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Abstract Uniaxial Compressive Strength (UCS) is the most widely used index of rock strength. Strength under confined conditions most often is characterized by a straight line Mohr-Coulomb failure envelope. Although required as input to engineering design, reliable values of one or both of these parameters often are not available to the design engineer because of the exacting requirements, and the cost of preparing specimens and conducting a sufficient number of tests, under uniaxial and confined pressure conditions. The Scratch Test was developed at the University of Minnesota in the late 1990s, when a remarkably strong correlation was discovered between the specific energy required to cut a shallow groove into the surface of a rock and the UCS (). The test now has matured into a reliable and relatively inexpensive practical procedure to provide the necessary engineering design information. The procedure has the added advantage that, except for a shallow groove cut along the edge of the core, the test is ‘non-destructive’, leaving the core available for other studies. This paper discusses the theoretical basis for the equivalence between the specific energy of cutting, ε, and the UCS (q), and indicates that the 1:1 relationship between these values has a sound mechanistic basis. The Mohr- Coulomb strength envelope also can be obtained by substitution of a blunt cutting tool in the Rock Strength Device (RSD) — or Scratcher — to determine the coefficient of friction for the rock.
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
Fracture Network Engineering: Combining Microseismic Imaging And Hydrofracture Numerical Simulations
Pettitt, W.S. (Itasca Consulting Group, Inc.) | Pierce, M. (Itasca Consulting Group, Inc.) | Damjanac, B. (Itasca Consulting Group, Inc.) | Hazzard, J. (Itasca Consulting Group, Inc.) | Lorig, L. (Itasca Consulting Group, Inc.) | Fairhurst, C. (Itasca Consulting Group, Inc.) | Sanchez-Nagel, M. (Itasca Houston, Inc.) | Nagel, N. (Itasca Houston, Inc.) | Reyes-Montes, J.M. (Applied Seismology Consultants Ltd) | Andrews, J. (Applied Seismology Consultants Ltd) | Young, R.P. (University of Toronto)
ABSTRACT: Fracture Network Engineering (FNE) is the engineering design of rock mass disturbance through the use of advanced techniques to model fractured rock masses numerically, and then correlate field observations with simulated fractures generated within the models. Microseismic (MS) monitoring is a standard tool for evaluating the geometry and evolution of the fracture network induced during a hydraulic treatment, principally by source locating MS hypocenters and visualizing these wi th respect to the treatment volume and infrastructure (Figure 1). The integrated use of Synthetic Rock Mass (SRM) modeling of the hydraulic fracturing with Enhanced Microseismic Analysis (EMA) provides a feedback loop where the SRM is constrained by the information provided by the MS data, and the in-situ behavior of the fracture network is better understood, which leads to informed decisions on future field operations. This paper discusses the technologies used in FNE and some of the developmental challenges we face in order to provide a more efficient and robust application of the approach. 1. INTRODUCTION The challenge of developing an effective network of fractures is part of a general issue that arises in many sectors of rock engineering; namely, how to characterize and predict the mechanical behavior of a rock mass through an engineering project. The analytical complexity of these problems, and inability to test the rock mass behavior directly on the large scale, has led to the development of a variety of empirical rules that are used widely in practical rock engineering design. As projects become more ambitious and extend beyond prior experience, such rules become increasingly unreliable. Therefore, attention is turning to numerical models, aided during development and validation by in-situ observation, to establish the large-scale response of rock in practical situations. Hydraulic treatments now are widely used to engineer a fractured rock volume.
- North America > United States > Texas (0.47)
- North America > Canada > Ontario (0.29)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
ABSTRACT A new approach to the prediction of rock mass behaviour, called Synthetic Rock Mass (SRM) modeling, has been developed in response to the demands of the mass mining industry, where successful caving and fragmentation of the rock mass demands a greater understanding of the joint fabric and its impact on rock mass strength brittleness and fragmentation. The method involves embedding a Discrete Fracture Network (DFN) into a Bonded Particle Model (BPM) of rock. Much of the work in producing a realistic SRM sample centers on accurate reproduction of the joint fabric present in the real rock mass. This paper focuses on some of the challenges associated with this process in the context of mass mining applications. It also touches on some of the challenges associated with representation of intact rock (and embedded joints) and concludes with a short review of SRM validation efforts.
- Europe (0.46)
- Oceania > Australia > Western Australia (0.29)
- North America > United States (0.29)
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (0.71)
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (1.00)
The Synthetic Rock Mass Approach - A Step Forward In the Characterization of Jointed Rock Masses
Ivars, D. Mas (Itasca Geomekanik AB) | Deisman, N. (Department of Civil & Environmental Engineering, University of Alberta) | Pierce, M. (Itasca Consulting Group, Inc) | Fairhurst, C. (Department of Civil Engineering, University of Minnesota)
ABSTRACT The Synthetic Rock Mass approach to jointed rock mass characterization (Pierce et al. 2007) is reviewed relative to existing empirical approaches and current understanding of jointed rock mass behaviour. The review illustrates how the key factors affecting the mechanical behaviour of jointed rock masses may be considered and demonstrates that the SRM approach constitutes a significant step forward in this field. This technique, based on two well-established methods, Bonded Particle Modelling in PFC3D (Potyondy and Cundall, 2004) and Discrete Fracture Network simulation, employs a new sliding joint model that allows for large rock volumes containing thousands of pre-existing joints to be subjected to any non-trivial stress path. Output from SRM testing includes rock mass brittleness and strength, evolution of the full compliance matrix and primary fragmentation. 1 INTRODUCTION "We don't know the rock mass strength. That is why we need an International Society," was the response of Professor Leopold Mueller, when asked, in Salzburg inMay 24, 1962, why he had just established the ISRM. Given the obvious difficulty of direct full-scale testing of a rock mass, progress in estimating the strength and general constitutive behavior of rock masses has been slow, and reliance has been placed on empirical classification rules and systems derived from practical observations. We do know that rock mass stiffness and strength typically decrease with increase in the scale of both size of the structure and duration of loading. This is usually attributed to the presence of joints and similar ‘planar’ discontinuities in the rock mass that areweaker than the intact rock. Reduction of strength with time of loading tends to be attributed to ‘weakening’of the ‘bridges’ of intact rock between the larger planar discontinuities (Einstein and Meyer, 1999) or, equivalently, ‘sub-critical crack growth’ (Kemeny, 2003) or ‘stress corrosion’ at the tips of discontinuities. Rock Mass Classification (RMC) systems were developed for use in Civil and Mining Engineering in response to the need for ways to ‘rank’ a specific rock mass, based in large part upon the joints and their weakening effect on the rock. By compiling histories of rock mass ranking relative to performance, it has been possible to develop relations for quantitative prediction of rock mass strength and modulus. Despite the fact that RMC systems and relations are in widespread use in engineering design, their ability to consider strength anisotropy (resulting form the joint network) and strain softening/weakening remains limited. Another important limitation of such systems is the inherent uncertainty of extrapolation beyond the limits of the experience from which the rules have been derived. A comprehensive discussion on this matter can be found in Mas Ivars (2007). Continuum mechanics is also applied to great benefit in rock mechanics and rock engineering, but it too has limitations.
- North America > United States (1.00)
- North America > Canada > Alberta (0.28)
- Europe > Austria > Salzburg > Salzburg (0.24)
- Well Drilling (1.00)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
ABSTRACT: An approach to the study of four practical problems of rock engineering using a micro-computer program is presented. The intent is to illustrate how a computer model, in these cases involving simple elastic behavior of the rock medium, sufficed to provide useful practical insight for the design. More sophisticated elastic/inelastic analysis, although available in the computer program, was felt to be not warranted in these cases, due principally to the absence of data on the mechanical properties of the rock mass. Specifics of the calculations and computations are minimized in this paper, but are explained in detail in several of the listed references. INTRODUCTION The development of powerful, relatively inexpensive, micro-computers and computer programs able to model rock engineering problems has given engineers a potentially very valuable design tool. The microcomputer can be located at the job-site, even in remote locations, allowing the actual behavior of the rock to be compared with predictions; and design change options to be examined, with minimum delay. However, the arrival of the microcomputer has not changed the rock. The large-scale heterogeneities and discontinuities, the variability and uncertainty of in-situ conditions remain, and must be considered in the design. Also, one has usually very limited detailed information on the mechanical properties of the rock mass prior to excavation, i.e., rock engineering problems are usually "data-limited." As has been noted, A rock mass is a complex assemblage of different materials and it is very unlikely that its behavior will approach the behavior of the simple models which engineers and geologists have to construct in order to under stand some of the processes which take place when rock is subjected to load. Hoek and Brown (1980) "Understand" is a key word in this statement. Flexible, 'user-oriented' computer programs are now available which can help the engineer develop an understanding of how a structure in or on rock is performing, and indicate possibilities for improving the design. Empirical design rules based on successful designs for (apparently) similar projects, are valuable and should be used as a check on a proposed design. They can not provide the understanding-and the associated awareness of possibilities for improving the design-that can come from the proper use of models. Starfield and Cundall (1988) have presented valuable guidelines on the use of models in rock mechanics, and note that Simplification is a crucial part of rock mechanics modelling. A model is an aid to thought, rather than a substitute for thinking..... They further advise.....plan the modelling exercise in the same way as you would plan a laboratory experiment. In particular, the modeler should ask, why am I building a model; how can I justify the particular model I am using; what did I learn from the modelling exercise? We have attempted to follow this approach to modelling and offer four examples as illustrations. All of them are, to varying degrees, "data-limited" and were studied using the two-dimensional finite-difference computer code, FLAC, (See References) on a microcomputer.
- Energy > Oil & Gas > Upstream (0.46)
- Materials > Metals & Mining > Potash (0.46)
- Well Drilling (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
ABSTRACT: In-situ stresses favor tensile stress development in drag bit cutting, but possible benefits to penetration rate are eliminated by the highly negative rake angles of PDC bits. Experiments confirm that in-situ stresses do not influence bit penetration rate. A simple Mohr-Coulomb criterion is found to provide a good qualitative explanation of the decline of penetration rate with increased mud pressure observed both in laboratory tests and in field drilling. 1 INTRODUCTION It is well known that in-situ rock stresses increase with depth in the earth crust and that these stresses, can cause collapse of the walls if the hole is not sufficiently supported internally as it drilled. In-situ stresses also produce stress concentrations across the bottom of the hole and questions are sometimes raised as to the influence of these concentrations on the drilling rate. Drilling muds, used to provide the internal support pressure needed to stabilize the bore-hole wall, also cause an associate substantial reduction in drilling rates compared to those obtained when mud pressure is absent or low. This paper describes computational and experimental studies carried out to examine the influence of in-situ stresses and mud pressure on the penetration rate polycrystalline Diamond Compact (PDC) bits when cutting Buxy limestone - a hard, fined-grained, essentially impermeable rock. 2 CONCENTRATION OF IN-SITU STRESSES DUE TO DRILLING OF A WELL-BORE It is assumed that the circular well-bore is vertical (i.e. parallel to the z axis in Figure 1), and that the principal in-situ stresses, all compressive, are parallel and normal to the borehole axis i.e. σx=σy=Q, and σz=R. The elastic stress concentrations produced in the vicinity of a drag bit cutting tool (of which the PDC tool is an example) at the bottom of the hole were computed using the finite element code VIPLEF developed at Ecole des Mines de Paris (ENSMP/CGES). The problem was analysed in two stages, as illustrated in Figure 2, viz, a) determination of the elastic stress concentrations at the bottom (flat) surface of the hole due to the in-situ stresses Q, R [Figure 2a), b) determination of the additional (local) stress concentrating effect in the immediate vicinity of the cutting tool due to the inclined slope change in geometry produced by the cutting action [Figure 2b]. Stresses imposed by the and by mud pressure in the not considered in the above cutting tool borehole are two stages. 2.2 Additional elastic stress concentrations due to inclined chip surface geometry The chipping action of a drag bit produces, more or less continuously, an inclined surface or slope ahead of the cutting edge of the bit. For the purpose of this study, it is assumed that the slope is inclined at 45" upwards from the (flat) cut surface. Since the depth of cut, h, is small compared to the diameter of the wellbore, it will be assumed that the stress σro acting across the bottom of the hole is constant over the depth (taken here to be 8h) affecting the stress concentration in the slope region.
- Europe > France (0.29)
- North America > United States (0.28)
- Well Drilling > Drill Bits > Bit design (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
ABSTRACT: This General Report, complemented by invited lectures by Dr. J. C. Roegiers and Dr. R. Hart, surveys some recent developments in analytical and numerical approaches to the study of the deformation and stability of deep excavations in rock, both small (boreholes) and large (tunnels, caverns). Emphasis is given to the classical closed-form analytical solution of elastic-plastic (inelastic) behaviour of rock around excavations to illustrate the influence of various factors that affect the constitutive behaviours, both elastic and inelastic, of the rock. Consideration of discrete discontinuities is essential to understanding of the stability of large excavations. INTRODUCTION One of the goals of this Symposium is to strengthen the dialogue between petroleum engineers and mining or civil engineers concerned with the development of stable excavations in rock at great depth. An obvious difference between the two concerns is, of course, the cross-sectional area of the excavations; the small petroleum boreholes and the much larger tunnels, stopes and caverns of mining and civil engineering. In the former, deformation and stability of the excavation are dependent principally on the mechanical properties of the rock material itself, whereas in the latter, controlling influence. Significant progress is being made in studies of both small-scale (borehole) stability and large excavation stability, but each tends to have a different 'flavour'. Borehole stability is amenable to laboratory investigation, for example, whereas behaviour of the large excavations require direct observation in the field for confirmation of analysis. In considering how best to review the progress being made in each, whilst also examining points of common concern to both, it was decided to supplement this report with two special lectures. One, by Dr. J. C. Roegiers, reviews recent developments in excavation stability research, with emphasis on borehole stability and petroleum engineering. The second, by Dr. R. Hart, reviews recent developments in discontinuum studies, with applications to large excavations in mining and civil engineering. This report will focus on a general discussion of stability around excavations, broadly applicable to both small and largescale excavations. CLASSICAL ELASTO-PLASTIC ANALYSIS Much of the discussion concerning stability of underground excavations, both small scale and large scale, starts from the classical problem of a circular hole in an homogeneous, isotropic, elasto-plastic medium loaded in plane strain by a uniform external compression P at infinity, and a uniform internal pressure Pi'. As P is increased, the strength of the rock at the wall of the excavation is eventually exceeded and an annulus of broken rock develops around the inner radius a, i.e. forming the 'plastic' [or 'inelastic' in Fig.1] zone. The thickness [(b - a) in Fig. l] of the inelastic zone to achieve this equilibrium at the interface will depend on the constitutive behaviour of the broken rock in this zone. A wide variety of modifications to this distribution (some for example showing discontinuities in the tangential stress at the elastic/inelastic interface), are possible, depending again on the constitutive behaviour of the broken rock [See, for example, Brady and Brown (1985)].
- Well Drilling > Wellbore Design > Wellbore integrity (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.95)
ABSTRACT ABSTRACT: Most of the papers designated as being within the topic of underground storage at this Symposium are concerned with aspects of radioactive waste isolation. Although this is, unquestionably, an important international application of underground storage, and one involving a considerable number of research investigations, the subject of underground storage is indeed much broader. Several major international conferences have been devoted exclusively to it. Applications include storage, under a range of temperatures and pressures, of oil and liquefied petroleum products, compressed air, heat, foodstuffs of various kinds, hazardous and 'nuisance' industrial by-products, and a variety of special applications, both civilian and military - some in use, others proposed. Storage may be in caverns excavated specifically for the purpose, exhausted mines may be adapted for storage or, in some cases, the material to be stored may be injected under pressure into the pore spaces of porous-permeable formations at depth. A variety of rock types and geological environments are used, e.g. excavations in salted or domal salt, where long-term creep closure of the openings is a concern; massive granite, where fluid loss through fissures may be important. Cavities may have spans of several tens of meters, and there is interest in achieving still larger excavations. As would be expected, this breadth of underground storage applications introduces a similarly broad range of questions in rock mechanics and rock engineering. The report will review these questions and recent developments in rock mechanics research, computational procedures, and design applications - and will also discuss the opportunities for a still greater range of applications of underground storage to current industrial and social problems.
- Reservoir Description and Dynamics > Storage Reservoir Engineering (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
East of the Rocky Mountains to the Appalachian Orogen, the background zones are defined primarily by Is There a Correlation Between EPRI 1.5
- North America > Canada > British Columbia (0.25)
- North America > Canada > Alberta (0.25)
- Geology > Structural Geology > Tectonics > Plate Tectonics > Earthquake (1.00)
- Geology > Structural Geology > Tectonics > Compressional Tectonics > Fold and Thrust Belt (0.92)
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Gravity Surveying (0.72)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.39)
ABSTRACT INTRODUCTION The stress redistribution accompanying the excavation of a deep tunnel may induce failure of the rock. The role of the support system is to Control the extent of the failed region and hence to limit closure of the t,,-nel within an allowable amount. In such circumstances, the design of the support system is generally based on the Ground Reaction Curve (GRC). The GRC is the relationship between the support pressure and the induced displacement at the tunnel wall for a circular tunnel under hydrostatic loading. In the calculation of the GRC (see Brown et al. (1983) for an exhaustive list of reference), the rock is generally treated as an elastoplastic material characterized by cohesive-frictional yield strength and by dilatancy during plastic deformation. A recent analytical development (Detournay, 1983) has allowed the generalization of the 0RC concept for some cases of non-hydrostatic in-situ stress fields (Detournay and Fairhurst, 1982). As an application of that development, this paper describes design charts that provide powerful means of performing parametric analysis for tunnels subject to non-hydrostatic loading. BACKGROUND The in-situ stress in a plane perpendicular to the tunnel axis can be decomposed into mean and deviatoric components, Po and So (see Fig. 1). Since it is assumed that the rock is characterized by a Mohr-Coulomb yield strength, the deviatoric invariant So must be less than the limiting value So given by (mathematical equation) (available in full paper) where Kp is the passive coefficient, Kp = (1 + sinF)/(1 - sinF) (F, friction angle); q is the unconfined compressive strength, (mathematical formula) (available in full paper) (c, cohesion). This constraint on the in-situ stress can similarly be expressed by imposing that the obliquity m of the in-situ stress be less than 1. The obliquity m is defined as m = So/So The obliquity m controls how the plastic zone around the tunnel develops and determines the computational effort necessary to completely define it. Provided that the obliquity is less than a critical value m,, that is a function of the friction angle F only (see Table 1), the extent and shape of the plastic zone are statically determined by the internal pressure p and the stress invariants Po and So. If the obliquity is greater than m, (but less than 1), the location of the elastoplastic interface is statically indeterminate and depends also on the deformation characteristics of the rock. Specifically it will be influenced by the shear modulus G, the Poisson ratio ¿, and the dilatancy angle F*. The relationship between the in-situ stress (normalized with respect to q) and the existence and shape of a plastic region around an unsupported tunnel is depicted in Figure 1. In all, four different types of behavior occur: Type 1: Elastic behavior only (region designated I) Type 2: Limited failure in a direction perpendicular to the major in-situ stress (region designated II) Type 3: Tunnel completely surrounded by an oval shaped yield zone (region designated IIb) Type 4: A "butterfly"-shaped plastic region around the tunnel (region designated III)