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We characterize the in-situ porosity and compressibility of a coarse-grained hydrate reservoir in Green Canyon Block 955 in the deepwater Gulf of Mexico by performing experiments both on a hydrate-bearing sandy silt pressure core and on the same reservoir material after reconstituting. Uniaxial consolidation experiments demonstrate a small difference in porosity between a reconstituted sandy silt sample (Sh = 0, n = ~ 0.38) and a hydrate-bearing sandy silt (Sh = 83%, n = 0.39-0.40) at in-situ effective stress (3.8 MPa). Both measured porosities generally agree with the in-situ porosity (~0.38 to 0.39) of the reservoir formation that was best-estimated from both LWD and calibrated PCATS densities. The compression index of pressure core at 3.8 MPa is ~ 0.05 to 0.1, slightly stiffer than reconstituted sandy silts (Cc = 0.11). This difference in porosity and compression behaviors between hydrate pressure cores and reconstituted material implies that (1) analysis of reconstituted sediments from hydrate-bearing pressure cores provides a simple and intuitive approach to understand some petrophysical components of the hydrate reservoir; and (2) the high-saturation hydrate in the pores of sediments makes the hydrate reservoir slightly less compressible, suggesting a non-contact-cementing hydrate morphology in the pressure core.

Permeability anisotropy (the ratio of the horizontal to vertical permeability) develops in mudrocks at the macroscale due to heterogeneities such as layering and at the element scale (i.e., within a single homogeneous layer or unit) due to decreasing porosity and increasing platy particle alignment. This work describes new experimental methods and results from a laboratory program using cubic specimens to investigate the evolution of mudrock permeability and resistivity at the element scale. A systematic study analyzes the evolution of the permeability anisotropy and electrical resistivity anisotropy using resedimented Boston blue clay (RBBC) over a stress range of 0.4-40 MPa; additional measurements are presented for three other mudrocks within varying clay fraction and clay mineralogy within the stress range 1.2-10 MPa. The permeability anisotropy and the conductivity anisotropy (inverse of the resistivity anisotropy) of all four mudrocks studied ranges from 1 to 2.2 over the porosity range 0.55-0.30. A nearly 1:1 correlation between the electrical conductivity anisotropy and the permeability anisotropy is observed to be independent of clay fraction or clay mineralogy. Key words: permeability anisotropy, electrical conductivity anisotropy, resedimentation, resistivity anisotropy. L'anisotropie de permeabilite (le rapport de la permeabilite horizontale a la verticale) se developpe dans la pelite a l'echelle macro en raison de l'heterogeneite telle que la stratification et a l'echelle de l'element (par ex., dans une couche homogene unique ou unitaire) en raison de la porosite decroissante et l'alignement lamellaire croissante des particules. Cet ouvrage decrit les nouvelles methodes experimentales et les resultats d'un programme de laboratoire en utilisant des echantillons cubiques pour etudier l'evolution de la permeabilite et de la resistivite de la pelite a l'echelle de l'element. Une etude systematique analyse l'evolution de l'anisotropie de permeabilite et de l'anisotropie de la resistivite electrique utilisant l'argile Boston bleu resedimente (RBBC--resedimented Boston blue clay) sur une intervalle de contrainte de 0,4 a 40 MPa; des measures supplementaires sont presentees pour trois autres pelitesa fraction d'argile et a mineralogie d'argile variablesa l'interieur d'une intervalle de contrainte de 1,2 a 10 MPa. L'anisotropie de la permeabilite et l'anisotropie de conductivite (inverse de l'anisotropie de la resistivite) des quatre pelites etudiees varient de 1 a 2,2 a l'interieur d'une intervalle de porosite de 0,55 a 0,30. A peu pres une correlation 1:1 entre l'anisotropie de la conductivite electrique et l'anisotropie de la permeabilite s'avere etre independante de la fraction d'argile ou de la mineralogie d'argile. [Traduit par la Redaction] Mots-cles: anisotropie de la permeabilite, l'anisotropie de la conductivite electrique, resedimentation, l'anisotropie de resistivite., Introduction Permeability anisotropy (the ratio of the horizontal to vertical permeability) develops in mudrocks at the macroscale due to heterogeneities such as layering and at the element scale (i.e., within [...]

A program of [K.sub.0]-consolidated undrained triaxial compression tests has been performed to investigate the effects of consolidation stress level on the compression and shear behavior of resedimented Boston blue clay (RBBC). Specimens were consolidated to maximum vertical effective stresses in the range 0.15-10 MPa and tested at three overconsolidation ratios (OCR): 1, 2, and 4. The results show that the virgin compression curves are essentially linear in e-log[σ'.sub.v] space over the consolidation stress range. However, the normally consolidated [K.sub.0] stress ratio increases with the level of consolidation stress. The stress-strain-strength properties measured in undrained shear are significantly affected by the consolidation stress level at each OCR and show indications of non-normalizable behavior. At high pressures, the undrained shear stress- strain behavior becomes more ductile, requiring larger strains to mobilize peak resistance and exhibiting less post-peak strain- softening. The undrained strength ratio ([s.sub.u][σ'.sub.vc]) is not uniquely controlled by OCR as suggested by the SHANSEP equation, but consistently decreases with increasing consolidation effective stress. There is notable reduction in the stiffness ratio ([E.sub.u]/[σ'.sub.vc]) with stress level, and significant decrease in the large-strain friction angle. Key words: clays, compressibility, laboratory tests, shear strength, stress effects, triaxial tests. Un programme d'essais triaxiaux non draines en compression et consolides en [K.sub.0] a ete realise afin d'evaluer les effets du niveau de la contrainte de consolidation sur le comportement en compression et en cisaillement de l'argile bleue de Boston re-sedimentee (ABBR). Les echantillons ont ete consolides jusqu'a des contraintes effectives verticales maximales de l'ordre de 0,15 a 10 MPa, et ont ete testes a trois ratios de surconsolidation : RSC = 1, 2 et 4. Les resultats demontrent que les courbes de compression vierges sont essentiellement lineaires dans l'espace e-log[σ'.sub.v] pour la gamme de contraintes de consolidation. Cependant, le ratio des contraintes normalement consolide en [K.sub.0] augmente suivant le niveau de contrainte de consolidation. Les proprietes en contrainte-deformation-resistance mesurees pendant le cisaillement non draine sont affectees de facon significative par le niveau de consolidation a chaque RSC, et demontrent des indications d'un comportement non normalisable. A fortes pressions, le comportement en contrainte-deformation sous cisaillement non draine devient plus ductile, demandant des plus grandes deformations pour mobiliser la resistance au pic et demontrant moins d'adoucissement par deformation apres le pic. Le ratio des resistances non drainees ([s.sub.u]/[σ'.sub.vc])n'est pas uniquement controle par le RSC, tel que suggere par l'equation SHANSEP, mais diminue de facon coherente avec l'augmentation de la contrainte effective de consolidation. On observe une reduction notable du ratio de rigidite ([E.sub.u]/[σ'.sub.vc]) avecl'augmentation du niveau des contraintes, et une diminution significative de l' angle de friction a grandes deformations. Mots-cles : argiles, compressibilite, essai en laboratoire, resistance au cisaillement, effets des contraintes, essais triaxiaux. [Traduit par la Redaction], Introduction The mechanical behavior of clays at high consolidation stresses is important to a number of engineering applications particularly in the oil and gas industry. Shallow oil reservoirs at depths [...]

This paper describes a series of laboratory tests conducted to assess the performance of a novel fluorescence-based in situ sensor for environmental contaminants. The sensor, which can be deployed downhole in a monitoring well, or incorporated into the shaft of a cone penetrometer, is less than 4 cm in diameter and uses a miniature microchip laser that produces ~200 ps pulses of ultraviolet radiation at a high repetition rate (~l0 kHz) to excite fluorescence in a wide range of compounds. Results from laser induced fluorescence tests on single compound aqueous solutions of benzene, toluene, and o-xylene (BTX) demonstrate the sensor's ability to perform contaminant analyses on compounds with fluorescence lifetimes on the order of 1 ns. A linear relationship between contaminant concentration and fluorescence intensity was observed for concentrations over several orders of magnitude from the sensor's detection limit (< 1 ppm for o-xylene) to solutions of pure BTX compounds at aqueous solubility. Owing to the microchip laser's short pulse length, fluorescence lifetimes were obtained directly from measurements without the need for spectral deconvolution. Analysis of data from these tests highlights the importance of differentiating a sensor's ability to detect, identify, and quantify compounds of interest--performance thresholds that ultimately define potential applications for the device. DOI: 10.1061/(ASCE)0733-9372(2007) 133:3(346) CE Database subject headings: Water quality; Fiber optics; Contaminants; Sensors; Monitoring.

This paper addresses the small-strain undrained shear behavior of clays based on an extensive testing program conducted on normally consolidated resedimented Boston blue clay (RBBC). The uniformity and reproducibility in the behavior of this soil permit a detailed study of the role of consolidation stress level, preshear consolidation stress path, preshear lateral stress ratio (K), rate of shear, and duration of laboratory aging on the small-strain ([[epsilon].sub.a] [less than or equal to] 0.1%) nonlinearity in undrained triaxial compression. The small-strain behavior of normally consolidated (NC) RBBC is measured using a LVDT-based device that is capable of resolving on-specimen axial strains smaller than 0.0001% strain over a 10% strain range, thus allowing full description of the small-strain nonlinearity. The testing program relies on a multistage testing approach developed to minimize specimen variability and reduce testing time. The small-strain nonlinearity of NC RBBC is found to be virtually independent of void ratio or stress level, all other testing conditions being equal. [K.sub.0]-consolidated RBBC presents the smallest linear region and the most rapid stiffness degradation (decrease in Young's modulus). Increases in K, strain rate and aging all cause a reduction in the small-strain nonlinearity of the soil. DOI: 10.1061/(ASCE)1090-0241(2007)133:1(72) CE Database subject headings: Clays; Young's modulus; Nonlinear response; Stiffness; Aging; Strain rate.

Tube sampling disturbance effects are investigated in this paper based on the results of constant rate of strain consolidation tests and unconsolidated undrained triaxial compression tests conducted on resedimented Boston blue clay sampled in the laboratory using a specifically designed device and employing various tubes differing in size, diameter to thickness ratio, and tip geometry. The effects of tube geometry were assessed based on comparison of the residual effective stresses, the reconsolidation strains, the undrained strength, and the one-dimensional drained compression behavior. Increasing degradation in the engineering properties was observed with decreasing diameter to thickness ratio (B/t), and the negative impact of a blunt tip geometry could not be compensated for even by a substantial increase in Bit. Comparison of these results to those obtained from triaxial element tests in which disturbance was simulated according to the ideal sampling approach (ISA), indicated that tube sampling is associated with far greater disturbances than what is accounted for by the ISA. Further, additional comparisons with the results of tests run on actual field samples of low over consolidation ratio Boston blue clay from two sites in the Boston area indicate that the behavior observed in the laboratory sampled soil is generally representative of actual field data. CE Database subject headings: Sampling; Clays; Shear strength; Simulation; Data analysis.

This paper describes a high-pressure, low-temperature triaxial testing system that has been specifically designed and built at the Massachusettes Institute of Technology in order to study the physical mechanisms controlling the strength-deformation behavior of frozen sands. The computer controlled system is capable of performing high-stress monotonic triaxial compression tests on specimens measuring D=3.6 cm x H=7.6 cm and incorporates advanced technology for temperature, strain rate, and loading control. One of the most important and unique features of the system is the technology used for the measurement of small axial strains that makes use of two miniature submersible linear variable differential transformers mounted on a pair of yokes that clamp to the specimen. A description of the specimen preparation equipment and triaxial testing techniques is presented to aid in developing standardized testing approaches, which are currently lacking in the literature. Representative test results on frozen Manchester fine sand are presented to demonstrate the capability of this system to accurately characterize the entire stress-strain and volumetric strain behavior in triaxial compression. Results are provided to illustrate the influence of relative density, confining pressure, strain rate, and temperature. CE Database subject headings: Triaxial tests; Sand; Frozen soils; Soil deformation; Test equipment.

Mudrock strength parameters are required to improve the prediction of fracture gradient during drilling in poorly consolidated formations. Understanding the influence that mineral composition and consolidation stress have on the mechanical properties of mudrocks aids safe well design. Small changes in the mudrock clay content are shown to have significant effects on two important engineering parameters: the lateral stress ratio at rest, K0, and the critical state effective friction angle, ϕ ′cs. A laboratory-testing programme using quartz silt and a Gulf of Mexico clay mixture investigates the effects of mudrock clay content on K0 and ϕ ′cs at two stress levels: 1 and 10 MPa. Values of K0 and ϕ ′cs were obtained by subjecting composition-controlled clay–silt specimens to a drained uniaxial vertical strain (K0 consolidation) phase, followed by an undrained compression triaxial shear phase. Triaxial tests illustrate consistent and systematic increases in K0 and decreases in ϕ ′cs, with increases in clay content at both stress levels. Stress dependence is observed through increases in K0 and decreases in ϕ ′cs with increases in stress level. Stress-dependent behaviour is shown to be more pronounced in mudrocks of high clay content. A predictive model is presented for K0 in normally consolidated mudrocks, as a function of clay content and effective stress. The model is used to calculate the fracture gradient (least horizontal stress) profile at the International Ocean Drilling Program (IODP) Expedition 308 Site 1324. The estimated fracture gradient illustrates the effects of clay content and consolidation stress on safe mud weight design. Thematic collection: This article is part of the Geopressure collection available at: https://www.lyellcollection.org/cc/geopressure [ABSTRACT FROM AUTHOR]

A laboratory testing program was conducted to identify and interpret the fundamental factors affecting the performance of a new microchip-laser based fluorescence sensor in soil and ground water. Investigations were performed using a versatile experimental apparatus designed to simulate the in situ interface between the laser induced fluorescence (LIF) sensor and contaminated media while providing complete control of test conditions. Attempts were made to isolate the effects of soil properties such as grain size, soil type, color, mineralogy, and organic content on in situ LIF observations. Test results indicate that soil has no measurable effect on the determination of pore fluid fluorescence lifetimes or the general form of pore fluid emission wavelength profiles. However, for a given contaminant concentration in the pore space of a soil with a narrow grain size distribution, decreases in soil grain size are accompanied by a decrease in the magnitude and variability of observed LIF signals. For soils containing a wide range of particle sizes, in-soil LIF observations are primarily influenced by pore space geometry in relation to the smallest particles present in the soil. These trends were found to be a primary function of the volume of pore fluid in a soil specimen that is in the direct path of laser excitation energy. Soil organic content and optical characteristics such as reflectivity also have potential influence on in-soil LIF observations, although on a secondary basis. After reviewing these experimental results, which indicate the relative impact of soil properties on fluorescence observations, a simple geometric model is presented that captures the primary effects of soil on pore fluid fluorescence observations.

Erosion tests were run on soft cohesive sediment beds freshly deposited from a concentrated slurry, in a large rotating annular flume. A total of seven tests were carried out with the bed age varying between 1.8 and 18.9 days. A surface type erosion was observed for the applied shear stress range (0.1 to 1 Pa). Following the increase in the water flow, the erosion rate increases quickly to a peak value and then drops off to about zero. The eroded depth was less than 8 mm for all beds, but the resistance to erosion at a given depth and for a given bed structure increased with increasing bed age. This phenomenon was attributed to thixotropy. The erosional strength of a given sediment layer is found to be one order of magnitude lower than its undrained and drained mechanical shear strengths measured with innovative testing methods. Hypotheses are given to explain that difference. However, at constant density and soil-water chemistry, the erosional and mechanical strengths seem to be affected by the same factors, i.e., bed age, structure, and temperature.

The foundation soil of an offshore Arctic gravity structure is subjected to complex loading conditions. In addition to radial shear stresses induced by the weight of a structure, large horizontal shear forces from ice loads can produce large rotations and even reversal in the direction of horizontal shear stresses acting on soil elements within the foundation soil. The Multidirectional Direct Simple Shear (MDSS) apparatus was developed to simulate, at the element level, these star of stress. The MDSS first consolidates a circular specimen under both a vertical stress ([[Sigma][prime].sub.vc]) and a horizontal shear stress ([[Tau].sub.hc] = [[Tau].sub.1]; setdown conditions). The specimen is then sheared undrained by applying a second independent horizontal shear stress ([[Tau].sub.2]; ice loading) at an angle [Theta] relative to the horizontal shear stress [[Tau].sub.1]. The experimental program of MDSS and Geonor Direct Simple Shear tests on normally consolidated Boston Blue Clay used [[Tau].sub.hc] = [[Tau].sub.1] = 0.2[[Sigma][prime].sub.vc] and varied [Theta] in 30 [degrees] increments from zero (shear in the same direction) to 180 [degrees] (shear in the opposite direction). The peak undrained resistance decreased almost twofold from [Theta] = 0 [degrees] to [Theta] = 120 [degrees], and the deformation behavior varied from very brittle at low [Theta] angles to becoming ductile at higher angles. These dramatic changes in foundation response are an important design issue.

The paper describes results from 25 [K.sub.0] consolidated-undrained triaxial compression tests on resedimented Boston blue clay using a computer-automated triaxial apparatus with lubricated end platens and a midheight pore-pressure measurement device. Specimens were consolidated to four overconsolidation ratios (OCR = 1, 2, 4, or 8), and for each OCR, undrained shear was performed using four axial strain rates (0.05%, 0.5%, 5%, and 50%/h). The results show that the undrained strength ([s.sub.u]) rate sensitivity (percent increase in [s.sub.u] per log cycle strain rate) across the two fastest strain rates does not vary with OCR and equals about 9%. However, across the three slower rates, increases in OCR cause a consistent decrease in the rate sensitivity that reaches zero at OCR = 8. For high OCR clay, increases in [s.sub.u] (if they occur) are caused by lower shear-induced pore pressures since the effective stress envelope at the peak strength does not vary with strain rate. For low OCR clay, increases in [s.sub.u] are caused by both lower shear-induced pore pressures and increases in the mobilized friction angle. A simple technique is proposed for modeling the rate dependent stress-strain curves of overcon-solidated clay.

This paper presents results of a laboratory investigation of the influence of the nonuniform stresses imposed by the Geonor direct simple-shear (DSS) apparatus on measured stress-strain behavior. The investigation concentrated on the influence of the apparatus on the measured strain-softening behavior of cohesive soils during constant volume (undrained) shear. Special DSS tests were conducted on an elastic material and cohesive soils at varying overconsolidation ratios. The experimental results clearly indicate that the nonuniformity of stresses imposed by the device during undrained shear causes a decrease in the vertical effective stress with increasing shear strain. This in turn causes a reduction in the measured horizontal shear resistance at large strains. The device-induced 'unloading' probably has relatively little effect on measured peak strengths in [K.sub.o] consolidated-undrained DSS tests but certainly contributes to the pronounced strain softening typically

Test results from the use of the Geonor direct simple shear (DSS) device to measure nonuniform stress-strain behavior on specimens of elastic rubber and actual soils are merely corroborative and allow conclusions to be made about the device. Tests on rubber specimens do not represent soil behavior but contribute in understanding the pronounced strain softening always observed at large shear strains during K(sub O) consolidated-undrained DSS tests on cohesive soils.