ABSTRACT: A solidification method by cement of dredged sludge has been performed in laboratory during these last three years. The treated sludge is contaminated by heavy metals. The objective of the research program was to assess the possibility of treating and reusing the solidified sludge as construction materials. First to evaluate the mechanical performances of the obtained geomaterials, axial compressive tests before and after immersion in water were run on cylindrical samples taking into account the percentages of cements and additives, and the types of storage. The environmental performances are obtained by leaching tests on monolithic and crushed samples. The paper presents this environmental aspect of solidification of sludge namely the porosity of the geomaterials and also describes the influence of the used additives and analysis of resulting leaching waters in relation with the initial heavy metals concentrations. INTRODUCTION Cement-based solidification/stabilization technique offers two main advantages that can help to overcome contaminated dredged material problems: First, the technique improves the physical and mechanical characteristics of the treated sediment, second, solidification/stabilization reduces the mobility of inorganic contaminants (e.g. heavy metals). The submitted results and findings are a part from on-going research and experimental program on solidification/stabilization (S/S) by cement and additives (Boutouil et al, 1997; Boutouil, 1998). First investigations concerned the setting of an experimental methodology practicable for the S/S treatment. This methodology includes sludge characterization (mainly geotechnical properties and contaminants concentrations) and the assessment of physical and mechanical characteristic improvement. Several factors were studied, such as: initial sludge water content, cement content and curing conditions and time (boutouil and Levacher, 1997; boutouil and Levacher, 1999). In addition to porosity, ultrasonic velocity and bulk density, compressive strength before and after immersion in water was the main indicator of physical integrity of the solidified sediment.

ABSTRACT: In Northern Bohemia, a new motorway crosses non-engineered landfills of clayey spoil from open cast coal mines. Recent fills are soft, unconsolidated, double porosity medium, originally consisting of lumps of typical dimensions from a few millimetres to a few hundred millimetres. The age of the fills is about 20 to 30 years and over this period they generally remained unsaturated down to the depths of 15 to 20 metres. Laboratory experiments with a model double porosity clayey material revealed high susceptibility to collapse. The site investigation involved both laboratory and in-situ testing. However, neither standard in-situ nor laboratory testing was believed to be representative enough for the field behaviour of the fill. Therefore an instrumented trial embankment was built on a site with about 30 metres of clayey fill. The settlement was found to be confined to the upper 20 metres of the fill. INTRODUCTION In Northern Bohemia, a new motorway between Prague (Czech Republic) and Dresden (Germany) has to cross a coal basin. The coal seam, which is up to 30 metres thick, is overlain by Tertiary overconsolidated clays and claystones. In the 20th century, the original roof-fall underground exploitation of the coal was replaced by large scale open cast mining, which reaches down to depths of about 150 metres. The spoil of the Tertiary clay and claystone has been dumped either in the open pits or in their neighbourhood. Some of these non-engineered fills reach a height over 100 metres. In some places, fly ash and municipal waste had been also deposited in the pits. On the periphery of the landfills, landslides are frequent. The largest one, involving about 140 million cubic metres, occurred in the coal basin area in 1985, as a consequence of the pore pressure build-up in a recent landfill.

ABSTRACT: The in-situ biochemical transformation "IBT" technology has been developed to treat contaminated soils. This technology is developed based on injecting a chemical reagent, in some cases together with catalysts or acids, directly into contaminated soils to transform, and thereby destroy contaminants such as heavy metals. This study presents a fully coupled solution flow-biochemical reaction-phase transformation numerical model for this special technology. The model is capable of predicting the whole process of a contaminant removal. The model is applied to a one-dimensional column system, where constant head conditions are applied at both ends and constant concentrations for both the chemical reagent and the contaminant at the bottom, as shown in the following Figure. As the process of the contaminant removal advances, the porosity at the middle of the column changes from the initial value, before the reaction front reaches the middle point, to the final state, when all of the contaminant has been removed (a); the hydraulic head at the middle point of the column changes from the initial steady state, when no contaminant is removed, to the final steady state, when all of the contaminant has been removed (b); less reagent is being consumed (c) and more contaminant is being removed out of the system (d). INTRODUCTION In both hazardous and non-hazardous waste management, the assessment of the potential for constituents contained in the source material to leach or otherwise be released to the environment is one of the most critical issues. Approaches to evaluate the potential release process of these constituents and their subsequent environmental risks are important in many situations such as pollution prevention, risk reduction, remediation and hazard identification. This study presents a fully coupled flow-reaction-deformation model to evaluate the leaching process of these constituents from solid wastes.

ABSTRACT: Collapsible behaviour of geomaterials, which is the expression of their complex structure, may seriously modify their constitutive modelling. Different kinds of collapses are classified starting with hydrocollapse, garlandlike compression curves, branching-off and diffusion collapse. Some examples of that behaviour are presented using fragmentary (granulated) clay, sugar ballotini and silica gel. Collapse occurring in different ways at the same set of state parameters illustrate the deterministically chaotic nature of collapses. Due to the structural changes of the material induced by collapses it is recommended that collapsing soils be treated separately within structurally homogeneous phases. INTRODUCTION Mathematical models of constitutive behaviour usually consist of smooth functions to guarantee uniqueness. Exceptionally only corners, e.g. of the yield surface, are accepted (Olszak et al., 1964). Since soil behaviour models are mostly derived from the continuous material models and the requirement of uniqueness is imperative, the same rule applies with geomaterials. Their structure, however, substantially varies from that of continuous materials and the analogy in the constitutive behaviour has to be often abandoned. Structural units (grains, particle clusters) in the course of deformation disintegrate, their mutual bonding gets broken, geometry of structural units arrangement changes (compression and shear fabrics), and internal stresses (suction, capillary forces) may become annihilated. Thus, constitutive functions with singularities are to be expected. Figure 1 presents a set of settlement measurements of a 6.5 m high fill consisting of clayey clods (two bottom curves depict subsoil settlement). Such fragmentary clay and claystone has been produced by mining activity (Calabresi et al., 1994; Feda, 1998), by excavating foundations of structures (Nakano et al., 1998) etc. Figure 1 shows that the time-settlement curve of the fill (max surface settlement up to 35 cm) consists of two branches meeting in the point of singularity (kink).

ABSTRACT: The electrical resistivity prospecting is becoming very useful for ground investigation,. because new computer methods have been developed and detailed electric resistivity distribution in ground can be indicated However, characterizations of resistivity for rock mass are not clarified, and it is not sufficiently understood that the measured resistivity values can indicate conditions of rock mass. In this paper, using 17 types of intact rock specimens and 2 types of rock specimens with single joint, the resistivity of these specimens are measured in the laboratory. From these measured data, the relation between resistivity of the rock specimens, saturation, porosity and aperture of discontinuity are discussed. Furthermore, these results obtained by between tests are applied to rock mass assessment in a tunnel. INTRODUCTION The resistivity value of rocks cover a very wide range, from around Ωm for shale to around 10 6 Ωm for fresh igneous rocks, and it is not unusual for rock in the same faces and same class to show variations in resistivity value of around an order of magnitude. For this reason quantitative assessment of geology from only the resistivity value of the rock is generally considered to be difficult. However, since the resistivity of a rock reflects small differences in its degree of alteration and its percentage water content, the distribution of resistivity values is useful information concerning soil properties and rock mass state). In order to assess rock masses using the results of electrical resistivity prospecting, the relationship of the electrical resistivity of the rock mass with the resistivity value for pore water or with saturation must be understood, as must relationships such as that between electrical resistivity for different types of rock and their mechanics, and the relationship between electrical resistivity and mechanics for weathered or fractured rocks.

ABSTRACT: Recently, the use of electrical prospecting with high spatial density of electrodes has increased and is being applied to underground investigations for tunnels, dams, landslides, and other civil engineering purposes. In order to characterize rock mass by using the resistivity distribution of ground obtained from these investigations, it is very important to understand the relationship between the electrical resistivity and engineering properties of rocks. In this paper, the resistivity of various types of rock is measured to elucidate the effect of physical properties of rock on resistivity. The resistivity of rocks has a tendency to decrease with increasing porosity. But, the resistivity does not always correspond to porosity even in the same kind of rock, because of different mineral compositions and pore geometry. The resistivity of rock increases with increasing the pore fluid resistivity, regardless of rock types. However, between 20 and 80 ohm-m which is available groundwater resistivity in rock mass, the resistivity of pore fluids had little effect on rock resistivity. The resistivity of rocks decreases with increasing water saturation up to a certain point, beyond which the degree of this drop becomes insignificant. And the resistivity of unsaturated rock exponentially increases with decreasing water saturation in the region of 20% or less. The tendency of resistivity change for clay content is different by types of smectite clays, while, on the whole, the resistivity decreases with increasing the smectite clay content. INTRODUCTION Fault fractures and altered zones which were developed by the volcanic activities and tectonic movements are widely distributed in Japan. Usually, geological reconnaissance, drilling and seismic refraction survey are undertaken in preliminary geological assessments for civil engineering projects. However, problems remain the accuracy of such data for rock mass classification in area of complicated geological structure and the expected behavior of groundwater.

ABSTRACT: Grouting is normally based on empirical relationships and on the experience of the grouting personnel. To assist grouting projects, a large number of researches using mathematical modeling have been carried out into the clarification of the flow processes during grouting. From this point of view, we constructed a mathematical model to explain the injection process to the rock voids by grouting materials. There are many models of the description of flow paths, clogging of cement suspension in rock voids, flow properties of the grouting materials, and so on. In this analysis, we supposed that the clogging process of the rock voids is occurred by the injection of cement grout. As to the analysis of the voids clogging process, the mass conservation law, in which filtration theory was used, was applied and the analysis was done in one dimension. In this analysis, the concentration and the filter coefficient were considered as parameters to make the injection phenomenon clear. As a result, the voids clogging process by the difference in the cement grout concentration could be explained very well. And the voids clogging process by the difference in the filter coefficient which is in the inside of the mass conservation law, was also explained. INTRODUCTION Controlling water flow through soil or fractured rock mass is important for various reasons. Water leakage into underground openings, with the lowering of the ground water table and consolidation settlements clay layers as a result, can cause surface damage to building. In order to reduce the water flow through soil or fractured rock mass, grouting is a commonly used method. In particular, in dams construction grouting is a very important method to ensure water-tightness and tightness because water seepage under dams causes energy loss and erosion of the damcore.

ABSTRACT: This General Report requested by the Organisers attempts to describe the state-of-the-art as perceived by the Reporter in the area of the determination of rock properties at great depth by physical methods. The paper focuses on laboratory studies of rocks under physical conditions simulating those crustal conditions in which a rock may be modelled as a cracked solid through which fluids may percolate. Current and upcoming developments in the study of compaction and dilatancy in such rocks under triaxial loading are summarised, and the intimate relation between rock mechanics and rock physics is brought out. An important special aspect of this study is the transition from cataclastic to plastic behaviour, which coincides with the elimination of dilatancy and probably of seismic activity. The paper also discusses the need for a strong parallel focus on crustal stress measurement, which is the missing link in the application of rock mechanics and rock physics to many engineering and Earth science problems, particularly in the context of plate tectonics theory, which has facilitated the systematic ordering of knowledge about the Earth's crust and its properties, processes, and evolution. 1. INTRODUCTION With increasing knowledge of the origin, processes, and properties of the Earth's crust, and increasing engineering and technological capacity to extract minerals and heat energy from great depths, there is naturally a growing desire to measure and understand the properties of rocks and rock masses at these depths. The concepts and theories of plate tectonics have in recent years enabled our knowledge of the crust to be ordered in a fundamental and systematic way more suited to useful physical and chemical modelling (e.g. see Bott 1982, Turcotte & Schubert 1982, Meissner 1986). This has stimulated a new interest in the nature, processes, origin and properties of the lower parts of the continental crust (e.g. see Dawson et al 1986), which are being increasingly probed, by electrical deep sounding methods (Haak & Hutton 1986), deep seismic reflection profiling (Meissner 1986, Matthews 1986, Smithson 1986), (which provide both rock samples and opportunities for close range measurements at great depths, see Raleigh 1985 and Behr et al 1987). Field studies by geophysical and geological methods enable the properties of the crust and of rock masses within the crust to be determined and measured, but this is dependent on a good understanding of rock properties at the crystal, grain, and atomic scales. The latter properties have to be determined in the laboratory, based on the laws of physics and chemistry. The subject of the present paper is the determination of rock physical properties in the laboratory within the perspectives of this Symposium. 2. LABORATORY MEASUREMENTS OF ROCK PROPERTIES Advances in laboratory techniques are enabling measurements to be made of rock physical and chemical properties under simulated crustal conditions corresponding to increasingly greater depths. Indeed it is now possible to simulate most crustal conditions, though there are very few laboratories at present that are fully equipped for measurements on rock samples under simulated conditions of great depth.

ABSTRACT: At great depth stresses are approximately equal to the strength of rock. That is why failure develops near such underground excavations. But this failure may not be entire because its value depends not only from stresses but also depends from strains. On the basis of experiments on compression specimens of rocks in rigid presses, particular on decreasing the cohesion with increasing the strains it was formulated the model of gradual shear failure of rocks. Models with constant parameters in the Coulomb formule for the cohesion do not reflect the real decreasing of cohesion and lead to diminish displacements of rock near underground openings. On other case models with instant decreasing the cohesion leads to essential greater displacements because unjustified diminish the cohesion in calculations. It was revealed when the model has been used to one-dimensional static problem of compression rock with circular hole. Also it has been calculated the dynamic problem of burst in rock. Another application of the model has been made to two-dimensional problem about influence the gradual failure of rock into geological break or dyke, which appear near underground opening on formation dangerous vertical tensile stresses. THE MODEL OF GRADUAL SHEAR FAILURE OF ROCKS Rocks contains many strucktural defects, holes and cracks. If stresses change through the distance much larger than the interval between structural defects, then such rocks may be regarded as a continuous medium. The main effect of structural defects and cracks consists in two main phenomena: in decreasing of a cohesion and in increasing of a crack porosity. These two phenomenon a develop simultaneously but gradually while the nonreversible shear strains increases. It follows from numerous experiments of Karman (1911),Byerlee (1968),Stavrogin and Protosenya (1985) and others, and have been used in developed by author the model of gradual shear failure of rocks (Korotkov (1980,1987,1989)).. The model consists of several main equations. In the beginning of failure of rocks there are some strengthening during small increasing of nonrevercible shear strains; it defines as prefailure. Further increasing of nonlinear shear strains causes the intensive decreasing of shear strength. This region defines as post failure. These effects may he described by the loading surface depending from nonreversible shear strains also pressure and temperature. The value of YP calculated only in the region of failure where pressure is not too high, usually less then 10 kbar, because at more high pressure the rock deforms without loss of compressive strength. The full volume is divided in two parts. It consists reversible part of solid framework and nonreversible volume of crack porosity. For the framework the equation of state was accepted with the consideration of effective value of pressure. Earlier theories used only one-term for description of nonreversible porosity, such as Rudnicki and Rise (1975) included only one term for description of dilatancy in rock. Other theories for granular material also used one term for description the dependence porosity from pressure. The model of gradual shear failure used more general description with including both mentioned terms.

ABSTRACT: Seismic methods are beginning to be used in hydrocarbon recovery assessment, in view of the growing need to better understand recovery, especially the compleity of reservoirs, leading to large uncertainties in estimated total recovery, recovery rates, and recovery method. Reservoir complexity is due to the spatial heterogeneity in porosity, permeability, clay content, fracture density, etc. These spatial variabilities cannot be inferred from well test data, logs, or cores. They may only be obtained from remote geophysical measurement, especially seismic measurement. Such measurements will assume a major role in helping to solve production and recovery problems. To achieve that it is necessary to better understand what it is that seismic waves can tell us about reservoir rocks, and how to extract the desired information. This review provides a brief summary of what we know at present about the relation between velocities in rocks and reservoir properties. 1 INTRODUCTION Seismic methods, notably reflection methods in exploration geophysics have been used in the past mostly to delineate rock interfaces in the earth's shallow crust, to delineate structures which might bear hydrocarbons or to describe pre-existing faults. Relatively little use has been made of seismic waves for the determination of the rock properties such as porosity, permeability, compressibility, saturation, pore pressure, fracture density, etc. Seismic methods are only beginning to be used in hydrocarbon recovery assessment, in view of the growing need to better understand recovery. The major problem is the complexity of reservoirs, leading to large uncertainties in estimated total recovery, recovery rates, and recovery method. Reservoir complexity is typically related to the significant spatial heterogeneity in porosity, permeability, clay content, fracture density, etc. These spatial variabilities may only be obtained, hopefully, from remote geophysical measurement, especially seismic measurement. A direct consequence of the heterogeneous nature of reservoirs is the complexity of their recovery processes, ranging from problems like the migration of the gas cap in reservoirs with discontinuous shales, overpressure zones, and the tracking of steam or temperature in thermal recovery in reservoirs with large spatial variations of permeability. For seismic methods to help solve production and recovery problems it is necessary to better understand what it is that seismic waves can tell us about reservoir rocks, and how to extract the desired information. This review provides a brief summary of what we know at present about the relation between velocities in rocks and porosity, saturation, pore pressure, fluid phase behavior, and hydrocarbons and temperature. 2 EFFECTS OF POROSITY AND CLAY CONTENT Shaly sandstones and shales are a major component of sedimentary basins and are of foremost relevance to hydrocarbon reservoirs. When both Vm and Vf are fixed, the only variable in the equation is porosity. To a first order this simple equation appears adequate for clean sandstones in the middle range of porosity (10% < φ < 25%). It is well known however that acoustic velocities of sandstones are also related to mineralogy, pore geometry, degree of consolidation, cementation, confining pressure, pore fluid, pore pressure, and temperature.

ABSTRACT: One of the present day challenges in the oil industry is the proper characterization of in situ reservoir rock properties prior to full scale development. In this respect, experimental data acquisition requires the simulation of representative reservoir conditions in the laboratory. This paper presents details of a novel multi-sample rock testing system and some results of resistivity measurements on 8 sandstone and 4 synthetic rock samples at simulated reservoir conditions. The combined effect of pressure and temperature on formation resistivity factor (FRF) and the Archie cementation factor (m) is also reported. For the sandstone and the synthetic rock samples tested, it is concluded that resistivity increases with pressure and temperature. A pore space network model has been used to gain an insight into the mechanisms of pressure effect on rock properties. 1. INTRODUCTION Fatt also concluded that laboratory measurements of formation resistivity factor, in which only external pressure is varied, are sufficient to study the effect of overburden pressure. Similar results were also reported by Wyble (1958) in the study of the effects of pressure on FRF, permeability and porosity. An increase of Archie cementation factor together with formation factor with pressure was pointed out by Wyble. Glanville (1959) showed greater effect of pressure on FRF and porosity in less porous, less permeable rocks. The reports of Brace et al (1965, 1968) and Timur et al (1972) also confirmed the significant increases in FRF by net confining pressures of the same magnitude as in reservoirs. A review of the studies of the electrical properties at high pressures was given by Parkhomenko (1982) showing that the electrical resistivity at high pressures is related to other rock properties such as porosity, permeability, rock structure and pore geometry. The effect of temperature on FRF has been investigated by Hilchie (1964) using consolidated sandstone and limestone samples. It was indicated that as the temperature increased while the net confining pressure remained constant, the FRF went through a minimum after which it increased. According to Hilchie, this significant change of FRF with temperature was a function of the percent of small pores of radius less than 0.5 micron and the clay content. Helander and Campbell (1966) presented their results of resistivity measurements on six synthetic bead cores and one synthetic sand core bonded by an epoxy resin at varying conditions of pressure up to 69 MPa and temperature up to 160 °C. A definite trend of change of FRF with pressure was noticed due to the changes of rock tortuosity, pore constriction and the change of the electrochemical double layer. The effect of temperature on FRF was not as well defined as the pressure effect because of the much greater experimental difficulty. Sanyal (1971) reported results of FRF measurements at different temperatures to a maximum of 149 DC using three sandstone and one limestone samples. A decrease in apparent formation factors with increasing temperature was found experimentally by Waxman and Thomas (1974) and was attributed to the effect of clay caution exchange capacity.

ABSTRACT: The paper reports the results of an experimental study concerning the influence of confining pressure on gas permeability of sandstones having different mineralogical composition, with permeability values ranging from 0.0009 md to 200 md and taken from a maximum depth of 4400 m. Correlations among permeability variation, initial permeability, porosity and other properties of the samples are shown. 1 INTRODUCTION Increasing demand for natural gas along with depletion of gas reserves has raised considerable interest in the possibility of exploiting gas-bearing formations of low permeability (see Haas et al.(1987)). As a result, greater attention has been given in recent years to tight sandstone technology since it has become obvious that methods of exploiting tight formations must be improved. Of particular importance is better understanding of the factors that modify the permeability of these formations both so as to avoid using exploitation techniques that excessively reduce permeability and choose the most indicated laboratory methods that will provide reliable data on the effective permeability of a formation. In recent years numerous interesting experimental and theoretical studies have been carried out on the permeability of tight sandstones. The aim of these studies was to investigate why decrease of permeability due to a decrease in pore pressure during exploitation are much greater than in normal sandstones (see Jones (1975),Jones and Owens (1980), Gangi (1978), Walls et al.(1982), Ostensen (1983), Freeman and Bush (1983), Wei et al. (1986), Kilmer et al. (19871, etc.). The phenomenon is still far from being understood. This is why the author is presenting the preliminary results of research carried out at the Istituto di Scienze Minerarie into the extent to which changes in permeability can be the effect of variations in overburden pressure and temperature, the characteristics of the reservoir fluids as well as the mechanical, physical and mineralogical properties of the rock itself. This paper examines in particular the decrease in sandstones' gas permeability caused by changes in confining stresses. The permeability of the rocks examined varied under laboratory conditions within the range of 0.0009 - 200 md and the sandstones presented differing mineralogical characteristics. Tests were performed on oven-dried cores at 110°C and cores dried in a humidity controlled oven. Only isostatic stresses were applied to the cores. The effect of artificially induced fractures was also examined. 2 APPARATUS AND EXPERIMENTAL PROCEDURE The apparatus used is suitable for measuring permeability to both gas and liquids with changing confining pressure (range 5 - 50 MPa) and temperature (range 10 - 150°C). Fig. 1 gives a simplified configuration of the equipment used to measure the permeability to gas. The core plugs are 2.5 - 5 cm long. They are cleaned in a solvent extractor, flushed with demineralized water to remove residual salt and then oven-dried at 110°C. The cores are then geometrically measured and weighted and their porosity determined under laboratory conditions. Tests on the oven-dried cores are carried out after each plug is wrapped with an overlapping layer of TEFLON.

ABSTRACT: Laboratory data are presented on the transport properties of three Fontainebleau Sandstone samples. Water permeability experiments under various pressure conditions were performed on fluid saturated cores by the mean of a 100 MFa permeameter. In addition, electrical conductivity of electrolyte saturated samples have been measured over a wide range of pore fluid conductivities. Classical laws fit well our data: some empirical parameters such as Archie's exponent and tortuosity factor are inferred. Comparing experimental data on transport properties to microstructural characteristics of the porous networks is proved to provide very useful informations about the flow processes in porous media. 1 INTRODUCTION Investigating the transport properties of rocks either on the field scale or on the laboratory scale has become an important issue in geophysical research. As a matter of fact, fluid flow processes play a major role in some important problems such as earthquake mechanics or radioactive waste repository. Permeability is for instance the main parameter which determines the recovery capability of oil reservoir rocks. Besides hydraulical flow processes, fluid saturated rocks behave as well as electrically conductive media: both permeability and electrical conductivity are controlled by the characteristics of the Porous networks which exist in such rocks. Permeability and electrical conductivity measurements are relatively easy to perform in laboratory: many studies on sandstones as well as on crystalline rocks can be found in the geophysical literature (e.g. Brace, 1980). In general, interpretations of such experimental results in terms of microstructural parameters are not common: it seems to be however a very attractive approach. Pressure dependence of the transport properties of rocks is of great importance. Its investigation can be achieved in laboratory testing by applying both Pore pressure and external hydrostatic pressure to the sample in a pressure cell. Such a procedure allows to simulate the in-situ pressure conditions and gives access to relevant transport parameters depending on the geological environment of the rock. In the next section, we describe our testing device. Then, we report both permeability and electrical conductivity data on three Fontainebleau Sandstone samples and finally we relate the experimental results to porosity structures previously observed on thin sections. 2 TESTING APPARATUS The experimental apparatus used consists of three major parts, namely the pressure cell, the confining pressure system and the pore pressure system. The maximum pressure capability is 100 MPa; every combination of pore pressure and confining pressure in the range 0.1 to 100 MPa is available. As strong electrolytes may be used, the pore pressure system connected to the sample is restricted to a minimum length by including a separator to avoid extensive corrosion in the circuit. The samples are cores, 2.0 cm. in diameter and about 4.0 cm. long. Silver ring electrodes are painted on the sample circumference at 0.5 cm. from each end. Two jackets are placed on the specimen to insure electrical insulation and to separate the pore fluid from the confining fluid. Electrical conductivity measurements are made at a fixed frequency (4 kHz) at room conditions.

ABSTRACT: A method for estimating the in situ thermal conductivity at basin scale from various well logs is presented. This method is based on the use of the geometric mean model for estimating the thermal conductivity of the different lithofacies of a given well; the various well logs are interpreted in terms of lithologic content and porosity; a mineralogic composition varying with the stratigraphy is assumed for each lithologic unit and a procedure for computing the in situ thermal conductivity profile is proposed. From there, the variations of the average thermal conductivity in each formation - obtained as an harmonic average over the depth - can be mapped at basin scale. The procedure is applied to a number of wells in the Viking graben (North Sea) and the resulting conductivity structure is compared to the present thermal structure. 1 INTRODUCTION Thermal conductivity of sedimentary rocks is a very important parameter for basin modelling: its value directly controls the vertical distribution of temperature. Unfortunately, in oil exploration boreholes, core samples are seldom and laboratory measurements of conductivity difficult to perform. Therefore, the thermal conductivity has to be estimated from the available, routinely recorded information such as well logs. The possibility of deducing thermal conductivity from well logs has been studied by various authors. A first approach is to define an empirical relationship between thermal conductivity and one or several well logs (Houbolt & Wells, 1980, Vacquier et al, 1988). However such an empirical relation has no physical basis and should be calibrated for each situation (Brigaud et al, 1989). An alternative approach, proposed by Brigaud et al (1989) and developped here, makes use of a composition model - the geometric mean model expressing the thermal conductivity of a multicomponent sedimentary rock as a function of its composition and structure. In this later case, the well logs are first interpreted in terms of lithologic composition and porosity; the available mineralogic information is also used for estimating the conductivity of the various lithologic end-terms. A vertical profile of thermal conductivity can then be computed using the relevant composition law, i.e. the geometric mean model. Although this later method is somewhat more laborious than a direct regression vs. well logs, it has the advantage of taking into account the actual mineralogic composition which is difficult to approach using well logs data alone. The results of this method have been found to yield consistent thermal conductivity estimates when compared with laboratory measurements (Brigaud et al, 1989) or to detailed temperature loggings. The purpose of this paper is to present the various aspects of a method designed for obtaining the detailed in situ thermal conductivity structure at basin scale. Then the procedure for estimating in situ thermal conductivity at the formation scale, using well logs as well as complementary information, is described in details. Finally, this technique is applied to a data set in the Viking graben in the North Sea; the conductive structure is described and compared with the thermal structure.

ABSTRACT: Typical curves for rock compressibility have been reviewed. Certain characteristic pressures have been distinguished and the volumetric modulus of elasticity has been expressed in a function of porosity. The characteristic pressures are responsible for the occurrence of the characteristic points on the curves representing the dependence between the confining pressure and strength, strain at failure, elasticity limit and Young's modulus. The influence of the pore pressure, of the interaction of water and of the permanent deformation of the rock due to pressure on the behaviour of these curves and on the characteristic pressures has been discussed. INTRODUCTION: The thermodynamic state of a rock is determined by pressure, temperature and its specific volume. Its mechanical properties depend on the state and the way the rock has been loaded. In particular, already at room temperature, the loading of the rock with hydrostatic pressure including merely the elastic strain, determines, according to the value of the pressure, the behaviour of the rock under deviatoric stress. A sufficiently high pressure produces permanent deformations of the rock, both of the brittle and ductile type. It becomes, eventually, besides temperature, one of the factors leading to phase transitions. Another factor determining the rock properties is the presence of the pore fluid under pressure. The fluid may act by way of pressure on the pore surfaces and by way of sorption which becomes, more intensive as the pore pressure increases. The present paper deals with the mechanical properties of rocks as depending on the confining pressure, on the hydrostatic pressure which leads to permanent deformations of the rock, by the pore pressure induced by an inert gas and by water present in the pores as an active fluid. Deformation of rocks under hydrostatic pressure The rock taken in the scale of a laboratory sample is made up of a solid phase, isometric pores and cracks. The solid phase of many rocks is characterized by a proportional dependence between the volumetric strain and the hydrostatic pressure (Fig. 1a). In a rock containing exclusively isometric pores the proportional dependence between the pressure and the volumetric pressure is usually retained and, according to the theoretical considerations of Walsh (1965 a), its coefficient of compressibility when compared with that of its solid phase (Fig. 1b for limestone) is on the increase. An example of a rock containing exclusively isometric pores and characterized by a non-linear pressure-volumetric strain relation is the sapropelic coal (Fig. 1b). The inflection of a part of the curve is probably due to the closing of the micropores between the crystallites and the easily deformable (in comparison with the solid phase of the above mentioned rocks) hydra.. carbon chains connecting them. According to Walsh (1965 a) the presence of cracks in the rock enhances its compressibility much more than the presence of isometric pores of the same porosity as that of the cracks. This is decidely due to the fact that the cracks are easily closed under growing pressure.

ABSTRACT: The article presents the results of experiments conducted to understand the effect of large overburden stress on electrical resistivity of three Indian sandstones. The intact rock specimens have been tested in high pressure triaxial setup under different confining pressures simulating rock overburden stresses. The maximum confining pressure of 12 MPa applied on rock specimens corresponds to a overburden of around 525 metres of rock. The studies included the combined effect of confining pressure and degree of saturation on electrical resistivity of these sandstones. An attempt has been made to correlate electrical resistivity with the strength properties of these rocks. 1 INTRODUCTION Engineers working in various fields such as mining, underground engineering, oil and gas etc. have well realised the importance of 'geophysical techniques' for subsurface explorations. These techniques possess very high potential to explore deep depths with fair degree of accuracy. Electrical resistivity is one such technique which is very much popular amongst engineers due to its suitability for variety of subsurface conditions and depths. The field electrical resistivity soundings when interpreted furnish complete information regarding strata in addition to depth of ground water table. The interpretation of field electrical resistivity soundings data to derive subsurface profiles involves converting observed apparent resistivity of strata at different depths into their true resistivity values which are then matched with those given in the standard tables leading to identification of various subsurface strata. The major drawback in this procedure is that, the resistivities of different materials available in standard tables are the resistivity values obtained in the laboratory under zero pressure conditions. However, the interpreted values of true resistivities of strata at different depths in the field corresponds to the values under overburden pressures depending upon their depths. This introduces an error in interpretation, the magnitude of which commensurates with the overburden pressures. Thus, it is necessary to apply the relevant corrections to improve the degree of accuracy of interpretation. Subsequently, this suggests an immediate need to understand the behaviour of rocks with reference to their electrical resistivity under high pressures simulating the overburdens. In view of this, in the present laboratory investigation an attempt has been made to study the effects of overburden pressures on electrical resistivity of intact rock specimens. To enable simultaneous applications of high pressures and measurement of electrical resistivity of rock specimens, special attachments to laboratory high pressure triaxial cell were designed and fabricated. 2 FACTORS INFLUENCING ROCK RESISTIVITY The electrical resistivity of rocks depends upon the applied pressure, among other factors. During the application of uniaxial pressure, Parkhomenko and Bondarenko (1960) observed a decrease in resistivity of crystalline rock under low pressure followed by resistivity increase at high pressures. Whereas, the effect of confining pressure on electrical resistivity of rocks reported by Brace et al (1965) indicated small increase in resistivity at low stress followed by large decrease in resistivity at high pressure. These contradicting observations clearly reveals that the influence of pressure on rock resistivity is a complex phenomenon and cannot be generalized.

Introduction This Symposium General Report attempts to highlight important developments in Rock Mechanics for applications to engineering problems at great depth. Much of the report was presented orally in session # 9, but in an abbreviated form. The many excellent written and oral contributions to the Symposium represent a technical richness that will take time to assimilate. We cannot mention all the technical content nor do justice to the effort that the Proceedings represent. We recommend that the reader scan the various General Reports and Invited papers to appreciate the breadth of technical content and the scope of the topic "Rock at Great Depth". Then, with this as background, the detailed papers will provide insight into a number of relevant Rock Mechanics problems in the areas of civil, mining and petroleum engineering, with links to geochemistry, solid body mechanics, geo-hydrology, applied mathematics, tectonics and geophysics. The interdisciplinary scope of the papers is astounding; when a mine designer and a geochemist sit down and discover common interests, when a drilling engineer and an applied mathematician outline similar views of a phenomenon, it speaks for the excitement of Rock Mechanics applications at great depth. The Session General Reporters and Workshop Presidents provided us with useful oral and handwritten comments. In particular, we thank A. Nur, D. Ortlepp, J. Geertsma, M. Chenevert, M. King, R. Widman, W. Bradley, C. Spiers, and O. Coussy for their opinions and comments. Conclusions from the Workshops are summarised, based on oral summaries provided by A. Guenot, W. Kessels, F. Cornet, and written comments by J. Sulem, I. Vardoulakis, P. Berest and Ph. Weber. The last-minute communication by B. Come has also been used. Before a general Symposium conclusion is attempted, we will address a number of current and central issues in Rock Mechanics – Unique aspects of the mechanics of geo-materials at great depth – Rapidly developing areas related to Rock Mechanics and – Specific issues that have arisen during workshops. 1.0 - UNIQUE ASPECTS OF ROCK BEHAVIOR AT GREAT DEPTH "Deep" is defined as 3 000 to 7 000 m, occasionally somewhat deeper, but still involving situations where the rock is physically encountered, as opposed to remotely probed. Below 10,000 m, one must speak of "geological" or "geophysical" depths. This may be the domain of the next generation of petroleum and rock engineers and applied earth scientists; currently, only the deep Kola Peninsula scientific borehole exceeds this limit. A number of special and important cases were addressed during the technical presentations. 1.1 - Rocks with Abnormal High Porosity with respect to Depth Exceptionally high porosities at depth are found in chalk, silt, and sandstone reservoirs as well as undercompacted shales. Examples include the Chalk reservoir of the Valhall Field in the North Sea, with beds of 50% porosity at 3 000 m depth; the "geo-pressured" reservoirs of the Gulf Coast, California, and many other basins; and high porosity shale cap rocks in many areas, usually with pore pressures well above hydrostatic.

ABSTRACT: After a short review of the ·Differential strain Analysis· method, several models based on elastic brittle fracture are given: it has been proved that only a hypothesis based on initial relaxed state of stress at the crack tip will respect both the propagation criterion and the stability condition. Several examples have made it possible to assess the influence of various parameters (Young''s modulus, surface energy and porosity) on the intensity of the microcraking. Finally, experimental results make it possible to confirm the model and establish a regional state of stress in the Middle East. RESUME: Après un bref rappel de la méthode. Differential Strain Analysis, plusieurs modèles, basés sur la mécanique des roches élastiques et fragiles, sont présentés. Il est prouvé que seule une hypothèse sur un état de contrainte initial relâche, en tête de fissure, permet de respecter à la fois le critère de propagation et le critère de stabilité dans le phénomène de microfissuration dû à la décompression d''un échantillon de roche. Plusieurs exemples permettent de chiffrer l''influence des différents paramètres intrinsèques (module''d''Young, énergie de surface, porosité) sur l''intensité de la microfissuration. Enfin, des résultats expérimentaux permettent de valider le modèle et de tirer un état de contrainte régional au Moyen Orient. ZUSAMMENFASSUNG: Mach einem kurzen Hirweis auf der "Differential Strain Analysis" -Methode, werden meherere Modelle vorgestellt, die auf der Mechanik von elastischen und zebrechlichen Gesteinen basiert sind. Es wurde festgestellt, daβ nur eine Hypothese, die einen initialen entspannten Spannungszustand am Riβkopf zugrunde liegt, die Ausbreitungs- und Stabilitätstkriterien erfüllen kann, im Microriβbildungsphänomen infolge der Dekompression eines Gesteinprüfstücks. Durch Mehrere Beispiele wurde der Einfluβ von verschiedenen Parametern (Youngs Modul, Fläche-energie, Porosität) auf die Microriβbildungsintensität bestimmt. Zum Schluβ, durch experimentelle Ergebnisse wurde das Modell für gültig erklärt. und ein regionaler Sparrungszustand im Mahenosten aufgestellt. 1 INTRODUCTION Considering recent problems which have arisen geothermal recovery projects in hot dry rocks, and the economic exploitation of hydrocarbon fields with low permeability, the knowledge of the state of stress in deep rocks has gained increasing importance regarding rock mechanics. The method used the most commonly for the last twenty years (i.e. hydraulic fracturing) although still the most reliable, is extremely expensive (especially offshore) and an operator will often hesitate to make such an outlay. This is why, for the last five years certain authors have been wondering whether a rock samp.1e, taken from its original block would retain in, its matrix a ·memory· of its present state of stress. This idea gave birth to the DSA (Differential Strain Analysis) method, developed by SIMMONS and al (1974). The method is based on the following assumption: ·When a rock sample is taken (by coring for instance) within a stressed deep layer, the material will microcrack in proportion to the pre-existing effective state of stress·. This principle involves certain complementary hypotheses: – before relaxation the material contains no open microcracks, – the relaxation of the state of stress is the only source of microcracks. Any other phenomena of a thermal (cooling of the core) mechanical (actual coring procedure) or other (knocks, transport, preparing the samples) nature, will not cause any extra microcracking. A cubic-shaped sample is then cut from the microcracked core, and strain gages are sticked in 9 directions (Six of which are independant) (Pig. 1). 2 RELAXATION AS A MICROCRACKING MECHANISM We will consider the rock at time to (i.e. just prior to coring) as a brittle elastic medium, with the intrinsic characteristics E (elasticity modulus), (Poisson''s coefficient) and {f (surface energy). This medium contains a certain number of elliptical defects, infinitely flat (but free of stress). The sample, initially stressed is gradually relaxed; the defects will open and propagate. The defects become microcracks. - The propagation criterion (GRIFFITH 1921): "The work of the stresses which relaxes along the crack during decompression is dissipated in various forms, in particular, in.elastic strain energy (opening of the microcrack) and energy of cohesion (propagation of the initial defect)". 3 VARIOUS TYPES OF MODEL Below we give three types of relaxation models. As will be seen, only one satisfies both the propagation criterion and the stability condition. 3.1· Equivalent fraction model (BTII) (Fig. 4) In this model it is considered that the transition from the state of stress a, to the state 0 is equivalent to the passage from the state 0 to the state intraction. This constitues the state at time to From a mechanical point of view, the action of a traction at infinity is equivalent to that of a pressure !i(1on the faces of the crack. This pressure will be the driving force of the microfissuration. 4 RESULTS AND DISCUSSIONS It has been decided to characterize the intensity of microcracking by the parameter A volume of the crack per unit of length when decompression is total.

INTRODUCTION This paper presents the characteristic deformation behaviour under static stress condition obtained from experiments, and the consideration on the common and different properties owing to the origin. The experiments performed mainly consist of consolidation test and conventional drained triaxial test on undisturbed rocks. PROPERTIES OF SOFT ROCKS As the term of soft rock is named after the nature of mechanical properties of rocks, it is interesting to consider the difference and situation between each rock using foundamental properties characterizing mechanical properties of soft rocks. Then, these relations were investigated using saturated water content or porosity as an index of compaction or density of rock, and unconfined compressive strength qu or tensile strength σ t as an index of the bonding or cementation strength. Figs. 1(Yoshinaka & Onodera 1978) and 2 show the relation of wsat to qu of sedimentary rocks, qu and σ t to n of weathered granite respectively. Fig. 1 appears to have no relation at glance, however the systematic relation can be distinguished from point of view of mineral and grain compositions, geological system of each sediment. For example, the sedimentary rocks belong to same geological system have a linear relation between w-log qu, and the angles of lines of linear arrangement reflect the consistency of rock forming materials, the geological environment and history, etc. From Fig. 1 it seems that sedimentary soft rock can be classified into the density dependent and cementation dependent types. Porosity of granite increases from 0.5% to 50% according with weathering. Mechanical properties of granite decrease remarkably, but almost quantity of intergranular bonding strength losses by increasing of n up to about 10–20 % as shown in Fig. 2. Therefore it may conclude that mechanical properties of highly weathered granite as soft rock mainly depend on the intergranular fabric and mechanical properties of grains. The w-qu relation obtained from Fig. 2 is shown by a dotted line in Fig. 1, in comparison. COMPRESSION BEHAVIOUR OF SOFT ROCKS To clarify the compression behaviour of soft rocks, the relation of void ratio to consolidation pressure (0.1–20 MPa) of many kinds of rocks are compiled in Fig. 3. The data used are in Table 1. To compare with soft rock to soil, the consolidation curves of sand and clay are also shown in Fig. 3. From Fig. 3, the following properties are obtained: The volumetric deformation curves of soft rocks under isotropic consolidation can be classified,into 3 patterns, A,B, and C,as shown in Fig. 4. (Figure in full paper) If these patterns are compared with those of soils, A and B may correspond to over consolidated clay or dense sand, and C may correspond to normally consolidated clay. But the compression behaviour of soft rock seems to contain fundamentally different elements from soils. A distinct yield point Py arises in case of A type which have relatively large void ratio, and the value of Py generally corresponds to qu. The compressibility suddenly changes at Py as boundary, and in low pressure under Py seems to depend on bonding strength of cementation.

INTRODUCTION A good number of projects have been constructed and several others are under construction/investigation in Eastern India. Experience in working in these projects dictates that the weak features of these sites are of various types and mostly hidden under thick overburden cover. The tropical climatic condition and high rain fall are responsbile for the formation of thick overburden and vegetation cover. In the high altitudes of the Eastern India including the Himalayan terrain, there are the extensive action of ice and water which have formed thick glacial, fluvioglacial and hill wash deposits. In general loose surficial deposit and weathering of rock to various extent are seen in most of the river valleyproject sites of Eastern India. For example, the Umling Dam Site (Fig. 1) of Meghalaya consists of thick riverine material and also thick surficial deposit followed by a mantle of weathered rock of considerable thickness. Sub-surface exploration mainly by drilling followed by water pumping tests is therefore carried out in almost all river valley projects to evaluate the rock condition at depth. Weak features like faulting, shattering, shearing and jointing are very prolific in the rock in many of the projects of Eastern India. Presence of soft clay seams, kaolinization of rock and karstic condition are some of the other weak features recorded from some project sites. This paper deals with the importance of water pumping test to reveal such weak features in hard rock with secondary permeability. Analyses of these weak features in hard rock indicate that the weak zones are highly permeable. It is, therefore, of importance that permeability characteristics of the weak zones be determined in relation to the intensity of fractures to identify and delineate the exact position of weak zones at depth. OUTLINE OF THE METHOD OF WATER PUMPING TEST Through a drill hole, a perforated tube fitted with two rubber packers at the two ends is lowered down to the depth where test is to be conducted. Water from a tank is pumped to the test section under varying pressures. A pressure gauge and a water meter record the applied pressure and water loss respectively. The most important consideration for this test is the use of right type of packer which can be tightly fixed with the rock wall of the drill hole without any chance of leakage through the contact planes of the packer and the rock. In recording the pressure it is to be ensured that the indicator moves equal distance to and froe with respect to the 'mark' noted as the applied pressure. The quantum of water that permeates through the rock fractures in a test zone per minute should be the same in the consecutive minutes provided there is uninterrupted flow. In practice test is conducted for 5 to 10 minutes and average value of per minute flow is taken so that in case of clay filling in joints, this will be flushed off in process of testing.