Skip Nav Destination
Filter
Filter
Filter
Filter
Filter

Update search

Filter

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

- Title
- Author
- Author Affiliations
- Full Text
- Abstract
- Keyword
- DOI
- ISBN
- EISBN
- ISSN
- EISSN
- Issue
- Volume
- References
- Paper Number

### NARROW

Format

Subjects

Date

Availability

1-20 of 24

Keywords: stress component

Close
**Follow your search**

Access your saved searches in your account

Would you like to receive an alert when new items match your search?

*Close Modal*

Sort by

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the 55th U.S. Rock Mechanics/Geomechanics Symposium, June 18–25, 2021

Paper Number: ARMA-2021-1833

... fracturing the formation (Peska and Zoback, 1995). A geomechanical analysis of a proposed well design will give an indication of the stability of a proposed well and help in reducing the issues that leads to loss of well integrity. wellbore integrity

**stress****component**shear failure reservoir...
Abstract

ABSTRACT: The role that geomechanics plays on stress, strain, and possible failure of a well must be better understood to ensure long-term well integrity and reduce the possibility of well failure. The local tectonic regime's stress-field affects not only the borehole during drilling but also affects the well system (casing-cement-rock) after construction. Failure of a well system is dependent on in-situ stress and on the well's trajectory (e.g., inclination and azimuth angle). Cylindrical stress distribution in cement and casing around well is also impacted by these factors and this study aims in identifying their impact on shear failure in cement. A combination of analytical solutions and Finite Element Method (FEM) simulations are used to study the stress distribution around the wellbore and within the well system. Analytical solutions consist of a plane-strain approach where the stresses at the material boundaries are calculated. For FEM, a commercially available software (COMSOL) is used to perform the stress analysis by specifying the initial stress condition in a 3D inclined well system. Failure criteria are discussed to estimate when a component of the well system might fail in tension, compression, or in shear. 1. Introduction Successfully drilling and completing a well requires that the well be designed to meet several criteria which affect not only flow performance but also well integrity. To ensure well integrity the design must consider the expected service environment, which includes the subsurface temperatures, fluid pressures, fluid chemistry, and geomechanical stresses. Geomechanical or in situ stresses exist everywhere in the earth's crust and their magnitude depends on subsurface depth, overburden pressure, pore pressure, and regional tectonic processes which vary on the spatial and temporal scale. In situ stresses are important throughout all stages of a well's life. During drilling, geomechanics plays an important role in wellbore stability and not accounting for geomechanics can lead to issues like wellbore breakout or loss of fluids due to hydraulically fracturing the formation (Peska and Zoback, 1995). A geomechanical analysis of a proposed well design will give an indication of the stability of a proposed well and help in reducing the issues that leads to loss of well integrity.

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the 52nd U.S. Rock Mechanics/Geomechanics Symposium, June 17–20, 2018

Paper Number: ARMA-2018-729

... Artificial Intelligence Simulation fracture propagation stress change equation reservoir property production well fracture

**stress****component**production fracture hydraulic fracture Ghassemi pore pressure pressure distribution horizontal**stress****component**reservoir pore pressure 1 1...
Abstract

ABSTRACT: Field experience has shown that infill or “child” well fractures could propagate towards the “parent” well and previously depleted zones causing unwanted communication between the infill and producer wells and negatively impact production. To investigate this problem, we present a geomechanical analysis of production induced stress reorientation around hydraulic fractures in a horizontal well, and simulate subsequent propagation of multiple hydraulic fractures from an infill well. The fully coupled model “Geo-Frac3D” which combines the boundary element method and the finite element method for rock matrix deformation/fracture propagation, and fracture fluid flow is used in this work. Simulation results show that production from hydraulic fractures in a horizontal well gives rise to a non-uniform pressure distribution leading to unequal changes in the reservoir stresses which may result in a complete stress reversal around the fractures and in the infill well zones. As a result, fractures from the infill well tend to propagate preferentially towards the “parent” well. The fracture propagation from the infill well before and after repressurization of the production fractures is also considered. Results demonstrate that production induced reservoir pore pressure and stresses have a very significant impact on the subsequent fracture propagation from the infill well and “frac -hit” issues. By repressurization of production fractures before the infill well fracturing, the “frac-hit” problems might be potentially mitigated. The simulation results agree well with more elaborate simulations that account for the layered reservoir properties.

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the 52nd U.S. Rock Mechanics/Geomechanics Symposium, June 17–20, 2018

Paper Number: ARMA-2018-893

... sizes often used in rock engineering, large uncertainties may exist which are likely to yield misleading stress estimates. reservoir geomechanics orientation Harrison reservoir simulation Martin Reservoir Characterization Upstream Oil & Gas

**stress****component**Artificial Intelligence...
Abstract

ABSTRACT: Obtaining reliable estimates of u stress, particularly principal stresses, is crucial for robust rock engineering design. However, due to the stress variability inherent in fractured rock masses, a key question that arises in practice is that of how many stress measurements are required to obtain stress estimates of acceptable reliability. In this paper, we investigate the effect of sample size – i.e., number of stress measurements – on the uncertainties associated with point estimations of both principal mean stress magnitude and orientation. We use Monte Carlo simulation in conjunction with a recently developed multivariate statistical model to simulate a large number of stress tensor samples of different sizes. We show (i) that the number of stress measurements required for obtaining estimates of acceptable reliability is practically impossible, and (ii) with the small sample sizes often used in rock engineering, large uncertainties may exist which are likely to yield misleading stress estimates.

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the 51st U.S. Rock Mechanics/Geomechanics Symposium, June 25–28, 2017

Paper Number: ARMA-2017-0882

... to solving a system of seven partial differential equations with the three

**stress****components**, specific volume, and three anisotropic hardening parameters being the basic unknowns. Parametric studies have been conducted to explore the influence of overconsolidation ratio and inherent anisotropy. The results...
Abstract

ABSTRACT: Different from the prevalent methods that treat rock formation as isotropic elastic, poroelastic, and/or elastoplastic materials, this paper presents a set of semi-analytical solutions for the wellbore stability problem by adopting the widely used anisotropic critical state plasticity model originally proposed by Dafalias, 1987. This model is capable of taking mechanical anisotropy into account and therefore the wellbore stability analysis presented in this paper is more realistic. By carefully choosing an independent auxiliary variable, the plastic zone solution is reduced to solving a system of seven partial differential equations with the three stress components, specific volume, and three anisotropic hardening parameters being the basic unknowns. Parametric studies have been conducted to explore the influence of overconsolidation ratio and inherent anisotropy. The results show that both these two plasticity features exert pronounced effects on the response of the drilled wellbore. In addition, the feature of anisotropy has also been discussed. It is found that there is a distinct difference between the results with and without considering the anisotropy in the wellbore stability problem.

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the 51st U.S. Rock Mechanics/Geomechanics Symposium, June 25–28, 2017

Paper Number: ARMA-2017-0154

... with time around the injection well: (1) liquefied domain, (2) multiple plastic domains, (3) elastic region. Inner plastic domains are prone to occur. structural geology pore pressure initiation Reservoir Characterization plasticity reservoir formation Upstream Oil & Gas

**stress****component**...
Abstract

ABSTRACT: This paper presents a novel study on geomechanics of fluid injection from a fully penetrating vertical wellbore into a weakly consolidated formation confined with soft rocks. For the first time, impacts of vertical confinement are incorporated to evaluate: flow-induced poro-elasto-plastic stresses, failure mechanism/s, and failure planes. A new fully-coupled numerical model is developed where the response of the injection layer in the plane perpendicular to injection flow is simulated through adopting “interface” – a plane on which sliding or separation can occur – analogous to the Winkler model. An assessment of pore pressures, stresses, and failure planes confirms two types of induced behaviors: dilation in the well vicinity; and compaction, a main cause of physical clogging which impacts competence of the operation. Numerical results describe multiple distinct zones evolving with time around the injection well: (1) liquefied domain, (2) multiple plastic domains, (3) elastic region. Inner plastic domains are prone to occur.

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the 51st U.S. Rock Mechanics/Geomechanics Symposium, June 25–28, 2017

Paper Number: ARMA-2017-0447

... of in-situ stresses should include both the magnitude and direction of all the principal

**stress****components**. An accurate estimation of the in-situ stress field is a prerequisite for a robust and reliable geomechanical analysis. reservoir geomechanics tensile fracture fluid pressure dfit analysis...
Abstract

ABSTRACT: The in-situ stress field could govern the mechanical response of a formation to drilling, stimulation, and depletion. Therefore, the in-situ stresses are essential input parameters for all geomechanical analyses, regardless of the complexity of the problem. The determination of in-situ stresses should include both the magnitude and direction of all the principal stress components. An accurate estimation of the in-situ stress field is a prerequisite for a robust and reliable geomechanical analysis.

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the 50th U.S. Rock Mechanics/Geomechanics Symposium, June 26–29, 2016

Paper Number: ARMA-2016-446

... the in-situ stress state within the Finite Elements framework is presented. It involves two steps: 1) an estimate of the

**stress****components**is given for integration point of the discretization, and 2) global equilibrium is verified and re-balancing nodal forces are applied if needed. While the second step...
Abstract

Abstract: An accurate description of the in-situ stress field in a rock mass is crucial in different areas of geo-engineering such as: underground excavations, hydrocarbon extraction, CO 2 storage, hydraulic fracture etc. In this paper, a novel methodology to numerically generate the in-situ stress state within the Finite Elements framework is presented. It involves two steps: 1) an estimate of the stress components is given for integration point of the discretization, and 2) global equilibrium is verified and re-balancing nodal forces are applied if needed. While the second step is a closed procedure based only on statics, the estimate of the in-situ stress field can be done in different ways in order to incorporate all the information available of the rock mass. In this paper, more traditional approaches are discussed and a new procedure based on the Airy stress function is described, in order to generate a stress state proposal at each Gauss point of the domain. Finally, the performance of different approaches is illustrated with a reservoir example. Introduction A rock mass or any geological material that is located at a certain depth is subjected to an in-situ stress field. This stress field is the result not only of the geometry and weight of the geologic structure but also of a non-trivial geologic history. This history may include complex phenomena such as deposition, compaction, erosion or tectonic events. Gravitational stresses are induced by the weight of the overburden, and often the vertical (or z) axis is a principal stress direction, while the other two principal stresses are contained in the horizontal plane (xy). Tectonic stresses may be the result of the tectonic movements at local or regional scale. The residual stresses are produced by strain energy locked-in in the rock from previous processes such as burial, lithification, denudation, heating and cooling. According to Friedman, 1972 a fraction of these residual stresses persist even after the rock is freed from boundary loads. When the in-situ stresses at a site are measured using any of the techniques available, the stress measure obtained includes the contributions from all those origins combined.

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the 49th U.S. Rock Mechanics/Geomechanics Symposium, June 28–July 1, 2015

Paper Number: ARMA-2015-150

... and Airy stress functions,

**stress****components**are investigated in a tensile positive fashion. Results are obtained in series form to facilitate parametric studies on the influence of the loading angle and geometric characteristics of the ring on the maximum tensile stress. Results indicate that for a ring...
Abstract

Abstract This paper attempts to provide a simple analytical solution for the calculation of stress tensors induced in a linear elastic ring of a brittle material subjected to parabolic loading over two symmetric strips of its outer perimeter. Using the Michell- Fourier series technique and Airy stress functions, stress components are investigated in a tensile positive fashion. Results are obtained in series form to facilitate parametric studies on the influence of the loading angle and geometric characteristics of the ring on the maximum tensile stress. Results indicate that for a ring with a small hole, the type of the imposed stress is crucial in determining the distributions of the stress components inside the ring domain, although it becomes almost negligible for a ring with a relatively large hole. In contrast, a large inner to outer ratio influences significantly the stress values at critical points of the ring experiencing the maximum tensile stress. 1. INTRODUCTION Stress and displacement analysis of cylindrical annular bodies under arbitrary tractions is one of the classic topics of Elasticity, with its major applications in Machine Design Theory and strength measurement of materials [1]. The ring test has been widely accepted as an indirect laboratory technique for measuring the tensile strength of a material in the shape of a circular solid cylinder (disc) containing concentric holes subjected to lateral compression until a tensile failure occurs. The growing application of the ring test in geotechnical engineering, particularly in rock mechanics, is directly tied to the ease of sample preparation and its unique breakage mechanism in a pure tensile mode. There is a vast body of literature devoted to calculating the induced stresses in the ring test aimed at producing relationships for estimating the tensile strength of a test material as functions of the ring’s geometrical aspect ratio and the imposed contact conditions. Timoshenko [2], Filon [3], Ripperger and Davis [4], Bortz and Lund [5], Hobbs [6], Jaeger and Hoskins [7], Chianese and Erdlac [8], and Kourkoulis and Markides [9], among others, have proposed analytical solutions for the ring problem. However, they are often limited to simplified stress assumptions at the contact, e.g. line-forces or uniform radial stresses, or Muskhelishvili's complex potentials [10] to account for the complicated boundary conditions, e.g. parabolic contact loadings. Despite the generality of complex-variable schemes; however, such approaches require excessive and complex mathematical rigour, limiting their application to broader disciplines. In contrast, focusing on the analytical-methodological aspect, this study attempts to construct a simpler and more convenient easy-to-use treatment for the study of stresses when the ring is subjected to parabolic radial compressive stresses over two finite arcs of its lateral surface (Figures 1 and 2).

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the 46th U.S. Rock Mechanics/Geomechanics Symposium, June 24–27, 2012

Paper Number: ARMA-2012-473

... potent influence on the failure and deformation behavior around openings. reservoir geomechanics stress ratio Artificial Intelligence in-situ rock stress field Reservoir Characterization orientation

**stress****component**maximum horizontal stress determination horizontal stress minimum...
Abstract

ABSTRACT: Since late in the 90''s, in-situ rock stress tests have been widely conducted to provide the quantitative information on the stress state of an engineering site at the design stage of an underground rock structure in the Kyungsang Basin, Korea. Totally, 270 in-situ stress measurements were conducted in the surface test boreholes at the depth from 20 m to 300 m by the hydraulic fracturing method using an engine driven wireline hydro-fracturing system. And almost of all the fracture tracing works were carried out using borehole scanning device to obtain more accurate and visualized information on induced fractures rather than conventional oriented impression packer method. In this paper, the overall characteristics of the current in-situ rock stress fields in the Kyungsang Basin are described with the results of measurement data set. The maximum horizontal stresses (SH) range from 1.18 MPa to 20.73 MPa and the minimum horizontal stresses (Sh) from 0.84 MPa to 10.92MPa at less than 300m in depth. Although the stress ratio (K) has strong anisotropies at less than 100 m in depth, it generally has a tendency to decrease and stabilize with depth. The average stress ratio (Kavg) ranges from 0.83 to 4.91 and the maximum stress ratio (KH) from 0.83 to 5.63. 1. INTRODUCTION The in-situ rock stress measurement and its applications have been regarded as one of the key branches in the geo-science fields such as rock mechanics, structural geology, civil engineering, and so on. Being different from a surface structure, the stability of an underground opening is largely influenced by many factors such as geological condition, mechanical properties of rock mass, initial stress state and geometry of an opening. Among these factors, the characteristics of in-situ rock stress have potent influence on the failure and deformation behavior around openings.

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the 46th U.S. Rock Mechanics/Geomechanics Symposium, June 24–27, 2012

Paper Number: ARMA-2012-649

... & Gas

**stress****component**geologic structure stress tensor fracture lamination natural fracture boundary anisotropic homogeneous case mechanism average normal stress lateral boundary heterogeneity anticline homogeneous case anisotropy 1. INTRODUCTION Folded geologic structures...
Abstract

ABSTRACT: Bending of geologic strata occurs in the formation of a variety of geologic structures. Such bending deformation causes redistribution in the stress and strains within the formation and may result in the formation of fractures. Quantitative estimates of the stress redistribution as well as estimation of the location and orientation of natural fractures is critical to many aspects of oil and gas production including wellbore stability, fracture containment, and production. Geomechanical analysis of folded structures commonly assumes that the rock is isotropic and homogeneous, which results in relatively simple mathematical formulas that are convenient for the estimation of the stress state, the location and orientation of induced fractures, as well as the change in permeability due to the fractures. However, such an approach ignores the rock properties as well as the heterogeneity present in many formations. The consequent spatial variability in properties within the rock unit can have a strong influence on where the rock mass deforms, where the maximum stresses occur and therefore where and how fractures are likely to form. The purpose of this paper is to review the literature on this topic and to illustrate the coupled effects of anisotropy and heterogeneity on the bending of geologic structures. A series of simple case studies is used to demonstrate which rock properties are most important to correctly characterizing folded geologic structures. It is demonstrated that when both lateral and vertical heterogeneity of the rock are accounted for, the in-situ stress state and the possible modes of failure become more complex and difficult to predict. Understanding these consequences is critical to the geomechanical analysis of folded structures and to applications to the oil and gas industry. 1. INTRODUCTION Folded geologic structures such as anticlines and synclines are important to the petroleum industry for a variety of reasons.

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the 46th U.S. Rock Mechanics/Geomechanics Symposium, June 24–27, 2012

Paper Number: ARMA-2012-197

... Upstream Oil & Gas reservoir geomechanics pore pressure

**stress****component**salt body tectonic factor subsalt formation plane stress pattern lowest value occur trajectory calculation prediction horizontal stress sectional view effective stress ratio numerical result principal stress...
Abstract

ABSTRACT: Two major aspects in the description of a stress pattern are the effective stress ratio and tectonic factor. This paper presents two case studies focusing on the stress pattern around salt bodies in the deepwater. The salt body geometries are modeled on the basis of a set of sectional seismic data. The geometry of the geomechanical model used in the calculation for a field at the Gulf of Mexico is a block with a height, width, and thickness of 10 km. An inclined cake-shaped salt body with a diameter of 6927 m is embedded in the model. A similar geometric scale is used for the second case study from the Campos basin of offshore Brazil. [n this case, a salt body with an irregular geometry has a thickness of 6024 m along the trajectory of wellbore. An anticline structure wa modeled at the bottom surface of the salt body. umerical re ults obtained with the FEM for each study include: 1) sectional views for the distribution of both the effective stress ratio and tectonic factor, and 2) diagrams of the distribution of the effective tres ratio and the tectonic factor along specific paths below and above the salt body, respectively. 1. INTRODUCTION For the I-dimensional (ID) prediction of the mudweight window (MWW), the following input is required: I) pore pressure (PP), overhurden gradient (OBG), and effective stress ratio and/or Poisson''s ratio; 2) cohesive strength (CS), friction angle, (FA) and/or uniaxial compression strength (UCS), and tectonic factor. The first part of the input data is required for the prediction of the upper bound of the MWW, which is the so-called fracture gradient (FG); the second part of input data is used for the prediction of the lower bound of MWW, which is shear failure gradient (SFG).

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the 46th U.S. Rock Mechanics/Geomechanics Symposium, June 24–27, 2012

Paper Number: ARMA-2012-108

.... Reservoir Characterization Upstream Oil & Gas machine learning hydraulic fracturing Artificial Intelligence

**stress****component**situ stress tensor information knowledge determination matrix reservoir geomechanics relation inverse problem layout rock mass rosette Rock mechanics variance...
Abstract

ABSTRACT: This paper aims to show why the determination of the in situ stress tensor is an inverse problem, as well as describing a Bayesian inverse problem technique for finding the components of the in situ stress tensor or the initial boundary conditions of the site using existing knowledge. Techniques for the evaluation of the reliability of calculated results will also be explained. Synthetic examples will be used in order to exemplify the calculations. Preliminary methods for calculating the in situ stress tensor as the initial data, if no previous tests are available, will also be shown. A synthetic example will be used to illustrate the application of the Bayesian Technique and evaluate the reliability of its answers, for two cases, considering 3D conditions in a continuous, homogeneous, isotropic and linearly elastic rock mass. 1. INTRODUCTION When measurements are made, as an example, in overcoring tests, they are only detecting the effects of the in situ stress tensor. Generally speaking when field tests are made they aim at determining the in situ stress tensor acting in a rock mass. In fact, however, they only measure strains, induced stresses or shut in pressures, etc. that are the response of the rock mass stress regime to some kind of perturbation introduced by men. For instance the magnitude of shut in pressure in the Hydraulic Fracturing Method is caused by the closure of an artificially created fracture, consequently preventing further flow onto it; therefore the process of creating a rock fracture and letting it close is a perturbation in the rock mass and the shut in pressure is the response of this process to the in situ stress tensor. Therefore, when measurements are made an inverse problem is always created and needs to be solved with inverse problem techniques.

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the 45th U.S. Rock Mechanics / Geomechanics Symposium, June 26–29, 2011

Paper Number: ARMA-11-129

.... There is induced anisotropy of horizontal stresses. Orientations of principal stresses are not longer vertical and horizontal and the vertical stress may not be the maximum

**stress****component**. For some geometries, vertical stress within and adjacent to the salt is not equal to the gravitational load (stress...
Abstract

ABSTRACT The goals of this work include reviewing the phenomena of stress rotation in the presence of faulting, salt bodies, and non-uniform distribution of physical rock properties, pore pressure, and tectonic deformation; numerically simulating the stress-field distribution for these cases at the field scale by using a 3D finite element method (the tectonic stress factor and gravity loads are included in the loading used in the analysis); and conducting a numerical analysis of the variation of stress orientation within formations caused by existence of salt body and/or pore pressure depletion. Examples from a field model which consists of a salt body of 7-km in diameter along with the Ekofisk field in the North Sea have been analyzed numerically. A 3D calculation of deformations of the formation matrix is combined with porous flow. Non-uniform initial stress field and non-uniform initial pore pressure field are constructed by means of user subroutines included in commercial finite element software. This paper also includes suggestions regarding stress orientation related topics, such as trajectory optimization and safe mud weight window design. 1. INTRODUCTION The orientation of the principal horizontal stress has an important influence on completion design, i.e., casing direction and hydraulic fracturing. Several tectonic and depositional mechanisms influence the orientation of the principal stresses: 1) relaxation of stresses adjacent to faults; 2) accumulation of stresses adjacent to faults prior to slippage; 3) halo kinetics, i.e., movement of salt masses; 4) slumping; and 5) rapid deposition of sediments on top of a subsurface environment dominated by strike-slip or reverse faulting. Stress rotation has been reported by several authors in various drilling environments that share common complex geological structures, including active tectonic regions, complex fault and joint systems, salt bodies, and depleted reservoirs. Stress rotation can be observed within one well or from one well to another well. It causes extremely expensive and difficult wellbore stability problems during drilling, completion, or production, and represents a challenge for the oil industry in both operation and modeling. As a result, a large effort has been expended to study and fully understand this phenomenon. Martin and Chandler reported a maximum horizontal stress rotation near two major thrust faults that were intersected during the excavation of the Underground Research Laboratory (URL) in the Canadian Shield [1]. In this region, the fault system divides the rock mass into varying stress domains. Above the fault system, the rock mass contains regular joint sets, in which the maximum horizontal stress is oriented parallel to the major sub-vertical joint set. Below the fault system, the rock is massive with no jointing; the maximum horizontal stress has rotated approximately 90° and is aligned with the dip direction of fracture zone. Stress rotation is commonly observed where the block of rock above the fault has lost its original load because of displacement above the fault; this results in considerably less maximum horizontal stress magnitude than the magnitudes below the fracture zone, where the maximum horizontal stress magnitude is fairly constant [1].

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the Vail Rocks 1999, The 37th U.S. Symposium on Rock Mechanics (USRMS), June 7–9, 1999

Paper Number: ARMA-99-1181

... 2 and 3) to determine how stressed they were and how much of their cross section could be removed without risking global pillar or back collapse. The main interest was to measure the vertical

**stress****component**rapidly, with a good accuracy and at low cost without any assumption regarding the state...
Abstract

ABSTRACT: Stress measurements in two pillars have been performed at Noranda's Gasp6 mine in order to evaluate the load they support so optimal ore recovery could be achieved by reducing their cross section. The paper describes the advantages of the stress measurement and' calculation methods used for the project. The modified doorstopper technique was found to be well suited to obtain accurate results with a minimum of unverified hypotheses at a relatively low cost. A total of ten measurements in two pillars were done in less than three days and led to results that are compared to stresses obtained from a 3D numerical analysis using the MAP3D boundary element code. INTRODUCTION Located in Murdochville on the Gasl? peninsula in Eastern Quebec, Noranda's Mines Gasp6 started underground operations in 1951 and has since been one of Noranda's leaders in mining and metallurgical operations. During the fifties and sixties, underground mining was done using the room and pillar method (Figure 1) which created a complex array of openings that have been remarkably stable over the years. As mining of the various ore bodies discovered over the years is coming to an end, the possibility of recovering parts of the huge pillars left in place during the early stages of mining is being investigated. As part of this investigation, a series of stress measurements have been performed near the base of two rectangular pillars of approximately 13 by 23 m in width and length and up to 37 m high (Figures 2 and 3) to determine how stressed they were and how much of their cross section could be removed without risking global pillar or back collapse. The main interest was to measure the vertical stress component rapidly, with a good accuracy and at low cost without any assumption regarding the state of stress in the pillars.

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the The 34th U.S. Symposium on Rock Mechanics (USRMS), June 28–30, 1993

Paper Number: ARMA-93-0541

... state law (thermoporous Hooke's law) relates the

**stress****components**c? to the three state variables [Equation available in full paper] (1) in which G, KB, á and áB are respectively the shear modulus, the drained bulk modulus, the Biot's coefficient and the drained thermal expansion coefficient...
Abstract

ABSTRACT INTRODUCTION Couplings [ 1] between rock, saturating fluid and temperature are an essential step to modelise correctly the mechanical behaviour of deep rocks. Nevertheless, in certain practical applications, the general thermoporoelastic problem can be strongly simplified, the state variables being decoupled. STATE LAWS OF THERMOPOROELASTICITY The relevant description of a thermoporoelastic transformation is based on the existence of three state variables e (strain tensor), T (temperature) and m (mass of injected fluid by unit of total initial volume) [2,3]. The first state law (thermoporous Hooke's law) relates the stress components c? to the three state variables [Equation available in full paper] (1) in which G, KB, á and áB are respectively the shear modulus, the drained bulk modulus, the Biot's coefficient and the drained thermal expansion coefficient. The second state law relates the pore pressure of the fluid to the three state variables [Equation available in full paper] (2) K. and 0q are the undrained bulk modulus and thermal expansion coefficient and P the fluid density in the reference state. The third state law relates the total entropy of the system to the three state variables that is [Equation available in full paper] (3) Ce being the specific heat under isochoric (no variation of volume) conditions.

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the The 29th U.S. Symposium on Rock Mechanics (USRMS), June 13–15, 1988

Paper Number: ARMA-88-0303

... geomechanics effective overburden prestress stress state procedure Reservoir Characterization

**stress****component**horizontal stress situ stress state elastic property body force boundary condition average overburden prestress Overburden Prestress prestress initial equilibrium stress state...
Abstract

Abstract Finite element analyses were used to illustrate the significantly different initial conditions that can result from different procedures for initializing the equilibrium stress state for analyses of complex geologic domains. The closest approximation to the desired initial equilibrium stress field resulted from using an iterative procedure to initialize the pre-existing stress field. Simple gravity loading, that is, the application of body forces to structurally complex domains with no pre-existing stresses, produced an initial equilibrium stress field that deviated from the in situ stress idealization selected for an example problem. 1 Introduction Numerical techniques such as the finite element method are frequently used for stress analyses of large geologic regions. Increasing computational capabilities are providing the potential to include larger geologic regions and more details of the geologic structure in stress analyses. This paper illustrates the need for special stress initialization procedures when establishing the initial equilibrium conditions for large scale analyses. The need arises because these analyses require the establishment of an initial equilibrium stress state that corresponds to the in situ stress field over the geologic domain of interest. The standard approach of applying body forces to the problem geometry is satisfactory for only a restricted group of problems. Analyses that include body forces, topographic relief, and stratigraphic units (e.g. Figure 1) require special considerations. The surface tractions, boundary displacements, body forces, and pre-existing stresses all combine to establish an initial equilibrium stress state throughout the modeled region. The initial stress state must closely approximate the measured or otherwise determined in situ stress state in order for the analysis results to be useful for interpreting the response of the geologic region. The process of stress initialization requires the distinction among three stress states: the pre-existing stress state, or simply the prestress, the equilibrium stress state, and the in situ stress state. The prestress is an initial stress state defined by the analyst at the beginning of the numerical simulation. The equilibrium stress state is defined as the components of the stress tensor that are in equilibrium with the applied surface tractions, boundary displacements, and body forces. For relatively simple problems, the initial equilibrium stress state will be identical to the pre-existing stress state. The in situ stress state is the natural stress state in the rock in the geologic domain of interest. An idealization (e.g. horizontal stress proportional to vertical stress) of the actual in situ stress state is usually modeled in numerical analyses. The stress initialization procedure must establish the desired initial equilibrium stress state, which is defined as an equilibrium stress state that closely approximates the geologic in situ stress state. Figure 1. Example problem for Stress Initialization(available in full paper) No Prestress. Subject the unstressed geologic problem domain to gravitational body forces to generate the initial equilibrium stress state. Solutions to boundary value problems vary significantly with initialized conditions and boundary conditions. Therefore, the attention given to establishing the initial equilibrium stress state may significantly influence the conclusions drawn from such calculations. The effects of three prestress conditions on the initial equilibrium stress state were examined in this study. These are:

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the The 29th U.S. Symposium on Rock Mechanics (USRMS), June 13–15, 1988

Paper Number: ARMA-88-0709

... measuring point stress state main drift pressure capsule

**stress****component**rock behaviour solar battery stress change displacement pressure variation drill hole roof sinkage mining process Key Questions in Rock Mechanics, Cundafi et aL (eds) ¸ 1988 Balkema, Rotterdam. ISBN 90 6191 835 9 Simple...
Abstract

ABSTRACT DEDICATION FROM THE FIRST AUTHOR: I should like to express my appreciation to Prof. Charles Fairhurst, whose infectious enthusiasm for rock mechanics has inspired me with respect and to my work there. Besides, he has opened the way for me to work in geotechnological field in Japan. This paper is a kind of canned food I grew and I would like to dedicate it to him although I am afraid the contents be unpalatable for him. INTRODUCTION In situ measurements of the rock deformations and the stresses induced by mining progress have been or are being carried out in two mines. In Yanahara Mine which is an underground iron mine, the induced displacements in roof rock have been measured by using the vessels communicated by a flexible tube and the stresses were measured by means of flat-jack and hydraulic fracturing techniques, and the stress changes have been monitored by pressure changes of the pressure capsules. The measurements have been carried out over an extended period of time and displacement and stress change measurements are still being carried out. Besides the measurements, the induced roof displacements were predicted by numerical analysis using Boundary Element Method to compare it with the roof sinkages measured. In Kokura Mine which is an underground limestone mine recently developed, the stress changes in rock around the primary opening, induced by excavation of secondary opening which is above or underneath the primary opening, are being monitored by means of pressure capsule. The floor displacement induced are also being measured by LASDIS (displacement meter coupled laser beam and solar batteries). Initial rock stress state and tangential stress at the wall around the primary opening were measured by double fracturing method and stress compensation method using lune-shaped flat-jack, respectively. The paper describes the outlines of the excavation processes, the measurement systems and the measured results related with excavation progress. Particularly, it is emphasized that pressure change measurement by pressure capsule is simple and capable monitoring for safe mining and its general response is remarkably related to mining location. SITES, MINING PROCESS AND MINING PLAN The mined spaces to date of Lower Deposit in Yanahara Mine, which were backfilled or under cutting now, are illustrated in Fig. 1. The positions where the instruments for four kinds of the measurements were set up are also shown in the figure. Initial stresses were measured twice at H1. Roof sinkage measurements were carried out over many Rows and Columns on various Levels for a long time. Only one series of the measuring points, V1-Vll, is shown in the figure. Wall stress measurements using lune-shaped flat-jacks were done at the places around the point F. Stress change measurements by hydraulic fracturing were carried out at H2 and H3, and stress variation measurements by means of pressure capsule were carried out at the places around the points, P0-P5. Recently, the big pillar along Row 21 located in the center of the deposit was partially extracted. Two extracted blocks are shown in the figure.

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the The 29th U.S. Symposium on Rock Mechanics (USRMS), June 13–15, 1988

Paper Number: ARMA-88-0461

... is initiated, only a limited amount of existing perforations will "participate" in subsequent production. drilling operation mechanism principal

**stress****component**generatrix Directional Drilling**stress****component**consideration breakdown pressure Upstream Oil & Gas failure initiation borehole...
Abstract

ABSTRACT This paper addresses the problem of failure and fracture initiation from deviated boreholes, with emphasis on the added complications introduced by the inclination of the borehole with respect to the in situ principal stress directions. The paper also discusses the implications of deviated wells with regard to completion and stimulation. 1 Introduction In thin reservoirs where horizontal wells provide a larger contact area; hence, a better immediate return upon investment. In irregular reservoirs as opposed to large blanket reservoirs, where inclined boreholes allow access to isolated pockets, without the need to drill a number of additional wells, or to add new platforms in offshore situations. In strongly anisotropic formations, where the ratio of the vertical to horizontal permeabilities hinders the production from a classical vertical completion. In naturally fractured reservoirs, where directional drilling provides a communication channel intersecting the family of dominant discontinuities. In situations where water/gas coning is of concern; highly inclined boreholes will definitely delay the "breakthrough time", allowing greater hydrocarbon recovery. In secondary waterflooding schemes where directional drilling technology allows the placement of a man-made "curtain" , resulting in a more efficient drive. Although extended reach drilling is by no means a new idea, only recently has the topic generated renewed interest in the petroleum industry as it could provide substantial economic enticements in the following situations: The reasons why most boreholes are "dropped back" to vertical, even from off-shore platforms at great expense, is due to the present lack of confidence in success-fully completing and stimulating highly inclined wellbores. The present day drilling technology allows a vertical hole to be deviated to horizontal within a 15 ft. milled-out section of the casing (build rate of 6 degrees/foot), using high angle whipstocks and articulated drive assemblies. Horizontal sections in excess of 3,000 feet have been successfully drilled under open hole completion schemes. The major issues, specific to drilling inclined holes are: (i) cutting removal and, (ii) borehole stability. Indeed, in deviated wells exceeding 60 degrees from vertical, chunks of rock usually remain at the highest bend location, rather than dropping to the bottom of the borehole and be re-ground. Once the hole is drilled, a steel casing is usually cemented into the well to iso-late the various producing intervals. Such a treatment is performed via pumping cement inside the casing and displacing the wellbore fluids in the annulus. In highly deviated holes, the concern is the potential of leaving an unbound "channel" along the upper generatrix of the borehole, due to liquid segregation. Special theological cement properties (e.g. turbulent flow regime, controlled setting time, expansion during setting,...) have taken care of most of these problems. What still remains unresolved is the question of hydraulically fracturing an in- clined borehole, especially the created geometry. On one end of the spectrum, a longitudinal .fracture could be initiated, resulting to "traditional" design and field eatments. On the other end, if a transverse .fracture is initiated, only a limited amount of existing perforations will "participate" in subsequent production.

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the The 26th U.S. Symposium on Rock Mechanics (USRMS), June 26–28, 1985

Paper Number: ARMA-85-0557-1

... of two kinds of rock, namely, granite and tuff. Fig. 1 Block diagram of AE apparatus(available in full paper) Upstream Oil & Gas experiment

**stress****component**cylindrical specimen residual strain monotonically MPa rock specimen total ae count creep strain specimen initial geostress...
Abstract

ABSTRACT 1. INTRODUCTION For the purpose of achieving safety design of an underground structure such as a power plant, it is necessary to evaluate initial geostress inside the bedrock. One way of measuring initial pressure is the in-situ overcoring method. In this study it was attempted to obtain initial ground pressure in bedrock by utilizing the Kaiser effect of AE. There is already a case reported in which initial geostress was estimated by utilizing the Kaiser effect (Hayashi). In order to estimate initial geostress by utilizing the Kaiser effect, it is necessary to solve the following problems in advance. Rock in situ has been subjected to the three principal stresses for a long time, and is in a saturated state of strain. (Hereafter, the saturated state of strain is defined as the state in which residual strain is sufficiently generated and in which no further strain can be recognized under a certain stress.) Therefore, in case initial geostress of the bedrock is to be obtained by the Kaiser effect from a rock specimen cored in situ, it is necessary to determine whether the Kaiser effect is being affected by initial geostress from a different direction. Then, it is also necessary to study the Kaiser effect characteristics of a rock specimen in which creep strain is recognized. This article explains the results of the experiments conducted to solve these problems. 2. EXPERIMENTATION APPARATUS AND METHOD OF EXPERIMENT Fig. 1 is a block diagram of the experimentation apparatus. The quantities measured in the experiments are of the stresses and strains to which the specimen is subjected under monotonic loading and of AE generated when the sample is subjected to stress. These data can be computerized and retrieved as relationships of stress-strains and total AE counts. The resonance frequency of the AE transducer used for this experiment was 140 kHz. The filter used was a band pass filter of 100 to 200 kHz and the threshold level was set at 380 mV for the lower level and 400 mV for the upper. One of the problems encountered in AE measurement concerns the elimination of noise. In the present experiment, electric noise generated by the measuring instrument itself was handled by proper grounding. Further- more, the noise generated by the loading plates coming into contact with the ends of the specimen was eliminated by placing thin sponges at both ends of the specimen (Murayama, 1984). The rock in its original location, which has been subjected to the three principal stresses for a long time, is in a saturated state of strain. Two methods were employed to create a saturated state of strain in the laboratory. These Here, a method of applying load repeatedly until there is no further increase in residual strain and a method of applying a constant stress by creep until a constant strain is obtained. The following experiments were conducted in order to study the Kaiser effect characteristics of the specimen in this saturated state of strain. The specimens used for these experiments were of two kinds of rock, namely, granite and tuff. Fig. 1 Block diagram of AE apparatus(available in full paper)

Proceedings Papers

Publisher: American Rock Mechanics Association

Paper presented at the The 21st U.S. Symposium on Rock Mechanics (USRMS), May 27–30, 1980

Paper Number: ARMA-80-0086

... field is particularly interesting because all

**stress****components**are compressive in the elastic solution. Thus it indicates that compressive strength of the plastic response should provide an important influence on the rock response. Upstream Oil & Gas disc cutter slot depth Imberg...
Abstract

INTRODUCTION Hard rock disc tunnel boring machines have been established as an effective alternative to drill and blast techniques. Through proper design of these large machines it has been possible to increase the forces that the cutter head can apply to the rock face and thereby increase the rate of penetration of the tunnel boring operation (e.g., Rad and Olson, 1974, Morrell and Larson, 1974, and McFeat-Smith and Tarkoy, 1979). More recently, pre-cut waterjet slots on the surface of the rock face have been proposed to enhance the cutting rates and/or reduce the loads needed to penetrate the wall. Laboratory tests have confirmed that waterjet slotting can be used to enhance the effectiveness of roller cutters. However, the cost of testing enough parameter sets to determine the most effective way to slot the surface is high and for this reason the present analytical study was performed. The general purpose of the study was to learn if precut slots are useful on Imberg Sandstone through a wide range of parameters, to learn what the range of this effect is, and to outline how parameters such as spacing and slot depth should be chosen in order to achieve selected penetration rates at desired loads. The theoretical problem of determining the load needed for a wedge indenter (or roller cutter) to fail a rock half space has been under investigation for several decades. There have been many papers published on this problem with a valuable collection of results by Chen (1975). In this text there is a complete description of the response to the flat indenter problem, the limit of wedge angle (180º) for a sharp indenter. The solution for a wedge indenter acting on a half space was first determined by Shield (1953). The solution is quite different from the flat indenter because there are no size scales determined by the geometry of the problem. Pariseau and Fairhurst (1967) have analyzed the force penetration characteristics for wedge penetration into rock for a variety of material properties. Effects of nonlinearities in the yield surface are also considered by Cheatham (1964) as well as Pariseau and Fairhurst (1967). This is an important result when considering whether or not the shear strength is linearly related to the pressure. Experimental data have been presented by Rad and Olson (1974) and by Morrell and Larson (1974) for different rocks. Results of these studies cannot be applied to Imberg sandstone because of different values reported for the internal friction angle. The theoretical elastic solution for a point load on a half space known classically as the Boussinesq solution (Timoshenko and Goodier, 1951) is also useful for gaining an understanding of the indentor-rock behavior. The stress field is particularly interesting because all stress components are compressive in the elastic solution. Thus it indicates that compressive strength of the plastic response should provide an important influence on the rock response.