Hydraulic Containment Research Articles

Extended finite element-based cohesive zone method for modeling simultaneous hydraulic fracture height growth in layered reservoirs

In this study, a fully coupled hydromechanical model within the extended finite element method (XFEM)-based cohesive zone method (CZM) is employed to investigate the simultaneous height growth behavior of multi-cluster hydraulic fractures in layered porous reservoirs with modulus contrast. The coupled hydromechanical model is first verified against an analytical solution and a laboratory experiment. Then, the fracture geometry (e.g. height, aperture, and area) and fluid pressure evolutions of multiple hydraulic fractures placed in a porous reservoir interbedded with alternating stiff and soft layers are investigated using the model. The stress and pore pressure distributions within the layered reservoir during fluid injection are also presented. The simulation results reveal that stress umbrellas are easily to form among multiple hydraulic fractures’ tips when propagating in soft layers, which impedes the simultaneous height growth. It is also observed that the impediment effect of soft layer is much more significant in the fractures suppressed by the preferential growth of adjoining fractures. After that, the combined effect of in situ stress ratio and fracturing spacing on the multi-fracture height growth is presented, and the results elucidate the influence of in situ stress ratio on the height growth behavior depending on the fracture spacing. Finally, it is found that the inclusion of soft layers changes the aperture distribution of outmost and interior hydraulic fractures. The results obtained from this study may provide some insights on the understanding of hydraulic fracture height containment observed in filed.

Hydraulic containment of TCE contaminated groundwater using pulsed pump-and-treat: Performance evaluation and vapor intrusion risk assessment

Remedial actions for groundwater contamination such as containment, in-situ remediation, and pump-and-treat have been developed. This study investigates the hydraulic containment of Trichloroethylene (TCE) contaminated groundwater by using pulsed pump-and-treat technology. The hypothetical research site assumed the operation of pulsed pump-and-treat to manage groundwater contaminated with 0.1 mg/L of TCE. at the pump-and-treat facility. Numerical models, employing MODFLOW and MT3DMS for groundwater flow and contamination simulations, were used for case studies to evaluate the performance and risks of pump-and-treat operation strategies. Evaluation criteria included capture width, removal efficiency, and contaminant leakage. Health risks from TCE leakage were assessed using a vapor intrusion risk assessment tool in adjacent areas. In the facility-scale case study, the capture width of the pump-and-treat was controlled by pumping/injection well operations, including schedules and rates. Pumping/injection well configurations impacted facility efficiencies. Pulsed operation led to TCE leakage downstream. Site-scale case studies simulated contaminant transport through pump-and-treat considering various operation stages (continuous; pulsed), as well as various reactions of TCE in subsurface environment (non-reactive; sorption; sorption and biodegradation). Assuming non-reactive tracer, TCE in groundwater was effectively blocked during continuous operation stage but released downstream in the following pulsed operation stage. Considering chemical reactions, the influences of the pump-and-treat operation followed similar trends of the non-reactive tracer but occurred at delayed times. Groundwater contamination levels were reduced through biodegradation. Cancer and non-cancer risks could occur at points of exposure (POEs) where the contamination levels approached or fell below TCE groundwater standards.

Comparing single and multiple objective constrained optimization algorithms for tuning a groundwater remediation system

Groundwater flow and particle tracking models are critical tools to simulate the natural system, contaminant fate and transport, and effects of remediation. Constrained optimization uses models to systematically explore the interplay between remedial design and contaminant fate, considering uncertainty. Sequential Linear Programming (SLP) provides a design alternative addressing a single goal (e.g. maximum hydraulic containment, maximum mass removal). Multi-objective algorithms like Nondominated Sorting Genetic Algorithm (NSGA-II) explore the tradeoffs among such objectives and more (e.g. cost, public-supply well contamination). We explore both approaches at a contaminated site in Long Island, New York USA. We compare the algorithms and ramifications on results. NSGA-II explores, at additional computational cost, explicit tradeoffs among multiple objectives, providing additional insights relative to SLP. The NGSA-II algorithm allows for graphical consideration of three objectives. SLP decision variables often settle at predetermined bounds. Bounds assignment thus differs from parameter estimation; bounds must be acceptable rather than safeguards.

Geomechanical insights on the importance of mechanical stratigraphy to hydraulic fracture containment

Geomechanical insights on the importance of mechanical stratigraphy to hydraulic fracture containment

Laboratory demonstration of the impact of weak interfaces and layered rock properties on hydraulic fracture containment and height growth

Hydraulic fracturing and waterflooding are both widely applied methods for improving the recovery of oil and gas resources. These methods have increasing commonality because many waterfloods are being carried out at high enough pressure to generate hydraulic fractures. Even so, it is challenging for engineers to make an optimal wellbore pressure design for layered and otherwise complex underground formations. An overly aggressive injection pressure may lead to uncontrollable fracture height growth into non-producing layers adjacent to the reservoir. In contrast, when using classical but highly simplified height growth models, the pressure limits can be far too conservative which may lead to lower recovery rates and inefficient use of resources invested in developing producing reservoirs. Therefore, it is necessary to investigate the mechanism of fracture height growth while considering the coupling effect from multiple dominated factors. This research contributes an experimental approach to evaluating the role of stresses, weak interfaces, and mechanical properties of a three-layer system in promoting or containing hydraulic fracture height growth from a central reservoir into neighboring barrier layers. In all cases, the experiments agree that the pressure required to induce substantial height growth exceeds the stress applied to the barrier layers and is far above classical predictions. Additionally, when the reservoir layer is softer than the barriers, the containment is sustained to even higher pressures than for layers with similar material properties. Finally, the experiments show that permeability of the barrier layer can induce a more sudden transition to uncontrolled height growth when fracture reaches the bedding interfaces. Hydraulic fracture height growth is mitigated by weak interfaces between layers. Unstable height growth typically requires fluid pressure to exceed the in-situ stress in the bounding layer(s). Contrasting layer stiffness and permeability often leads to further mitigation of height growth.

Semipermeable membrane behavior of geosynthetic clay liners

The focus of this paper is on providing an overview of the results of the nearly 20 years of research related to the discovery, examination, and potential benefits of semipermeable membrane behavior of bentonite-based geosynthetic clay liners (GCLs) commonly used as barriers or components of barriers in a variety of hydraulic and chemical containment applications, such as water and chemical retention ponds, tailings and coal ash impoundments, and solid waste landfills. First, the concept of solute restriction underlying semipermeable membrane behavior and the development of a solute-restriction or membrane efficiency coefficient (ω) and chemico-osmosis (q π) are described. Second, previously measured values of ω are presented for clays and GCLs for the purpose of illustrating the physical and chemical factors affecting ω. Third, the potential benefits of both ω and q π in terms of hydraulic and chemical containment applications are illustrated, and the relative importance of ω versus q π is described. Finally, some of the remaining issues related to the semipermeable membrane behavior of GCLs, such as the uniqueness of the measured ω and the persistence of ω at high salt concentrations, are discussed.

Effect of stress and material barriers on hydraulic fracture height containment in layered formations

Effect of stress and material barriers on hydraulic fracture height containment in layered formations

The Impact of Layering and Permeable Frictional Interfaces on Hydraulic Fracturing in Unconventional Reservoirs

Summary The impacts of formation layering on hydraulic fracture containment and on pumping energy are critical factors in a successful stimulation treatment. Conventionally, it is considered that the in-situ stress is the dominant factor controlling the fracture height. The influence of mechanical properties on fracture height growth is often ignored or is limited to consideration of different Young’s moduli. Also, it is commonly assumed that the interfaces between different layers are perfectly bounded without slippage, and interface permeability is not considered. In-situ experiments have demonstrated that variation of modulus and in-situ stress alone cannot explain the containment of hydraulic fractures observed in the field (Warpinski et al. 1998). Enhanced toughness, in-situ stress, interface slip, and energy dissipation in the layered rocks should be combined to contribute to the fracture containment analysis. In this study, we consider these factors in a fully coupled 3D hydraulic fracture simulator developed based on the finite element method. We use laboratory and numerical simulations to investigate these factors and how they affect hydraulic fracture propagation, height growth, and injection pressure. The 3D fully coupled hydromechanical model uses a special zero-thickness interface element and the cohesive zone model (CZM) to simulate fracture propagation, interface slippage, and fluid flow in fractures. The nonlinear mechanical behavior of frictional sliding along interface surfaces is considered. The hydromechanical model has been verified successfully through benchmarked analytical solutions. The influence of layered Young’s modulus on fracture height growth in layered formations is analyzed. The formation interfaces between different layers are simulated explicitly through the use of the hydromechanical interface element. The impacts of mechanical and hydraulic properties of the formation interfaces on hydraulic fracture propagation are studied. Hydraulic fractures tend to propagate in the layer with lower Young’s modulus so that soft layers could potentially act as barriers to limit the height growth of hydraulic fractures. Contrary to the conventional view, the location of hydraulic fracturing (in softer vs. stiffer layers) does affect fracture geometry evolution. In addition, depending on the mechanical properties and the conductivity of the interfaces, the shear slippage and/or opening along the formation interfaces could result in flow along the interface surfaces and terminate the fracture growth. The frictional slippage along the interfaces can serve as an effective mechanism of containment of hydraulic fractures in layered formations. It is suggested that whether a hydraulic fracture would cross a discontinuity depends not only on the layers’ mechanical properties but also on the hydraulic properties of the discontinuity; both the frictional slippage and fluid pressure along horizontal formation interfaces contribute to the reinitiation of a hydraulic fracture from a pre-existing flaw along the interfaces, producing an offset from the interception point to the reinitiation point.

Hydrologic evaluation of a poplar phytoextraction system

This paper reports the results of a seven-year study of a phytoremediation system consisting of 349 hybrid poplars (Populous deltoids x Populus nigra ‘DN-21’) that were emplaced to reduce the migration of impacted groundwater toward a nearby stream. For the relatively small tree stand, the achievement of hydraulic containment was challenged by several factors, including topographic constraints on tree placement, spatial heterogeneity in depth-to-groundwater, and lack of controls on surface runoff. However, the interpretation of measured diurnal water table fluctuations indicated substantial and increasing levels of groundwater extraction, consistent with poplar sap flow measurements collected during two growing seasons. The project also provided unique educational experiences for undergraduate and graduate students from multiple academic disciplines who participated in monitoring, site maintenance, and data interpretation. Novelty statement The paper adds to the limited literature on poplar-based phytoextraction of contaminated groundwater by describing a seven-year case study with detailed hydrologic measurements. Novel elements include (1) a very large data set of poplar sap flow measurements that provides insight into potential spatial and temporal variability, and (2) a detailed application of an under-utilized analytical tool (water table fluctuations) to evaluate hydraulic capture.

The Influence of Mixing Orders on the Microstructure of Artificially Prepared Sand‐Clay Mixtures

The mixing order of silica sand, clay (kaolinite), and water controls the microstructure of resulting artificial soil samples. Most homogeneous microstructures can be achieved by applying the mixing order “sand‐water‐clay.” The following methods were used to validate this statement: (1) optical observation, (2) X‐ray tomography, (3) scanning electron microscopy, and (4) Mercury intrusion porosimetry. For all samples, clays are mainly organized in a homogeneous matrix but are also dispersed heterogeneously in micrometer‐sized layers surrounding sand particles, particularly where sand grains show a greater roughness. At water contents ≥1.5 wL, the microstructures are visually similar from the mm to μm scale whatever mixing order is used. However, for water contents lower than 1.5 wL, the mixing order controls the distribution of the clay particles. This paper proposes a motivated choice of a preparation protocol of artificial clayey materials to be used in laboratory experiments. It might contribute to better understanding and modeling grain movements and arrangements in artificial muds, used for instance in underground mining, foundation settlement, hydraulic containment, road construction, soil stabilization, and in natural soils in the occurrence of soil liquefaction, industrial brick manufacturing, and in studying shear processes in tectonic fault zones.

Hybrid Sorbents for 129I Capture from Contaminated Groundwater.

Radioiodine (129I) poses a risk to the environment due to its long half-life, toxicity, and mobility. It is found at the U.S. Department of Energy Hanford Site due to legacy releases of nuclear wastes to the subsurface where 129I is predominantly present as iodate (IO3-). To date, a cost-effective and scalable cleanup technology for 129I has not been identified, with hydraulic containment implemented as the remedial approach. Here, novel high-performing sorbents for 129I remediation with the capacity to reduce 129I concentrations to or below the US Environmental Protection Agency (EPA) drinking water standard and procedures to deploy them in an ex-situ pump and treat (P&T) system are introduced. This includes implementation of hybridized polyacrylonitrile (PAN) beads for ex-situ remediation of IO3--contaminated groundwater for the first time. Iron (Fe) oxyhydroxide and bismuth (Bi) oxyhydroxide sorbents were deployed on silica substrates or encapsulated in porous PAN beads. In addition, Fe-, cerium (Ce)-, and Bi-oxyhydroxides were encapsulated with anion-exchange resins. The PAN-bismuth oxyhydroxide and PAN-ferrihydrite composites along with Fe- and Ce-based hybrid anion-exchange resins performed well in batch sorption experiments with distribution coefficients for IO3- of >1000 mL/g and rapid removal kinetics. Of the tested materials, the Ce-based hybrid anion-exchange resin was the most efficient for removal of IO3- from Hanford groundwater in a column system, with 50% breakthrough occurring at 324 pore volumes. The functional amine groups on the parent resin and amount of active sorbent in the resin can be customized to improve the iodine loading capacity. These results highlight the potential for IO3- remediation by hybrid sorbents and represent a benchmark for the implementation of commercially available materials to meet EPA standards for cleanup of 129I in a large-scale P&T system.

Lattice simulation of hydraulic fracture containment in the North Perth Basin

The results of numerical simulations of hydraulic fracturing based on the concept of lattice, a grain based method, are presented. Five cases of numerical simulations were conducted to analyze the effects of changing rock properties and in-situ stresses on hydraulic fracture propagation and its containment. The study was done based on the data from one of the shale gas wells in the North Perth Basin (NPB) in Western Australia and the hydraulic fracturing lab experimental data on a 50 mm cubical sample. The hydraulic fracturing initiates and propagates within Carynginia Formation surrounded by the Irwin River Coal Measures (IRCM) Formation from the top and Kockatea Formation at the base. The lab experiments were upscaled to both intermediate and field scales to simulate fracture propagation in the viscosity dominated regime. Penetration parameters, including the depth and area of the fracture crossing the interface, were proposed to characterize fracture containment capacity. It was observed that the fracture is contained by both IRCM and Kockatea Formations due to the large contrast between the minimum horizontal stresses in these layers and that of the Carynginia formation. However, as quantified by the penetration parameters, the fracture propagates more easily into the IRCM Formation with higher brittleness than Carynginia Formation. Kockatea Formation with lower brittleness than that of Carynginia Formation inhibits vertical migration of the fracture, i.e. results in more visible fracture containment. The results suggest that decrease in rock brittleness inhibits fracture propagation and lower minimum horizontal stress contrast leads to fracture containment.

How Can We Make Pump and Treat Systems More Energetically Sustainable?

Pump and treat (P&T) systems are still widely employed for the hydraulic containment of contaminated groundwater despite the fact that their usage is decreasing due to their high operational costs. A way to partially mitigate such costs, both in monetary and environmental terms, is to perform heat exchange (directly or with a heat pump) on the groundwater extracted by these systems, thus providing low-carbon and low-cost heating and/or cooling to buildings or industrial processes. This opportunity should be carefully evaluated in view of preserving (or even improving) the removal efficiency of the remediation process. Therefore, the heat exchange should be placed upstream or downstream of all treatments, or in an intermediate position, depending on the effect of water temperature change on the removal efficiency of each treatment step. This article provides an overview of such effects and is meant to serve as a starting reference for a case-by-case evaluation. Finally, the potentiality of geothermal use of P&T systems is assessed in the Italian contaminated Sites of National Interest (SIN), i.e., the 41 priority contaminated sites in Italy. At least 29 of these sites use pumping wells as hydraulic barriers or P&T systems. The total discharge rate treated by these plants exceeds 7000 m3/h and can potentially provide about 33 MW of heating and/or cooling power.

Evaluating a Simple Fracturing Criterion for a Hydraulic Fracture Crossing Stress and Stiffness Contrasts

Hydraulic fracture height containment is a critical issue in the development of unconventional reservoirs. The extent of fracture height growth depends on a variety of factors, particularly stress and stiffness contrasts between adjacent layers. Accurate simulation of fracture growth and containment requires a reliable fracturing criterion. The virtual crack closure technique (VCCT) is a widely used method for computing energy release rate. However, it is based on the assumption that a small crack extension does not significantly alter the state of the crack tip, which is generally not the case when a fracture crosses strong stress and/or stiffness contrasts. In this work, we assess the applicability and accuracy of a modified virtual crack closure technique (MVCCT) for a fluid-driven fracture in breaking through interfaces with significant stress and/or stiffness contrasts, through comparisons with analytical and reference numerical solutions. The results show that significant error could occur when the fracture tip is very near or at stress/stiffness interfaces. However, this error is localized to the interface and proves to be inconsequential to the predicted penetration depth into the rock layer beyond the interface. This study validates the applicability of MVCCT in 3D hydraulic fracturing simulation in strongly heterogeneous rock formations.

What we know, what we don’t know, and things we do not know we don’t know about hydraulic fracturing in high stress environments

Hydraulic fracturing in many Australian Basins, particularly the Cooper Basin has been successful in higher permeability, structured conventional plays. However, adaptation of North American strategies to Australia’s complex, and highly stressed unconventional areas has resulted in less than adequate performance to progress further investment into widespread development these resources. This presentation will explore the obvious differences between Australian and North American stress settings, and the problems manifested by those differences in hydraulic fracture containment and behaviour. Further, as more unconventional targets are attempted, complementary strategies need to be considered based on fundamental geomechanical principles, relative to these basinal environments. This presentation will explore several problems, emerging potential solutions, and areas of ongoing research with the purpose of aiding Australia to tap into a vast supply of potential unconventional resources, which are currently under-appraised.

Effect of in-situ stress contrast on fracture containment during single- and multi-stage hydraulic fracturing

Hydraulic fracture containment behaviour under varying in-situ stress conditions was studied for single- and multi-stage hydraulic fracturing using a fully coupled hydro-mechanical model. Single-stage fracturing under varying and non-varying minor principal stress conditions showed good agreement with the corresponding analytical predictions. Multi-stage fracturing under non-varying stress conditions displayed a strong stress shadow-induced asymmetry of fracture propagation about the injection well. As the fluid pressure dissipation after fracturing in the numerical simulations is assumed to be negligible before the subsequent fracturing stage, it was observed that the fractures can extend even after the actual injection time as a result of the stress shadow generated during subsequent fracturing stages. The stress contrast between adjoining layers and the pay zone was found to be somewhat effective in containing fractures within the pay zone, although the asymmetry of fracture profiles was still apparent. It was also observed that the stress shadow effect is sufficiently significant in some cases that the fractures have the preference to penetrate into higher stress adjoining layers than propagating within the initially lower-stress pay zone, which is generally unfavourable. Fluid injection time was found to have a major influence on overall fracture propagation during multi-stage fracturing and the fractures were observed to be fully and only within the pay zone, delineating the effective containment, for simulations with optimized injection times. In addition, our simulations show that, based on the fact that fractures can be further driven by the stress shadows of subsequent fracturing stages, strategically-selected injection times for each fracturing stage can produce fractures that fully and only occupy the pay zone, which can save a considerable amount of injection fluid. This has direct positive implications for project economics and will help minimize potential issues associated with deep fluid injection, such as groundwater contamination and induced seismicity.

Uncertainty analysis of hydraulic fracture height containment in a layered formation

The prediction of hydraulic fracture height growth is of extreme interest in various engineering practices. To fully understand the dependence of the fracturing height in complex underground geological structures, it is crucial to develop theoretical and numerical hydraulic fracturing models to identify the key variables and their interactions to hydraulic fracture height containment. In this work, we adopt a three-dimensional hydro-mechanical coupling cohesive zone finite element model supported by logging data from a practical engineering project. A novel response surface method with Box–Behnken design is introduced to evaluate the statistical significance of tested variables and to forecast the optimal variable combinations for hydraulic fracture height. The key controlling variables are sorted according to their statistical significance from the analysis of variance, and only the minimum lateral stress ratios in mudstone layer and conglomerate layer are highly statistically significant. The minimum lateral in situ stress contrast is the predominant influence of fracture height containment regarding to their significant negative correlation, while the Young’s modulus contrast is probably not an important parameter in terms of direct control of fracture height. Upon optimization, 41 optimized variable combinations were achieved and could be served as references in regulating this engineering practice or even similar events.

A study on the mechanical interaction between soil and colloidal silica gel for ground improvement

In this paper, we explore the mechanical performance of colloidal silica grout to assess its potential for ground stabilisation and hydraulic barrier formation during decommissioning of major industrially contaminated sites. We consider two colloidal silica -soil systems: sand grouted with colloidal silica and kaolin clay mixed with colloidal silica. The aims of the paper are to evaluate the drained stress-strain behaviour (1-D compression and shear resistance) of colloidal silica-soil systems and to determine the particle interactions between soil and colloidal silica at a micron-scale so as to provide an understanding of the macroscopic mechanical behaviour. Two different colloidal silica-soil interaction mechanisms have been found: formation of a solid, cohesive matrix for the case of grouted sand, and increase of the clustering of clay particles for the case of clay mixtures. This paper illustrates for the first time that even under drained conditions colloidal silica can provide mechanical improvement. Colloidal silica-grouted sand showed an increased stiffness and enhanced peak friction angle, while still having a very low hydraulic conductivity (~10−10 m/s), typical of intact clay. Similarly, clay-colloidal silica mixtures showed reduced volumetric deformation, increased stiffness for low values of stress (~100 kPa), and increases in both the peak and the ultimate shear strength. Our results show that colloidal silica could be deployed in environments where not only hydraulic containment is critical, but where reduced deformation and enhanced resistance to shearing would be beneficial, for example in landfill capping or in the outer fill layers of embankments designed to minimise internal seepage and infiltration.

Lattice simulation of laboratory hydraulic fracture containment in layered reservoirs

Hydraulic fracture containment in layered reservoirs is simulated using a numerical model that couples fluid flow with a lattice representation of the solid with quasi-random distributed nodes connected by springs. We consider the influence of horizontal stress contrasts between layers, vertical stress, material fracture toughness, and the presence of horizontal weak interfaces. Observed results define distinct regions in a parametric space characterized by height growth, containment, and growth along the horizontal weak interface (T-shape growth). These numerical results match well to laboratory experimental benchmarks, and they extend the parametric study beyond what can be considered in the laboratory.

Impact of the anisotropy of fracture toughness on the propagation of planar 3D hydraulic fracture

Sedimentary rocks often exhibit a transverse isotropy due to fine scale layering. We investigate the effect of the anisotropy of fracture toughness on the propagation of a planar 3D hydraulic fracture perpendicular to the isotropy plane: a configuration commonly encountered in sedimentary basins. We extend a fully implicit level set scheme for the simulation of hydraulic fracture growth to the case of anisotropic fracture toughness. We derive an analytical solution for the propagation of an elliptical hydraulic fracture in the toughness dominated regime—a shape which results from a particular form of toughness anisotropy. The developed numerical solver closely matches this solution as well as classical benchmarks for hydraulic fracture growth with isotropic toughness. We then quantify numerically the transition between the viscosity dominated propagation regime at early time—where the fracture grows radially—to the toughness dominated regime at large time where the fracture reaches an elliptical shape in the case of an elliptical anisotropy. The time scale at which the fracture starts to deviate from the radial shape and gets more elongated in the direction of lower toughness is in accordance with the viscosity to toughness transition time-scale for a radial fracture defined with the largest value of fracture toughness. Similarly, the toughness dominated regime is fully reached along the whole fracture front when the time gets significantly larger than the same transition time-scale defined with the lowest value of toughness. Using different toughness anisotropy functions, we also illustrate how the details of the complete variation of fracture toughness with propagation direction governs the final hydraulic fracture shape at large time. Our results highlight toughness anisotropy as a possible hydraulic fracture height containment mechanism as well as the need for its careful characterization beyond measurements in the sole material axes (divider and arrester) directions.