The introduction of any alterations in or around a rock masses physical environment provide for a great variability in its associated properties. These variability’s are one of the key concerns of geological engineers that are particularly interested in understanding subsurface physical and chemical interactions. The askew nature associated with these heterogeneous properties however causes great difficulty in explaining the exact relationships that exist throughout these sub-surface systems by simple means. This is an important aspect of rock mechanics in which its state and condition have the ability to drastically affect the associated parameters between two nearly similar samples of the same rock mass. This again raises another key distinction in the differences of solid rock mass versus that of disturbed rock mass and property. A solid rock mass is considered homogenous with uniform, isotropic properties while a disturbed rock mass may have variation or discontinuity of these properties. Faults, fracture and other discontinuities often form from the introduction of stress changes which alter the in-situ stress distributions around the reservoir and surrounding rock matrix. These stress changes can be induced by natural or man-made means; such as tectonic plate movement or hydraulicfracturing, respectively. The response of the rock matrix relies heavily on the ratios of in-situ stress to induced or applied stresses. This is otherwise known as a stress differential. These stress differentials control the overall response of a material based upon their inherent properties and related behavior. The magnitude of the stress differential is a key parameter in regards to the study of deformation and failure, or more specifically for this research that of fault reactivation as slight fluctuations to the surrounding stress fields may alter stability and thus create a potential for reactivation. In other cases it may take a much larger stress magnitude to reactivate these same areas, however this depends upon their relative state of stress and surrounding environmental conditions.
The objective of this research was met by considering different cases of single, two, and three fractures and quantifying stress variation around the inducedhydraulic fractures through time by studying the unique behavior of Von Mises and principal stresses. Figure 23 describes the transientbehavior of maximum principal and Von Mises stresses in the field. This plot illustrates both maximum principal stress and Von Mises stress depicting similar behavior through time, defining Von Mises stress as an applicable culmination of stresses for analyzing their transient patterns. Figure 23 shows four distinct stress behaviors, seen through the period of injection. At early time, the magnitude of the principal and Von Mises stresses increases rapidly as the injected fluid is starting breaking through the formation and there is a large stress accumulation around the initiated fracture. After analyzing various simulations, it was also observed that at the earlier time of fracture propagation there is a rapid deformation of the solid medium, and the model offers a larger number of solutions due to intensive fracture width and pressure updates values for each time step. Then, the increment between time steps is increasing, and the stress magnitude slows down as the fracture tip is moving away from injection point till it reaches its maximum value at later time, when the stress value at the fracture tip is still very high, and stress profiles at the fracture head are reaching their maximum values while the stress profiles at the fracture tail are also still high ( Figure 24 ). At a later time, there is a decline in stress magnitude due to the injection fluid energy loss and a significant decay in stress values at the fracture tip with stress magnitude finally reaching a constant value at later injection time. Therefore, to avoid stress interference during sequential hydraulicfracturing, it important to monitor the transient principal and Von Mises stressbehavior in the reservoir, and avoid initiating sequential fracture propagation until the stress magnitude in the reservoir, influenced by the previous fracture, reaches a steady state.
1. The force of friction is directly proportional to the applied load. 2. The force of friction is independent of the apparent area of contact.
The coefficient of friction is defined as the ratio of shear to normal stress acting between the surfaces during sliding. Different physical mechanisms are involved in the sliding of rock at various pressures. At low pressure the surfaces can move with respect to one another by lifting over the interlocked irregularities, however, at very high pressure this effect is suppressed and the surfaces then slide by shearing through the irregularities. Based on numerous laboratory experiments on a wide variety of rock types, Byerlee (1978) show that the frictional behavior of rocks could be fit by the following bilinear empirical expression:
The inducedstressfield caused by hydraulicfracturing plays a key role in controlling the formation characteristics of fractures and is the essential prerequisite for optimal design of fracturing parameters. In order to determine the disturbance range of inducedstressfield on fracture morphology, the multiple factors analysis and optimization are an important inspect. Setting the inducedstress control range (ISCR) as the evaluation objective, it can be defined as the combined response of the peak value of inducedstress difference and stress steering distance, taking them as double evaluation indexes. Six uncertain fracture param- eters with a reasonable range are used to fit the response of evaluation indexes. Through the finite element numerical simulation method, the inducedstressfield around the fractures can be calculated and the evaluation indexes are described quantitatively. Applying the multi-factor orthogonal test method, combined the matrix analysis model with the fuzzy comprehensive evalua- tion model, these fracture parameters are evaluated and optimized. The results show that the influence factors on the ISCR in the descending order are determined as follows: fracture height, fracture net pressure, Poisson’s ratio, maximum and minimum horizontal stress ratio, fracture spacing and its number. According to the multi-factors sensitivity analysis results, the selected levels of different factors are optimized and the combination of parameters optimization is screened out. It provides a theoretical basis to control the reservoir stressfield for the optimization of the fieldfracturing treatment.
as many of the items connect to multiple topics. Below is a non-ex- haustive list of possible impacts/issues which may be considered in the technical reports. While the IA has been developed to focus on High Volume HydraulicFracturing (HVHF) in Michigan (defined by the Michigan Department of Environmental Quality as hydrau- lic fracturing activity intended to use a total of more than 100,000 gallons of hydraulicfracturing fluid), data and analyses may cover a range of activity depending on topic or issue.
We model the decision to ban fracking as an irreversible decision in a context of uncertainty and learning for three reasons. First, in practice, fracking is a relatively new technology and little is known about it 11 . This uncertainty becomes resolved over time as the industry learns best practices, as municipalities learn how to regulate, as the public becomes familiar with the technology, and as the body of scientific analysis grows. Second, the decision to frack for most policymakers today is irreversible. Many of the potential damages associated with fracking (e.g., groundwater contamination) can have irreversible consequences and once fracking is allowed, the industry will resist rule changes after investing in a jurisdiction 12 . Irreversibility aligns our finite horizon dynamic model with the QOV literature, though uncertainty is never completely resolved. Third, fracking moratoria have been successfully enacted or adopted in the US, at both the state and local levels, as well as internationally. These temporary bans represent a delay in an irreversible action and allow the decision to be revisited in the future. The QOV approach to environmental problems says that uncertainty that resolves over time, potentially irreversible environmental damage, and the ability to postpone the decision lead to an additional benefit of delaying a project. In this case, even when the expected net present value of undertaking a project is positive, it may be economically optimal to delay the project and revisit the decision with better information. This model allows us to quantify the value of learning in the context of local fracking decisions and to present a positive economic analysis of its effects on local policy.
has become one of the most attractive regions for shale gas exploration in Eu- rope. Throughout the period 2010–2015, 72 exploratory drillings were made (as of 4.01.2016), while hydraulicfracturing was carried out 25 times. Employing new drilling and shale gas prospecting technologies raises a question pertaining to their impact on the environment. The number of chemical compounds used (approxi- mately 2000) for the production of new technological fluids may potentially pollute the environment. The fact that the composition of these fluids remains undisclosed hinders the assessment of their impact on the environment and devising optimal methods for managing this type of waste. The presented work indicates the chemical compounds which may infiltrate to groundwater, identified on the basis of techno- logical fluids characteristics, as well as the review of studies pertaining to their im- pact on potable water carried out in the United States. The study focused on marking heavy metals, calcium, sodium, magnesium, potassium, chlorides and sulphates in the surface waters collected in proximity of Lewino well.
Hydraulicfracturing has become one of the major problems in rock fill dam, since it plays a significant role in the initiation and extension of cracks in the clay core. Hydraulicfracturing may occur in the upstream face of clay core of a rock fill dam in the case the vertical effective stress in the core is reduced to levels that are small enough to allow tension fracture to occur. This situation may arise if the total stress in the core is reduced by an arching effect where the core settles relatively to the rock fill. Pore water pressure in the core will also increase during impounding, and this will further reduce the effective stress in the core. Wedging due to water pressure may crack the upstream face of clay core. Loftquist indicated that arching in the clay core of a rock fill dam may result in leakage and internal erosion based on his observation on thin impervious cores of the 26m high Holle dam and 34m high Harspranget dam as being as low as half of the normal overburden pressures. The incident in Hyttejuvet dam in Norway that caused unexpected leakage occurred during the first filling of the reservoir, Kjaernsli and Torblaa. Similar incidents for the unusual leakage occurred just before the reservoir became full during the initial filling of Balderhead dam in England reported by Vaughan et al. The failure of Stockton and Wister dams in USA were suspected as being due to hydraulicfracturing, Sherard. An investigation to the leakage that occurred at Viddalsvatn dam in Norway indicated that hydraulic
Advances in high-volume hydraulicfracturing and horizontal drilling techniques require the injection of 10-20 million liters (2-5 million gallons) of fluids at high pressure to fracture the target formation and thus stimulate reservoir permeability. 2-4 Fracture fluid, that is typically composed 98-99% water and sand, 1-2% fracturing chemicals, 2, 5, 6 mixes with the subsurface brine and returns to the surface as produced water. 5, 6 Produced water typically has an elevated total dissolved solids (TDS) concentration that ranges from 5,000 to 300,000 mg/L, 7-9 including high concentrations of sodium, calcium, barium, strontium, chloride, bromide, and naturally occurring radioactive material (NORM). Among the NORM, radium is the most common due to its soluble nature in a large spectrum of pH conditions. 9-11 Moreover, the organic content of produced water can vary greatly by wellsite depending on the additives in the fracturing fluid. Previous results show that organic concentration in produced waters from shale plays can range between 1.2 – 5,804 mg/L TOC. 12, 13 Thus, both fracture fluid and produced water characteristics
`Oil sands' exist in some parts of the world as thick deposits in deep and semi-deep underground layers. For extraction of oil from oil sand deposits, one of the widely used methods, as described above, is hydrofracturing, in which hot water/steam is injected into the wells at a very high rate and temperature. Although sand is a cohesionless material, the viscous bitumen that exists in the porous medium causes the combination of sand and bitumen to behave like a porous rock that may experience fracturing due to high injection pressure. The study of types and patterns of fracture in uncemented oil sand deposits, by means of numerical modeling, is the basic objective of this paper. For decades, petroleum engineers have been de- veloping models for simulating hydraulicfracturing in oil reservoirs. In the early 1960's, the industry felt the need for a design tool for this fast growing technique. In response to this need, a number of two-dimensional (2-D) models were developed for designing hydraulicfracturing treatments. This type of simple closed form solution has been used by the industry with some success; however, as the technology progressed from low volume/rate to high volume/rate treatments in more sophisticated and massive hydraulicfracturing projects, the industry demanded more rigorous design methods in order to minimize costs. In the last 20 years, a number of 2-D and 3-D numerical models have been developed (some of these models will be discussed later). The most common equations used in these numerical models are uid ow and heat transfer equations, which are usually solved iteratively. Geomechanical aspects are incorporated in some of the models, mostly in an uncoupled manner. Mainly vertical or horizontal planar fractures were considered, based on the 2-D closed form solutions mentioned above. The degree of sophistication of these models varies considerably and their results cannot be vali- dated with much condence. The main problem in validating these models is that the conguration of the induced fracture is not really known; therefore, the results of the model are usually evaluated based on uid injection pressure measurements and/or the production history of the well.
Exponent’s Atmospheric Sciences staff has experience serving a wide range of industrial and government clients around the world. Team members have been influential in the evolution of air quality modeling. Exponent scientists have participated in the original development of, or contributed to, five of the seven U.S. EPA models recommended in the Guideline on Air Quality Models. Most notable of these is the CALPUFF model, an advanced non-steady-state meteorological and air quality modeling system recommended by the EPA as the preferred model for assessing long-range transport of pollutants and their impacts on Federal Class I areas or for near-field applications involving complex
Physicians for Social Responsibility (PSR) is concerned about the multiple serious threats to human health posed by hydraulicfracturing. PSR supports a precautionary approach that includes a moratorium on the use of hydraulicfracturing until such time as impartial federal agencies such as the U.S. Environmental Protection Agency develop and implement enforceable rules that provide adequate protection for human health and the environment from fossil fuel extraction processes that use hydraulicfracturing.
of cohesive element to simulate hydraulicfracturing to generate permeable belts, this is vital importance for oil exploration. Due to the property of oil shale, using cohesive element to simulate, it establishes mathematical models for hydraulicfracturing and its fracturing rules. On the condition that injecting high pressure fracturing fluid into pre-crack in oil shale, it conducts the numerical simulation. We can get the rules of stress distribution and pore pressure of oil shale including crack dynamic extension rules, fracturing fluid filtrating loss rules and how the amounts of fracturing fluid injected affects crack extension in the progress of hydraulicfracturing. In the end, the research will offer a theoretical basis and guidance to actual project.
Biocides are used in unconventional oil and gas (UOG) practices, such as hydraulicfracturing, to control microbial growth. Unwanted microbial growth can cause gas souring, pipeline clogging, and microbial induced corrosion of equipment and transportation pipes; UOG operators are using many techniques only because conventional oil and gas operations have used them in the past, and biocide use optimization has not been a priority. Indeed, biocide efficacy has been put into questioned as microbial surveys show an active microbial community in hydraulicfracturing produced and flowback water. Flowback water presents an increased risk to surface aquifers and rivers/lakes near the UOG operations that the conventional oil and gas operations don’t have. Some biocides, and their degradation products, have been highlighted as chemicals of concern for their toxicity towards human and environmental health especially considering UOG operations. The selective antimicrobial pressure they cause has not been seriously considered. This article discusses the potential pathways of environmental biocide exposure, identifies potential risks, and highlights important knowledge gaps that need to be addressed to properly incorporate antimicrobial resistance risk into UOG environmental and health risk assessments.
enjoyment of their properties, emotional distress as to one plaintiff, 7 inconvenience and
discomfort, and personal injury. The complaint also requests punitive damages and preliminary and permanent injunctions against future contamination, as well as reasonable attorneys’ fees. As for discovery, on January 28, 2013, the parties agreed to and the Court signed a Stipulated Case-Management Order that provides deadlines for Phase I discovery which focuses on causation of the alleged contamination or damages to the Price No. 1 well and of the alleged personal injuries suffered by a minor plaintiff. The Court limits and specifically sets out the topics that the parties can cover in their discovery requests. Plaintiffs can request Defendants to provide information about the drilling and construction of the well, including the substances and chemicals used during all phases of development (drilling, casing, cementing, and fracturing), the number of fracturing stages, the depth of each fracturing stage, sources of water, analysis of flowback water, how and where production water was stored, analyses or testing results related to subsurface geology and groundwater migration, and the sampling or testing of produced water, any potable water, and groundwater within 10 miles of the well. Defendants can request medical records, an independent medical examination, analyses and testing of water from any well alleged to be contaminated, construction and maintenance records of the well, and how Defendants’ activities or substances/chemicals caused the injuries alleged.
The surface gradient in the plastic zone is significantly higher than that in the elastic zone with an abrupt change in crack geometry at the elastic plastic interface, which is due to the assumption of rigid-plastic behavior. The pro- nounced deformation in the plastic zone suggests that the stress analysis based on deformed geometry is more realistic. Stressfield in the plastic zone
236 Of the major elements initially present in the shales, Ca was released into the 237 fracturing fluid to the greatest extent. In all experiments the release of Ca was initially 238 rapid, before plateauing at reasonably stable values within 48 h (Figure 1a). The steady- 239 state Ca concentrations differed among the four shales and did not correspond directly to 240 the Ca content of the solid phases. The highest aqueous Ca concentration was recorded 241 for the EF shale, followed by the M, the GR, and finally, the B shales (Figure 1a). Yet, 242 the initial solid Ca content of the GR shale exceeded that of the M shale (Table 1). The 243 maximum aqueous Ca values during three weeks of reaction were EF (318 mg L -1 ), M
The dynamicresponse analyses of functionally graded materials subjected to mechanical loads are investigated under ambient temperature and also deals with the linear vibration of functionally graded material plates in therm al environments. Transientresponse analysis is the most general method for computing forced dynamicresponse. The purpose of transient analysis is to compute the behavior of a structure subjected to time-varying excitation. The transient excitation is explicitly defined in the time domain. All of the forces applied to the structure are known at each instant of time. The study of dynamicbehavior of FGM plate is very much important for the design of advanced structure. Finite element method is used to study the static and dynamic analyses. The governing dynamic equilibrium equations are derived by the Hamilton’s principle. A clamped FGM square plate is used for the study of direct transientresponse analysis in thermal environment. In the present analysis, zero initial conditions are assumed and damping is neglected. The time derivatives in the semi-discrete model were approximated by using the Newmark direct integration method.
Francis turbine. They demonstrated that the radial gap has a big influence in the runner natural frequencies (about 40-50% of reduction against the natural frequency in air depending on the mode- shape) and lower in the shaft and generator natural frequencies.
In all of these works, the boundaries were always thought to be completely rigid. However, this is not always true for the real prototype runner. Head and lower covers that confine the runner are not completely rigid and have their own dynamicbehavior, which may affect the dynamicbehavior of the runner. Presas, et al. , observed in their investigation with a reduced scale pump turbine model that the nearby boundaries may not behave as completely rigid, which may affect the dynamicbehavior of the runner. However, this phenomenon could not be investigated in detail. Petter, et al., studied the housing effect on the modal behavior of a low specific speed Francis runner through installing the runner in air, in water and in the turbine house. They also found that some modes with high modal displacements on the disc became difficult to be distinguished probably due to the high damping. Valentín, et al. , experimentally studied the dynamicbehavior of a vibrating disk submerged in a fluid-filled tank and confined with a nonrigid cover, and they found that when the natural frequencies of casing and disk are in the same frequency range, the dynamicbehavior of the disk was affected especially when the distance between disk and cover was small. Huang, et al. , investigated numerically and experimentally the natural frequencies and modal shapes of the head cover of a pump turbine prototype, confirming that its dynamicbehavior is complex and has to be considered when studying natural frequencies of prototype runners.
As it is defined in this Note, effective governance balances compet- ing interests, such as pursuing economic benefits and protecting the environment, and engages the critical actors in the regulatory pro- cess. Moreover, effective governance demands dynamic interaction in the regulatory process between the state government, local govern- ments, environmental groups, and the public. Effective governance is necessary to provide the oil and gas industry with clear expectations; to give state and local governments the opportunities to either con- flict or cooperate with one another and thus to effectively experiment toward better policy; and to ensure that the concerns of environmen- tal groups are heard. This Part discusses the current governance op- tions for regulating fracking. However, these governance options are not the most effective means of addressing the state, local, and indus- try-based concerns associated with hydraulicfracturing. Therefore, Part V suggests a more effective governance option in the form of state-local dynamic federalism.