Derek Elsworth

• Professor (Full) at Pennsylvania State University

Gouge in fault zones generally undergoes grain breakage during shear slip events, resulting in changes in both shear mode and pore structure. We establish a discrete element model representing shearing of granular fault gouge for increasing normal stresses but constant shear velocity (v = 6 μm/s) to investigate the effects of grain breakage on shea...

Granites are representative of generic crystalline rocks characterized by their complex crystal-grain structure. Variations in the composition, size, shape and orientation of mineral grains result in pronounced heterogeneity and anisotropy at the microscopic scale, significantly influencing mechanical properties as well as the initiation and propag...

Epidote is a common and abundant metamorphic mineral in geothermal systems driven by hydrothermal–rock interaction. Precipitation of epidote on natural fracture/fault surfaces potentially alters frictional resistance and stability in geothermal reservoirs and thus the potential to spawn earthquakes. Elevated pressures due to fluid-injection during...

The projected evolutionary history of the Moon and observed occurrence of moonquakes suggest that brittle faulting is present in the shallow lunar crust. The main component of the lunar crust, plagioclase, shows velocity-strengthening behavior in the range of crustal temperatures. Chang'e 5 samples of lunar regolith show a mineral composition almos...

Carbon dioxide (CO2) and hydrogen (H2) can be symbiotically stored in coal seams, as an effective method for storing H2 to facilitate the transition from fossil-based energy systems to renewable sources and for sequestering growing amounts of captured CO2 to meet carbon neutrality goals. The key challenge in this process lies in determining the int...

Fluid overpressure from the water released by subducted sediments and oceanic crust is an important mechanism for generating earthquakes via brittle failure and frictional instability. If unstable, such fault materials may also host diverse fault reactivation mechanisms from slow slip events to moderate-sized earthquakes in cold subduction zones. W...

The heterogeneity of the mineral grain structure and presence of pre-existing flaws significantly impacts fracture propagation within amorphous crystalline rocks. We explore the macro-mechanical response derived from microfracture evolution for fluid-driven fracturing (hydraulic fracturing) in a granite with pre-existing flaws. We introduce a hydro...

Understanding the flow and transport characteristics and mechanisms of CO2 in water-saturated carbonate gas reservoirs is crucial for enhancing CH4 recovery and CO2 sequestration. We developed a multiphase multicomponent numerical model for gas and water phases, which considers the multiple transport mechanisms between CO2-CH4 and CO2-water and cou...

Here we define and report the relationship between the maximum seismic magnitude (M) and injection volume (ΔV) through fluid-injection fault-reactivation experiments and analysis. This relationship incorporates the in situ shear modulus (G) and fault pre-stress as a fraction of the strength drop (c), expressed as M = c/(1-c) GΔV. Injection response...

Hydraulic fracturing then fluid circulation in enhanced geothermal system (EGS) reservoirs have been shown to induce seismicity remote from the stimulation – potentially generated by the distal projection of thermoporoelastic stresses. We explore this phenomenon by evaluating stress perturbations resulting from stimulation of a single stage of hydr...

Epidote is a common hydrous mineral present in subduction zones subject to greenschist metamorphic conditions – and potentially an important control on the fault stability-instability transition observed under greenschist facies. We explore controls on this transition through shear experiments on simulated epidote gouge at temperatures of 100–500 °...

This paper presents a new five-step method to evaluate shale gas formations with intricate pore networks. The method overcomes challenges posed by traditional workflows through an improved workflow and a new unconventional petrophysical model: (a) the new model accurately defines components of shale gas formations, including effective and isolated...

We exploit nonlinear elastodynamic properties of fractured rock to probe the micro‐scale mechanics of fractures and understand the relation between fluid transport and fracture aperture under dynamic stressing. Experiments were conducted on rough, tensile‐fractured Westerly granite subject to triaxial stresses. We measure fracture permeability for...

As a particularly common mineral in granites, the presence of feldspar and feldspar‐chlorite gouges at hydrothermal conditions has important implications in fault strength and reactivation. We present laboratory observations of frictional strength and stability of feldspar (K‐feldspar and albite) and feldspar‐chlorite gouges under conditions repres...

Fracture/fault instability induced by fluid injection in deep geothermal reservoirs could not only vary the reservoir permeability but also trigger hazardous seismicity. To address this, we conducted triaxial shear experiments on granite fractures with different architected roughnesses reactivated under fluid injection, to investigate the controls...

Typical in the development of enhanced geothermal systems (EGS), fluid injection for hydraulic stimulation and fracturing hosts the potential for induced seismicity by reactivating deep faults. We use granite cores from the Pohang EGS site in low velocity shear experiments on simulated fault gouges at confining stresses of 110 MPa, temperatures of...

We investigate the transport properties of CO2-CH4 under high pressure conditions in both dry and variably saturated porous and fractured carbonates containing native H2O and CH4. The specific focus is on determining optimal CO2 injection rates for maximizing CH4 recovery. A series of experiments involving fluid displacement at the core scale is co...

Epidote and chlorite are both low-grade metamorphic minerals that are widely distributed in deep granite geothermal reservoirs. Hot fluid circulation promotes the precipitation of epidote and chlorite coatings on natural faults and fractures and this can in turn exert control on fault/fracture frictional stability. We use simulated epidote/chlorite...

Fluid-induced shear reactivation of pre-stressed faults poses a project terminating risk during reservoir stimulation in geothermal, CO2 sequestration, wastewater disposal injection and hydraulic fracturing operations. Micro-earthquakes (MEQs) can be tolerated but fluid injection is capable of triggering large earthquakes that can cause major damag...

Microbially-induced calcium carbonate precipitation (MICP) is favored over traditional grouts for remediating fine rock fractures due to its water-like viscosity. We quantitatively investigate the spatial distribution and sealing efficiency of microbially-mediated CaCO3 precipitation for horizontal-flow MICP-grouting in both horizontal (HHF) and ve...

CO2 injection is a promising technology for enhancing gas recovery (CO2-EGR) that concomitantly reduces carbon emissions and aids the energy transition, although it has not yet been applied commercially at the field scale. We develop an innovative workflow using raw data to provide an effective approach in evaluating CH4 recovery during CO2-EGR. A...

We explore the dynamics of gas sorption and diffusion in coal in impacting key mechanisms controlling coal and gas outburst phenomena. We apply a unique time-resolved technique to examine millisecond-resolved gas transport kinetics of CO2 and CH4. In particular, we define gas transport response for two distinct coals: one outburst-prone (JH) and th...

Laumontite is a common and potentially frictionally unstable hydrothermal alteration product present in deep faults of the Gonghe EGS reservoir. We characterize the friction‐stability characteristics of synthetic laumontite gouge under in situ reservoir conditions. The pure laumontite gouge is frictionally strong (μ = 0.73–0.98) and the quartz/laum...

Induced seismicity triggered during hydraulic fracturing for shale gas exploitation in the Sichuan Basin has aroused wide public concern with these earthquakes closely correlated with the reactivation of faults within the reservoir. The target shale reservoirs in the Sichuan Bain are currently located in the Longmaxi formation. To explore instabili...

We explore the controls of stress magnitude and orientation relative to bedding on the resulting morphology/topology of hydraulic fractures using a combined finite-discrete element method (FDEM). Behavior is shown conditioned by the ratio of principal stresses \(\lambda ={\sigma }_{3}/{\sigma }_{1}\) and relative inclination of the bedding. When th...

Sand screenout, the most frequent incident during hydraulic fracturing, is one of the major threats to operational safety and efficiency. Screenout occurs when advancing hydraulic fractures are blocked by injected proppant-slurry, stall, and develop fluid overpressure. Because massive wells are still being hydraulically fractured every year, operat...

We link changes in crustal permeability to informative features of microearthquakes (MEQs) using two field hydraulic stimulation experiments where both MEQs and permeability evolution are recorded simultaneously. The Bidirectional Long Short-Term Memory (Bi-LSTM) model effectively predicts permeability evolution and ultimate permeability increase....

(Free Access before February 14, 2024) (https://authors.elsevier.com/a/1iK0m1H%7Ec%7ELlpw) Storing CO2 in shale formations is an essential complement to the resources of geological CO2 sequestration and the achievement of carbon neutrality. However, previous estimations have reported significant discrepancies in estimating CO2 storage resources. T...

Understanding the physical mechanisms which link fluid injection with triggered earthquakes is critical in minimizing hazard in subsurface fluid‐injection operations. Currently, injection‐induced changes in effective stress on faults are considered as the main criterion in triggering seismic fault slip. However, rate of change in effective stress,...

As a particularly common minerals in granites, the presence of feldspar and altered feldspar-chlorite gouges at hydrothermal conditions have important implications in fault strength and reactivation. We present laboratory observations of frictional strength and stability of feldspar (K-feldspar and albite) and altered feldspar-chlorite gouges under...

We explore the impacts of stress-and fluid-pressure-driven frictional slip on variably roughened faults in Gonghe granite (Qinghai Province, China). Slip is on an inclined fault under simple triaxial stresses with concurrent fluid throughflow allowing fault permeability to be measured both pre-and post-reactivation. Under stress-drive, smooth fault...

Hydraulic fracturing pressure is one of the key criteria in defining the pumping schedule and in dimensioning surface plants for fracturing operations. However, it is difficult to predict at a practical field scale due to the complex determining factors, involving geological, hydrodynamic and rock mechanical parameters. This study proposes a synthe...

(Free sharing link before December 16, 2023 https://authors.elsevier.com/a/1h%7E%7EB4s9Hw9t60) Storing CO 2 and H 2 in underground reservoirs represents an effective approach to sequester increasing amounts of captured CO 2 for carbon neutrality and to store H 2 to promote clean energy revolutions. However, commercial/pilot-scale CO 2 /H 2 storage...

Plain Language Summary Earthquakes begin and propagate within the fluid‐saturated rocks of Earth's crust. Many investigators have suggested that high pore fluid pressure (Pp) is essential for slow earthquakes and tremor. These studies rely on the idea that changes in Pp can impact rupture propagation speed by dilatant volume increase during faultin...

Nanodarcy level permeability measurements of porous media, such as nano-porous mudrocks, are frequently conducted with gas invasion methods into granular-sized samples with short diffusion lengths and thereby reduced experimental duration; however, these methods lack rigorous solutions and standardized experimental procedures. For the first time, w...

As a particularly common minerals in granites, the presence of feldspar and altered feldspar-chlorite gouges at hydrothermal conditions have important implications in fault strength and reactivation. We present laboratory observations of frictional strength and stability of feldspar (K-feldspar and albite) and altered feldspar-chlorite gouges under...

The impact of loading rate is a vital issue in the study of the time-dependent behavior of rock masses. A sample containing a single inclined joint is represented by the particle flow code and used as an analog to examine the rate-dependent behavior of jointed rock. A series of numerical triaxial compression tests are completed at various loading r...

Identifying changes in coal permeability with gas pressure and accurately codifying mean effective stresses in laboratory samples are crucial in predicting gas-flow behavior in coal reservoirs. Traditionally, coal permeability to gas is assessed using the steady-state method, where the equivalent gas pressure in the coal is indexed to the average o...

Controls on fluid transfer into massive hydraulic fractures are investigated due to reactivation of, and proppant penetration into, oblique fractures transecting the main fracture face during long-term reservoir depletion through tightly constrained laboratory experiments. Permeability evolution of fracture-contained proppant permeability/conductiv...

Understanding and mitigating fluid-injection-induced-seismicity is a key need in the routine implementation of net-zero-carbon energy (CCS, geothermal) and other industrial operations (hydraulic fracturing, subsurface wastewater disposal). We directly constrain the impact of pre-existing critical stresses on the relation linking seismic moment to i...

Ground-surface accelerations warn of incipient natural hazards—but threshold criteria remain indistinct. We use a model of localizing deformation within a encapsulating compliant halo to accurately project time-to-failure and to discriminate between ultimate stable and unstable rupture. A heterogeneous distribution of displacement histories and rel...

Multi-seam mining often leads to the retention of a significant number of coal pillars for purposes such as protection, safety, or water isolation. However, stress concentration beneath these residual coal pillars can significantly impact their strength and stability when mining below them, potentially leading to hydraulic support failure, surface...

The occurrence of dangerous coal and gas outbursts seriously threaten safety in underground coal mining. Thus, defining the spatio-temporal evolution of the mechanisms that contribute to these outbursts is of great significance in defining optimal countermeasures for outburst prevention. A dynamic system-based mechanism of coal and gas outbursts is...

Layered and heterogenous fissured rock masses are ubiquitous in nature. Fissures exert significant influence as release surfaces and nucleation sites for failure in layered rock masses. However, key mechanisms controlling microcrack initiation and extension in layered and heterogenous rock masses remain unclear. We complete a suite of numerical (gr...

This study presents a new data-driven approach to interpreting fracture evolutions by analyzing the dynamic matching between proppant injection and fracture propagation. Proppant settling in low-viscosity fluids accumulates at the bottom of the fracture, compresses the flowing channel, and increases the net pressure in fractures due to increasing f...

In this study, we conduct laboratory experiments reproducing fracture slip on both propped and unpropped fractures in Marcellus shale to explore the role of shear deformation as a primary control on permeability evolution and its correlation with initial stress state, shear stress magnitude and loading rate, and proppant loading concentration. For...

The Gonghe Basin in northwest China has significant potential for the recovery of deep geothermal fluids. However, a large number of earthquakes were observed during stimulation by hydraulic fracturing with the maximum magnitude reaching ~ M L 2. To understand the mechanisms of deep fault stability and the clusters of earthquakes, we recovered seve...

Earthquakes are destructive natural hazards with damage capacity dictated by rupture speeds. Traditional dynamic rupture models predict that earthquake ruptures gradually accelerate to the Rayleigh wave speed with some of them further jumping to stable supershear speeds above the Eshelby speed (~2\documentclass[12pt]{minimal} \usepackage{amsmath} \...

Pore fluids are ubiquitous throughout the lithosphere and are commonly cited as the cause of slow-slip and complex modes of tectonic faulting. We investigate the role of fluids for slow-slip and the frictional stability transition and find that the mode of fault slip is mainly unaffected by pore pressures. We shear samples at effective normal stres...

Measurements of coal permeability are normally analyzed without considering the interaction among microfracture and pore size distributions within the sample (control volume). Without this inclusion, nearly all permeability predictions are monomodal as reported in the literature. However, experimental observations are multimodal for most cases. In...

Fluid injection into enhanced geothermal system (EGS) reservoirs can reactivate subsurface fractures/faults and trigger earthquakes—requiring that frictional stability and permeability evolution characteristics are adequately evaluated. This behavior potentially becomes more complicated when the impacts of temperature and cycled thermal stresses, a...

The significant effect of gas sorption induced swelling on shale permeability has been observed through laboratory measurements and explained through permeability models over the past decades. However, there are lab observations that cannot be explained by these models. This knowledge gap prompts this review. Our goal is to form perspectives on how...

Coal permeability is significantly affected by the multi-scale pore-fracture size distribution. More importantly, the pore-fracture size is changed by the effective stress, swelling/shrinkage under the influence of gas sorption, and different flow mechanisms. In conventional dual-porosity models, these effects are normally studied separately and th...

Nano-darcy level permeability measurements of porous media, such as nano-porous mudrocks, are only practically feasible with gas invasion methods into granular-sized samples with short diffusion lengths and thereby reduced experimental duration; however, these methods lack rigorous solutions and standardized experimental procedures. For the first t...

Proppant is often used to enhance reservoir stimulations, such as hydraulic fracturing and hydraulic shearing; however, the influence of proppant on the shear deformation of fractures and the potential consequent-induced earthquakes are rarely explored. We explore the systematics of frictional behavior, deformability and dilatancy of proppant-fille...

Fluid injection-triggered seismicity has increased dramatically over the last decade with elevated pore fluid pressures acting as a prime culprit. Thus, understanding the effect of pore fluid pressure on the mechanical and hydrologic behavior of fractures and faults will illuminate the contributing and dominant physical processes. We present concur...