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By D. W. McDonald, N. A. Duke, R. L. Hauser

"The NERCO Con Mine is situated in the amphibolite facies aureole of the Western Plutonic Complex overprinting the Yellowknife Greenstone Belt. Metamorphic grade of the upright monoclinal basaltic succession decreases from hornblende-amphibolite facies along the border of the batholith to greenschist facies. Metamorphic isograds, subparalleling the faulted margin of the batholith, transect volcanic stratigraphy and coincide with major goldbearing shears.Gold mineralization is confined to north-striking, west-dipping shear zones where hangingwall amphibolite facies mineral assemblages retrogress to chlorite-carbonate-sericite-sulfide bearing schists hosting multiple generations of quartz-ankerite veins. The gold-producing portions of the Con and Campbell Shears occur where these structures transect an east trending thermal corridor. The corridor is defined by granitic plugs and a number of related breccia bodies, that can be traced outwards from the batholith across the greenstone belt.Prograde reactions of greenstone during amphibolitization effectively liberate fluids that partition metals. With retrograde reactions at shear zones, gold is precipitated with quartz due to the destabilization of sulfide and arsenic complexes. The coupling of regional prograde metamorphic and restricted retrograde metasomatic overprints suggest mineralization is temporally related to emplacement of the Western Plutonic Complex. Economic gold concentrations within the intrusive corridor indicates enhanced metamorphic overprint of hornfelsed greenstones enveloping satellite intrusives peripheral to the main batholith."

Jan 1, 1993

By J. Shanks

In 1920 the writer presented some notes, embodying his experience with storage-battery locomotives as main under-ground haulage-motors at Brazeau collieries. (1) Since that date these motors have stood up well to the test of maximum output and heavy overloads, having accomplished all that was expected of them. The notes presented in 1920 gave a brief description of the conditions under which these motors were working at Brazeau collieries, also the cost, per ton mile, of operating them. The cost per ton mile has since then been appreciably reduced, by working the locomotives nearly to capacity and under more ideal haulage conditions, on both shifts. It is not the intention of the writer to repeat what was written in 1920, but rather to give members the benefit of his experience in operating different types or designs of locomotives; to draw their attention to the drawbacks of some designs, and to the improvements made in some of the more recent storage-battery locomotives put on the market, as regards efficiency, upkeep, and safety. Because of their flexibility storage-battery locomotives have advantages over any other type of haulage, where grades are suitable to their use. The number in use in the mines in the United States has increased enormously during the past few years, and this method of haulage is, at the present time, attracting the attention of British and Continental mining engineers.

Jan 1, 1924

By J. Lee, K. B. Min, J. Rutqvist

Shear slip of fractures in fractured rock masses is a critical issue for many geological engineering applications, such as the design of underground nuclear waste repositories, enhanced geothermal systems (EGS), and geosequestration of CO2. This paper presents new development of the TOUGH-UDEC simulator for analysis of coupled thermal-hydraulic-mechanical (THM) processes in fractured porous media. As an alternative to developing a single coupled THM code in discontinuum, two existing wellestablished codes, namely TOUGH2 and UDEC, are coupled to cover coupled THM analysis of multiphase fluid flow, heat transfer, and deformation in fractured porous media. TOUGH2 is widely used for modeling heat transfer and multiphase, multicomponent fluid flow, and UDEC is a well-known discrete element code for rock mechanics, which have been verified and used by many groups all over the world. Although a sequential coupling of two codes is less efficient than having a single code in principal, a big advantage with coupling of TOUGH2 and UDEC is that both codes are well tested and widely applied in their respective fields. When linking two codes, the coupled equations cannot be solved simultaneously; they should be solved sequentially, with coupling parameters passed to each equation at specific intervals. After solving thermal-hydraulic equations through the TOUGH2 model, pressure (P) and temperature (T) information is delivered to UDEC model. Pressure information is directly stored at the center of each UDEC zone and domain, however, temperature information is interpolated from zone-centers to the corners nodes. After solving the mechanical equation through the UDEC model—considering new pressure and temperature—calculated fracture apertures are converted to equivalent permeability and porosity for TOUGH2 flow analysis. The solution was calculated by iteratively following an explicit sequence for numerical efficiency. Verification examples are presented to demonstrate the capabilities of the coupled TOUGH-UDEC simulator.

Jan 1, 2015

By S. Balideh

A good understanding of the behavior of broken rock helps to make more informed decisions regarding slope stability and waste dump issues in mines. The cohesion coefficient of rock has little influence on the strength of broken rock; therefore, a criterion based on friction and cohesion of intact materials does not provide an accurate analysis for the strength of broken rock. This paper illustrates the effective strength of broken rock through a brief literature review about failure of intact rock and rock masses. The complete stress- strain curve and some important points of residual strength of rock are summarized in this paper.

Jun 1, 2012

By K. Kawagishi, K. Matsumoto, Y Koizumi, H. Harada

A new burner rig for cyclic and hot corrosion testing of Ni-base superalloys and high-temperature coatings has been developed at the National Institute for Materials Science (NIMS) in Japan. The concepts of the rig design include: use of kerosene as fuel, easy operation for materials research and multi-specimen testing capability per test run. The burner rig consists of six blocks including combustion block, corrosion-solution injection block, furnace block, specimen block, controller block and outdoor facility block. During verification testing, it was confirmed that the rig had accurate specimen temperature control within ±1? from 600 to 1100? and automated easy operation. Cyclic testing of several Ni-base superalloys was conducted. The results from 50 cycle testing indicated that a new NIMS alloy developed for 1700? class gas turbine had higher oxidation resistance than CMSX-4. This new burner rig testing capability at NIMS can be very useful for future oxidation, hot corrosion and coating durability studies.

Jan 1, 2010

By Xuehui Xia

Abstract -There are a number of sedimentary exhalative massive sulfide (SEDEX) deposits in the Proterozoic Langshan-Zhaertai rift at the western segment of the northern margin of the North China platform in China, including more than ten large, medium and small deposits located in a belt of 300 km EW by 50 km to 100 km NS, with large Cu, Pb, Zn, Ag, and S reserves. In several representative SEDEX deposits in the rift, the mineralizing elements are prominently zoned, horizontally or vertically, with Cu decreasing but Pb increasing from west to east, Cu decreasing but Zn increasing from bottom to top, and Zn restricted to the bottom half. The ore-hosting rocks, characterized by a clear manganese halo, have developed a polymetallic mineralization in positive relation with their carbon contents. Their isotopic aspects are: ?34S has relatively large positive values, fluctuating between +5‰ and +35‰, compared with Pb isotopic compositions which are less variable, with a model age of 1600 Ma to 1800 Ma, showing that they are mantle-derived. The mineralizing materials were associated undoubtedly with the contemporaneously faulting events in the rift. The deposits owe their origin to seafloor exhalation, with sedimentary rocks as their hosts.

Jan 1, 1999

By Youngsoo Song, Hyunjung Kim, Junhyun Choi, Siyoung Q. Choi, Gahee Kim

In this study, for the first time, to confirm the effect of bacterial growth phase on the malachite flotation were investigated in a well-controlled Hallimond tube system. The test results showed that the bacteria in the stationary phase exhibit two-fold greater floatability than those in mid-exponential phase. To understand the observed flotation behavior, complementary cell characterization tests and cell attachment tests were conducted. Interestingly, the bacteria at both phases exhibited similar surface properties as well as almost identical amount of cells attached onto the malachite, suggesting that the growth phasedependent flotation behavior cannot be attributed to the variation of cell surface properties and the extent of cell adsorption. On the other hand, cell detachment tests revealed that the amount of cells detached from the malachite surface is greater for the mid-exponential phase than the stationary phase due to the higher fluid drag applied to the cells at the mid-exponential phase, which was explained by the differences in the size and shape of attached bacteria onto the malachite surface. These morphological characteristics were found to cause the bacteria of mid-exponential phase to be separated highly sensitive and easy from malachite surface due to the fluid flow. Second, scale-up selective bioflotation tests were carried out in a 1 L Denver cell in malachite–silica binary mixture systems. Through the tests, we optimized the cell concentration and the malachite fraction in the feed. Overall, high malachite selectively was observed under optimized conditions (both recovery and grade showed more than 90%). The trend was in agreement with classical DLVO interaction energy profiles, which show the relative magnitudes of the adhesive forces between the mineral and the attached cell under equal hydrodynamic conditions.

Jan 1, 2016

By Angela L. Paveley

Economic viability of base metal mining is complicated by a volatile market that can cause fluctuations in the growth and stability of the mining industry. Nickel is mined primarily for use in manufacturing industrial stainless steel and plating materials. It is essential that nickel production be sufficient to respond to current and future market demand. A Post-Pillar cut and fill mining complex is currently producing nickel sulfide in Northern Manitoba. From 2006 this area has shown a steady increase in the annual production, rising from 11 million pounds to 25 million pounds in 2010, and accounting for 33% of the total production for the Manitoba Operations. It is expected that fine-tuning the mining process can safely enhance ore recovery, improve production consistency, and increase economic viability of the deposit. The Post-Pillar Optimization study was initiated by the local technical and operational departments at the mine and analyzed from July 2010 to March 2011. The purpose of this study was to determine if portions of non-recoverable pillars can be slashed without jeopardizing pillar strength. This ideal case would optimize ore recovery and reduce variability in the ore mining rate. Numerical modeling and geo-mechanical material properties analyses, completed by the rock mechanics group, define the maximum drift width at 32 feet and the minimum pillar width at 18 feet. Thus, it was suggested that up to 3 feet could be slashed from two sides of the standard 24 foot pillars without damaging ground integrity. The field data collected indicates that additional ore could be recovered without compromising the safety of the workplace and the integrity of the complex. Consequently, technical and operational groups work jointly to achieve pillar optimization. Approximately 500,000 pounds of nickel was extracted from the complex via pillar optimization from July 2010 to March 2011. Economic analyses show the pillar optimization method developed for the mining complex is a proven, value-added opportunity. The mining complex remains a safe workplace and has retained ground integrity.

Nov 1, 2011

By T. C. Chudy, C. C. Hamilton, G. R. Lane

The selection and provision of mineralogical services to assist in developing a GeoMetallurgical program for a Cu Porphyry Mine in South America is covered in this paper and presentation. The objectives of the study were to provide a rapid mineralogical scoping protocol to support and confirm results of sequential Cu leach data and to provide detailed mineralogical analysis of four composites and products on which locked cycle test-work were performed. Results showed good reconciliation was achieved between measured chalcopyrite and secondary Cu mineral contents with leach data using a linear intercept mineralogical procedure by TIMA (Tescan Integrated Mineral Analyser), as well as a generally positive correlation between pyrite and Cu-sulphide grain size. Size-by-size analysis of Composite feeds and test products was used to outline comparisons between feeds on a mineralogical basis and provide liberation and association data with which to diagnose and better explain performance. Identifying key mineralogical drivers to Cu recovery and concentrate grades using these results, a greater understanding of the role of chalcocite and pyrite on metallurgical performance was established. INTRODUCTION As a global supply of copper, porphyry copper deposits are typically very large, often in excess of a billion tons of ore (Keeney, Walters, & Kojovic, 2011; McMillan & Panteleyev, 1980) with grades typically between 0.2 and 1.2% Cu, and up to 2% Cu in places. They are also a source of gold. The complexity of copper porphyries arises from their classically zoned nature, the type of host rock, as well as whether or not they have been overprinted by oxidation, weathering and supergene enrichment (Sillitoe, 2011). Zones of alteration and other geological attributes give rise to varied mineralogy, ore mineral textures and material properties, all of which result in different processing characteristics. Due to the interdependencies of geological and processing characteristics, it is vital to study links between the geology at the macro-scale and mineralogical features down to millimeter and micrometer scale (mineral content and texture) and their influences on mineral processing behaviour (Cropp, Goodall, & Bradshaw, 2013). The growing field of GeoMetallurgy aims to provide an Orebody Knowledge framework by which to gather such information as it pertains to: (1) Understanding and predicting likely flotation response; (2) Guiding relevant test work to investigate and validate links, interdependencies, theories and data interpretation/evaluation; (3) Populate a block model with relevant information and; (4) Implement and refine the model for ongoing optimization and control. Specific questions addressed by using mineralogy often include flotation diagnostics as aids to interpretation, causes of dilution and losses to tailings, as well as guidance to sampling for test work (Cropp et al., 2013).

Jan 1, 2019

By D. F. Machuca-Mory

The new algorithm for high-order simulation of ore deposit grades termed HOSIM is based on the concept of spatial cumulants. The algorithm is tested using data from Apensu, a structurally controlled gold deposit in Ghana. The required high-order spatial structures are obtained from a training image or analogue of the deposit. Using the available drillhole data and training image, HOSIM realizations are able to model well the grades and geometry of the large and well sampled mineralized structures. However, under-sampled small structures remain difficult to model. HOSIM offers a promising alternative for the spatial simulation of complex non-Gaussian orebody attributes of interest.

Jan 1, 2011

By H. Dundar

An extensive testwork was performed around the HPGR plant at GoldFields Ghana Limited Tarkwa Gold Mine. The HPGR was used to prepare the feed for heap leaching. The circuit was configured in such a way that the edge material from the HPGR discharge was recycled for further crushing while the product from the centre reported to the heap leach section. The set-up of the Polysius HPGR provided an opportunity to study the effect of different design and operating variables. This paper will discuss the results from the tests performed to assess the effect of rolls? speed and applied pressure on the capacity and the grinding efficiency of the HPGR. Applying different pressure values appeared to have an influence on the amount of edge material recycled.

Jan 1, 2012

By D. Y. Li, C. D. Ma, T. Zhou, T. J. Cheng

In this paper, a number of experimental tests are carried out to study the strength difference on rectangular prismatic marble specimens with different height-to-width (H/W) rations. The specimens have a nominal size of 45×15 mm in the compressive cross-section (W×T) and different heights (H = 22.5 mm, 45 mm, 60 mm and 90 mm). It is to say that the height-to-width ratios are equal to 0.5, 1.0, 1.33 and 2.0, respectively. The quasi-static uniaxial compressive tests are finished by a servo-controlled INSTRON machine (the strain rate at about 10-5/s), and the dynamic compressive tests are finished by a diameter of 50 mm cylindrical SHPB apparatus (the strain rate reaching about 101/s). The rock failure process of marble specimens is captured by a high speed camera in order to distinguish the fracture propagation behaviour. It is found that the compressive strengths increase when the H/W ratio of marble specimen changes from 2.0 to 1.0 due to the end clamping effect both for quasi-static and dynamic loads. However, when the H/W ratio changes from 1.0 to 0.5, the apparent compressive strengths decrease both for the two loading conditions. The strength decrease of short marble specimens may be attributed to the change of failure mode from shear to slabbing, which can be identified by the fracture patterns of the specimens. Based on the uniaxial compressive tests, the slabbing strength of the marble was found to be about 40% of its UCS for the specimens with a nominal height-to-width ratio of 2.0. In addition, it is found that the dynamic increase factors (DIF) are affected by the specimen’s aspect ratios. It implies that the same aspect ratios should be used to compare the dynamic and static compressive strength of rocks. Meanwhile, both the static and dynamic tensile strengths of the marble are obtained by the Brazilian disc tests. The ratio of the dynamic tensile strength to the static tensile strength of the marble is about 2.68.

Jan 1, 2015

By H. J. B. Couto, J. G. S. Puelles, M. L. Torem, R. H. Rojas, A. G. Merma

Understanding the limits of fine particle flotation is fundamental to achieving a significant and selective separation. Conventional flotation processes are not suitable to treat these particles because of their low collision efficiency. This problem can be overcome by decreasing the bubble size or by increasing the apparent particle size. However it is worth noting that the use of small bubbles or micro bubbles also involves some disadvantages such as their low momentum resulting in a slower process comparing with conventional flotation. Electroflotation is an attractive alternative for treating fine particles with small bubbles less than 100 µm, generated by the electrolysis of water. In this sense, this study assesses the effect of current density and pH on bubble size in a binary electroflotation cell. An increase in the bubble generation rate was reported with an increase in current density. In addition, at acid pH values, the size of oxygen bubbles increased and conversely decreased at basic pH values; this may be due to the electrostatic attraction between the oxygen bubbles and the anode resulting in a greater nucleation time. An opposite trend was observed with the hydrogen bubbles. These results are in agreement with their electrokinetic studies, which reported that at acid conditions the bubble surface may be positively charged for both the hydrogen and the oxygen bubbles. Finally the bubble size was slightly affected by the electrolyte concentration, resulting in smaller diameter bubbles at higher concentrations.

Jan 1, 2016

The article presents an outline of methods and certain results of laboratory tests, underground tests and model tests, aimed at assessing performance of a powered shield support on the floor of low strength parameters. The tests were conducted within the framework of GEOSOFT project co financed by Research Fund for Coal and Steel (RFCR-CT-2010-00001). The described research works were conducted by Central Mining Institute (Glówny Instytut Górnictwa), Janina coal mine and Becker-Warkop

Aug 1, 2013

By Michael J. Beare

Requirements of both local permitting and international fundraising are forcing increasing numbers of projects in Russia and CIS to carry out dual technical studies. The principal focus of Russian mining project design is to satisfy local regulatory requirements. However, the technical documents are not generally accepted by international banks for project finance outside Russia. Similarly, international study documents are not accepted for permitting in Russia. The purpose of this paper is to compare and contrast Russian and international approaches to mine technical studies and draw conclusions from this. The Russian design and permitting system is centered around two key statutory technical documents termed the TEO Konditsy and the TEO Project. These documents are subject to regulatory approval and are broadly equivalent to the international prefeasibility study and the feasibility study respectively. A comparison of study criteria suggests similar approaches are used for the main technical disciplines in project design by the time projects are at the point of construction, but there is divergence on environmental matters where the OVOS (Russian ESIA equivalent) differs from an ESIA in some significant areas. The key differences relate to project footprint, level of technical detailed required for baseline studies, level of public consultation, consideration and disclosure of information, labour, coverage of community and social issues and the preparation of a Social and Environmental Management System (SEMS). It has been noted that the Russian Design Institutes often leave the detailed economic analysis until after the TEO Konditsy. A common problem is design teams tend to look for ?technological solutions? without due concern for project economics. The end result of this can be mines that are overcapitalized and hence sub-optimal. It can be concluded that Design Institutes have the monopoly on Russian permitting reports and this is likely to continue. Similarly, Russian institutes generally do not prepare feasibility studies to international standards and this is likely to continue to be the case. Therefore to achieve the requirement of dual technical studies, the international consultants and Russian Design Institutes will need to cooperate on a joint work program. Key issues will be to ensure the most appropriate option studies are carried out at the right stages, that project economics are considered throughout the study, and that the environmental work program covers the additional studies necessary for the ESIA.

May 1, 2009

By Laxman M. Amaratunga, David N. Yaschyshyn

"In the mining industry several types of fills are used for backfill operations. They are broadly categorized into three basic types: rock fill, hydraulic/slurry fill, and paste fill. Recently, paste fill has become the popular alternative for backfilling because of its many environmental and operational advantages including its ability to use total tailings, both fine and coarse fractions.Amaratunga and Annor (1989) first presented the concept of agglomeration of fine tailings, which are otherwise excluded from backfilling, for utilization in backfill as a readily available supplementary fill material. Previous experimental work investigated the use of agglomerated fine gold mill tailings in low density slurry fills (60 -70% pulp density), consisting of varying agglomerate and tailings compositions.This paper presents the ongoing research into utilizing these agglomerates in a high density paste fill (70 -85% pulp density). Various binder dosages, curing period and combinations of pellet to tailings ratios were studied. Slump of the raw fill and compressive strength of the cured fill were examined. Results from the above study indicate that agglomerated tailings paste fill (ATPF) has superior strength characteristics when compared to total tailings paste fills.IntroductionThe Canadian mining industry produces more than 500 million tonnes of tailings and waste rock annually. These tailings consist of a coarse fraction and a fine fraction and can be either reactive (acid generating) or non-reactive. Most mining operations utilize the coarse fraction for backfilling while the fines have been traditionally disposed of in surface tailings ponds. Recently, paste fill has been developed which uses a fraction of the fine tailings (10 - 30% w/w of >45 µ,m) in the fill. This development allows a mining company to use a portion of the fines for backfill, but still requires surface impoundment of the unused portion of fine tailings. Reactive tailings have the added problem of generating acid after being oxidized in the presence of air and water. Treating acid mine drainage (AMD) seepage from these ponds has proven to be a costly environmental problem and long term liabilty.One practical method to reduce the environmental impacts associated with the tailings pond and to modify the physical and chemical properties of the fine mill tailings so that they can be utilized and disposed of in an environmentally safe manner through surface or underground applications is through agglomeration using the Cold-Bond Tailings Agglomeration technology (CBTA). Amaratunga and Annor (1989) first presented the concept of agglomeration of fine tailings for use as coarse aggregates for underground backfill, gravel or surface covering material. CBT A reduces the necessity of impounding tailings on surface while providing a suitable coarse aggregate resource material for practical use. Although the CBT A technology has been mainly limited to pelletization agglomeration alone, other forms of agglomeration like pressure agglomeration which include the techniques of briquetting and extrusion have also proven successful (Amaratunga, 1995)."

Jan 1, 1996

The dissolution of chalcopyrite has received a significant amount of attention. The predominant paradigm of investigation is that its rate of dissolution is limited or passivated by a surface coating or film of material. The common candidates for such a passivating coating are numerous: polysulfide coating, metal deficient layers, copper sulfide coating, bornite layers, jarosite precipitates, and elemental sulfur films. While this line of explanation, that is, the explanation based on passivation, seems to have won some form of consensus with researchers, there is another explanation for the results that can account for all the results observed. Crundwell (1988) proposed that the solid state properties of chalcopyrite, in particular, the semiconducting properties, are responsible for the observed behaviour of chalcopyrite. The purpose of this paper is to outline the semiconductor mechanism of dissolution, and to show how this mechanism accounts for all the observed phenomena recently reported in the literature. The paper outlines the semiconductor mechanism of dissolution, shows how this mechanism accounts for the dissolution

Jan 1, 2014

By M. R. MacIver, M. P. Pawlik

"An image analysis method based on chord length distributions is applied to the batch settling of polyacrylamide flocculated kaolin suspensions. Two features of the interaggregate void space, the void chord length distribution mean and the white-to-black distribution ratio are extracted from an image series obtained over the two hour settling experiments. This approach produces three signal values, from two different probability distributions that can be measured as an indication of underlying sediment bed density and aggregation state. Further work is required on the physical interpretation of the signal, the image acquisition conditions, and the parameter selection methods. It is suggested that this chord length based feature extraction technique may be a useful signal to monitor during batch settling or thickening.INTRODUCTIONFew in situ techniques are available that can be used to directly measure aggregate properties within sediment beds in thickeners or secondary settlers. Typical process variables monitored include rake torque and height, bed level and pressure, feed rate and density, underflow rate and density, settling rate, and overflow turbidity; yet these process variables are only weakly related to process dynamics (Concha et al. 2014). Additional process monitoring signals, based on the direct measurement of aggregate properties could improve solid-liquid separation control and allow the extraction of more detailed information from batch settling experiments.Several optical methods exist for measurement of moving suspensions of aggregated solids in the dilute concentration regime, such as focused beam reflectance measurement (Peng and Williams 1994), and the turbidity fluctuation method (Gregory 1985). In the more concentrated region of a thickener, acoustic backscatter penetration and attenuation measured with an acoustic probe and changes in the underlying solid concentration in the highly concentrated, near-bed region of a thickener as a function of height and time (Hunter et al. 2012). While machine vision for froth monitoring has been thoroughly studied with at least five commercialized technologies (Aldrich et al. 2010), its’ application to the study of thickening has been limited."

Jan 1, 2016

By H. Utsunomiya

Most magnesium alloy sheets show low deformability in rolling. Edge cracks and transverse fractures are common difficulties. In addition, rolled sheets show well-developed basal texture <0001>//ND. The texture causes high anisotropy in mechanical properties and low formability in subsequent metal forming. Differential-speed rolling, where the upper and the lower rolls rotate at different speeds, introduces shear deformation through the thickness. Not rolling texture but shear texture evolves in the sheet so that the asymmetric rolling can be a method of texture control. However the primary slip system of the hcp alloy, is basal, the shear texture should be also basal. Differences between the two basal textures, i.e., the rolling texture and the shear texture, have not been understood completely. In this study, conventional (same-speed) rolling and differential-speed rolling have been applied to commercial AZ31B sheets at 623K. Microstructures, textures and mechanical properties of the rolled sheets before/after annealing are compared. It is found that the basal texture is more pronounced by the asymmetric rolling. On the other hand, the asymmetric rolling is effective to decrease the grain size and the planar anisotropy.

Jan 1, 2006

By D. R. Schmitt, Q. Jia, R. Kofman

"Tests were carried out on clear glass blocks containing borehole aligned with and at an angle to applied principal stress states in order to study the growth of drilling induced tensile fractures. The samples were illuminated such that photoelastic fringes could be video recorded during the measurements; this was useful in assessing states of stress and in determining fracture initiation. Axial drilling induced fractures were observed at the azimuths of the applied uniaxial stress as would be expected from the concentrated stresses. En echelon fractures were observed from the borehole deviated at 45° to the direction of the compression. These preliminary and currently qualitative results show that glass blocks serve as a useful test medium for studies of stress concentration and drilling induced fracture creation. INTRODUCTIONWith the increasing exploitation of unconventional oil/gas reservoirs using deviated drilling in recent years, the effects of the in-situ stress on the success of energy production have become more critical than ever before. Knowledge of the state of stress in the earth enables us to determine well trajectories, well locations, hydraulic fracturing design and production rates, but knowing the crustal stress is always challenging. Strictly, it can only be obtained to varying quantitative degrees by accessing the earth through drilling. Failure of the rock at the borehole wall produces borehole breakouts (e.g., Bell & Gough, 1979; Haimson & Herrick, 1986; Zoback et al., 1985) and drilling-induced tensile fractures (DITF) (e.g., Aadnoy, 1990; Aadnoy & Bell, 1998; Barton et al., 1997; Brudy & Zoback, 1999; Davatzes & Hickman, 2010; Peska & Zoback, 1995). Thus, it is important to understand the failure mechanism of the rock in the vicinity of the borehole. A number of closed-form expressions have been developed that allow the stress concentrations to be calculated in the vicinity of a borehole including Kirsch’s (1898) 2-D plane strain solution and 3D formulae for elastically isotropic (Hiramatsu and Oka, 1962) and anisotropic (Lekhnitskii, 1981; Amadei, 1983) continua. These solutions have been applied in numerous studies (e.g., Ong, 1994; Ong & Roegiers, 1996; Vahid & Ghassemi, 2011; Jia & Schmitt, 2014; Ito et al., 2001) to analyze the failure mechanisms of drilling-induced tensile fractures (DITF) on the borehole wall."

Jan 1, 2015