Pore Pressure Research Papers - Academia.edu (original) (raw)

This paper deals with the solution of the stress, displacement, and pore pressure field induced by the drilling and~or the pressurization of a vertical borehole. The rock, which is permeated by fluid, is assumed to behave as a poroelastic... more

This paper deals with the solution of the stress, displacement, and pore pressure field induced by the drilling and~or the pressurization of a vertical borehole. The rock, which is permeated by fluid, is assumed to behave as a poroelastic material with compressible constituents, following the Biot theory. The analytical solution is derived in the Laplace transform space, and is transformed to the time domain using an approximate numerical inversion technique. The solution reveals a full range of coupled poroelastic effects which provide potential mechanisms for delayed borehole instability and shear fracture initiation inside the rock.

The estimates for geological CO 2 storage capacity worldwide vary, but it is generally believed that the capacity in saline aquifers will be sufficient for the amounts of CO 2 that will need to be stored. The effort required to select and... more

The estimates for geological CO 2 storage capacity worldwide vary, but it is generally believed that the capacity in saline aquifers will be sufficient for the amounts of CO 2 that will need to be stored. The effort required to select and qualify a geological storage site for safe storage will, however, be significant and storage capacity may be a limited resource regionally. Both from a economic and resource management perspective it is therefore important that potential storage sites are exploited to their full potential.

This paper reports results from centrifuge tests designed to investigate capillary rise in soils subjected to different gravitational fields. The experimental programme is part of the EU-funded NECER project (Network of European... more

This paper reports results from centrifuge tests designed to investigate capillary rise in soils subjected to different gravitational fields. The experimental programme is part of the EU-funded NECER project (Network of European Centrifuges for Environmental Geotechnic Research), whose objective is to investigate the appropriateness of geotechnical centrifuge modelling for the investigation of geoenvironmental problems, particularly with reference to partially saturated

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with... more

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright

The Storegga Slide occurred 8200 years ago and was the last megaslide in this region where similar slides have occurred with intervals of approximately 100 ky since the onset of continental shelf glaciations at 0.5 Ma. A geological model... more

The Storegga Slide occurred 8200 years ago and was the last megaslide in this region where similar slides have occurred with intervals of approximately 100 ky since the onset of continental shelf glaciations at 0.5 Ma. A geological model for the Plio-Pleistocene of the area explains the large scale sliding as a response to climatic variability, and the seismic stratigraphy indicates that sliding occurs at the end of a glaciation or soon after the deglaciation. The slides are in general translational with the failure planes related to strain softening behaviour of marine clay layers. The destabilisation prior to the slide is related to rapid loading from glacial deposits with generation of excess pore pressure and reduction of the effective shear strength in the underlying clays. Basin modelling has shown that excess pore pressure generated in the North Sea Fan area is transferred to the Storegga area with reduction of the slope stability in the old escarpments in distal parts of the Storegga Slide. The slide was most likely triggered by a strong earthquake in an area 150 km downslope from the Ormen Lange gas field and developed as a retrogressive slide. The unstable sediments in the area disappeared with the slide 8200 years ago. A new ice age with infilling of glacial sediments on top of marine clays in the slide scar would be needed to create a new unstable situation at Ormen Lange. q

Objective. To determine the role of articular cartilage lipids in its load-bearing function. Design. Normal and delipidised, bovine articular cartilage specimens were statically loaded and both the hydrostatic excess pore pressure and... more

Objective. To determine the role of articular cartilage lipids in its load-bearing function. Design. Normal and delipidised, bovine articular cartilage specimens were statically loaded and both the hydrostatic excess pore pressure and creep strain were measured. From this the compression stiffness of the skeletal structures of both types of matrices was determined.

A predrill estimate of pore pressure can be obtained from seismic velocities using a velocity-to–pore-pressure transform, but the seismic velocities need to be derived using methods having sufficient resolution for well planning purposes.... more

A predrill estimate of pore pressure can be obtained from seismic velocities using a velocity-to–pore-pressure transform, but the seismic velocities need to be derived using methods having sufficient resolution for well planning purposes. For a deepwater Gulf of Mexico example, significant differences are found between the velocity field obtained using reflection tomography and that obtained using a conventional method based on the Dix equation. These lead to significant differences in the predicted pore pressure. Parameters ...

Shales are a major component of sedimentary basins, and they play a decisive role in fluid flow and seismic-wave propagation because of their low permeability and anisotropic microstructure. Shale anisotropy needs to be quantified to... more

Shales are a major component of sedimentary basins, and they play a decisive role in fluid flow and seismic-wave propagation because of their low permeability and anisotropic microstructure. Shale anisotropy needs to be quantified to obtain reliable information on reservoir fluid, lithology and pore pressure from seismic data, and to understand time-to-depth conversion errors and non-hyperbolic moveout. A single anisotropy parameter, Thomsen's δ parameter, is sufficient to explain the difference between the small-offset normal-moveout velocity and vertical velocity, and to interpret the small-offset AVO response.

Catastrophic flank collapses have occurred at many stratovolcanoes worldwide. We present a three-dimensional (3-D) slope stability analysis for assessing and quantifying both the locations of minimum edifice stability and the expected... more

Catastrophic flank collapses have occurred at many stratovolcanoes worldwide. We present a three-dimensional (3-D) slope stability analysis for assessing and quantifying both the locations of minimum edifice stability and the expected volumes of potential failure. Our approach can search the materials underlying a topographic surface, represented as a digital elevation model (DEM), and determine the relative stability of all parts of the edifice. Our 3-D extension of Bishop's [1955] simplified limit-equilibrium analysis incorporates spherical failure surfaces, variable material properties, pore fluid pressures, and earthquake shaking. Although a variety of processes can trigger collapse, we focus here on gravitationally induced instability. Even homogeneous rock properties strongly influence the depth and volume of the least stable potential failure. For large failures in complex topography, patterns of potential instability do not mimic local ground surface slope alone. The May 18, 1980, catastrophic failure of the north flank of Mount St. Helens provides the best documented case history to test our method. Using the undeformed edifice topography of Mount St. Helens in an analysis of dry, static slope stability with homogeneous materials, as might be conducted in a precollapse hazard analysis, our method identified the northwest flank as the least stable region, although the north flank stability was within 5% of the minimum. Using estimates of the conditions that existed 2 days prior to collapse, including deformed topography with a north flank bulge and combined pore pressure and earthquake shaking effects, we obtained good estimates of the actual failure location and volume. Our method can provide estimates of initial failure volume and location to aid in assessing downslope or downstream hazards.

This paper presents a complete finite-element treatment for unsaturated soil problems. A new formulation of general constitutive equations for unsaturated soils is first presented. In the incremental stress-strain equations, the suction... more

This paper presents a complete finite-element treatment for unsaturated soil problems. A new formulation of general constitutive equations for unsaturated soils is first presented. In the incremental stress-strain equations, the suction or the pore water pressure is treated as a strain variable instead of a stress variable. The global governing equations are derived in terms of displacement and pore water pressure. The discretized governing equations are then solved using an adaptive time-stepping scheme which automatically adjusts the time-step size so that the integration error in the displacements and pore pressures lies close to a specified tolerance. The non-linearity caused by suction-dependent plastic yielding, suction-dependent degree of saturation , and saturation-dependent permeability is treated in a similar way to the elastoplasticity. An explicit stress integration scheme is used to solve the constitutive stress-strain equations at the Gauss point level. The elastoplastic stiffness matrix in the Euler solution is evaluated using the suction as well as the stresses and hardening parameters at the start of the subincrement, while the elastoplastic matrix in the modified Euler solution is evaluated using the suction at the end of the subincrement. In addition, when applying subincrementation, the same rate is applied to all strain components including the suction.

The horizontal compressive stress orientations for Mandapeta field in Krishna-Godavari (K-G) basin had been calculated from borehole breakout data using four-arm dipmeter caliper logs. The minimum horizontal stress magnitude for Mandapeta... more

The horizontal compressive stress orientations for Mandapeta field in Krishna-Godavari (K-G) basin had been calculated from borehole breakout data using four-arm dipmeter caliper logs. The minimum horizontal stress magnitude for Mandapeta field was calculated from pore pressure data using poroelastic equation. Threedimensional (3-D) stress modeling using finite element analyses has been carried out for layered sediments and faulted layered sediments in the Mandapeta sub-basin. The length and width of the models are chosen as 5 km and 2 km respectively. Vertical depths of models are considered for sediments at depth 2 km to 5 km. This paper presents a numerical study of stress distributions (contours and trajectories) around fault models of layered geometries, submitted to overburden and unequal horizontal compressive loads. Reorientation and magnitude variation of in-situ stresses near faults and stress discontinuities across faults are observed. Changes in the stress patterns are observed at the interfaces between sediments due to faulting and sedimentbasement layers due to contrast in elastic constants. Remarkable stress gradients are observed between the sediment and basement. Magnitudes of normal component of stress decrease near the faulting whereas shear stress magnitudes increase at the faulting site. There is increase of horizontal principal stresses in the downthrown faulted layers. The maximum horizontal principal stress rotates about 90°just adjacent to the fault. Fluid flow at depth of oil reservoir could be indirectly influenced by the stress contours and by geometries of the stress trajectories. Fluid migration in low permeability reservoir may occur in response to mean stress gradients induced by the tectonic loading. The areas of high mean stress gradient are located at the interface between sediment and basement whereas the areas of low mean stress gradient is exactly coinciding with the areas of upper sediments.

Time-lapse traveltime shifts of reflection events recorded above hydrocarbon reservoirs can be used to monitor production-related compaction and pore-pressure changes. Existing methodology, however, is limited to zero-offset rays and... more

Time-lapse traveltime shifts of reflection events recorded above hydrocarbon reservoirs can be used to monitor production-related compaction and pore-pressure changes. Existing methodology, however, is limited to zero-offset rays and cannot be applied to traveltime shifts measured on prestack seismic data. We give an analytic 3D description of stress-related traveltime shifts for rays propagating along arbitrary trajectories in heterogeneous anisotropic media. The nonlinear theory of elasticity helps to express the velocity changes in and around the reservoir through the excess stresses associated with reservoir compaction. Because this stress-induced velocity field is both heterogeneous and anisotropic, it should be studied using prestack traveltimes or amplitudes. Then we obtain the traveltime shifts by first-order perturbation of traveltimes that accounts not only for the velocity changes but also for 3D deformation of reflectors. The resulting closed-form expression can be used efficiently for numerical modeling of traveltime shifts and, ultimately, for reconstructing the stress distribution around compacting reservoirs. The analytic results are applied to a 2D model of a compacting rectangular reservoir embedded in an initially homogeneous and isotropic medium. The computed velocity changes around the reservoir are caused primarily by deviatoric stresses and produce a transversely isotropic medium with a variable orientation of the symmetry axis and substantial values of the Thomsen parameters and ␦ . The offset dependence of the traveltime shifts should play a crucial role in estimating the anisotropy parameters and compaction-related deviatoric stress components.

Ellatzite is the biggest open-pit mine in Bulgaria. It is operated by Ellatzite-Med AD, part of the group of companies GEOTECHMIN, producer of copper-gold and molybdenum concentrates. In 2012 the company launched a project for development... more

Ellatzite is the biggest open-pit mine in Bulgaria. It is operated by Ellatzite-Med AD, part of the group of companies GEOTECHMIN, producer of copper-gold and molybdenum concentrates. In 2012 the company launched a project for development of a Complex monitoring system for safety-critical slope monitoring with full coverage of the entire pit. The design and construction phases of the System were gradually implemented within a period of 15 months and were successfully completed in July 2013. The Monitoring system includes GNSS receivers, robotic total stations, various geotechnical sensors and one of the world's first installations of Guardian FPM360 software package. This article describes the main methods and solutions applied in the System design and implementation of the project and the theoretical concepts, specifications and principle of operation of the implemented System.

Strain energy concept has been employed by the researchers for the assessment of liquefaction phenomenon which is a disastrous type of earthquake-induced failure in saturated soils. The efficiency and predictability conditions of strain... more

Strain energy concept has been employed by the researchers for the assessment of liquefaction phenomenon which is a disastrous type of earthquake-induced failure in saturated soils. The efficiency and predictability conditions of strain energy concept for liquefaction potential assessment are investigated herein using effective stress numerical analyses. Several earthquake ground motions were introduced to the base of a calibrated numerical model using an advanced fully coupled constitutive model. Results of the numerical analyses indicate that earthquake-induced excess pore pressure is more rigorously proportional to strain energy compared with the other examined intensity measures. Subsequently, a simple relationship was derived using the results of dynamic analyses to predict cumulative strain energy density in terms of magnitude, source to site distance, and effective overburden pressure. This relationship, which tries to guarantee the predictability condition of strain energy demand, has demonstrated a successful capability in discrimination between the liquefied and non-liquefied case histories recorded after several well-known earthquakes. This study has provided a practical linkage between numerical analysis and field observations. Finally, it is concluded that although strain energy approach possesses a great conceptual efficiency in liquefaction potential assessment, its precise prediction in actual field conditions involves some difficulties.

Fracture gradient of formation is a key to determine the casing setting depth in drilling oil/gas wells. In addition, for projects, such as hydraulic fracturing and enhanced oil recovery injection, knowing the fracture gradient of the... more

Fracture gradient of formation is a key to determine the casing setting depth in drilling oil/gas wells. In addition, for projects, such as hydraulic fracturing and enhanced oil recovery injection, knowing the fracture gradient of the injection zone is necessary. Also, the pressure integrity of the exposed open hole dictates the maximum allowed wellbore pressure. Several theoretical and operational methods for predicting fracture pressures have been developed and refined. A Leack-off test, which is the most reliable and common method for evaluating fracture pressure gradient, is performed by too much cost and time and also this test cannot be performed at several points. In the present article, a novel technique is presented to obtain an estimation of fracture pressure gradient from drilling operation data reports. This method is based on the effect of pore pressure and confining pressure on compressive strength of rock and, consequently, on drilling speed. Artificial neural networks were implemented to build a simulator for the rate of penetration and analyze the effect of hydrostatic pressure of wellbore on the rate of penetration. The presented method was performed on field data of an Iranian southern field and the results were satisfactorily close to the actual measured fracture pressure by an average error of about 1%.

The Taupo Volcanic Zone (TVZ) of New Zealand is characterised by extensive volcanism and by high rates of magma production. Associated with this volcanism are numerous high-temperature ( > 250°C) geothermal systems through which the... more

The Taupo Volcanic Zone (TVZ) of New Zealand is characterised by extensive volcanism and by high rates of magma production. Associated with this volcanism are numerous high-temperature ( > 250°C) geothermal systems through which the natural heat output of 4200 f 500 MW is channelled. Outside the geothermal fields the heat flow is negligible. The average heat flux from the central 6000 km2 of the TVZ, which contains most of the geothermal fields, is 700 mW/m3. This heat flux appears to be more concentrated along the eastern margin of the TVZ.

High-performance concrete (HPC) are subject to spalling under certain thermal and mechanical conditions. Spalling results mainly from two processes: a “thermo-mechanical” process in which the stress originates in the gradients of thermal... more

High-performance concrete (HPC) are subject to spalling under certain thermal and mechanical conditions. Spalling results mainly from two processes: a “thermo-mechanical” process in which the stress originates in the gradients of thermal deformation within the material, and a thermo-hydral process where spalling is due to the build-up of gas pressure fields in the porous network. This paper deals with the thermo-hydral process. An original device was designed in order to make simultaneous measurements of pressure and temperature at various positions in a concrete specimen (30×30×12 cm3) heated on one face up to 800°C. The specimen was also continuously weighed during the tests, thus, the mass loss, resulting mainly from water transport and loss, was recorded. This campaign was carried out on an ordinary concrete (OC) and a HPC (90 MPa). As expected, the pressure peaks were much higher than in HPC (40 bars) than in OC (20 bars). In HPC, these pressures exceeded the saturated vapor pressure. It is demonstrated that the thermal expansion of liquid water and the transport of water towards the inner part of the specimen play a significant role on the build-up of gas pressure. The experimental correlation between the pressure peaks and the plateau in the temperature curves confirmed the hypothesis that the drying front is preceded by a quasi-saturated layer that acts as a moisture clog.

The aim of this study is to define the Vp and Vp/Vs structure of the fault zone ruptured by the M L 5.1 earthquake of October 15, 1996 which occurred near Reggio Emilia (central-northern Italy). A 1-month-long seismic sequence followed... more

The aim of this study is to define the Vp and Vp/Vs structure of the fault zone ruptured by the M L 5.1 earthquake of October 15, 1996 which occurred near Reggio Emilia (central-northern Italy). A 1-month-long seismic sequence followed the mainshock and occurred in a small region along the outer border of the northern Apenninic belt, at depth ranging between 10 and 17 km. P-and S-wave arrival times from 304 aftershocks recorded by two local dense seismic arrays installed in the epicentral region have been inverted to obtain one-and three-dimensional velocity models by using state of the art local earthquake tomographic techniques. Velocity models and aftershock relocation help us to infer the seismotectonic of the region. Earthquakes originated along a NW-dipping backthrust of a NE-trending main thrust, composing the western part of the broad Ferrara Arc. A main high Vp and high Vp/Vs region delineates a pop-up structure in the center of the area. The high Vp/Vs within the pop-up structure supports the presence of a zone with increased pore pressure. The hypocentral depth of both mainshock and aftershocks is greater than those usually found for the main seismogenic regions of the Apenninic belt. P-wave velocity values in the seismogenic area, obtained by tomography, are compatible with rocks of the Mesozoic cover and suggest that seismicity occurred within the Mesozoic units stack at present by compressional tectonics.

This paper describes the monitoring of several existing landslides in an urban area near Wollongong in the state of New South Wales, Australia. A brief overview of topography and geology is given and reference is made to the types of... more

This paper describes the monitoring of several existing landslides in an urban area near Wollongong in the state of New South Wales, Australia. A brief overview of topography and geology is given and reference is made to the types of slope movement, processes and causal factors. Often the slope movements are extremely slow and imperceptible to the eye, and catastrophic failures are quite infrequent. However, cumulative movements at these slower rates do, over time, cause considerable distress to structures and disrupt residential areas and transport routes. Inclinometers and piezometers have been installed at a number of locations and monitoring of these has been very useful. The performance of instrumentation at different sites is discussed in relation to the monitoring of slope movements and pore pressures. Interval rates of inclinometer shear displacement have been compared with various periods of cumulative rainfall to assess the relationships.

Purpose: This study is conducted to develop a simplified mathematical model to describe the lift mechanics of downhill skiing and snowboarding, where the lift contributions due to both the transiently trapped air and the compressed solid... more

Purpose: This study is conducted to develop a simplified mathematical model to describe the lift mechanics of downhill skiing and snowboarding, where the lift contributions due to both the transiently trapped air and the compressed solid phase (snow crystals) are determined. To our knowledge, this is the first time that anyone has attempted to realistically estimate the relative contribution of the transiently trapped air to the total lift in skiing and snowboarding. Methods: The model uses Shimizu's empirical relation to predict the local variation in Darcy permeability due to the compression of the solid phase. The forces and moments on the skier or snowboarder are used to predict the angle of attack of the planing surface, the penetration depth at the leading edge, and the shift in the center of pressure for two typical snow types, fresh and wind-packed snow. We present numerical solutions for snowboarding and asymptotic analytic solutions for skiing for the case where there are no edging or turning maneuvers. The force and moment balance are then used to develop a theory for control and stability in response to changes in the center of mass as the individual shifts his/her weight. Results: Our model predicts for fine-grained, windpacked snow that when the velocity (U) of the snowboarder or skier is 20 mIs j1 , approximately 50% of the total lift force is generated by the trapped air for snowboarding and 40% for skiing. For highly permeable fresh powder snow, the lift contribution from the pore air pressure drops substantially. Conclusion: This paper develops a new theoretical framework for analyzing the lift mechanics and stability of skis and snowboards that could have important applications in future ski and snowboard design.

Because of the rapid drawdown there will be a decrease in the slope stability which might lead to instability in slopes that do not have sufficient level of safety against failure. This paper presents an investigation of slope stability... more

Because of the rapid drawdown there will be a decrease in the slope stability which might lead to instability in slopes that do not have sufficient level of safety against failure. This paper presents an investigation of slope stability during drawdown depending on the soil permeability, drawdown rate and drawdown ratio, considering the nonlinear material and loading conditions. For this purpose, a coupled transient seepage and deformation analyses (including consolidation), together with the stability analysis, were performed using the FEM for submerged slopes. Nonlinear elasto-plastic behavior of the slope soil is taken into account while analysis of the generation and dissipation of pore pressure is carried out.

The dynamics of the late Wisconsin Lake Michigan Lobe of the Laurentide Ice Sheet, as interpreted by sediment-landform assemblages along its southeastern margin, are consistent with fast flow driven by high subglacial pore pressures. A... more

The dynamics of the late Wisconsin Lake Michigan Lobe of the Laurentide Ice Sheet, as interpreted by sediment-landform assemblages along its southeastern margin, are consistent with fast flow driven by high subglacial pore pressures. A major advance of the Lake Michigan Lobe terminated at the Kalamazoo Moraine, where proglacial glaciotectonic activity, marginal stagnation, and release of subglacial meltwater marked the extent of the advance. A large portion of the Valparaiso ''Moraine'', west of the Kalamazoo Moraine, is actually a drumlinized, till-capped upland plain rather than an ice-marginal landform assemblage. Lacustrine sediment, underlying the surficial diamicton in the Valparaiso upland, is glaciotectonically deformed to a depth of 10 m. The deformed interval consists of folded sandy and silty lacustrine sediment, which is in places sharply truncated by the overlying diamicton. Decoupling of the glacier from its bed is suggested by a discontinous thin bed of sand at the base of the diamicton, and by the sharp truncation of deformed lacustrine sediment. The association of drumlins, proglacial and subglacial deformation, marginal stagnation, and major ice-marginal outwash-fan deposition are indicative of fast flow, perhaps in a surge. These characteristics are consistent with a terrestrial ice-stream model for the Lake Michigan Lobe. r

The Storegga Slide occurred 8200 years ago and was the last megaslide in this region where similar slides have occurred with intervals of approximately 100 ky since the onset of continental shelf glaciations at 0.5 Ma. A geological model... more

The Storegga Slide occurred 8200 years ago and was the last megaslide in this region where similar slides have occurred with intervals of approximately 100 ky since the onset of continental shelf glaciations at 0.5 Ma. A geological model for the Plio-Pleistocene of the area explains the large scale sliding as a response to climatic variability, and the seismic stratigraphy indicates that sliding occurs at the end of a glaciation or soon after the deglaciation. The slides are in general translational with the failure planes related to strain softening behaviour of marine clay layers. The destabilisation prior to the slide is related to rapid loading from glacial deposits with generation of excess pore pressure and reduction of the effective shear strength in the underlying clays. Basin modelling has shown that excess pore pressure generated in the North Sea Fan area is transferred to the Storegga area with reduction of the slope stability in the old escarpments in distal parts of the Storegga Slide. The slide was most likely triggered by a strong earthquake in an area 150 km downslope from the Ormen Lange gas field and developed as a retrogressive slide. The unstable sediments in the area disappeared with the slide 8200 years ago. A new ice age with infilling of glacial sediments on top of marine clays in the slide scar would be needed to create a new unstable situation at Ormen Lange.

Compressional and shear-wave velocities ( V p and V s) of 210 minicores of carbonates from different areas and ages were measured under variable confining and pore-fluid pressures. The lithologies of the samples range from unconsolidated... more

Compressional and shear-wave velocities ( V p and V s) of 210 minicores of carbonates from different areas and ages were measured under variable confining and pore-fluid pressures. The lithologies of the samples range from unconsolidated carbonate mud to completely lithified limestones. The velocity measurements enable us to relate velocity variations in carbonates to factors such as mineralogy, porosity, pore types and density and to quantify the velocity effects of compaction and other diagenetic alterations. Pure carbonate rocks show, unlike siliciclastic or shaly sediments, little direct correlation between acoustic properties ( V p and V s) with age or burial depth of the sediments so that velocity inversions with increasing depth are common. Rather, sonic velocity in carbonates is controlled by the combined effect of depositional lithology and several post-depositional processes, such as cementation or dissolution, which results in fabrics specific to carbonates. These diagenetic fabrics can be directly correlated to the sonic velocity of the rocks. At 8 MPa effective pressure V p ranges from 1700 to 6500 m/s, and V s ranges from 800 to 3400 m/s. This range is mainly caused by variations in the amount and type of porosity and not by variations in mineralogy. In general, the measured velocities show a positive correlation with density and an inverse correlation with porosity, but departures from the general trends of correlation can be as high as 2500 m/s. These deviations can be explained by the occurrence of different pore types that form during specific diagenetic phases. Our data set further suggests that commonly used correlations like ``Gardner's Law'' ( V p-density) or the ``time-average-equation'' ( V p-porosity) should be significantly modified towards higher velocities before being applied to carbonates. The velocity measurements of unconsolidated carbonate mud at different stages of experimental compaction show that the velocity increase due to compaction is lower than the observed velocity increase at decreasing porosities in natural rocks. This discrepancy shows that diagenetic changes that accompany compaction influence velocity more than solely compaction at increasing overburden pressure. The susceptibility of carbonates to diagenetic changes, that occur far more quickly than compaction, causes a special velocity distribution in carbonates and complicates velocity estimations. By assigning characteristic velocity patterns to the observed diagenetic processes, we are able to link sonic velocity to the diagenetic stage of the rock.

Pore pressure analysis is a key issue during the well drilling planning stage. Usually, the well geopressure analysis is developed in one dimension (1D), that is, only on the well location along its whole depth. However, we can increase... more

Pore pressure analysis is a key issue during the well drilling planning stage. Usually, the well geopressure analysis is developed in one dimension (1D), that is, only on the well location along its whole depth. However, we can increase the number of dimension to visualize spatially the pressure behavior with respect to time, depending on information available. The increment in dimensions allows us to include the geological characteristics of the area to improve drilling well planning. The paper describes the geopressure analysis experiences performed in the Presidente Aleman Field in Chicontepec Basin. This field is located one-kilometer south-west of Papantla, Veracruz, México and it has an area of 206.9 km 2 . In recent drilling campaigns, more than 160 wells were drilled, however, to develop the present work we gather information from 14 scattered wells around the field. These types of wells were termed "template-wells", because they were the first drilled into the template with all sort of logs, tests and samples. The behavior of earth-pressures (overburden pressure, pore pressure and fracture pressure) was outlined using shale compaction behavior with depth. The analysis depicts geological characteristics of the Chicontepec basin and Presidente Aleman Field. Then, the origin of abnormal pore pressure, depth of fluid retention, behavior of normal compaction trends around the field is discussed. In addition, we present the variability of rock density and its effect over the overburden stress together with fracture pressure distribution and drilling experiences.

Terzaghi (1948) planteó que durante el proceso de depositación de sedimentos en una cuenca, el agua está atrapada en los sedimentos se libera por efecto de su propia densidad y el peso de los sedimentos. Esto origina que los sedimentos se... more

Terzaghi (1948) planteó que durante el proceso de depositación de sedimentos en una cuenca, el agua está atrapada en los sedimentos se libera por efecto de su propia densidad y el peso de los sedimentos. Esto origina que los sedimentos se compacten y se mantenga una presión de poro hidrostática equivalente a la densidad del agua de la formación. Por el contrario, si el agua no se puede liberar durante el depósito y el sepultamiento, los sedimentos no se compactan y el agua atrapada incrementa su presión debido a la carga litostática. Cuando este fenómeno ocurre, se dice que la presión de poro diverge de la presión de poro normal o en términos de compactación, la compactación diverge de su tendencia de compactación normal. De acuerdo con Hottman y Johnson (1965), para definir una zona sobrepresiones, es necesario desarrollar un análisis de puntos de lutita. Este análisis consiste en seleccionar intervalos cuya litología sea principalmente lutita, utilizando un registro litológico de pozo como el de rayos gamma, sin embargo, un registro afectado por condiciones del agujero o formación (pozo fuera de calibre o formaciones radioactivas no lutíticas) comúnmente conducen a interpretaciones erróneas en el análisis de puntos de lutita y por consiguiente en la determinación de la presión de poro.
Este artículo describe un método nuevo de análisis de presión de poro basado exclusivamente en la teoría de la compactación normal de los sedimentos y la manera en que estos divergen cuando su tendencia normal se ve interrumpida El proceso consiste en generar tendencias de compactación paralelas a la tendencia de compactación normal e interpretar las tendencias paralelas y transicionales observadas en los registros de pozo o sísmica para generar un área divergente. Una vez definida el área divergente, se puede utilizar cualquier método basado en registros para calcular la presión de poro. Usando el área divergente, se mejora el pronóstico de presión de poro evitando el uso de registros litológicos que pueden generar desviaciones en la interpretación de las zonas sobrepresionadas. Asimismo se muestra la metodología aplicada a varios casos de pozos mexicanos.

A cap rock's capacity to seal hydrocarbons depends on its wettability and the sizes of the pore throats within the interconnected pore system that the leaking hydrocarbons must penetrate.These critical pore throat sizes are often poorly... more

A cap rock's capacity to seal hydrocarbons depends on its wettability and the sizes of the pore throats within the interconnected pore system that the leaking hydrocarbons must penetrate.These critical pore throat sizes are often poorly constrained in hydrocarbon exploration, partly because measurements of pore throat sizes have not been performed, and partly because pore throat measurements on a few individual samples in the cap rock may not be representative for the seal capacity of the top seal as a whole.

This paper discusses the applicability of two simple models for predicting pore water pressure generation in nonplastic silty soil during cyclic loading. The first model was developed by Seed et al. in the 1970s and relates the pore... more

This paper discusses the applicability of two simple models for predicting pore water pressure generation in nonplastic silty soil during cyclic loading. The first model was developed by Seed et al. in the 1970s and relates the pore pressure generated to the cycle ratio, which is the ratio of the number of applied cycles of loading to the number of cycles required to cause liquefaction. The second model is the Green-Mitchell-Polito model proposed by Green et al. in 2000, which relates pore pressure generation to the energy dissipated within the soil. Based upon the results of approximately 150 cyclic triaxial tests, the writers show that both models are applicable to silty soils. A nonlinear mixed effects model was used for regression analyses to develop correlations for the necessary calibration parameters. The results show that the trends in both ␣ and pseudoenergy capacity calibration parameters for the Seed et al. and Green et al. pore pressure generation models, respectively, differ significantly for soils containing less than and greater than ϳ35% fines, consistent with the limiting fines content concept.

After Darcy proposed his law for the water flow through sands, the generalizations and vulgarizations abounded and the Darcy's proposal was intended to be applied to very different kinds of fluids and materials albeit the proposal was... more

After Darcy proposed his law for the water flow through sands, the generalizations and vulgarizations abounded and the Darcy's proposal was intended to be applied to very different kinds of fluids and materials albeit the proposal was originally referred exclusively to the water flow through sands. And although a few authors warned that the discharge velocity versus hydraulic gradient relationship is valid only in a limited grain size range, the proposition is so general that it becomes void of meaning. In this paper we do propose that the Darcy's Law proportionality ratio is not dependent exclusively on the permeable material grain size characteristics as stated in current textbooks. In clean sands, gravels and boulders the flow occurs in closed channels and should be analyzed with current hydraulic concepts. On the other end, in fine grained materials the mineralogical characteristics of the silts and clays control the capillary water flow.

Cone penetration test (CPT) allows for the soil type to be determined from the measured values of cone resistance (q t ) and sleeve friction (f s ). Since the cone penetrometer progressed from the mechanical cone to the electrical... more

Cone penetration test (CPT) allows for the soil type to be determined from the measured values of cone resistance (q t ) and sleeve friction (f s ). Since the cone penetrometer progressed from the mechanical cone to the electrical piezocone (CPTu), the reliability of the determination of soil type also improved by pore pressure (u) measurement. This paper references several published methods of soil profiling. All but two of these apply cone resistance plotted against the friction ratio (R f ). A new method for soil profiling has been developed by plotting effective cone resistance (q E ) versus sleeve friction with a compiled database from 20 sites in 5 countries. This paper presents two soil profiling methods based on the piezocone and compares them with three specific cases containing sand, normally consolidated clay and overconsolidated clay. Both methods result in an accurate soil type determination.

La predicción de los perfiles de presión presentes en el subsuelo, constituye la etapa más importante de la planeación y diseño de la perforación de pozos exploratorios. Se sabe a nivel mundial que los problemas generados por las... more

La predicción de los perfiles de presión presentes en el subsuelo, constituye la etapa más importante de la planeación y diseño de la perforación de pozos exploratorios. Se sabe a nivel mundial que los problemas generados por las presiones anormales, cuestan a la Industria de la perforación varios millones de dólares al año e incluso, en algunos casos, la factibilidad de perforar pozos. En México, nos hemos dado a la tarea de reevaluar los modelos de predicción de presión de poro y de definir tendencias de compactación normal para proporcionarles a los Ingenieros de Perforación herramientas mas precisas, que les permitan fundamentar con mayor certeza dos de las etapas más críticas del diseño de un pozo: (1) seleccionar el peso del lodo óptimo y (2) definir las mejores profundidades de asentamiento de las tuberías de revestimiento.

The pore pressure prediction is the most important process in the design of drilling wells. This paper depicts a new methodology to analyze pore pressure based on both, the normal compaction theory of sediments and the way that normal... more

The pore pressure prediction is the most important process in the design of drilling wells. This paper depicts a new methodology to analyze pore pressure based on both, the normal compaction theory of sediments and the way that normal behavior diverges when it is interrupted. Much has been written on the topic; however, even today a high percentage of non-productive time (NPT) in drilling activities is related to pore pressure and wellbore instability problems. Here, a new methodology is proposed to improve the accuracy of calculated pore pressure from well logs and seismic data. Moreover, this new methodology allows, under specific conditions, to determine pore pressure in carbonates and other reservoir rocks. The compaction process defines the normal trend of porosity indicators with depth, the fluid retention depth and those rock bodies diverging from a normal compaction trend. The divergence detection procedure includes the identification of both, transitional changes of the porosity indicators (shale) and those that are parallel to normal compaction trend (reservoir rock); they allow to build a divergent area. When the divergent area is defined, the pore pressure calculation can be done using a pore pressure model based on normal compaction theory and well logs or interval velocity data from seismic. Misleading prediction of geopressures for a particular area are linked to: misunderstandings of pore pressure origins there, the limited scope of pore pressure models based on well logs and to miscalculations of the key parameters of pore pressure models. This work discuss the impact of these key parameters in the pore pressure prognosis. Analysis of actual cases showing the impact of miscalculation of overburden stress on pore pressure estimations, normal compaction trend definition and pore pressure calculations are presented using divergent area along with the Eaton model. The conclusions support the following statements: well log density data cannot be used to calculate the overburden pressure and under some conditions, the divergence methodology can be used to calculate pore pressures in carbonates. Furthermore, the divergent area method eliminate the use of shale points in pore pressure prognosis.

A method is used to obtain pore pressure in shaly sandstones based upon an acoustic model for seismic velocity versus clay content and effective pressure. Calibration of the model requires log data-porosity, clay content, and sonic... more

A method is used to obtain pore pressure in shaly sandstones based upon an acoustic model for seismic velocity versus clay content and effective pressure. Calibration of the model requires log data-porosity, clay content, and sonic velocities-to obtain the dry-rock moduli and the effective stress coefficients as a function of depth and pore pressure. The seismic P-wave velocity, derived from reflection tomography, is fitted to the theoretical velocity by using pore pressure as the fitting parameter. This approach, based on a rock-physics model, is an improvement over existing pore-pressure prediction methods, which mainly rely on empirical relations between velocity and pressure. The method is applied to the Tune field in the Viking Graben sedimentary basin of the North Sea. We have obtained a high-resolution velocity map that reveals the sensitivity to pore pressure and fluid saturation in the Tarbert reservoir. The velocity map of the Tarbert reservoir and the inverted pressure distribution agree with the structural features of the Tarbert Formation and its known pressure compartments.

Stability analysis of Surabhi landslide in the Dehradun and Tehri districts of Uttaranchal located in Mussoorie, India, has been simulated numerically using the distinct element method focusing on the weak zones (fracture). This is an... more

Stability analysis of Surabhi landslide in the Dehradun and Tehri districts of Uttaranchal located in Mussoorie, India, has been simulated numerically using the distinct element method focusing on the weak zones (fracture). This is an active landslide on the main road toward the town centre, which was triggered after rainfall in July-August 1998. Understanding the behaviour of this landslide will be helpful for planning and implementing mitigation measures. The first stage of the study includes the total area of the landslide. The area identified as the zone of detachment is considered the most vulnerable part of the landslide. Ingress of water and increased pore pressures result in reduced mobilized effective frictional resistance, causing the top layer of the zone of detachment to start moving. The corresponding total volume of rock mass that is potentially unstable is estimated to 11.58 million m 3 . The second stage of this study includes a 2D model focussing only on the zone of detachment. The result of the analyses including both static and dynamic loading indicates that most of the total displacement observed in the slide model is due to the zone of detachment. The discontinuum modelling in the present study gives reasonable agreement with actual observations and has improved understanding of the stability of the slide slope.

When piles are installed by jacking or driving, they cause substantial changes in the state of soil located near the pile. These changes result from the complex loading imposed on the soil by expansion of a cylindrical cavity to make room... more

When piles are installed by jacking or driving, they cause substantial changes in the state of soil located near the pile. These changes result from the complex loading imposed on the soil by expansion of a cylindrical cavity to make room for the pile, by multiple cycles of shearing in the vertical direction as the pile gradually moves down into

We present a new petro-elastical and numerical-simulation methodology to compute synthetic seismograms for reservoirs subject to CO 2 sequestration. The petro-elastical equations model the seismic properties of reservoir rocks saturated... more

We present a new petro-elastical and numerical-simulation methodology to compute synthetic seismograms for reservoirs subject to CO 2 sequestration. The petro-elastical equations model the seismic properties of reservoir rocks saturated with CO 2 , methane, oil and brine. The gas properties are obtained from the van der Waals equation and we take into account the absorption of gas by oil and brine, as a function of the in situ pore pressure and temperature. The dry-rock bulk and shear moduli can be obtained either by calibration from real data or by using rock-physics models based on the Hertz-Mindlin and Hashin-Shtrikman theories. Mesoscopic attenuation due to fluids effects is quantified by using White's model of patchy saturation, and the wet-rock velocities are calculated with Gassmann equations by using an effective fluid modulus to describe the velocities predicted by White's model. The simulations are performed with a poro-viscoelastic modeling code based on Biot's theory, where viscoelasticity is described by generalizing the solid/fluid coupling modulus to a relaxation function. Using the pseudo-spectral method, which allows general material variability, a complete and accurate characterization of the reservoir can be obtained. A simulation, that considers the Utsira sand of the North Sea, illustrates the methodology.

Pore pressure prediction in parts of the Onshore Niger Delta Sedimentary Basin using seismic reflection data has been carried out. The Bower's technique of velocity-to-pore pressure transform was adopted. The seismic velocities were... more

Pore pressure prediction in parts of the Onshore Niger Delta Sedimentary Basin using seismic reflection data has been carried out. The Bower's technique of velocity-to-pore pressure transform was adopted. The seismic velocities were derived from the seismic data using layer cake velocity model and were later compared with the available sonic logs velocities obtained from the area. Parameters in the velocity-to-pore pressure transform were estimated using the seismic interval velocities. The top of overpressure zone is about 3500 m which is in agreement with available data. The overpressure occurs within the shale rich region of the Agbada and top of Akata Formations in the basin. Comparison of the overpressure zone with available geophysical logs shows that the interval has lower bulk density, lower interval velocity and high porosity. With regard to the young age of the basin, the factors that might be responsible for the overpressure are mechanical compaction, chemical compaction and hydrocarbon generation. The results of the analysis revealed that the overpressure in the area is associated with simple rollover structures bounded by growth faults, especially the hanging walls. This method of pore pressure prediction is very useful because it helps to predict pore pressure ahead of the bit.

Geoscientific data from several wells drilled in onshore and offshore parts of the Cauvery and Krishna-Godavari basins, two main hydrocarbon producing basins located in the east coast of India, have been used to determine pore pressures... more

Geoscientific data from several wells drilled in onshore and offshore parts of the Cauvery and Krishna-Godavari basins, two main hydrocarbon producing basins located in the east coast of India, have been used to determine pore pressures and fracture pressures in the subsurface formations. We have estimated pore pressure based on Zhang's porosity model. Variations of normal compaction curves across the basins are demonstrated here. This study also proposes simple relationships among the parameters used in Eaton's equation for estimating the fracture pressure. Relations established based on the available data in this current study are compressional and shear sonic velocities against bulk density, Poisson's ratio against depth, and the overburden stress against depth. These empirical relationships can be used to predict fracture gradient for the future drilling locations in these basins. The pore pressure in Cauvery basin is shown to be almost hydrostatic in nature, which is due to normal sedimentation rate. High sedimentation rate in the Miocene section of the KG basin is found to be the main reason for over-pressure development.

Prediksi tekanan pori sebelum proses pengeboran menjadi hal yang sangat penting karena dapat merepresentasikan efektifitas tutupan, pemetaan migrasi hidrokarbon, serta analisa konfigurasi tutupan dan geometri cekungan. Disisi lain... more

Prediksi tekanan pori sebelum proses pengeboran menjadi
hal yang sangat penting karena dapat merepresentasikan
efektifitas tutupan, pemetaan migrasi hidrokarbon, serta
analisa konfigurasi tutupan dan geometri cekungan. Disisi
lain penentuan tekanan pori dapat membantu dalam
pembuatan desain program casing dan lumpur. Pada daerah
Matindok, tekanan pori diturunkan dari kecepatan seismik
2D yang diperoleh dari hasil pemodelan kecepatan interval
dengan menggunakan metode Coherency Inversion, dimana
metode coherency inversion mampu untuk memprediksi
kecepatan interval lebih akurat untuk daerah yang
berstruktur kompleks yang memiliki kurva moveout yang
non-hiperbolik. Dengan menggunakan beberapa persamaan
empirik, tekanan pori diraih dengan menurunkan densitas
sebagai fungsi kedalaman, Total Stress (S), dan tekanan
hidrostatik (PH) yang selanjutnya tekanan pori ini akan
digunakan untuk melihat adanya zona overpressure dan
melihat efektifitas tutupan

Pore pressure prediction plays important role prior to drilling for mitigation of various major hazard caused by over pressure, predicting compartment of reservoir, subsidence prediction, hydraulic fracturing design and geomechanics... more

Pore pressure prediction plays important role prior to drilling for mitigation of various major hazard caused by over pressure, predicting compartment of reservoir, subsidence prediction, hydraulic fracturing design and geomechanics modeling. Seismic wave plays important role in pore pressure prediction of porus rock indirectly. Relationship among seismic wave parameters and porus rock are studied intensively using rock physics. Poroelastic parameter will be main role in relating impact of confining pressure to effective stress as well as pore pressure. Effective stress is equal to average of normal stress on surface grains when confining stress is applied to rock frame. Differential stress is difference between confining pressure and pore pressure. There are difference concept between effective stress and differential stress due to stiffness of rock. The coefficient of effective stress is the important parameter in predicting accurately the pore pressure. Some popular methods in pore pressure prediction are based on Eaton's method or Bower's method. The popular Eaton method assumes that effective stress coefficient is assumed has value of 1. The value of effective pressure, however, from lab measurements of previous authors and our laboratory measurement are vary with depth instead of constant value. The older shale usualy has value of effective stress coefficient less than 1. We propose to modify Eaton's equation as well as Bower's equation which consider effective stress coefficient. Relationship among velocities and effective stress of some various rocks in Indonesia is presented : shale, carbonate, and sandstone, using laboratory of seismic rock physics measurements. It is including soft and non soft rock which has effective stress coefficient less than 1.The relation among velocity and effective stress coefficient is unique in each lithology. Pore pressure prediction should considers various parameters of rock physics and poroelasto mechanics, i.e.: effective pressure coefficient, relationship between seismic velocity and effective pressure. It is since the velocity of P wave is influenced by pore's geometry, fluid, pressures, lithology, anisotropy and fracture. The proposed method presents workflow for handling some of ambiguity in pore pressure prediction, i.e.: fluid, lithology, porosity, pressure. This workflow considers multivariable parameter of reservoir, i.e.: fluid content, porosity, lithology or Vshale, hydrostatic pressures and pore pressure itself.

Dry and brine-saturated clay aggregates ranging from pure smectite to pure kaolinite were compacted in the laboratory. Experiments were conducted by increasing vertical effective stress up to 50 MPa to study the changes in physical... more

Dry and brine-saturated clay aggregates ranging from pure smectite to pure kaolinite were compacted in the laboratory. Experiments were conducted by increasing vertical effective stress up to 50 MPa to study the changes in physical properties of mudstones during burial. The results suggest that the physical properties (porosity, density, acoustic velocity, etc.) of mudstones vary greatly with increasing effective stress, clay mineralogy and fluid content. Kaolinite aggregates are much more compressible than those composed of smectite. Brine-saturated clay mixtures are much more compressible than dry clay mixtures. Brine may soften and lubricate the clay matrix compared to dry clays, resulting in higher compressibility in the brine-saturated state. The lesser degree of compaction of dry smectite compared to dry kaolinite aggregates can be explained by the differences in grain size as kaolinitic clays have much larger grains than smectitic clays. The extremely fine-grained nature of smectite implies that the imposed vertical stress is distributed over a very large number of grain contacts so that the force per contact area is very low in smectite compared to that in coarse-grained kaolinite. At 20 MPa effective stress, corresponding to about 2 km burial depth with hydrostatic pore pressure, brine-saturated pure kaolinite compacted to 20% porosity, while pure smectite retained 41% porosity. Brinesaturated clay mixtures show higher V p and lower V s than dry clay mixtures. A pronounced difference in V s was observed among the brinesaturated clay mixtures. The lowest V s as a function of vertical effective stress was found for pure smectite. For a given porosity value, smectitic clays have higher velocities and elastic moduli than the kaolinitic clays. The V p /V s ratio is significantly higher in smectite than in kaolinite aggregates. Treating mudstones as a uniform class of rocks introduces significant errors in estimates of physical properties, which are strongly affected by the clay mineralogy, grain size, the amount of other minerals present and fluid content. Our results have implications for well log interpretation and mudstone and shale property determinations from seismic data at shallow burial depth (o2 km, 80 1C), above depths where significant chemical compaction takes place. r

This paper describes a range of geophysical research activities at the Australian Resources Research Centre based around the development of an experimental capability to validate theoretical and numerical modelling predictions of... more

This paper describes a range of geophysical research activities at the Australian Resources Research Centre based around the development of an experimental capability to validate theoretical and numerical modelling predictions of geophysical properties of reservoirs and seals. Laboratory tests performed on reservoir sandstones, shales and artificial sandstones under a range of controlled triaxial stress conditions allow the full anisotropic elastic tensor to be calculated from ultrasonic measurements on a single core. The analysis of elastic properties and anisotropy in relation to varied stress, pore pressure and fluid saturation can provide significant insight for both exploration (e.g. pore pressure prediction) and production (4D seismic feasibility studies for changes in pore pressure and saturation during production). Ultrasonic data from core measurements are related to seismic response through theoretical analysis of frequency effects and the methodologies developed from this research are subsequently tested on 3D seismic data. Understanding the causes and degree of anisotropy, for example, are critical for depth conversion, imaging, fluid identification (e.g. AVO) and dynamic Poisson's ratio.

Spatial and temporal variations of pore water pressure within slopes in response to rainfall that lead to slope failure, are one of the major uncertainties in evaluating slope stability. This paper reports on the study of slope stability... more

Spatial and temporal variations of pore water pressure within slopes in response to rainfall that lead to slope failure, are one of the major uncertainties in evaluating slope stability. This paper reports on the study of slope stability with respect to pore water pressure variation with rainfall during actual failure in September 2011. The studied slope, situated near the peak of Doi-Inthanon national park, Northern Thailand, consisted of granitic residual soil fill that suffered from soil erosion and shallow failure. The KU-tensiometers were installed to monitor both pore water pressure and suction in the slope. Various laboratory and field tests were conducted, namely, direct shear tests on both fully saturated and unsaturated soils, soil water characteristic curve, and field infiltration tests. Two-dimensional (2-D) Back analysis of slope stability, for failure event in 2011 suggested that the critical pore water pressure distribution can be assigned to the ru value of about 0.43 or u=0.43H. Based on three dimensional (3-D) stability analysis, the pore water pressure can be 30% higher when compared with the 2-D analysis. 2-D Finite Element seepage analysis appeared to capture general trend of pore-water pressure change reasonably well. However, it seemed to underpredict the pore-water pressure at failure especially for depth greater than 2 meters.

The Costa target areas exhibit the variability of slope instabilities needed to improve our understanding of sediment physical and mechanical properties in areas prone to sliding. That is why in this project, we have analysed the... more

The Costa target areas exhibit the variability of slope instabilities needed to improve our understanding of sediment physical and mechanical properties in areas prone to sliding. That is why in this project, we have analysed the different slope failures events from different parts of the Costa target areas, which reflect diverse triggering mechanisms. The aim of the first part of this study was to identify the geotechnical response of the sediment to different external mechanisms (earthquake, rapid sedimentation and gas hydrate melting). We have focused on the relation between external mechanisms and the consequence change in the in-situ stress state and the physical, mechanical, and elastic properties of the sediment. In the second part of the paper, the geotechnical properties of the sediment from different Costa areas are presented. Comparison between observed geotechnical properties and the theoretical behaviour was done in order to improve our understanding of the origin of the different observed slides.

A geomechanical assessment of the Naylor Field, Otway Basin, Australia has been undertaken to investigate the possible geomechanical effects of CO2 injection and storage. The study aims to evaluate the geomechanical behaviour of the... more

A geomechanical assessment of the Naylor Field, Otway Basin, Australia has been undertaken to investigate the possible geomechanical effects of CO2 injection and storage. The study aims to evaluate the geomechanical behaviour of the caprock/reservoir system and to estimate the risk of fault reactivation. The stress regime in the onshore Victorian Otway Basin is inferred to be strike-slip if the maximum horizontal stress is calculated using frictional limits and DITF (Drilling Induced Tensile Fracture) occurrence, or normal if maximum horizontal stress is based on analysis of dipole sonic log data. The NW-SE maximum horizontal stress orientation (142ºN) determined from a resistivity image log is broadly consistent with previous estimates and confirms a NW-SE maximum horizontal stress orientation for the Otway Basin. An analytical geomechanical solution is used to describe stress changes in the subsurface of the Naylor Field. The computed reservoir stress path for the Naylor Field is ...