bluuebunny/crossref_metadata_2025 huggingface dataset:
A Study of Progressive Failure in Porous Rocks Using Numerical and Experimental Modeling
Authors: Bianchi P. , Selvadurai P. A. , Vasquez A. Salazar , Dal Zilio L. , Gerya T. , Madonna C. , Wiemer S.
Published: September 2022

Physical mechanisms governing natural and induced earthquakes are still poorly understood and, despite the relevance, this lack of knowledge limits the usefulness of Geoenergy projects and severely undermines their societal acceptance. Due to the difficulty in retrieving direct measurements and observations to understand these important processes, we study laboratory acoustic emissions in combination with numerical models to shed light on the physics governing seismicity. A dry sample of Berea sandstone was tested to failure under a confining pressure of 40 MPa in a triaxial machine (LabQuake). Using in-house developed conical-type piezo-electric transducers, which are absolutely calibrated and exhibit a flat, broadband response between 100 kHz and 1.5 MHz, we are able to investigate the generated acoustic emission clouds by locating the single events and by inverting for their moment tensor solutions. Furthermore, numerical simulations are performed using a finite difference two-dimensional continuum-based fully coupled thermo-mechanical visco-elasto-plastic numerical modeling tool. We are able to image and locate regions of high stress and strain and, thus, to identify potential nucleation zones of seismic events and compare them at a first order with our experimental results.

1 INTRODUCTION

Many scientists and engineers are seeking strategies and alternatives to counteract climate changes. Among others, green energies are being investigated by the research community; Geoenergy related applications, such as enhanced geothermal systems (EGS), are thought to have a critical role (e.g., Scheck-Wenderoth et al., 2013; Lu, 2018; Wu and Li, 2020). However, the injection or extraction of fluids in the subsurface is a well-known cause of perturbation of the effective stress of a rock formation (e.g., Hubbert and Rubey, 1959), which may eventually lead to induced seismicity (Majer et al., 2007). In the last decades, various geothermal reservoir projects were the cause of some damaging earthquakes, which subsequently gave rise to the abandonment of such projects (e.g., Deichmann and Giardini, 2009; Grigoli et al., 2018). The societal acceptance of geothermal projects is thus severely influenced by such induced earthquakes (Trutnevyte and Wiemer, 2017; Grigoli et al., 2017) which, furthermore, are source of outstanding economic impact on the society (Mignan et al., 2015; Trutnevyte and Wiemer, 2017). Despite significant research efforts, the physical mechanisms governing induced seismicity are still not entirely understood and this lack of knowledge severely limits the potential of Geoenergy applications.
Reduced-Order THMC Coupled Simulation of Nuclear Waste Disposal in Shale
Authors: Chang K. W. , LaForce T. , Nole M. , Stein E. R.
Published: September 2022

Thermal and hydrological behaviors of multiphase pore fluids in the presence of heat cause the near-field thermo-hydro-mechanical-chemical (THMC) coupled processes that can influence performance of geologic radioactive waste repositories. This hydro-thermal impacts may perturb the geomechanical stability of the disturbed rock zone (DRZ) surrounding the drifts in a shale-hosted deep geologic repository, which links heat/fluid flow and chemical/reactive transport between the engineered barrier system (EBS) and the host rock. This work focuses on integrating the effects of a near-field geomechanical process driven by buffer swelling into TH simulations to reduce dimensionality and improve computational efficiency. This geomechanical process can reduce the DRZ permeability, potentially influencing the rate of radionuclide transport and exchange with corrosive species in host rock groundwater that could accelerate waste package degradation. The sensitivity test with variation in host rock permeability indicates that less permeable shale retards re-saturation of the buffer, such that slower increase of swelling pressure delays reduction of DRZ permeability.

1. INTRODUCTION

Clay-rich sedimentary strata (shales and argillaceous formations) are one of the potential geologic media for disposal of radioactive waste in the United States [Shurr (1977), Gonzales & Johnson (1985)] due to their low permeability, high sorption capacity, typically reducing porewaters (which limit radionuclide solubility), and ability to deform elastically/plastically, which promotes self-healing of fractures [Neuzil (2013)]. However, clay-rich rocks tend to be less conductive thermally due to mineral composition [Schon (2011)], which implies that the evolution of shale-based repository systems may be more sensitive to thermal loading/unloading.

In the near-field, the buffer and the host rock mainly influence each other thermally by heat flow, hydraulically by single- or multi-phase fluid flow, mechanically when the buffer absorbs water from the rock and swells, and also chemically by exchange of solutes between groundwater and pore water in the buffer. The changes in hydrological, mechanical and geochemical characteristics of the disturbed rock zone (DRZ) will affect the overall behavior of radioactive waste geological repositories by redistributing stress states, creating additional pathways of solute/radioactive transport or fluid flow [Tsang et al. (2005)]. These simultaneous actions will induce a number of Thermo-Hydro-Mechanical and Chemical (THMC) processes that will significantly affect the evolution and long-term performance of the nuclear waste repository system [Bernier et al. (2017)].
Influence of Curing Time on Oil Well Cement Properties Using Nanoclay
Authors: Ahmed Abdulmalek , Mahmoud Ahmed Abdulhamid , Gowida Ahmed , Elkatatny Salaheldin
Published: September 2022

Cement matrix is exposed to several loadings, which can harm its key properties and impede its functions, especially at the early age of forming the cement matrix where its properties are not entirely developed. Nanoclay is a powder material with very fine-grained particles which was used as a secondary additive to enhance the properties of cement. This work evaluates the early-time properties of oil well cement prepared with nanoclay powder and compares it with the properties of the base cement (without nanoclay). Several cement samples were prepared and cured for different times (12, 24, 48 and 72 hours) where the compressive strength, permeability, Poisson’s ratio and Young’s modulus of each sample were examined. The results indicated that the compressive strength of both cement systems increased with the increase of the curing time and the nanoclay-based sample had higher strength than base cement. The permeability of the cement decreased as the time of curing increased for the two cement systems and nanoclay cement had lower permeability. Moreover, the Poisson’s ratio decreased and Young’s modulus increased with curing time for both systems and the addition of nanoclay increased its Poisson’s ratio and reduced its Young’s modulus.

1. INTRODUCTION

During the practice of drilling operations, cement slurry is pumped into oil and gas wells for the purpose of sealing the rock formation from the well by cementing the steel casing to the wellbore (Backe et al., 1998). Moreover, cement slurry is also used for controlling a zone where considerable losses of drilling mud are happening and setting a kickoff plug for the wellbore (Nelson and Guillot 2006). The main requirements for long term zonal isolation are the proper placement of the cement, providing low permeability, good mechanical durability and the ability to be adapted during the changing conditions of the wellbore (Zhang et al., 2020).
Control Measures to Manage Seismic Risk at the LaRonde Mine, a Deep and Seismically Active Operation
Authors: Sasseville G. , Turcotte P. , Falmagne V.
Published: September 2022

The LaRonde mine is a world-class deposit of gold-copper and zinc-silver along the Cadillac Fault in the Abitibi-Témiscamingue region of Quebec, Canada. Since its inauguration in 1988, the LaRonde mine has produced over 7 M ounces of gold. Mining operations currently extend 3.2 km below the surface with plans to reach 3.4 km. The LaRonde mine has been dealing with induced seismicity daily since 2003. The seismic activity can exceed MRichter 2, and the pro-active management of seismic risk is a key element to operate this mine at that depth and under these seismically active conditions.

Seismic risk at the LaRonde mine is currently managed through a combination of control measures, including a ground-control-driven mining sequence and level design, dynamic ground support systems, and procedures to limit workforce exposure. These control measures have evolved over time and been adapted to the seismic risk as the operation becomes deeper and larger. The main objective is to maintain a safe work environment while meeting production requirements.

Seismic risk management is an ongoing concern at the LaRonde mine. This paper presents the current state of the strategic and tactical control measures implemented on site to manage seismic risk at the LaRonde mine, and it documents some of the impacts on operational flexibility and performance. The effectiveness of control measures must be quantified to measure improvements year after year and to identify and correct observed deficiencies.

1. INTRODUCTION

Mining at great depth generally involves challenging geotechnical conditions and management of seismicity. Innovation and continuous improvement of mining practices are required to face evolving challenges and maintain a safe work environment. An example of this process at the LaRonde mine is the development of innovative ground support solutions to manage the challenging ground conditions in a strongly foliated and highly deformable rock mass. Seismicity was recorded in the early stages of mining from the Penna shaft, with the first damaging seismic events observed in 2002 as described in Mercier-Langevin and Hudyma (2007). Seismic risk management has been an integral part of mine planning since that time.
A Case Study on Terrestrial SfM Photogrammetry Slope Change Detection Without Stable Ground Control Points
Authors: Butcher B. , Walton G. , Kromer R. , Gonzales E.
Published: September 2022

Daily remote monitoring of slope processes using terrestrial structure from motion (SfM) photogrammetry is a relatively new technique in engineering geology. In this study, a five-camera photogrammetry monitoring station was installed in the Siguas River Valley near Majes, Peru in December 2020 for long-term monitoring and study of slope processes. The study area includes a retrogressive rockslide-debris slide with areas of rockfall sourced from the head scarp, areas of water-driven erosion, and other related geomorphological processes ranging from 100 to 900 m away from the camera stations. Challenges with photo and point cloud alignment accuracy and, ultimately, change detection accuracy arise due to the constant ground movement and lack of suitable locations for ground control point (GCP) installation. In this paper, we investigate point cloud alignment methods for the purpose of change detection at sites where the distance from the photogrammetry station to the area of interest is variable and where there are no stable GCPs. Additionally, we present preliminary change detection results in relation to landslide movement rates at the site. For the tested methods that produced reasonable results, the average rate of movement for the rockslide-debris slide was estimated to be between 3 and 35 cm per month, on average.

1. INTRODUCTION

Intensive cropland irrigation in dry climate regions has been linked to increased landslide occurrence, and this relationship has recently become of increased interest to the geohazard scientific community (Garcia-Chevesich et al., 2021). An example of one such area is the Majes district in southern Peru, roughly 150 km to the west of Arequipa. The Siguas River runs through the Majes district, providing drinking water for local populations, water for industrial uses, and water for cropland irrigation. Since the mid 1970’s the amount of land dedicated to irrigation-dependent agriculture has continued to increase along the Siguas River (Lacroix et al., 2020). The north bank of the Siguas River, where it is adjacent to irrigated land, has had numerous landslides in the last four decades, while the southern bank of the river, which remains mostly unirrigated, has had minimal landslide activity within the same timeframe (Graber et al., 2021).
A New Constitutive Model for Rock Salt Viscoplasticity: Formulation, Implementation, and Demonstrations
Authors: Reedlunn Benjamin
Published: September 2022

This paper presents the formulation, implementation, and demonstration of a new, largely phenomenological, model for the damage-free (micro-crack-free) thermomechanical behavior of rock salt. Unlike most salt constitutive models, the new model includes both drag stress (isotropic) and back stress (kinematic) hardening. The implementation utilizes a semi-implicit scheme and a fall-back fully-implicit scheme to numerically integrate the model’s differential equations. Particular attention was paid to the initial guesses for the fully-implicit scheme. Of the four guesses investigated, an initial guess that interpolated between the previous converged state and the fully saturated hardening state had the best performance. The numerical implementation was then used in simulations that highlighted the difference between drag stress hardening versus combined drag and back stress hardening. Simulations of multi-stage constant stress tests showed that only combined hardening could qualitatively represent reverse (inverse transient) creep, as well as the large transient strains experimentally observed upon switching from axisymmetric compression to axisymmetric extension. Simulations of a gas storage cavern subjected to high and low gas pressure cycles showed that combined hardening led to substantially greater volume loss over time than drag stress hardening alone.

1 INTRODUCTION

Rock salt constitutive models are used to simulate the evolution of mines, boreholes, storage caverns for gases and liquids, and nuclear waste repositories in rock salt formations. A wide variety of models have been proposed for rock salt, yet even the damage-free (micro-crack-free) thermo-viscoplastic behavior remains difficult to capture. The Munson-Dawson model, for example, was recently extended in Reedlunn et al. (2022), but it still cannot capture monotonic hardening behavior over the full range of strain rates typically utilized in laboratory tests (10−12 to 10−4 1/s), or transient non-monotonic hardening behaviors, such as the Bauschinger effect and reverse (inverse transient) creep (Reedlunn, 2020, Section 1).
Coupled THMC Simulation Based on Explicit Fracture Representation Using Extrinsic Cohesive Zone Model
Authors: Ogata S. , Maeda Y. , Fukuda D. , Yasuhara H. , Inui T. , Kishida K.
Published: September 2022

We presented a new coupled thermal-hydraulic-mechanical-chemical (THMC) simulator by combining the numerical models that can explicitly introduce the rock fracture surfaces to reproduce the processes of changing permeability as realistically as possible. Then, the presented simulator was applied to estimate the long-term evolution in the permeability of a rock mass within a geological disposal system of high-level radioactive waste (HLW). The numerical predictions showed that the time-dependent decrease in permeability was observed only within specific fractures where the geochemical creep (i.e., pressure dissolution) had been induced after disposal of HLW into disposal cavity. This permeability drop was caused by the fracture sealing due to pressure dissolution at asperity contacts in the fracture that depended on the characteristics of each fracture (fracture formation, aperture, closing stress and contact area). Overall, it was implied that the presented simulator had a possibility to reveal the detailed spatial distribution of permeability within a natural barrier during a long-term disposal period of HLW.

1. INTRODUCTION

When examining the performance of the geological disposal facility of high-level radioactive waste (HLW) for preventing the migration of radionuclides, it is significantly important to numerically simulate the evolution processes of permeability within a rock mass that works as a natural barrier. During the disposal period of HLW, the convolved phenomena such as rock fracturing during excavation of disposal cavity, heat radiation from waste package, fluid-driven transport, and kinetic dissolution/precipitation of the minerals may occur within a natural barrier. The complex interactions between these phenomena, namely, coupled thermal-hydraulic-mechanical-chemical (THMC) interactions, may bring about the change in permeability of a rock mass.

Particularly, permeability distribution within a natural barrier is influenced by the transition of a rock mass from continuum to discontinuum due to the short-term rock fracturing during the excavation of the disposal cavity. In addition, subsequent occurrence of mineral reactions (e.g., pressure dissolution, free-face dissolution/precipitation) within rock fractures after disposing HLW may have non-negligible impacts on permeability evolution over the long-term. Pressure dissolution is a mineral dissolution caused at the asperity contacts within rock fractures, which may depend on compressive stress acting on a fracture plane and temperature (Yasuhara et al. (2011)). Previous work by Yasuhara et al. (2011) have shown that pressure dissolution can cause the permeability reduction of rock fractures by several orders magnitude over a long duration.
The Mechanical Properties of Three Types of Shale Oil Reservoirs and Its Influence on Hydraulic Fracturing
Authors: Wang Xiaoqiong , Qian Yuping , Wang Junhua , Kong Fanxi , Ge Hongkui
Published: September 2022

The premise of hydraulic fracturing is to have an accurate and detailed understanding of the rock mechanical properties and fracture propagation law of shale reservoir. In this paper, a systematic and comprehensive evaluation of the mechanical properties is carried out based on the shale oil reservoir in the south of Songliao Basin, Jilin Province. Based on the analysis of the mineral composition, the microstructure, rock mechanics of three types of shale oil reservoirs in the laboratory, combined with the field fracturing, logging data and the in-situ stress, the fracture propagation law of the three types of reservoirs is obtained, and the suggestions for fracturing are put forward. The results showed that there are two significant characteristics in the study area. One is the development of bedding, which is easy to form horizontal fractures. Influenced by bedding and stress, it is not suitable for horizontal well fracturing. The other is the high content of clay minerals, and the applicability of conventional slick hydraulic fracturing fluid is poor. It is suggested to use vertical well or directional well to carry out volume fracturing. In this way, the effect of bedding can be effectively used to open and communicate the bedding and form a larger fracture network.

1. INTRODUCTION

Hydraulic fracturing is the key technology of shale oil and gas development. Through large-scale volume fracturing of shale oil and gas reservoir, a dispersion volume fracture network (volume fracturing) is formed (Cipolla et al., 2008), so that shale oil and gas stored in ultra-low permeable shale reservoir can be developed industrially (Cipolla et al., 2008; Guo et al., 2014; Sierra et al., 2010). The premise of hydraulic fracturing is to have an accurate and detailed understanding of the rock mechanical properties and their influences on hydraulic fracture (Vernik et al., 1992; Vernik et al., 1997; Clarkson et al.,2013). The formation and extension mechanism of hydraulic fracture in shale oil reservoir is complex. It is of great significance to master the formation mechanism of artificial fracture network for evaluating the effectiveness of hydraulic fracturing.
Numerical Study of Three-Dimensional Blast-Induced Damage Patterns Resulting from Simultaneous Borehole Blasting of Hard Rocks
Authors: Thomas R. N. , Bird R. E. , Paluszny A. , Zimmerman R. W.
Published: September 2022

Simultaneous detonation of charges in closely spaced boreholes is a commonly used blasting technique for frag-mentation and construction. Blasting is a challenging phenomenon to model, due to the complexity of the mechanical deformation, fracturing, and fragmentation, and the spatial scales involved. Blast wave models must consider the possibility of constructive interference between separate waves in three-dimensions. A three-dimensional finite element method is used to study the induced damage in a general hard rock tunnel blast setting. The Johnson Holmquist-2 elastoplastic-damage model is used to quantify shear and tensile failure. In simulations with two blastholes separated by up to one meter, damage patterns emanating from boreholes interact to form self-organizing ‘fracture-like’ structures. Mechanical interaction between the two blasts is a function of the input charge wave properties, blasthole separation, and distance along the charge, with high concentrations of damage at the free boundary representing the tunnel wall. Constructive interference between the two blast waves is not shown to directly induce additional damage zones, and instead, interaction results from the overlap and slight extension of each blasthole’s damage zone towards the other.

1 INTRODUCTION

Drilling and blasting continues to be a key method for mining and excavation (Lu et al., 2012). Many blasting applications, such as bench blasting or tunnel excavation, involve drilling and blasting multiple holes in close proximity to one another in order to generate overlapping fractured zones (Cho and Kaneko, 2004). Efficient use of explosives reduces costs, improves sustainability, and ensures that the extent of the excavation disturbed zone is minimized, the latter being an important constraint for the construction of radioactive waste disposal facilities (e.g., Tsang et al., 2005; Kwon et al., 2009) and many civil engineering projects (e.g., Sharafat et al., 2019). Due to the complex physics of blasting and rock fragmentation, a fully mathematical description of the process is not possible, and blast operation designs often make use of empirical formulas (Liqing and Katsabanis, 1997). In particular, the dynamic weakening (damaging) of rock introduces challenges for models, and upscaling of damage is necessary to avoid resolving the complex geometry of fracturing and fragmentation. Numerical approaches are therefore used widely to understand the process of blasting (e.g., Liqing and Katsabanis, 1997; Yilmaz and Unlu, 2013; Yang et al., 2015; Hajibagherpour et al., 2020; Ji et al., 2021; Pu et al., 2021).
Impact of Undrained Pore Pressure Response on Expected Failure Stress in Anisotropic Shales
Authors: Duda M. I. , Holt R. M. , Stenebråten J. F. , Stroisz A. M.
Published: September 2022

The connection between undrained pore pressure response to stress in shales and fault reactivation, drilling problems and microseismicity observed at significant distances from hydrocarbon reservoirs and injection zones has not been thoroughly studied and is usually disregarded in geomechanical modelling workflows. In our study, we examine to what extent the inclusion of the pore pressure response affects the amplitude of total stress changes expected to cause shear failure in several overburden and outcrop shales. We combine poroelastic pore pressure coefficients and Mohr-Coulomb failure envelope parameters estimated through triaxial laboratory experiments to model the total stress increases at failure for a wide range of loading scenarios and medium orientations. We consider both isotropic and anisotropic pore pressure parameters - we explore the differences in modelling outcomes the two sets of parameters yield, as well as the impact of the individual parameters on the expected stresses at failure. We observed that shear failure in shales is expected at significantly lower stresses changes and is plausible in a much wider range of loading paths once the undrained pressure response in considered, and therefore we postulate that it should be taken into account during injection or production operations safety assessment.

1. INTRODUCTION

Injection into or production from a subsurface reservoir have been documented to lead to fault activation, microseismic activity, and borehole stability issues in the reservoir and its surroundings (e.g., Pine et al., 1983; Raleigh et al., 1976; Zoback & Harjes, 1997). In some cases, these undesired phenomena occurred in the over-and underburden at significant distances from the reservoir subjected to pore pressure change (e.g., Odonne et al., 1999; Rutqvist et al., 2008; Segall, 1989).

This has triggered an ongoing discussion of the causes of these events. Until now, it was primarily associated with pore fluid migration through fractures and fault planes throughout low permeable under- and over-burden, as well as with stress transfer (e.g., Vasco et al., 2018; Verdon et al., 2011; Williams-Stroud et al., 2020; Zhou et al., 2008) caused by injection- or production-induced pore pressure changes in the reservoir (e.g., Geertsma, 1973; Morita et al., 1989; Rudnicki, 1999).
Experimental Study on Fracturing and Proppant Setting in Unconsolidated Sand Formation
Authors: Zhang R. , Ito T. , Tenma N.
Published: September 2022

In the development of methane hydrates, the improvement to produce gas at commercial requirements is a current challenge. Hydraulic fracturing technology is a feasible way to increase permeability by forming artificial fractures. During the fracturing process, proppants are usually injected into induced fractures. These proppants keep the fractures open, thereby maintaining fractures permeability. However, the MH formation is unconsolidated and soft, unlike rock formation for which proppants are suitable. Currently, the understanding on the effectiveness of proppant is absent. In this study, we evaluated the effect of proppant and experimentally reproduced the process of hydraulic fracturing to create fractures and inject proppant . The experimental results of proppant stability evaluation showed that in the unconsolidated sand layer, proppant can play a certain role in maintaining the fracture opening, and it is difficult for the sand to invade the proppant layer. The proppant injection experiment showed that increasing the flow rate allowed the proppant to be injected more smoothly.

1. INTRODUCTION

As a potential unconventional natural gas resource, methane hydrate has received a lot of attention. Currently, producing natural gas from methane hydrate is technically possible. Japan has conducted two offshore production trials in 2013 and 2017. In the second production trial, the two production wells produced at average rates of 3400 m3/day and 9200 m3/day, respectively (Yamamoto, 2019), below the minimum commercialization requirement of 50,000 m3/day estimated by MH21 (The Research Consortium for Methane Hydrate Resources in Japan).

To produce methane gas from the methane hydrate (MH) reservoir, it is necessary to dissociate MH into methane gas and water. The depressurization method is an effective way for MH dissociation. This method will increase the pressure difference between the wellbore and the formation, resulting in consolidation of formation. Then, the permeability of these areas will decrease, which is not favorable for efficient methane gas production. Hydraulic fracturing is a feasible way to increase permeability by forming artificial fractures. The fracture extending from the production well to the surrounding ensures a flow path through the low permeability section. This significantly increases the drainage area, thereby increasing productivity. Fracturing usually was used in the hard and consolidated rock formations. MH-bearing formations are soft and unconsolidated sand and the properties of the formation are completely different from those of hard and consolidated rock. Therefore, the feasibility of fracturing in MH formation still needs further research.
Effects of Anisotropic Poroelasticity on Stress and Pore Pressure Changes Around Subsurface Reservoirs and Storage Sites
Authors: Holt R. M. , Bakk A. , Duda M.I. , Yan H.
Published: September 2022

Stresses and pore pressures change around depleting hydrocarbon reservoirs or fluid injection sites as result of reservoir pore pressure change. Such changes influence the stability of new wells drilled and may lead to fault activation, resulting in induced seismicity and possibly to casing damage in existing wells. Forecasting requires reliable geomechanical modeling of the reservoir and its surroundings. Classical analytical solutions are too simple, so numerical models are required. The rocks surrounding reservoirs are often anisotropic (like overburden shale), but their anisotropic elasticity is normally neglected, either because of model limitations, or in lack of input data. Here, however, the impact of anisotropy along with the elastic contrast between undrained surroundings and drained (isotropic) reservoir rock is addressed through a series of numerical scenarios. It is shown that isotropic models are unable to reproduce the stress changes predicted by the anisotropic models. Pore pressure changes may be underestimated by neglecting the anisotropic nature of the poroelastic Skempton parameters.

1. INTRODUCTION

Stress evolution around hydrocarbon reservoirs caused by depletion and around storage sites caused by injection of, e.g., wastewater or CO2, can be handled by analytical methods, such as the classical theory of Geertsma (1973). Although more sophisticated analytical, as well as numerical geomechanical models exist, the role of anisotropy in such computations has not been addressed in a systematic manner in the literature. We use a finite element method (FEM) to simulate stress changes in anisotropic surroundings (shales) around an isotropic reservoir. Because of its low permeability as a cap rock, the shale response will remain undrained within reservoir lifetime, unless leakage occurs through faults or other permeable conduits. Such pore-pressure changes are often ignored; however, they may have a crucial impact on drilling efficiency and borehole stability during infill drilling. In the reservoir rock, pore pressure will change in accord with fluid flow out of or into the reservoir, and the rock behavior will be described by drained moduli.
Research on the Influence of Hydration on the Evolution Law of Shale Pore Structure
Authors: Yang C. , Jia K. K. , Zhang X. R. , Wang L. L.
Published: September 2022

In this paper, shale is used as the research rock sample and sandstone is used as the control rock sample. Different types of supersaturated solutions are used to form a special humidity environment to complete the control of the water saturation of the rock samples. The T2 distribution curves of the two rock samples under different relative humidity were obtained by nuclear magnetic resonance (NMR) technology. Comparing the T2 distribution curves of different relative humidity, it is found that the pores of shale are dominated by small pores, while the pores of sandstone are dominated by large pores. The quality analysis of water-saturated samples shows that the porosity of sandstone is about 12%, and the porosity of shale is about 4%. The relationship between relative humidity and water saturation is plotted, and it is found that the adsorption capacity of shale to water is much stronger than that of sandstone. By drawing the capillary force curve of the sample and fitting the Van-Genuchten (VG) model, the VG model parameters of the sample are obtained, the m of sandstone is 0.28, the α of sandstone is 34.5, and the m of shale is 0.38, the α of shale is 0.12. The above research on the evolution law of shale pore structure is of great significance to the further study of the law of its physical parameters.

1. INTRODUCTION

Since 2000, the United States took the lead in launching the shale gas revolution due to major breakthroughs in horizontal drilling, hydraulic fracturing and other extraction technologies (Ciardo and Lecampion, 2021). According to prediction (Zhang et al., 2008), the global shale gas resource is 456 × 1012 m3, which is equivalent to the sum of the conventional natural gas, coalbed methane and tight gas in the world (471 × 1012 m3). Therefore, the commercial exploitation of shale gas is considered to be the most exciting and major achievement in the field of petroleum engineering in the past 100 years, which will change the global energy pattern greatly (Mi et al., 2010). In the Shale Gas Development Plan (2016-2020), the National Energy Administration of China pointed out that during the "Thirteenth Five-Year Plan" period, the production of shale gas will be 30 billion cubic meters by 2020, and the annual production volume will be 80-100 billion cubic meters by 2030. It can be seen that the development of shale gas exploitation also plays an important role in our country’s energy development.
The First Pressuremeter Testing Campaign on Wireline Formation Testers in Deep Boreholes
Authors: Elkhoury Jean E. , Elias Quincy K. , Prioul Romain , Peyret Emilie , Wilcox Ailsa , di Giovanni Mauro , van der Hulst Tim , Bérard Thomas , Desroches Jean , Garrard Rodney , Giger Silvio B.
Published: September 2022

Pressuremeter testing (PMT) is a formation test that consists of inflating a packer downhole, while measuring packer pressure exerted on the borehole wall as a function of injected fluid volume. Provided the stiffness of the packer is known and large enough compared to that of the formation, changes in packer pressure associated with changes in injected fluid volume provide a direct measurement of formation stiffness and, along with the relevant length-scales, produces an in situ static formation shear modulus, a very important parameter for Mechanical Earth Model calibration. Here, we report on the first field-scale campaign of PMTs in deep boreholes performed using a wireline formation tester (WFT) tool. These PMT measurements were carried out alongside a stress measurement campaign, to fully characterize potential sites for a deep geological repository for radioactive waste in Switzerland. The initial field trials highlighted challenges in calibrating packer stiffness, key in inferring formation stiffness. We overcame the challenges in packer characterization by adopting a true single packer configuration and by performing reference PMT measurements in casing and formations of known stiffness. Then, we performed PMT inflation and deflation cycles to infer in situ static shear moduli at every station tested. PMT-derived static shear moduli results are consistent with static shear moduli derived from sonic logs using independent dynamic-to-static elastic moduli transformations. The precision of the in situ PMT static shear moduli increases as the stiffness of the measuring system, WFT, increases with respect to formation stiffness. These first results show the viability of in situ PMT in deep boreholes with a wireline formation tester tool as it can be performed at multiple depths in a single run, in a time-efficient manner, and in combination with micro-hydraulic and sleeve fracturing stress tests for an integral approach to in situ geomechanical assessment.
Sensitivity Analysis of the Dry Density Distribution of a Bentonite Buffer in a Deep Geological Repository for Spent Nuclear Fuel
Authors: Gharbieh H. , Pulkkanen V.-M. , Navarro V. , Asensio L.
Published: September 2022

Bentonite buffers consisting of compacted blocks and pellet fills with different installation densities are used as engineered barriers in the KBS-3 deep geological final disposal concept for spent nuclear fuel. In this work, a sensitivity analysis was performed to identify the most influential parameters for the density homogenization of the bentonite buffer. In total, 16 input parameters related to 1) the THM models developed for compacted blocks and pellet fills, 2) the buffer design and 3) the thermal and hydraulic boundary conditions were studied. The output variable was the heterogeneity degree that was defined to quantify the remaining density differences in the buffer. For the analysis, 34 numerical full-scale simulations were performed with varying input parameter value combinations prescribed by a definitive screening design (DSD), which allows for the statistically reliable estimation of the effects of the different parameters. The results indicate that three parameters are most relevant for the homogenization in the buffer: the elastic stiffness of the inter-pellet pores related to the triple porosity model developed for pellet fills, the width of the outer pellet-filled gap and the microstructural swelling capacity of the bentonite. On this basis, recommendations for control of the homogenization in the buffer are given.

1. INTRODUCTION

In the KBS-3 final disposal concept, planned for example in Finland, a bentonite buffer is emplaced between a spent nuclear fuel containing canister and the crystalline host rock in a deep geological disposal facility. The installation gaps surrounding the highly compacted bentonite blocks are filled with pellets and the block densities vary by location, which leads to an uneven dry density distribution of the buffer at initial state. The wetting of the installed buffer induces swelling, which in turn leads to a complicated mechanical evolution of the buffer. After the wetting phase, a desired feature of the buffer is a sufficiently even dry density distribution, which is important for evaluating the fulfillment of the safety functions assigned to it, such as limiting the advective mass transport and protecting the canister from detrimental mechanical loads (Posiva & SKB, 2017).
Insights into Triaxial Testing Using Coupled Acoustic Emission and Distributed Optical Fiber Strain Measurements
Authors: Salazar A. V. , Selvadurai P. A. , Niu Z. , Bianchi P. , Rabaiotti C. , Madonna C. , Wiemer S. , Germanovich L. N.
Published: September 2022

During the failure of geomaterials, quasi-static (aseismic) and dynamic (seismic) deformation have been observed in laboratory and field experiences. The measurement of both is required for in-depth understanding into the progressive failure of rocks, and to reduce the risk associated with induced seismicity. The study of acoustic emission (AE) in the laboratory is commonly used to study how localized events can coalesce into a larger dynamic fracture nucleation. How energy is partitioned into driving the seismicity versus larger aseismic dissipative processes is not fully understood but by simultaneous measurement of seismic and distributed quasi-static deformation, we can investigate these phenomena.

This paper presents the results of a triaxial test on a dry, intact Rotondo granite sample implemented with both optical fibers to measure the distributed strain and calibrated AE sensors to derive a physical representation of the seismic sources. We show that quasi-static deformation can be measured using distributed measurement methods that show evidence of strain localization. Fiber optics show complex spatial distribution in strain near failure due to shear fracture forming in the later stages. The spatial expression of seismicity and a post-test X-Ray computed tomography scan show two macro-fractures inside the sample, reconstructing their development. A qualitative temporal and spatial correlation was observed between the strain localization and the nucleating fractures through measurements of both the fiber optic strain and the seismicity. The seismic deformation accounted for 0.04 percent of the total anelastic deformation.

1 INTRODUCTION

Petroleum and geothermal energy projects inject fluid into the rock mass to enhance production. This large-scale injection operation perturbs the subsurface stress field, which induces the nucleation of seismic events (King Hubbert and Rubey, 1959; Deichmann and Giardini, 2009). This induced seismicity continuously raises public safety concerns, delaying or canceling projects specially geothermal ones (Majer et al., 2007; Ellsworth, 2013; Grigoli et al., 2018). Mitigating injection-related seismic hazards has become a major challenge for geoscientists and geothermal engineers. Solutions to this complex problem rely first on an in-depth understanding of the mechanical deformation during progressive failure of rocks. Scotti and Cornet (1994) and Cornet et al. (1998) gave field evidence that seismic and aseismic deformation is involved during large-scale fluid injection. Bernard (2001) acknowledged the necessity to develop crustal models that include both inertial and slow instabilities to assess seismic hazard. We extend his proposition to study the seismic and aseismic deformation at the laboratory scale.
Novel Environmentally Friendly Nano-Additives for Drilling Fluids
Authors: Yang J. , Kane A. , Didriksen T. , Thorshaug K. , Stenerud G. , Vågenes B. , Lund B. , Latham J.-P. , Xiang J. , Velmurugan N. , Gerbaud L. , Sellami H.
Published: September 2022

The potential for environmentally friendly nano-additives based drilling fluids is extended here in the context of the ongoing EU project ‘ORCHYD’ where a hybrid drilling technology is developed by combining High Pressure Water Jet (HPWJ) and Percussive Drilling to improve the efficiency of deep geothermal drilling. In this work, different types of nanomaterials such as graphene oxide, hybrid nano silica and their composite nanomaterials are used as additives in a water-based drilling fluid. The influence of additives on the rheological properties and the friction of the drilling fluid has been investigated. The laboratory results showed that an increase in the concentration of additives will increase the viscosity of fluids. A significant reduction in the coefficient of friction (during wear testing of steel material) was also revealed with the addition of GO and chemical functionalization. The need for further characterizing and the perspective to upscale the enhanced nano-additives based fluids for HPWJ and percussive drilling application, in deep geothermal conditions, are discussed.

1. INTRODUCTION

This study is performed in the context of the EU project ORCHYD, https://www.orchyd.eu/proiect/, where an innovative drilling tool combining (high pressure water jetting and percussive drilling) will be developed to increase hard rock drilling rates, in deep geothermal wells. The potential of new green additives to the drilling fluids is thus investigated to account for the best compromise for efficient jetting, cutting and transport of the rock particles, and the lifetime extension the drilling tools.

Deep geothermal reservoirs are being targeted for renewable energy supply worldwide (Huttrer, 2021), however the high pressures and high temperatures in deep geothermal wells impose significant challenges for desiring drilling fluids. Over the past decade, various additives such as polyacrylamide, organic modified clays, poly carboxylic acids, asphaltic compounds, treated lignite have been used in the drilling fluid to optimize the rheological properties, filtration control and reduce the fluid loss, shale inhibitors and thereby improving wellbore stability (Boyou et al., 2019; Vryzas et al. 2017). However, most of the polymer-based materials degraded thermally and chemically at relative low temperature, which lowers their effectiveness.
Measurements of Elastic Moduli and Stress Dependence of Geothermal Rocks
Authors: Kleich S. J. , Folsom M. , Sherman C. , Feigl K. L. , Hampton J. C.
Published: September 2022

In the WHOLESCALE project we aim to simulate the temporal evolution and spatial distribution of stress in and around the geothermal reservoir at San Emidio, Nevada, United States. To constrain stress modeling efforts, we perform laboratory measurements of static and dynamic elastic stiffnesses using oriented rock samples collected from outcrops located near the San Emidio geothermal field. In this paper, we seek to understand (1) the static and dynamic elastic properties of the rock formations, (2) the existence or absence of anisotropy or heterogeneity-controlled behavior at the millimeter to centimeter scales, (3) whether the elastic properties are stress dependent, and (4) whether there exists any stress induced anisotropy under reasonable net mean stress variations. To evaluate the existence of anisotropy or heterogeneity, we measure ultrasonic velocities, Vp and Vs, at 45-degree increments around the circumference of oriented cylindrical specimens for each rock type. Combining the three-dimensional velocity data with geological and textural descriptions, we address whether the materials are heterogeneity-controlled and/or anisotropic at the plug scale. Static and dynamic elastic moduli were also measured at the net mean stresses of interest for each of the rock types obtained. Dynamic stress dependence and whether the material contained stress induced anisotropy was evaluated via stepped hydrostatic ultrasonic velocity measurements.

1. INTRODUCTION

The geothermal field at San Emidio has provided more than two decades of data collection, with power first being produced in 1987 (Feigl et al., 2022). Since 1987, three DOE-sponsored projects have been awarded to study the geothermal resource at San Emidio. The first DOE-sponsored project (DOE award DE-EE0002847) conducted exploratory drilling between 2010 and 2014 (Feigl et al., 2020). The second and third DOE-sponsored projects (DOE awards DE-EE0007698 and DE-EE0009032) are currently underway to characterize the geothermal resource at San Emidio and to further investigate stress in the geothermal system. One of these DOE-sponsored projects is called WHOLESCALE. As such, the WHOLESCALE acronym stands for "Water and Hole Observations Leverage Effective Stress Calculations and Lessen Expenses".