature.

INTRODUCTION

The global heavy oil resources are abundant. The proven recoverable heavy oil resources are 126.74 billion tons, 71% of which are distributed in the Americas and the Middle East (Liu et al., 2019; Shah et al., 2010). The key to exploiting heavy oil is to reduce viscosity and improve fluidity(Al-Samhan et al., 2022; Wang et al., 2023). Thermal recovery is the most commonly used method for heavy oil extraction at home and abroad (Bueno & Mejía, 2022). However, in heavy oil thermal recovery, the large reservoir depth, strong formation heterogeneity, and high crude viscosity, will lead to low thermal energy utilization, high development cost, and low extraction efficiency (Khelkhal et al., 2022). CO2 is a commonly used replacement medium, with various special mechanisms such as replenishing formation energy, reducing crude oil viscosity, extracting light components and blending (Kumar et al., 2022). Meanwhile, CO2 as a greenhouse gas seriously impacts on global climate, and CO2 utilization and storage can effectively reduce carbon emissions, so CO2 is of great significance for thick oil development (Lan et al., 2019).
Numerical Simulation of Sandstone Degradation Under Freeze-Thaw Cycles with Grain-Based Model
Authors: Huang C. , Zhu C. , Ma Y.
Published: September 2023

In this study, the grain-based model (GBM) is used to evaluate the influence of freeze-thaw cycles (FTCs) action on the mechanical properties of sandstone. Five mineral components of sandstone are built in the numerical model based on GBM. To explore the influence of FTCs, water particles are distributed on the boundaries of different mineral components. Inter-particle heat conduction module captures the heat transfer process, resulting in temperature redistributions and the development of thermal strains. A modified elastoplastic model is used to capture the accumulation of residual strain that occurred during the ice-water phase change. The micro-cracks in sandstone samples after FTCs reflect the damage caused by FTCs. The uniaxial compressive test is carried out to evaluate the deterioration of FTCs on uniaxial compressive strength (UCS) and Young's modulus of sandstone specimens. Furthermore, it is found that the brittleness of sandstone is decreased with the increasing freeze-thaw cycles. These numerical results prove that the GBM developed in this study can be used to capture the deteriorative effects of FTCs on sandstone. This study provides a better understanding of the influence of FTCs on the mechanical properties of sandstone, which might be helpful for the design and assessment of climate-resilient infrastructure.

INTRODUCTION

Global warming has exposed more and more areas undergoing freeze-thaw cycles. The freeze-thaw cycles deteriorate the mechanical properties of rock which raises the risk of geotechnical infrastructures failure in these regions. At temperatures below 0 °C, the water contained within pores solidifies into ice, resulting in a volume increase of approximately 9 % (Hou et al. 2021). This volume expansion caused by the phase change of water increases the frost-heaving pressure on the surrounding rock, which produces microcracks or enlarges the pre-existing joints of rock masses (Wang and Zhou 2018). The increasing discontinuities in rock mass allow more water to fill into rock and cause damage to the physical and mechanical properties of rock under freeze-thaw cycles. Therefore, it is significant to understand the damage mechanism of rock under freeze-thaw cycles for the safe design of civil infrastructures in cold regions.
Amphibolites Study from Various Borehole Depth
Authors: Lokajícek T. , Aminzadeh A. , Svitek T. , Petružálek M. , Prikryl R.
Published: September 2023

In this study the elastic properties of crystalline rocks – amphibolites from different boreholes were studied. We studied the depth effect on the elastic properties of mineralogically quite homogenous rocks – amphibolites. The samples were taken from three different crustal levels – shallow (tens of meters) Stařechov (Czech Republic), medium deep (first thousands of meters) KTB (Germany), and deep crustal depths (up to 12 km) KSDB3 (Russia). The elastic properties were first determined experimentally using high-pressure apparatus and 3D ultrasonic testing. The effect of main rock fabric components were evaluated using the method of inverse calculation from experimental data. There was found an increase of P-wave velocity, P-wave stiffness elastic constants with the depth for 19 samples, collected from different depth, and all loaded to 400 MPa of hydrostatic pressure. This fact can be explained by the stress memory effect. Stiffness constants and Young modulus were determined for primary material orientation

INTRODUCTION

Elastic anisotropy is a crucial physical property of crustal rocks namely when reflecting deformational history of the rock. Knowledge of the anisotropy of deep crustal rocks (e.g., Kern et al. 1991) is of special interest for studies focused on the evolution of the crust. The relationship between amphibolite elastic properties and mineral composition and/or rock fabric has been extensively studied in the past (Siegesmund et al. 1989). The influence of microcracks on the elastic wave velocity and its anisotropy has been noted in many previous studies (Crampin 1977, Babuška and Pros 1984 among others). Numerous studies are focused on the systematic study of elastic properties of rocks extracted from boreholes e.g., KTB (Berckhemer et al. 1997) or KSDB3 (Nikitin et al., 2001, Saikia et al. 2021). In all of these studies, there is missing comparative research concentrated on the relationship between the actual depth of rock occurrence and its elastic properties.
Nuclear Magnetic Resonance Experimental Study on Pore Structure Effect of Deep Shale Under Liquid Nitrogen Freezing
Authors: Qu Hai , Chen Xiangjun , Liu Ying , Liu Xu , Zeng Zhijun
Published: September 2023

The freezing of liquid nitrogen (LN2) can affect the rock's structure, which can be used in the extraction of natural gas from deep shale formations. However, its effect on the pore structure of the shale remains unclear. To address this issue, this study subjected three different types of deep shale: Carbonaceous (C) shale, siliceous (Si) shale and calcareous (Ca) shale. The mineral composition was determined by X-ray diffraction (XRD). And the physical properties of deep shale were analyzed by nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). The evolution of porosity of shale samples under LN2 cooling by different lithology, rock temperature and cyclic cooling were compared to explore the effect of LN2 freezing on the pore structure. The results of this study indicated that LN2 fluid would be a promising source of longitudinal and bedding fractures in carbonaceous shales. And the resulting fractures would increase the permeability of the shale. In addition, repeated freezing also lead to the formation of conductive fractures in the shale. In conclusion, since LN2 has low-temperature properties, has a freeze-damaging effect on reservoir rocks and promotes microfracture development, it is important to inject LN2 as fracturing fluid during the reservoir process to improve the effect of fracturing transformation.

INTRODUCTION

As an important component of unconventional oil and gas resources, shale gas has played an important role in recent years in meeting the growing global demand for fossil energy (Alfi et al., 2019; Qu, Hu, et al., 2022; Wu et al., 2017). As shale gas reservoirs are characterized by low pore permeability and large burial depth, corresponding production enhancement measures need to be implemented to achieve effective extraction of shale gas. In response to the problems of water scarcity and environmental pollution caused by hydraulic fracturing, the liquid nitrogen (LN2) waterless fracturing proposed in recent years can be one of the key technologies for effective development of deep shale gas and alleviating water scarcity (Qu, Tang, et al., 2022). The cold impact effect of LN2 on the rock is used to reduce the difficulty of rock fracturing, thus improving the fracturing effect of the reservoir (Qu et al., 2023). Therefore, it is important to clarify the study of the fracturing mechanism of low-temperature LN2 on deep shale rocks and explore the feasibility of LN2 fracturing in deep shale rocks for the guidance of shale gas development (Qu, Liu, et al., 2022; Wu et al., 2019; Yang et al., 2021).
The Effect of Quantity and Spacings of Notches on Hydraulic Fracturing at Different Stress Regimes
Authors: Powlay B. , Karakus M. , Amrouch K. , Chester C.
Published: September 2023

Due to the increased understanding of mining techniques previously uneconomical larger orebodies are becoming viable and block caves are increasingly common. One such technological advance is the use of Hydraulic Fracturing.

With the majority of research for hydraulic fracturing being focused on reservoir development, a need to better understand how this translates into mining is required. Exploring how fractures initiate, grow, and the influence of notch spacings and density, more knowledge is gained around prescribing fractures to the mining industry and environments needs.

By using multiple perforations, due to coalescing of fractures, more complex fracturing could be through the change in localized stresses. To understand the influence of fracture density, lab work was undertaken looking at how density of notches and notch spacing influence the fracture growth, breakdown pressure, and propagation pressures in Adelaide Black Granite under two different stress regimes.

The results show that location of notches has minimal impact on pressures but create changes in the fracture direction. This work confirms that with multiple notches this technique can be used to change fracture propagation. providing solid foundation for designing campaigns with multiple simultaneous injections, and fractures density within the mining industry.

INTRODUCTION

Block caving is gaining traction as a viable method of mining within hard rock mining environments. As easy shallow depth orebodies are becoming rare and scarcer, then methods to extract deeper orebodies safely has become a need of the industry.

Block caving has an initially high outlay of costs and slow turn around in producing tons relative to Sub Level Caving methods, but in the long term requires less active development and low running costs alongside the ability to design footprints to meet the needs of the stresses, structures and environments, it equates to an economically sound, customizable, and relatively simple mining method.

The challenges faced with the block cave mining method, and future caves that are established at depths are mostly related to the higher stress environment and cave propagation and stalling. A way to mitigate these risks is through the use of hydraulic fracturing. By inducing fractures in a favorable manner into the environment stress can be redistributed, highly stressed zones can be activated, and competent rocks weakened for the promotion of cave growth
Stress-Dependent Characteristics of Coal Permeability in Gasification Zone of Underground Coal Gasification
Authors: Zhao Yufeng , Dong Zhen , Chen Yanpeng , Chen Hao , Xue Junjie , Chen Shanshan , Zhang Mengyuan , Peng Yan
Published: September 2023

Underground coal gasification (UCG) is an environment friendly way to produce coal resource and its efficiency depends on gas flow through porous medium. Therefore, the flow behavior especially the stress-dependent permeability characteristics are important topics for the UCG. The stress-dependent permeability characteristics in combustion zone are widely investigated, while, ones in gasification zone are rarely investigated but they are important for gas flow from injection wells to production wells. In this study, first, permeability tests for coal after heating below 500°C were conducted under various confining pressure. Secondly, microscopic structures of coal samples after heating were observed by the scanning electron microscope (SEM). Finally, the stress-dependent permeability characteristics of coal after heating were discussed and a model involving thermal-mechanical effect was built. The main results show that (1) permeability decreases and then increases with temperature. The increase magnitude of permeability becomes obvious at 200°C and it rises significantly up to 430% at 500°C. (2) the stress-dependent behavior of permeability decreases with temperature. The decrease magnitude can be 60%. (3) samples’ microscopic structures are affected by coal pyrolysis after heating and further affect permeability characteristics. Before 200°C, obvious change of microscopic structure is width increase of existing microscopic fractures. After 200°C, lots of new microscopic fractures are generated and macroscopic fractures may also be generated in some samples. (4) considering impacts of stress, thermal swelling and microscopic fracture generated by coal pyrolysis on permeability, a model is generated and its mean error is less than 4.3%.

INTRODUCTION

Underground coal gasification (UCG) technology, as a cutting-edge technology for clean coal, has developed rapidly in recent years and has also been the focus of academic and industrial circles[1]. This technology can mine deep and ultra-deep coal seams that cannot be mined by ordinary mining technology. The coal reserves of these coal reservoirs are often much higher than those of the middle and shallow coal seams. In addition, since the redox reaction occurs in the formation, the raw coal is converted into clean energy based on CO, CH4, and H2 in the original position[2]. This process leaves the ash produced by gasification in the ground and avoids environmental pollution. It also saves the cost of transporting coal to the ground under normal mining conditions [3].
Elastic Anisotropy of Typical Rocks at Grimsel and Bukov URLs
Authors: Petruzalek M. , Aminzadeh A. , Lokajicek T. , Vavrycuk V.
Published: September 2023

We present the elastic anisotropy of two rock samples from two underground research laboratories (URL) that are focused mainly on the investigation of functionality of deep repositories: (1) BUK sample – migmatized paragneiss, typical for the test site of the URL Bukov, Czech Republic; (2) GRM sample - Central Aare granite, a predominant host rock of the URL Grimsel, Switzerland. We used a detail ultrasonic measurement of P and S wave velocity to obtain a general form of stiffness tensor with 21 independent elastic constants for selected pressure levels from 0.1 to 100 MPa. The transformation of tensor to its principal coordinate systems shows: the Bukov migmatized gneiss is orthorhombic, whereas the Grimsel granite is transversely isotropic under atmospheric pressure. The anisotropy strength of both rocks decreases with applied confining pressure due to closing of preferentially oriented cracks. Grimsel granite becomes almost isotropic at high pressures. A great part of anisotropy in the Bukov paragneiss remains even under high pressures due to its texture. Both rocks are anisotropic under the equivalent of the overburden pressure acting at the in-situ URL conditions.

INTRODUCTION

Rocks, in general, display elastic anisotropy, as a combined effect of preferential orientations of their constituents: crystals, mineral grains and microcracks (eg. Babuska and Cara, 1991). This anisotropy depends on acting stresses, as was demonstrated by the pressure dependence of seismic velocities (eg. Pros et al. 1998). At lower pressures (<50 MPa), the elasticity and its anisotropy is controlled by the cracks with characteristic exponential increase in seismic velocity. Above the crack closing pressure, the velocity/pressure relation becomes linear depending on rock matrix (crack free) properties.

The ultrasonic sounding is a laboratory technique to determine the anisotropic elastic constants for a different symmetry types, most commonly the transverse isotropy (Sarout et al., 2007) or orthorhombic symmetry (Sano et al., 1992). With decreasing level of symmetry, the number of independent elastic constants is increasing up to 21, for the most general case of triclinic symmetry. Lokajicek and Svitek (2015) presented an experimental approach to estimate such a stiffness tensor estimated from the ultrasonic sounding performed on the spherical specimen in 132 independent directions for three waves with different wave polarizations (P, SH, SV). In this experiment, the symmetry type or its orientation does not have to be known/supposed before the experiment, or may even change with the applied pressure (Lokajicek et al., 2020). The obtained general stiffness tensor can be simplified for the higher symmetries by rotation into its principal coordinate system (Aminzadeh et al., 2022).
Stochastic Homogenization of the Elastic Properties of Highly Anisotropic Shales
Authors: Charlton T. S. , Rouainia M. , Aplin A. C.
Published: September 2023

In this paper, we present a stochastic mean-field homogenization model for upscaling the elastic properties of shale from grain-scale to core-scale. The model encompasses several levels, from the solid clay particles to a porous organic-clay matrix to the hard silt-sized inclusions to, finally, a microcracked composite. The uncertainty in the homogenized properties is considered by representing the key model parameters as random variables and quantifying the response through Monte Carlo simulation. We pay particular attention to the anisotropy of the shale elastic response, which we assume is transversely isotropic. The approach is illustrated using a case study of the Fort Simpson shale, which forms the upper fracture barrier in the Horn River Basin of NW Canada and has been shown to be highly anisotropic. The results of a comprehensive nanoindentation testing campaign, oriented both parallel and perpendicular to the bedding plane, are used to obtain the grain-scale, micromechanical statistics. Model predictions are compared with microseismic wave velocities measured in the field and good agreement is found.

INTRODUCTION

The growing momentum in the energy transition is leading to a surge in interest in subsurface energy and decarbonization systems, such as geological storage of CO2 and hydrogen, and the construction of nuclear waste repositories. Shales, or mudstones, represent important components of these technologies as their low matrix permeability makes them ideal for preventing fluid leakage over the long-term. Obtaining geomechanical properties is one of the key technical challenges because it is often problematic to conduct standard rock mechanics tests on shales due to sample recovery and preparation difficulties. The elastic anisotropy of shale is particularly difficult to characterize as it cannot be measured using wireline logs (Worden et al., 2020). Understanding and predicting elastic anisotropy is important in subsurface engineering (Favero et al., 2018), and for the interpretation of seismic reflection data (Sayers, 2005).
Performance of High Energy Absorption (HEA) Panel to Prevent Flyrock
Authors: Saliba E. C. , Nunes A. L. L. S.
Published: September 2023

The biggest environmental impact from excavation by rock blasting and open-pit mining is flyrock. It consists of the projection of a rock boulder or splinter at the blast moment, which may hit a construction, buildings causing damage and being a safety liability to people around. Therefore, slope protection is important in rock blasting operations. This is a successful case study that presents and analyses a new slope protection technique, developed by Nunes (2017), that uses high energy absorption metallic panels known as HEA panels. This technique was designed to be used at rock slope blasting at an industry zone. The case was accompanied and analyzed to verify its behavior during the subsequent blasting events. The analyses showed that the technique had satisfactory development, with the advantage that flyrock is eliminated without the necessity of any other protection and can be used again on each excavation progress and as stabilizing lining to the remaining rock slope after being excavated.

INTRODUCTION

The blasting operations nearby urban and industrial area is sensible and demands extra care due to the infrastructure around them and the possibility of somebody getting injured during the process.

One of the major environmental impacts of an open pit blast is the flyrock which is a fragment of a rock, that can be any size, it flies after the blast with no calculated direction which may hit the surrounding infrastructures or persons, causing damage and it is a risk to those who live nearby.

The main cause of a flyrock is a miscalculation on the detonation plan, especially the reduced bore spaces, higher benches with too deep holes, reduced hole plugging, and excessive explosive loading. Flyrock events may also be influenced by rock mass characteristics. If the rock mass is too fractured with joint spacing at the blast moment most likely will release boulders that may be projected to long distances.
Investigation of Parameters Affecting Seismic Potentials in a Deep Longwall Mine
Authors: Khademian Z. , Van Dyke M. A. , Beale J. , Wickline J.
Published: September 2023

Seismicity can be induced by rock failures or slips along geologic structures around mine workings. Depending on their intensity and proximity to the working area, seismic events may raise safety concerns in underground mining operations. However, the geological and mining parameters leading to destructive seismic events are poorly understood. Monitoring seismic events coupled with geomechanical modeling can be useful tools for understanding underlying mechanisms and main factors causing destructive seismic events. This paper reviews seismic events recorded in a deep longwall mine (>450 m) in Virginia and evaluates the geologic conditions that lead to areas with high seismic event activities (> 1 ML) during mining of longwall panels. Two pseudo two-dimensional models of areas with high and low seismic event activities are constructed in 3DEC software. The variation in the energy content of elastic models is monitored, and potentially damaging events with compression-type and shear-type signatures are identified. The modeling results are compared with historic seismic data to evaluate the model performance in forecasting the seismic potential in each model. The results show the applicability of energy balance calculations for forecasting the approximate location and timing of destructive seismic events.

INTRODUCTION

One source of potential hazards for underground mining operations is mining-induced seismicity. Seismic events during mining are recognized to be violent failure in close proximity to the mining area. The violent failures can occur due to sudden crushing of rock in compression or sudden slip along preexisting weakness planes such as fault and dyke contacts. Deployment of seismic networks and recording the events during the operation has become one of the industry routines for managing risks associated with the seismicity. However, in most cases the main challenge is to find the link between geologic structures, mining parameters, and seismic activities. If no clear link is apparent, it is difficult to design effective proactive measures to reduce seismic potential in a mining design. To better understand the causal mechanism of mining-induced seismicity, seismological and rock mechanics’ analyses need to be mutually investigated.

Following (Salamon, 1970), many studies have shown the energy budget consideration as the missing link between seismology and rock mechanics (Sears, 2009; Garvey, 2013; Khademian & Ozbay, 2018) One possible approach is to use numerical modeling to analyze the state of energy of the rock before and after mining. The occurrence and intensity of a seismic event can be recognized when there is a relatively significant release of energy in the system. However, the uncertainty in the required field data to perform such analyses has limited their applicability.
Temperature Distribution of Heavy Oil Reservoirs Under Radio Frequency Heating and Analysis of Influencing Factors
Authors: Xiao Jiexian , Gao Deli , Dong Xuelin , Feng Chaochao , Wang Zhengxu
Published: September 2023

Heavy oil is increasingly gaining more concerns from all over the world. However, the steam methods applied broadly are gradually being abandoned due to low efficiency and high carbon emissions. Therefore, a radio frequency (RF) heating technology is proposed which mobilizes heavy oil by using RF electromagnetic wave (RF-EMW) rather than steam. To accurately obtain the temperature distribution of heavy oil reservoir, an electromagnetic-thermal coupling model is established initially. The model considers the thermal properties change the heavy oil reservoir with temperature. Afterward, the model is validated by experimental data. Finally, the influence of several key factors on the reservoir temperature are discussed. Calculation results display that the maximum heating radius of the RF heating technology is up to 10m, which indicates that RF heating has obvious technical advantages. The model considering the varying specific heat brings about lower reservoir temperature around the wellbore, and the maximum temperature is obviously higher than that in the case of varying thermal conductivity. In addition, the reservoir temperature can be enhanced by increasing the relative permittivity of reservoir, porosity, electrical conductivity and saturation of water. The research results are intended to provide important guidance for the field application of RF heating technology.

INTRODUCTION

With the decrease of conventional crude oil, heavy oil is being exploited increasingly by a major thrust of petroleum companies. While the high viscosity of heavy oil is the main factor leading to low oil production. Several practices have demonstrated that increasing temperature helps to reduce the crude oil viscosity (Ali S, 2003). Fig. 1 shows the viscosity change with temperature for the heavy oil sample from the WanT 1 Oilfield, Xinjiang of China (Wang et al., 2019).

Current thermal recovery technologies include steam flooding, SAGD and combustion. But those methods have gradually exposed the technique flaws of low profit, high carbon emission and environmental disruption. Therefore, it is urgent to develop new mining technologies. In recent years, RF heating method appears and considered to be a viable technology for extracting heavy oil. It can effectively deliver more thermal energy to reservoir and extract oil from reservoirs cracks where steam method is ineffective. Besides, the RF heating process does not emit carbon dioxide to the atmosphere and its recovery efficiency can be improved to 25-36% compared with a typical steam injection (Abraham et al., 2016; Saeedfar et al., 2016; Hu et al., 2016). Therefore, in order to achieve large-scale and efficient development of heavy oil, it is necessary to carry out in-depth research on this technology.
Vermiculite Particles as an Additive for Oil Well Cement
Authors: Ahmed Abdulmalek , Elkatatny Salaheldin , Adebayo Abdulrauf R. , Mahmoud Ahmed Abdulhamid
Published: September 2023

The process of cementing a well is essential to ensuring the well doesn't collapse. The cement slurry is pumped into the annulus between the casing and the formation. Cement restricts the movement of formation fluids while also supporting the casing. Different types of additives have been used in the design of cement to alter cement properties to meet downhole requirements. This study aims to investigate the impact of vermiculite particles on heavy weighted oil well cement. Base cement and vermiculite cement were prepared and cured under high pressure and high temperature. Viscosity was used to describe the slurry properties, while for the hardened cement samples, the elastic, petrophysical, and strength properties were described by the Poisson's ratio, permeability, and compressive strength, respectively. Moreover, the particles settling was measured by the density variation across the cement column. It was observed from the results that the performance of vermiculite cement is better than the base cement (without vermiculite). Vermiculite cement exhibits excellent properties compared to the base cement, which represents by lower viscosity (reduction of 8%), higher Poisson's ratio (an increase of 7%), lowere Young's modulus (a reduction of 9.4%), minimizing the density variation by 95%, reducing the cement permeability by 46% and improving the compressive strength by 24%.

INTRODUCTION

The process of cementing oil wells has been an integral part of the oil industry for many years. Oil well cementing is a process that is used to form a permanent bond between the wellbore and the casing and to seal or isolate formations that contain oil and gas (Ahmed et al., 2022c). It ensures the structural integrity of the well, as well as provides economic benefits. Oil well cementing has been identified as a critical factor in ensuring the structural integrity of oil wells.

According to Ingraffe et al. (2014), oil well cementing plays a vital role in preventing the migration of hydrocarbons from one formation to another. This is because the cement forms a barrier between the formation and the wellbore, thus preventing any contaminants from entering the wellbore. Furthermore, the cement can also help to prevent the formation of fractures, which can cause a loss of pressure and weaken the integrity of the wellbore. In addition to this, the cement also helps to protect the wellbore from corrosion and other environmental factors that can cause structural damage.
Impact of Production Scheme on Pressure-Sensitive Reservoirs After Hydraulic Fracturing
Authors: Liu Sen , Zheng Leyi , Li Wenjie , He Jiajun , Liang Tianbo
Published: September 2023

Tight oil reservoirs are typically pressure-sensitive, which can affect the well productivity and oil recovery rate when the reservoir pressure decays. In this paper, the pressure-sensitive of reservoir rock is studied using CT-monitored corefloods, during which the change of permeability and porosity of the rock can be determined under different effective stresses; meanwhile, numerical simulations are conducted to understand the conducted to understand the impact of flowback and production schemes on the oil recovery rate in the field scale. After the reservoir rock sample is saturated with the sample oil, different effective stresses are applied on the rock; the oil is continuously flooded through the sample, during which the porosity change is recorded through CT scans, and the pressure change across the rock is recorded to calculate the rock permeability at different time. After the numerical simulation results are history matched with the experimental results, different flowback and production schemes are studied. After fracturing, the bottom pressure was reduced to 15MPa by different steps. The change of permeability and porosity of the rock and its influence on oil recovery rate under different production schemes were observed. During production, the effective stress in the reservoir increases from about 10 MPa to 50 MPa. According to the pressure-sensitive experiment results, the permeability and porosity of the rock decreased to 22% and 89%. When the pressure sensitive effect is considered, the 10-year recovery rate is reduced from 27% to 17%, and the flowback rate is reduced by 13%.The numerical simulation results show that the rapid production scheme has the highest production and flowback rate, increasing the oil recovery rate by 6% and the flowback rate by 5.9% compared with the three or five steps. The change of production scheme has no significant effect on the relief of pressure-sensitivity and the well should be quickly flowback considering the potential effect of water-sensitivity. The change of rock permeability and porosity are firstly quantified in-situ using a CT-monitored coreflood. Combining the experimental and numerical simulation results, the production scheme can be optimized pressure-sensitive reservoirs.
A Study on the CO2 Jet Erosion Natural Gas Hydrate with the Influence of Temperature and Confining Pressure
Authors: Hu Xiao , Zhang Yiqun , Wu Xiaoya , Wang Haizhu , Cui Xu
Published: September 2023

Natural gas hydrate (NGH) has been regarded as important potential energy resource. CO2 jet erosion HBS can be combined with Radial Jet Drilling (RJD) technology to achieve high efficiency and low-cost gas hydrate mining. The replacement of CO2 hydrate and CH4 hydrate can also be used to form a stable cap layer on the hydrate reservoir to achieve CO2 storage. In this study, the Arbitrary Lagrangian Euler (ALE) method is used to establish a heat-liquid-solid coupling model for water/CO2 jet erosion HBS, and the CO2 phase change is considered. The influence of different temperature and pressure on jet erosion effect was studied. The results indicate that confining pressure has an inhibitory effect on jet erosion ability, which gradually weakens as the confining pressure increases from 5-10MPa. At confining pressures ranging from 0.1-2.5MPa, the erosion volume decreases with rising temperature due to the gaseous CO2 in the submerged environment, resulting in reduced resistance. The erosion effect is influenced by the characteristics of the jet. At 2.5-5MPa, the CO2 in the submerged environment undergoes a phase transition from gaseous to liquid. At 5-10MPa, the erosion volume increases with temperature due to the liquid CO2 in the submerged environment, resulting in relatively higher resistance. The erosion effect is affected by the fluid in the submerged environment. Additionally, under equivalent temperature and pressure conditions, CO2 jet exhibits superior erosion effectiveness compared to water jet. This study can provide theoretical basis and technical ideas for using RJD technology to mine hydrate and achieve "carbon peak and carbon neutrality".

INTRODUCTION

Natural gas hydrate is a kind of clean energy with great potential (Sloan, 2003). It is commonly found in marine sediments and permafrost at continental margins, especially in marine sediments (Chong et al., 2016; Michael et al., 2019). The global amount of organic carbon in NGH is twice that of fossil fuels combined (Yu et al., 2019; P. Zhang et al., 2021). So far, many countries in the world have successively formulated the exploitation plan of gas hydrate (Xiao & Zhang, 2021). It can be predicted that the research and exploitation of NGH will remain the focus of global attention for a long time in the future.
Hydro-Geomechanical Observations During Multistage Hydraulic Stimulation at the Bedretto Underground Laboratory, Switzerland
Authors: Bröker K. , Ma X. , Gholizadeh Doonechaly N. , Hertrich M. , Hansruedi M. , Giardini D. , _ _ , Rinaldi A. P. , Clasen Repollés V. , Obermann A. , Wiemer S.
Published: September 2023

A series of hydraulic stimulation experiments were performed in the Bedretto Underground Laboratory for Geosciences and Geoenergies in Switzerland to answer questions about the creation of an engineered geothermal reservoir in crystalline rocks. A 400 m long stimulation borehole was divided into 15 intervals by a multi-packer system. In this work, we present preliminary results of interval 8 in which two injection phases were performed with a 3.5 months gap in between. The two phases differ in the injected volume and injection protocol (pressure vs. flow rate controlled). Within the interval, we mapped a cluster of sub-parallel pre-existing open fractures that are reasonably well oriented for reactivation in the estimated stress field. The interval pressure and flow rate data from the injections reveal a reactivation of the pre-existing fractures, associated with a large increase in injectivity. A comparison of the expected stress field around the stimulation interval with the observed reactivation pressure indicates that the fractures were likely reactivated by hydraulic shearing. The reactivation is also supported by other data sets from the extensive monitoring network, e.g. distributed temperature and strain sensing.

INTRODUCTION

Engineered geothermal systems (EGS) have received increasing interest in recent years because they are considered a low emission, renewable energy source (Lu, 2018; Aghahosseini and Breyer, 2020). An EGS aims to extract geothermal energy from crystalline basement rocks with low permeability. The permeability is enhanced either by hydraulic shearing of natural fractures or shear zones, or by hydraulic fracturing of intact rock, or by a mixture of both (McClure and Horne, 2014). This permeability enhancement is often linked to induced seismicity, which can reach damaging levels if large fault zones are reactivated (e.g. Deichmann and Giardini, 2009; Evans et al., 2012; Ellsworth et al., 2019). To address this challenge, several scaled-down in situ hydraulic stimulation experiments have been conducted in underground research laboratories in representative crystalline rock types (e.g. Amann et al., 2018; Zimmermann et al., 2019; Schoenball et al., 2020; Fu et al., 2021).
Real-Time Seismic Wave Velocity Prediction for Accurate Source Location in Underground Mines Based on Machine Learning
Authors: Mukhamedyarova Z. , Suorineni F. , Maksut Z. , Meiramov R. , Yazici A.
Published: September 2023

The objective of this study is to develop machine learning techniques to forecast seismic wave velocities in real-time amidst the constantly changing conditions of underground mining. As human-induced seismicity in underground mining can negatively impact productivity, safety, and operating costs, it is crucial to have an accurate predictor for the source of microseismic events. To simulate the dynamic conditions of underground mining, laboratory experiments using AE systems and concrete blocks mimicking homogeneous rocks were conducted. The concrete blocks were of various sizes with different hole diameters and lengths representing variations in extraction ratio with mine maturity. Stress-induced fractures were produced using a static cracking agent. The blocks were tested with the voids empty and filled with various cement to sand ratios representing backfill in mining. The data collected from AE measurements, such as seismic wave velocity, arrival time, AE hits, and energy, were utilized to train different machine learning models, including linear regression, neural networks, Random Forest Decision Tree, and Gradient Boosted Decision Tree. The Gradient Boosted Decision Tree model demonstrated the highest accuracy with a mean absolute error of 7.15 m/s. The capability to predict seismic wave velocity in real-time would lead to better identification of the location of seismic events, ultimately improving the safety and efficiency of underground mining operations.

INTRODUCTION

This study specifically examines seismicity caused by underground mining operations. A seismic event refers to the sudden release of energy from the Earth crust, which leads to the propagation of seismic waves. In the mining industry, this release of energy can result in damage to equipment, injury, or even fatalities, in which case it is referred to as a rockburst (Feng et al., 2019). The impact of rockbursts and seismicity on mine safety, productivity, and costs is substantial. Despite this, predicting rockbursts remains a challenging task due to limitations in current knowledge and technology (Trifu and Suorineni, 2009). To address this issue, the implementation of microseismic monitoring systems in deep underground mines has become vital in managing mining-induced seismicity. These systems are critical in the management of seismic hazards, thus enhancing worker safety and mining productivity.