Atmospheric and oceanic stable isotope signatures of a cold-air outbreakin Iceland during YOPP SOP1 and IGP

Publisher's version (útgefin grein)North-Atlantic Cold-air outbreaks are weather events characterised by extensive fluxes of latent heat to theatmosphere. Understanding the water budget of these weather events is important for the weather impact indownstream coastal areas. We use here observations of the stable isotopic composition of water vapour andprecipitation, expressed by the quantities dD, d18O, d17O and the secondary parameters d-excess and 17O-excess,to extract information about the origin and condensation history of water vapour evaporating during a period ofcold-air outbreaks north of IcelandIcelandic research institute (RANNÍS 152229

Combining the modified discrete element method with the virtual element method for fracturing of porous media

Simulation of fracturing processes in porous rocks can be divided into two main branches: (i) modeling the rock as a continuum enhanced with special features to account for fractures or (ii) modeling the rock by a discrete (or discontinuous) approach that describes the material directly as a collection of separate blocks or particles, e.g., as in the discrete element method (DEM). In the modified discrete element (MDEM) method, the effective forces between virtual particles are modified so that they reproduce the discretization of a first-order finite element method (FEM) for linear elasticity. This provides an expression of the virtual forces in terms of general Hook’s macro-parameters. Previously, MDEM has been formulated through an analogy with linear elements for FEM. We show the connection between MDEM and the virtual element method (VEM), which is a generalization of FEM to polyhedral grids. Unlike standard FEM, which computes strain-states in a reference space, MDEM and VEM compute stress-states directly in real space. This connection leads us to a new derivation of the MDEM method. Moreover, it enables a direct coupling between (M)DEM and domains modeled by a grid made of polyhedral cells. Thus, this approach makes it possible to combine fine-scale (M)DEM behavior near the fracturing region with linear elasticity on complex reservoir grids in the far-field region without regridding. To demonstrate the simulation of hydraulic fracturing, the coupled (M)DEM-VEM method is implemented using the Matlab Reservoir Simulation Toolbox (MRST) and linked to an industry-standard reservoir simulator. Similar approaches have been presented previously using standard FEM, but due to the similarities in the approaches of VEM and MDEM, our work provides a more uniform approach and extends these previous works to general polyhedral grids for the non-fracturing domain.acceptedVersio

Comparing mechanical and ultrasonic behaviour of a brittle and a ductile shale: Relevance to prediction of borehole stability and verification of shale barriers

Borehole collapse during drilling operations in shale formations is a well-known and costly problem within the petroleum industry. Recently it has become evident that shales may also form sealing barriers around the casing, reducing the need for cement jobs on new wells, and reducing costs for plugging and abandonment of old wells. The forming of such barriers involves large deformations of shale through creep and plastic processes. Hence, it is important to be able to characterize to what extent shales may fail in a brittle or ductile manner, in both cases causing possible hole instabilities during drilling, and in the case of ductile shales, enabling permanent sealing barriers. Triaxial failure tests, creep tests and tests tailored to follow the failure envelope under simulated borehole conditions have been performed with two soft shales. One shale fails in a more brittle manner than the other and fails to form a sealing barrier in the laboratory. The more ductile shale has been proved to form barriers both in the laboratory and in the field. By comparing their behavior, it is seen that the ductile shale exhibits normally consolidated behaviour, while the more brittle shale is overconsolidated. This points to the stress history and possibly cementation as keys in determining the failure mode. In addition, porosity, clay content, ultrasonic velocities, unconfined strength and friction angle may be used as indicators of brittle or ductile post-failure behaviour. Ultrasonic velocity and in particular attenuation measurements are shown to be sensitive to the failure initiation process, although stress sensitivity is much lower in the ductile than in the brittle case. The experiments provide values for anisotropic velocities as well as P-wave impedances that are necessary for open as well as cased hole log interpretation, in particular for barrier verification and possibly for monitoring of barrier formationpublishedVersio

Laboratory experiments on ultrasonic logging through casing for barrier integrity validation

Verification of annular barriers is essential for well integrity, with ultrasonic methods being central in well integrity testing for many decades. By doing ultrasonic pitch-catch measurements on a bench top laboratory setup developed to replicate an oil well casing, we were able to show that the beam width,-6dB, of the leaky Lamb wave propagating in the pipe widens only from 14 to 20.4 mm after 140mm of propagation in the pipe. This indicates that the excited Lamb wave has beam-like features, with litle spreading perpendicular to the propagation direction, hence, can be used to evaluate a limited area of the pipe. When introducing two pipes in the experimental setup, as an extension of a previously conducted simulation study by Viggen et al. [1], we could observe multiple Lamb wave packets being excited in the pipes. By adjusting the setup to replicate casing eccentricity, the effects of this could be observed in the measurement

Laboratory Experiments on Ultrasonic Logging Through Casing for Barrier Integrity Validation

Verification of annular barriers is essential for well integrity, with ultrasonic methods being central in well integrity testing for many decades. By doing ultrasonic pitch-catch measurements on a bench top laboratory setup developed to replicate an oil well casing, we were able to show that the beam width,-6dB, of the leaky Lamb wave propagating in the pipe widens only from 14 to 20.4 mm after 140mm of propagation in the pipe. This indicates that the excited Lamb wave has beam-like features, with litle spreading perpendicular to the propagation direction, hence, can be used to evaluate a limited area of the pipe. When introducing two pipes in the experimental setup, as an extension of a previously conducted simulation study by Viggen et al. [1], we could observe multiple Lamb wave packets being excited in the pipes. By adjusting the setup to replicate casing eccentricity, the effects of this could be observed in the measurement

Comparing mechanical and ultrasonic behaviour of a brittle and a ductile shale: Relevance to prediction of borehole stability and verification of shale barriers

Borehole collapse during drilling operations in shale formations is a well-known and costly problem within the petroleum industry. Recently it has become evident that shales may also form sealing barriers around the casing, reducing the need for cement jobs on new wells, and reducing costs for plugging and abandonment of old wells. The forming of such barriers involves large deformations of shale through creep and plastic processes. Hence, it is important to be able to characterize to what extent shales may fail in a brittle or ductile manner, in both cases causing possible hole instabilities during drilling, and in the case of ductile shales, enabling permanent sealing barriers. Triaxial failure tests, creep tests and tests tailored to follow the failure envelope under simulated borehole conditions have been performed with two soft shales. One shale fails in a more brittle manner than the other and fails to form a sealing barrier in the laboratory. The more ductile shale has been proved to form barriers both in the laboratory and in the field. By comparing their behavior, it is seen that the ductile shale exhibits normally consolidated behaviour, while the more brittle shale is overconsolidated. This points to the stress history and possibly cementation as keys in determining the failure mode. In addition, porosity, clay content, ultrasonic velocities, unconfined strength and friction angle may be used as indicators of brittle or ductile post-failure behaviour. Ultrasonic velocity and in particular attenuation measurements are shown to be sensitive to the failure initiation process, although stress sensitivity is much lower in the ductile than in the brittle case. The experiments provide values for anisotropic velocities as well as P-wave impedances that are necessary for open as well as cased hole log interpretation, in particular for barrier verification and possibly for monitoring of barrier formatio

Comparing mechanical and ultrasonic behaviour of a brittle and a ductile shale: Relevance to prediction of borehole stability and verification of shale barriers

Borehole collapse during drilling operations in shale formations is a well-known and costly problem within the petroleum industry. Recently it has become evident that shales may also form sealing barriers around the casing, reducing the need for cement jobs on new wells, and reducing costs for plugging and abandonment of old wells. The forming of such barriers involves large deformations of shale through creep and plastic processes. Hence, it is important to be able to characterize to what extent shales may fail in a brittle or ductile manner, in both cases causing possible hole instabilities during drilling, and in the case of ductile shales, enabling permanent sealing barriers. Triaxial failure tests, creep tests and tests tailored to follow the failure envelope under simulated borehole conditions have been performed with two soft shales. One shale fails in a more brittle manner than the other and fails to form a sealing barrier in the laboratory. The more ductile shale has been proved to form barriers both in the laboratory and in the field. By comparing their behavior, it is seen that the ductile shale exhibits normally consolidated behaviour, while the more brittle shale is overconsolidated. This points to the stress history and possibly cementation as keys in determining the failure mode. In addition, porosity, clay content, ultrasonic velocities, unconfined strength and friction angle may be used as indicators of brittle or ductile post-failure behaviour. Ultrasonic velocity and in particular attenuation measurements are shown to be sensitive to the failure initiation process, although stress sensitivity is much lower in the ductile than in the brittle case. The experiments provide values for anisotropic velocities as well as P-wave impedances that are necessary for open as well as cased hole log interpretation, in particular for barrier verification and possibly for monitoring of barrier formatio

Combining the modified discrete element method with the virtual element method for fracturing of porous media

Simulation of fracturing processes in porous rocks can be divided into two main branches: (i) modeling the rock as a continuum enhanced with special features to account for fractures or (ii) modeling the rock by a discrete (or discontinuous) approach that describes the material directly as a collection of separate blocks or particles, e.g., as in the discrete element method (DEM). In the modified discrete element (MDEM) method, the effective forces between virtual particles are modified so that they reproduce the discretization of a first-order finite element method (FEM) for linear elasticity. This provides an expression of the virtual forces in terms of general Hook’s macro-parameters. Previously, MDEM has been formulated through an analogy with linear elements for FEM. We show the connection between MDEM and the virtual element method (VEM), which is a generalization of FEM to polyhedral grids. Unlike standard FEM, which computes strain-states in a reference space, MDEM and VEM compute stress-states directly in real space. This connection leads us to a new derivation of the MDEM method. Moreover, it enables a direct coupling between (M)DEM and domains modeled by a grid made of polyhedral cells. Thus, this approach makes it possible to combine fine-scale (M)DEM behavior near the fracturing region with linear elasticity on complex reservoir grids in the far-field region without regridding. To demonstrate the simulation of hydraulic fracturing, the coupled (M)DEM-VEM method is implemented using the Matlab Reservoir Simulation Toolbox (MRST) and linked to an industry-standard reservoir simulator. Similar approaches have been presented previously using standard FEM, but due to the similarities in the approaches of VEM and MDEM, our work provides a more uniform approach and extends these previous works to general polyhedral grids for the non-fracturing domain.acceptedVersio