ABSTRACT: This paper establishes an analytical model for dolomite acid-etched damage at the laboratory scale with the combination of reaction kinetics of acid-rock and damage mechanics, where the damage variable is defined as the reduction of effective bearing area. In addition, the expression of damage variable will be derived in calculus and simplified by the definition of dimensionless variable. The microscopic mechanism of acid-etched damage process has been revealed analytically, with a theoretical preliminary exploration of the coupling effect of acid damage and mechanical parameters. Combined with Lemaitre's equivalent strain principle to visualize dynamic change of the elastic modulus, and the deterioration dynamics of elastic modulus has been described quantitatively after plotting the damage trend graph under different dimensionless variables, which can provide reference for the prediction of fracture pressure and guide the design of deep acid fracturing. 1. Introduction The acid fracturing technology degrades the rock mechanics parameters of the reservoir through the dissolution between the acid and rock, and can effectively reduce the fracture pressure, which is one of the efficient measures to develop deep carbonate reservoirs (Wei et al., 2018). The acid rock reaction changes the microscopic material composition and structure inside the rock, which changes the macroscopic mechanical characteristics of the rock. During the acid-etched process, chemical dissolution occurs at the interface between the acid and the rock, causing uneven dents on the rock surface. On the one hand, it causes damage to the reservoir rock, which manifests the deterioration of mechanical parameters; on the other hand, it also forms high-speed channels of oil and gas which can increase diversion capacity. At present, scholars have conducted a lot of research on rock damage during acid-etched. The experimental research has been carried out firstly and found that water has a significant effect on the fracture of single crystal quartz (Atkinson et al., 1981), and the adsorption of water vapor reduces the free energy on the mineral surface; Through theoretical analysis, the chemical process, dissolution and solid-state diffusion and alteration in the water-rock system all have important effects on the rheology of crustal rocks (Kirby, 1984). These early explorations indeed provided a basis and reference for future research on acid rock; Hutchinson et al. (1993) used limestone as the experimental object, and used different chemical solutions to simulate the acid type. It is found that limestone dissolves in acidic solution, while it follows the law of physical dissolution in sodium salt solution, which has begun the research of acid rock action. However, the dissolution of rock in acid is only the most basic experimental phenomenon, and further exploration is needed for the research of rock mechanical properties. Haneef et al. (1993) used electronic probes and other techniques to conclude that the corrosion of granite and other materials is more serious than that of a single case when they are in the grounding position. This research result confirms the dissolution effect of rocks under the action of acid rock from a microscopic point of view; The triaxial compression experiment is conducted to study the influence of different concentrations of salt solution on the friction coefficient of sandstone cracks systematically (Feucht et al., 1990). The research method of triaxial compression test began to show its advantages for the study of acid rock action, which has been widely used in subsequent related research.

Abstract The hydraulic fracturing method of rock stress testing as described in ASTM (ASTM D4645-08) and ISRM (Haimson & Cornet, 2003) is conducted to characterize in-situ stress for a variety of applications in the energy, civil, mining, and geotechnical fields. A review of downhole and surface equipment utilized to perform the hydraulic fracturing method is presented. Significant improvement in the performance of open-hole hydraulic packer systems has been achieved over the past 20 years as a result of production-style hydraulic fracturing treatments in block cave mining in Australia and Chile. In one mine alone, it is estimated that more than 250,000 treatments have been conducted. As a result, inflatable straddle packer systems that can withstand up to 90Mpa are now readily available and cost effective due to the volume of equipment manufactured for block cave mining. The pressure and flow required to perform successful tests varies widely depending on rock type, rock quality, depth and local stress regimes. A simple analysis is presented to demonstrate that a one-size-fits-all technical specification of minimum recommended pressure and flow requirements can result in unnecessary project costs. Introduction The hydraulic fracturing method of rock stress testing as described in ASTM (ASTM D4645-08) and ISRM (Haimson & Cornet, 2003) standards is conducted to characterize in-situ stress for a variety of projects in the civil, mining, and geotechnical fields. While the exact pressure and flow required to complete a successful field campaign is impossible to predict, it is critical to have a sound estimation of what is reasonably expected. Underestimating the equipment requirements can result in an unsuccessful and costly test campaign, whereas erring on the side of caution, i.e. over-specifying pressure and flow requirements, can result in unnecessary cost and effort for a given project. The purpose of this paper is to explore "right sizing" the field equipment for successful in-situ stress measurements with the intent to provide a resource for those who are specifying job requirements to contractors, and for those contractors who are tasked with carrying out the field measurements.

ABSTRACT: A series of fracture and flow tests are being performed at the Sanford Underground Research Facility (SURF) as part of the EGS Collab project. The tests involve generating a communicating fracture(s) between two boreholes, and monitoring flow through the generated fracture(s). To perform these tests a robust, remotely operable pressure system is required, as much of the flow testing will be performed over long periods of time when the equipment is not monitored. The system utilizes several pumping systems to include air driven liquid pumps, syringe pumps, and a triplex pump. The syringe pumps and triplex pump are connected to a data acquisition and control system, and can be controlled remotely for pressure and flow. The triplex pump is controlled using a variable frequency drive and a pneumatically actuated back pressure control valve on an integrated flow bypass line. A secondary back pressure control valve can be used to generate back pressure in the production side of the system. The injection and production test intervals are connected at the surface via high-pressure tubing and a differential pressure gauge, and downstream of the production well a series of sensors are in place for detecting tracers injected into the system. The pressurization system is connected to the in situ fracture through a pair (one in each of the boreholes) of straddle packers with a proprietary measurement tool in the packer interval. The tool, dubbed the SIMFIP (Step-Rate Injection Measurement for Fracture In Situ Properties) packs off and allows flow into and out of the interval along with collecting data from numerous sensors. Data from the shakedown of the system, performed at Sandia National Laboratories prior to field deployment, will be presented.

ABSTRACT: Expandable rock bolt, as an efficient ground control product, is widely used in underground mines. However, its capacity and service life are significantly reduced if the metallic body is subjected to corrosion. In some hard rock mines in the US, highly corrosive ground conditions exist and the bolts corrode within a few months after installation. To provide mining industry a corrosion resistant expandable bolt, Keystone Mining Services, LLC (KMS) analyzed corroded bolt samples, identified root causes, evaluated properties of various coating materials, and developed a new Python M3 TM rock bolt that is protected with an innovative PyFlexU2 TM coating. The Python M3 TM bolt features improved steel chemistry for reliable performance and modified profile for better inflation, surface preparation, and coating application. With a flexible, adhesive, and highly corrosion-resistant undercoat, and a very hard sacrificial topcoat, the PyFlexU2 TM coating system provides the Python M3 TM a superior protection against chemical corrosion and physical scratch damage. The product has been tested in the most challenging conditions including extreme laboratory corrosion tests and field borehole scratch insertion tests. With demonstrated performance, the product has been embraced by hard rock mines in the US. This paper identifies the root causes of the bolt corrosion, briefs analysis process, and details laboratory and underground test results on the Python M3 TM rock bolt coated with PyFlexU2 TM . 1. INTRODUCTION

ABSTRACT: This work is performed in the framework of feasibility study of underground repository for High-Levels radioactive Wastes. Based on the design concept of ANDRA, the retrievability of waster packages requires ensuring the mechanical stability of the steel liner for several thousand years. During the lifetime of repository, the host rock is subjected to various coupled loadings, such as mechanical loading/unloading, ventilation and temperature variation. Moreover, the steel liner may be corroded by the eventual contact of groundwater coming from the host rock and then induce a degradation of its useful properties, including strength, permeability, gas production, volumetric expansions, etc… The combinative effects of the steel corrosion and the evolution of host rock deformation may induce an eventual structural failure of steel liner and an amplified fracture damage zone in the host rock. Therefore, the long-term safety of the repository requires a detailed study on the thermo-hydro-mechanics coupling effect including corrosion phenomena on the response of host rock. In view of this, a disposal tunnel supported by a steel liner is simulated and analyzed. Using THM coupling model, a series of parametric study is then performed to identify the influence of different corrosion phenomena, for instance, the corrosion velocity, the volumetric expansion of corrosion products and the mechanical properties of corrode steel as well as the temperature. The analysis of numerical results allows us capture the important issues controlling the influence of corrosion process of steel liner on the THM response of claystone 1. INTRODUCTION

Abstract The construction of some civil and mining structures requires the installation of rock bolt to strengthen, consolidate and stabilize the rock-rock, rock-concrete or concrete-concrete interfaces. In this paper, an experimental study was put on to validate non-destructive methods aiming at detecting the state of corrosion in these rock bolts in real condition. The acoustic techniques were applied on rock bolts that were embedded in concrete blocks and submitted to accelerated corrosion using the impressed current corrosion method. In fact, ultrasonic pulse echo measurements were taken every 24 hours. In addition, an acoustic emission system was attached to the corroded blocks as well as a reference block, in order to monitor the corrosion activity during the corrosion process. Half-cell potential was also performed at the beginning and in the end of the corrosion process. For ultrasonic pulse echo measurements, a quantitative assessment of the energy of the echo from the walls and the end of rock bolts shows a decrease of the energy in the rock bolts when they suffer from corrosion. While the energy of the echoes stays unchanged in the absence of corrosion. 1. INTRODUCTION Corrosion of metallic materials in concrete and in rock is a major problem in the construction and repair industry. Visual inspection of metallic systems once installed does not provide proper indications of the current problem. Non-destructive methods are then very useful. Hadjigeorgiou et al. studied corrosion that affects the rock bolts in mining in Canada, and they recommended monitoring of the effectiveness of the rock bolts in order to evaluate their current state [1]. Baxter et al [2] observed that rock bolts will inevitably be affected by corrosion, and some explanations were provided: • Injecting the bolts with cement grout or resin is often not well-performed, as several voids could be observed. • Bolts injected with resin usually show more signs of corrosion. • Corrosion is higher near the bolt head, mainly due / to poor sealing with grout. And impact of external environment.

Abstract In this paper, a disposal cell for the high level radioactive wastes (HLW) is studied in order to identify and demonstrate the coupled phenomena evolving in HLW repository. In the disposal cell, the overpack and container, which represent important engineering barriers of disposal cell, may be corroded by the eventual arrival of underground water coming from host rock. The corrosion of metallic components induces a degradation of its useful properties including strength, permeability and volumetric expansions, etc. Based on the concept of disposal cell, different materials (i.e. clay, steel and air) are taken into account in numerical simulation. Their mechanical behaviour are characterised by different constitutive models respectively. In order to overcome the eventual numerical difficulties and quantitatively reproduce the closing process of spaces presented in the disposal cell, numerical methods are formulated to descript the long-term corrosion behaviour of steel and the progressive closure of spaces between the geological barrier and different engineering barriers. The numerical results show us that the spaces can be closed with the volumetric expansion created by the steel corrosion and allows us to obtain some quantitative results on the processes developed in the disposal cell with the consideration of the progressive corrosion of metallic components.

ABSTRACT: This paper presents the results from a 5 year laboratory and in situ investigation into the cause of corrosivity of rock support systems in underground hard rock mines. Long term in situ monitoring of corrosion was complemented by controlled investigations in corrosion chambers. During site visits, samples of corroded support units were collected from several mines and subsequently analyzed using S.E.M. and photomicrography. A series of controlled experiments in the corrosion chambers qualified and quantified the influence of minerals and rock deposits on the corrosion rate of steel and rock support. 1. INTRODUCTION Despite great strides in the design and implementation of ground control systems, it has been difficult to eliminate ground falls. One quality control issue related to support is related to a reduction in support capacity over time due to corrosion of the reinforcement and surface support units. This is illustrated in Figure 1. A corroded wire mesh failed and therefore, it no longer provided the support for which it was designed for. The reduction in support capacity due to corrosion may not be explicitly considered in the selection and design of an underground support system, as demonstrated by Figure 1. Quite often, corrosivity is found to be the issue during an investigation in the mechanisms and cause of failure that may have resulted in a fall of ground. Usually the investigation puts an emphasis on fracture analysis, and in doing so, this may identify the contribution of corrosion to a unit or system failure, [1]. Fracture analysis focuses on the separation of a solid body into two or more parts under the action of stress. The stress would have initiated and propagated the formation of cracks. A ductile fracture mechanism is characterized by considerable plastic deformation prior to and during propagation of the crack.

ABSTRACT Horizontal drilling has been applied in tight-gas reservoirs to enhance drainage and, when combined with fracturing stimulation, often results in a high-productivity well. Throughout the last several years, developments in openhole horizontal completions have been designed to stimulate the entire horizontal interval by segmenting the well with mechanical devices, such as compression set packers and chemical swelling packers. The advanced completion system with a series of mechanical openhole packers was designed to generate hydraulic fractures in each desired interval while the mechanical packers provide mechanical diversion at high differential pressures. This paper examines the hydraulic fracturing process under the influence of packers under in-situ stress conditions. Boundary element analysis incorporating the fiction stress method (FSM) and the displacement discontinuity method (DDM) is preformed to simulate the fracturing process. The boundary element method (BEM) is used because it does not require any artificial boundaries for unbounded problems and is well-suited for modeling fractures. Stress distributions around transverse fractures are investigated to understand the influence of existing fractures. The results indicate that the sealing pressure of the open hole packers against the borehole must be carefully selected to avoid generating unwanted fractures along edges of the packers. 1. INTRODUCTION The number of horizontal wells drilled has increased significantly in the past decade, along with more technical developments in horizontal completion methods and fracturing stimulation in unconventional, low-permeability reservoirs. Early techniques, such as the use of limited entry and bullheading, provide little improvement compared to vertical wells. Throughout the last several years, developments in openhole horizontal completions have been designed to stimulate the entire horizontal interval by segmenting the well with mechanical devices, such as compression set packers and chemical swelling packers. Two techniques have proven successful at creating transverse fractures in horizontal wells. In cemented and cased horizontal wells, if the wells are drilled in the direction of the minimum stress and then perforated with short intervals (no more than four times the openhole diameter of the wellbore), a transverse planar fracture will be generated. In openhole horizontal wells, hydrajet perforating is necessary to create a clean, non-damaged, fairly large and continuous path through the borehole wall into the formation [1]. The eroded tunnel should be created along the maximum horizontal in-situ stress and will help initiate transverse fractures in either a normal or strike slip stress regime. An advanced completion system with a series of mechanical openhole packers to generate fractures in each desired interval is studied using the BEM. Boundary element analysis incorporating the FSM and DDM are performed to simulate transverse fractures initiated from horizontal wellbores. The BEM is used because it does not require any artificial boundaries for unbounded problems and is well-suited for modeling fractures. Previous works in literature primarily study stress distributions around the wellbore wall and tangential stress distribution along the packer-influenced zone caused by different packer pressures throughout formations [2, 3]. There is a lack of analysis on the axial stress distribution along the wellbore and influence of generated fractures on the subsequent fracturing stage.

ABSTRACT: This paper presents the results of on-going investigations in several underground hard rock mines in Canada. Since the summer of 2007 a series of regular site visits was undertaken in order to monitor the performance of support systems. Site visits originally focused on visual assessment of the performance of support systems and collecting failed support elements for subsequent laboratory investigations. Furthermore, water samples were recovered and analyzed. The influence of atmospheric corrosion on the loss of capacity of support systems was also recorded. Underground mine atmosphere is characterised by high humidity, gas from engines and blasting and fine dust particles of different mineralogical composition. The presence of these conditions has an adverse influence on the ability of steel based support systems to withstand corrosion. A field testing program was designed to evaluate the type and rate of corrosion in the encountered underground mining environments using corrosion coupons. Coupons were recovered at regular time intervals and were subsequently tested in the laboratory. Tensile strength tests were performed on corrosion coupons installed in different underground conditions to establish correlations between the observed corrosion rate (mass loss) and reduction of steel strength. This has significant implications on the long term performance of support systems in corrosive mining environments. 1. INTRODUCTION The design and installation of reinforcement and support systems in underground mines is well advanced. Nevertheless, despite great strides in design and quality control practices it has been difficult to eliminate ground falls. Although ground falls can be attributed to a range of causes such as inadequate design and poor installation, a common problem is the reduction in the capacity of support systems over time. In certain cases this reduction in capacity can be attributed to the corrosion of support systems. The impact of corrosion is illustrated in Figure 1 where a corroded metal strap has sheared and failed, i.e. it no longer provides the support for which it was designed. The loss of support capacity over time is not explicitly considered in the design of support systems. Quite often the emphasis would appear to be on fracture analysis to identify whether support corrosion was a contributing factor following ground falls [1]. Some operating mines have made efforts towards developing classification systems [2, 3, 4], pertaining to the susceptibility of an environment towards corrosion. For a variety of reasons these classification systems have not gained widespread acceptance. This paper summarizes on-going work to gain an improved insight on the factors that contribute to the corrosion of support systems in selected Canadian mines. The investigation program combines on site analysis with comprehensive laboratory experiments and testing. The long term objective is to develop sufficient data and understanding that can be used in the selection of appropriate support strategies, and eventually to a reliable assessment of the predicted useful life of a support system. 2. MINING ENVIRONMENT Previous work by the authors focused on monitoring environmental conditions at several underground mines displaying a range of mining and operational conditions, [5, 6].

Abstract Stress corrosion cracking (SCC) has been reported to be a significant cause of premature failure of rockbolts in Australian coal mines [1]. At some mine sites, failure of rockbolts due to SCC has occurred well within the twelve to eighteen month design life of longwall gateroads. Failure is often associated with installations in coal and carbonaceous shales containing clay bands. The use of very high tensile grade steel is commonly used in many of these mines and it is thought that the low impact toughness of this steel may be a significant contributor to SCC failure. While laboratory corrosion studies have been undertaken to assess the metallurgical influence on SCC, the results do not correlate with field observations. A possible contributor to the enhanced incidence of premature failure in recent years may be due to the increase in extraction width from 250 m to 400m in many Australian longwall mines that can lead to an increase in the loading on the rockbolt. This paper examines the current state of knowledge concerning rockbolt failure in Australian coal mines. 1. INTRODUCTION Australia is the world's largest exporter of coal worth nearly $A22.5 billion in export earnings in 2006-07. While longwall mining accounts for approximately only 18% of total coal production, this proportion is likely to increase as surface open cut operations reach their economically viable limits [2]. The incidence of stress corrosion cracking (SCC) of rockbolts has been reported in several of the thirty-odd longwall mines operating in Australia, with at least three mines reporting a high incidence of premature failed bolts [1]. The School of Mining Engineering at the University of New South Wales has recently commenced a research project into SCC of rockbolts in Australian coal mines. The objectives of the project are to identify the environmental causes of SCC and ultimately provide a tool for the identification of SCC high risk environments within a coal mine. The subsequent knowledge and understanding gained about the SCC environment will be applied in building a laboratory facility for testing of various rockbolts. The laboratory facility will enable the development and testing of new coal mine rockbolts to withstand SCC. 2. ROADWAY STRESSES IN AUSTRALIAN LONGWALL MINES The extraction of coal using the longwall coal mining system involves large areas of coal some 250m wide by 2000m long which need to be initially blocked out. These areas are delineated by development tunnels or roadways driven within the coal using Continuous Miners or similar coal cutting machinery. The roadways are cut into the near horizontal coal seam forming a rectangular profile. Weak to moderate strength sedimentary rock layers are present in the roof and floor of the roadway, typically these include shales, claystones, siltstones and sandstones. Over the years various means have been employed to ensure the stability of these roadways and other underground excavations as the surrounding rock mass is subjected to high levels of stress.

ABSTRACT: We developed a new reusable gage designed upon a concept completely different to that of the conventional ones. The gage allows us to measure the tangential deformation of borehole wall. We tested the gage by a laboratory experiment and examined how it could measure accurately borehole deformation caused by packer inflation. The rock specimen had two drilled borehole of 76 mm in diameter with hydraulically-induced axial fractures. The results show that the deformation measured by the gage located near by the fracture mouth increased linearly with the packer pressure initially and it deviated from the initial trend afterwards. The deviation from linearity of the deformation-packer pressure curve was associated with the fracture opening. Then we confirmed that the packer pressure at the beginning of deviation was close to the reopening pressure Pr estimated by the Kirsch equation, i.e. Pr = 3S h - S H , where S H and S h (S H = S h ) are the biaxial compressive loads externally applied to the specimen as the direction of S h being normal to the fractures. This indicates that we can estimate the magnitude of S H from the detected reopening pressure and the Kirsch equation on condition that the magnitude of S h is estimated using other approaches. 1. INTRODUCTION Change in stress of rock mass should appear as borehole deformation. Based on this principle, many researchers attempted to estimate the change in rock stress from borehole deformation. To do that, various ways have been proposed so far for measuring borehole deformation such as the USBM gage, the cell of Bonnechere, the CSIR HI cell etc [1]. The former two are reusable, and they can be installed quickly into boreholes. For the last one, gluing is required so that relatively long time is needed for installation and it can not be reused. On the other hand, the change in rock stress affects tangential deformation of borehole wall more sensitively than its diametrical deformation as can be seen easily. However, the conventionally-developed reusable gage such as the USBM gage and the cell of Bonnechere can measure only diametrical borehole deformation but not tangential one, while the fixed cell such as the CSIR HI cell can measure tangential borehole deformation. Taking account of this situation, we developed a new gage which allows us to measure the tangential deformation of borehole wall. For the installation of the new gage into boreholes, the cementing or gluing is not required so that it is reusable and allows quick installation. We tested the new gage by a laboratory experiment and examined how it could measure accurately borehole deformation caused by packer inflation. 2. A NEW DEFORMATION GAGE Fig. 1 shows the deformation gage developed in the present study. The gage has a part of two thin beams made of phosphor bronze and strain gages of four in total are attached on both sides of the beams. There is a short leg at the center of each beam. When the gage is pressed against the borehole wall somehow, the two legs of the deformation gage contact with the borehole wall, and afterwards they move following the tangential deformation of the borehole wall.

ABSTRACT: When mining at great depth, on going time-dependent deformations or unexpected rock failures due to high stress may be experienced. In order for ground support to survive the large displacements and control the rock mass, yielding cable bolts have been developed in South Africa and Australia. Decoupling of a significant length of the strand from the cement grout to allow for large displacement of the reinforc ement element means the system is effectively a point anchored system. Consequently, for cable bolts the performance of the barrel and wedge anchor becomes critical to achieve effective load transfer. Failure by sliding of anchors relative to the strand under low loads has been observed in several underground mines in the Eastern Goldfields of Western Australia. This is attributed to a combination of poor installation practices and corrosion. The results from a number of cable bolt barrel and wedge combinations placed within a corrosion chamber and subsequently pull tested to determine the load-displacement response are examined. The results show that after 7 months in the corrosion chamber the barrel and wedge used with a yielding cable bolt failed at loads significantly less than the strand capacity. The service life can be extended to more than 10 months with the application of barrier corrosion protection. On the other hand, galvanising of barrel and wedge anchors is not recommended. INTRODUCTION Corrosion of barrel and wedge anchors and the consequences for the entire cable bolt performance is poorly understood, despite the common use of cable bolts in Australian underground mines since the 1970s. The use of barrel and wedge anchors to restrain plates, straps and mesh in cable bolt reinforcing applications commenced in the early 1980s in Australian mines [1]. Recent developments in cable bolt design have meant an increased reliance on anchors to be serviceable for long periods of time, especially for applications where the strand is decoupled from the cement grout. Anchor failures after short time durations and under low loads have been observed in several underground mines in the Eastern Goldfields of Western Australia (e.g. Fig. 1). Failure is often characterised by the barrel and wedge remaining intact after being found on the floors of drives with no evidence of strand rupture [1]. Approximate

ABSTRACT: A new methodology is presented to determine 3-D hydraulic conductivity tensor for a fractured rock mass through 3-D discrete fracture fluid flow modeling. First, a 3-D stochastic fracture network model was built and validated for a gneissic rock mass based on the fracture data mapped from scanline surveys at the site. This validated fracture network model was combined with the fracture data observed on a borehole to generate a stochastic-deterministic fracture network system in a cubic block around each packer test conducted in the same borehole. Each packer test was simulated numerically applying a developed discrete fracture fluid flow model to estimate the influenced region or effective range for the packer test. A block size of 60 feet with the packer interval located at the center of this block was estimated for the influenced region. Using this block size, the average flow rate per unit hydraulic gradient (defined as the transmissivity multiplied by mean width of flow paths) field for fractures was calibrated at different depth regions around the borehole by numerically simulating the packer tests conducted at different depth regions. The average flow rate per unit hydraulic gradient of the fractures in the immediate vicinity of the borehole was considered to be quite different to the average flow rate per unit hydraulic gradient of the fractures at a significant distance away from the borehole. A relation was developed to quantify the ratio between these two parameters. Representative Elementary Volume (REV) for the hydraulic behavior of the rock mass was then estimated to be a block size of 50 feet. Finally, the hydraulic conductivity tensor in 3-D was obtained. The principal directions of hydraulic conductivity were found to be consistent with the existed fracture system. Further, the geometric hydraulic conductivity calculated was found to be comparable to the hydraulic conductivity estimated through the radial flow assumption in continuum porous media. INTRODUCTION Currently used methods for estimating threedimensional (3-D) hydraulic conductivity tensor using either aquifer pumping test or packer test data are based on the assumption that the groundwater is flowing through a geologic continuum (Bear, 1972; Marsily, 1985; Hsieh and Neuman, 1985). These methods can generally be applied when wells penetrate the porous geological media such as alluvial deposits, but may have limited applicability when the geological medium is dominated by a fracture system that has well defined fracture sets. The porous, continuum media assumption is based on an average flow within a Representative Elementary Volume [REV] (Bear, 1972; Marsily, 1985). Even though the REV is small for porous media, for fractured rock masses it can be very large or in some cases may not exist (Kulatilake and Panda, 2000). If the REV does not exist, or is larger than the distance between the pumping and observation wells or the packer test hole and observation wells, it is not appropriate to use the equivalent continuum approach to analyze the aquifer pumping or packer test data for fractured rock masses. Before applying an equivalent continuum approach for a rock mass, one should investigate the REV for the hydraulic behavior of the rock mass. The REV for the hydraulic behavior is defined as the size beyond which the rock mass hydraulic conductivity tensor remains the same. For sizes larger than or equal to REV size, the equivalent continuum approach can be applied for the rock mass with a second-rank, symmetric, positive-definite hydraulic conductivity tensor. Estimation of the REV for hydraulic behavior of a highly heterogeneous, anisotropic rock mass requires monitoring of groundwater level of a significant number of obs

ABSTRACT: A circular, servo-controlled, biaxially loaded Shear-Permeability frame, approximately 2 m in diameter, was fabricated and used to investigate the coupled hydraulic-mechanical response of natural and artificial fracture surfaces to normal and shear loading. Loads are provided by two independent actuators, equipped with 0.89 MN load cells. The computer controlledata acquisition system and digital to analog chips provide displacement control while maintaining the specified normal and shear stress boundary conditions. Using the existing actuators, a 200 mm by 300 mm fracture plane can be loaded to about 23 MPa of normal stress or a shear stress of about 10.5 MPa. The normal and shear displacements of each fracture plane are measured using two LVDT's on each corner of the sample. An inflatable packer system provides boundary control for flow and transport experiments within the fracture plane during repeated cycles of normal and shear loading at temperatures that range from 6øC to 80øC. INTRODUCTION Direct shear machines have been used extensively to determine the shear strength parameters of soils for many decades and their designs are well-documented in the soil mechanics literature. However, direct shear machines for testing rock and discontinuities in rock have only been used extensively during the last three to four decades. Standardized methods for the design of direct shear machines and the shear test procedures to be followed are given by Gyenge & Herget (1977) and Brown (1981). These authors stated that the six basic components of a conventional shear machine include: 1) A shear box which houses the fractured rock sample and consists of a stationary half and a half that is moveable along the direction of shearing. The sample is encased in the shear box with an encapsulating material such that the plane of discontinuity is coincident with the shearing plane. 2) A mechanism for applying a force normal to the shearing plane, such as a hydraulic jack, and capable of being maintained at a constant value (accuracy of 1-2%). 3) A mechanism for applying a shear force to one half of the shear box along the plane of the discontinuity, and capable of shearing the sample at a uniform rate of displacement (I.2 120 mm/hr). Shear displacement should not be greater than 10% of the sample length (the direction of shearing should be reversible). 4) Equipment, such as load cells with an accuracy of + 2%, for independent measurement of normal and shear forces. 5) Equipment for measuring normal and shear displacements, such as electric transducers fixed on the sample as close to the joint as possible. 6) An automatic data acquisition system to measure, record and display results during testing. Jaegar (1971) stated that, in principle, the direct shear system has five degrees of freedom: horizontal and vertical translation in addition to rotation about a vertical axis and two horizontal axes. The above author considers that a sixth degree of freedom, lateral translation, should however be added to the list. Figure I shows the six degrees of freedom (3 translations and 3 rotations) in a direct shear system. The number of degrees of freedom in the design of a direct shear machine should reflect the in-situ conditions the experiment attempts to simulate. In most systems, the horizontal (shear) displacement and vertical (normal) displacement are controlled while lateral displacement and all rotations are prevented. Crawford and Curran (1981) describe a shear machine with three degrees of freedom

ABSTRACT INTRODUCTION In-situ stresses are key parameters in the design of a hot-dry-rock (HDR) operation for the extraction and the economic use of geothermal energy. In-situ stresses control the operation pressure to activate pre-existing fracture / joint-systems, determine the underground fluid flow paths, or influence borehole stability in un-cased borehole sections. The HDR geothermal research site at Soultz-sous-Forets (France) near the western margin of the Upper Rhine Graben is one of the possible candidates for a future European HDR-prototype with a target reservoir temperature of 175°C at only 3.5 km depth. During the first project phase (1986-1990) borehole GPK-1 was drilled to a depth of 2000 m. In the granitic section between 1376 m and 2000 m, eight hydrofrae or injection tests were conducted [1]. These tests were characterized by several technical problems caused by using conventional packer technology in the hostile downhole environment (high temperature of 140 °C, high gas and salt content of the borehole fluid). In spite of the problems, five tests yielded sufficient pressure and fracture orientation data to conduct an inversion type stress analysis [2]. The result of the computations yields the following stress profile for the depth interval between 1458 m and 2000 m: Sh, MPa = 15.1 + 0.0179 (z, m 1458) Ss, MPa = 24.8 + 0.0198 (z, m1458) Sv, MPa = 0.024' z, m direction of Ss: N 155 ° ± 3°. Due to the limited data base of only five tests a valid extrapolation of this stress profile to reservoir depth was impossible. The determination of stresses down to reservoir depth, therefore, asked for the conduction of deeper and more reliable hydrofrae stress testing. Such tests also required the development of a new hydrofrae tool based on aluminum packers adequate to the hostile downhole environment.

ABSTRACT INTRODUCTION The Underground Research Laboratory (URL), near Pinawa, Manitoba has been excavated in granitic rock belonging to the Lac du Bonnet batholith, one of many intrusions of the Canadian Shield. The batholith is 75x25 km in surface area and extends downward about 10 km. Its age has been estimated at 2680 Ma. Two major thrust faults dipping 25-30 ø to southeast have been encountered at URL, Fracture Zone 3 at about 100 m depth, and Fracture Zone 2 at about 280 m (Figure 1). Fracture Zone 2 in particular appears to be the boundary between two separate stress fields. Based on previous stress measurements using a variety of techniques, such as USBM overcoting, microseismic, convergence, and hydrofracing there are strong indications that the principal horizontal stress magnitudes increase considerably below Fracture Zone 2, and that their directions rotate with respect to those established at the higher elevations (Figure 1). However, no measurements have been conducted below the 420 level. We carried out a total of 14 hydraulic fracturing tests and 9 oriented-packer impressions in borehole HF1, a 100 m vertical N-size hole drilled downward from the floor of 420 level, URL. Details of the procedures, results, interpretations, and stress calculations are presented in the following chapters. TESTING EQUIPMENT AND PROCEDURE The equipment used in these hydraulic fracturing measurements was especially prepared for the very high breakdown pressures anticipated. Previous tests were on occasion unsuccessful in fracturing the rock below Fracture Zone 2 due to equipment pressure limitations (typically 0-60 MPa). The hydraulic system used in the present tests was upgraded so that it can be operated safely at pressures reaching 100 MPa. Downhole pressure transmitters were placed in a sealed housing on top of the straddle packer for the purpose of downhole monitoring of test-interval and packer pressures. During testing, the downhole packer and test-interval pressures and the flow rate were continuously monitored and recorded simultaneously on a 3-channel strip chart analog recorder, a data tape recorder, and a microprocessor (PC) via an analog-to-digital converter. Testing procedures were similar to those described in earlier publication by Haimson. We used an impression packer orienting tool to obtain an oriented trace of the induced hydraulic fracture on the test-hole wall. Fracture traces on the impression packer were marked with respecto a scribe line on a transparent sheet for later detailed analysis.

ABSTRACT: Conductivity estimates Kp, from packer tests are the normal basis for sto- chastic continuum (SC) models of sparsely fractured rock. The scale of the tests is often much smaller than the scale on which the rock acts as an equivalent porous medium (EPM). Therefore extrapolation of test results to the scale of blocks in a SC model, based on continuum assumptions, is questionable. This paper demonstrates an alternative method for extrapolation of Kp, data, based on discrete fracture network (DFN) model- ing. 3-D rock blocks were simulated based on fracture geometric and packer test data from Finnsjtn, Sweden. Constant-pressure packer tests were simulated in these blocks, and the results were compared with field data to validate the fracture model. Effective block-scale conductivities Kb, were estimated by modeling steady-state flow through the blocks. Probabilistic estimates were obtained of the relationship between Kp, estimates and Kb, for block scales from 15 to 50 m. The DFN model predicts that the correlations between Kp, and Kb, are poor, even for the smaller blocks. INTRODUCTION Predictive modeling of water flow in sparsely fractured, low-permeability rock is required for design of high-level nuclear waste repositories and other types of under- ground facilities such as gas storage caverns. Problems in modeling this rock arise from the tendency for the flow to be concentrated within fractures. Interconnections among fractures to form flow paths can be highly irregular on scales of concern for site model- ing. This is evident from the high variability of heads seen in the vicinity of tunnels in tight, sparsely fractured rock. To model this rock, its strongly heterogeneous and effectively random nature must be represented. Two types of models which do this are: -Discrete fracture network (DFN) models. -Stochasticontinuum (SC) models. DFN models represent the discrete flow paths explicitly, whereas SC models represent blocks of the rock mass in terms of an "equivalent porous medium" (EPM). The more detailed representation used in DFN models has thus far restricted use of these models to rock volumes smaller than (200 m)3. SC models are viewed as being more tractable for site-scale modeling. Unfortunately, the properties of rock blocks on the scale of the constituent blocks of SC models cannot be measured directly in the field. Therefore it is difficult to obtain answers to two critical questions: -Does the rock behave as an EPM on the block scale? -If so, then how should the block-scale conductivities be estimated from packer tests? The first question has been treated extensively in the literature (e.g., Long et al., 1982; Khaleel, 1989). This paper focuses primarily on the second question, which has not thus far been examined using a discrete fracture approach.

ABSTRACT ABSTRACT Pore-fluid/rock chemical interactions on both short and long time scales can produce significant pore structure and mineralic changes that can markedly alter transport properties, such as fluid permeability. The introduction of the chemical factor requires modification of experimental systems and methodologies developed for measurements in which chemical effects are minimal. Particular attention must be given to temperature effects, fluid chemistry, fluid/rock reactions and kinetics, fluid flow rate, and fluid/experimental-system reactions. The ability to obtain very low, steady flow rates at constant fluid pressure is important for study of some fluid/rock systems. Minimization of metal corrosion is of paramount importance and requires choice of proper metals, such as titanium, and certain Ti-alloys and Ni-alloys. In this paper, we briefly discuss the relevant chemical factors affecting system and experimental design. The primary focus, however, is on the characteristics of highly corrosion resistant metals, thermal and chemical resistant jacketing materials, and the attributes and limitations of various flow-rate and back-pressure control systems and flow-rate measurement systems. INTRODUCTION There is an ever increasing need to develop models that predict variations of transport properties, such as permeability, associated with natural or man-induced pore-fluid/rock chemical interactions, particularly at elevated temperature and stress states. The introduction of the chemical factor, however, requires modification of measurement systems and experiment methodology developed for property measurements in which chemical effects are minimal. Particular attention must be given to factors related to fluid chemistry, fluid/rock reactions and kinetics, fluid flow rate, and fluid/experimental-system reactions. The elevated temperature state enhances reaction rates and modifies reactions, but it also introduces additional experimental difficulties, such as enhanced metal corrosion and changes or possible degradation of system-component materials, thus imposing physical limitations to their use or system capabilities. In terms of system design, special attention must be given to choice of corrosion resistant metals, sample jacketing materials, fluid flow-rate control and measure- ment, fluid-sampling systems, and back-pressure regulation systems. Specifics of experiment design also are influenced by reaction kinetics and scientific objectives. In this paper, we discuss many of these important aspects, with emphasis on details associated with fluid permeability systems and measurements. CHEMICAL FACTORS RELEVANT TO SYSTEM AND EXPERIMENT DESIGN The nature of the alteration of pore-structure and associated transport properties depends, in part, on the initial pore-fluid chemical composition, rock mineralogy and the P-T regime. In general, the choice of a working fluid is dictated by the specific geologic or man-induced conditions or process(es) being studied. System design requires anticipation of the probable range of fluid chemistries and temperatures to be used, which largely determine the choice of corrosion resistant metal(s) to be utilized in the system. The more chemically reactive natural pore fluids typically are saline, containing significant concentrations of chlorides and metal ions, such as Na, Ca, K, Mg. Halide ions, especially in the presence of certain metal ions, low pH and elevated temperature are particularly conducive to metal corrosion. Fluid corrosivity depends equally upon the pH and Eh conditions. Extremes in pH generally enhance corrosion of many metals. The role of Eh is metal specific.

ABSTRACT 1 ABSTRACT This paper presents the results from prototype testing of a new device developed to determine the rock mass deformation modulus during hydraulic fracturing stress measurements. The tool combines a modified U.S. Bureau of Mines borehole deformation gage and standard hydraulic fracturing straddle packers to allow displacement measurements of the borehole wall along three diametrical axes in the pressurized test interval. The deformation modulus is evaluated through utilization of a closed-form elastic solution for a thick- walled cylinder, and the magnitudes and orientations of the in situ stress field are concurrently determined by conventional methods. Enhancement of hydraulic fracturing data interpretation may also be possible by using borehole displacement measurements to monitor induced fracture propagation and improve the definition of break- down, fracture reopening, and shut-in pressures. 2 INTRODUCTION The Basalt Waste Isolation Project (BWIP), conducted for the U.S. Department of Energy by Rockwell Hanford Operations, is assessing the feasibility of long-term disposal of high-level nuclear waste in the basalt flows beneath the Hanford Site near Richland, Washington. This investigation was performed at the Near- Surface Test Facility (NSTF) as part of the in situ stress measurement program. Rock mass deformation properties and in situ stresses are among the most important parameters necessary to assess the stability of underground structures. These parameters are often very difficult to accurately determine, particularly in a closely jointed rock such as basalt. The straddle packer borehole deformation gage (SP/BDG) allows concurrent measurement of these parameters at a single location and avoids many of the shortcomings associated with conventional borehole jacking methods (e.g., Hustrulid 1976). 3 EQUIPMENT AND INSTRUMENTATION A complete description of the design and development of the SP/BDG packer assembly is given by Kim & Cramer (1984). A schematic of the SP/BDG system is given in figure 1, with a detailed schematic of the modified BDG shown in figure 2. Six cantilevers are oriented across three borehole diameters and contact the borehole wall through rigid pistons. Any change in borehole diameter deflects the cantilevers, with the deflection measured by bonded resistance-type strain gages. Two strain gages mounted on each of the six cantilevers are wired to form a half-bridge circuit, which is then coupled with the companion cantilever on that axis to create a full-bridge circuit. To make the BDG compatible with existing packers and boreholes, the BDG diameter is changed from the conventional 38 mm to 76 mm. Figure 1. Schematic of straddle packer borehole deformation gage.(available in full paper) Figure 2. Schematic of the modified borehole deformation gage in the test interval. (available in full paper) The BDG has an inner mandrel with two independent channels. This allows passage of fluid from the upper to lower packer and also pro- vides a conduit for interval fluid to flow on the inner side of the pistons. The interval conduit is necessary to allow the BDG to "float" in the interval and also to provide a mechanism to keep the BDG pistons in contact with the borehole wall during pressurization of the interval.