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Results
Abstract The long-term thermal-hydraulic-mechanical response of a generic salt repository for high-level nuclear waste is investigated. In-drift emplacement of the waste packages and subsequent backfill of the drifts with crushed salt are assumed. The aim of this research is to evaluate the long-term integrity of the natural salt and consolidated backfill barriers. For this purpose, we use an updated version of the TOUGH-FLAC simulator, able to deal with large strains and creep. The simulator also includes state-of-the-art constitutive relationships and coupling functions. The Lux/Wolters constitutive model for natural salt is used. The simulations are two-way coupled and include the stages of excavation, waste emplacement, backfilling and a post-closure period of 100,000 years. The simulation results show that the excavation damaged zone is healed within the first years and that the backfill reconsolidation is complete within the first decades. Depending on the magnitude of the pore pressure relative to the minimum principal stress, hydraulic damage within the host rock may occur at a larger scale. The comparison of coupled simulation results with those issued from a case that disregards the mechanical processes shows the necessity to account for the mechanical effect in order to accurately predict the long-term evolution of the barriers.
- Research Report > New Finding (1.00)
- Research Report > Experimental Study (0.86)
- Water & Waste Management > Solid Waste Management (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.93)
Abstract Thermally-induced, non-reversible compaction with volumetric strains of up to more than 1% has been observed in laboratory compaction tests with core plugs of several different shales. While thermally-induced compaction is known to occur in unconsolidated clays, relatively large compaction of caprock shales at temperatures even below in-situ temperature was rather unexpected. The observed thermally-induced compaction follows a creep-like behavior and is accompanied by increases in ultrasonic velocities.
- Europe > Norway (0.30)
- North America > United States (0.28)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Integration of geomechanics in models (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.94)
A Novel Direct Measurement of Formation Pore Pressure
Choi, J.C. (Norwegian Geotechnical Institute (NGI)) | Park, J. (Norwegian Geotechnical Institute (NGI)) | Viken, I. (Norwegian Geotechnical Institute (NGI)) | Bohloli, B. (Norwegian Geotechnical Institute (NGI)) | Skomedal, E. (Statoil ASA) | Godager, Ø (Sensor Developments AS) | Borgersen, K. (Sensor Developments AS) | Casseres, A.G. (Dong Energy A/S)
Abstract This study is to analyze pore pressure data acquired with a novel measurement system that is installed for a pilot test just outside a cased well within a sand formation in the North Sea. The system uses a wireless communication through casing to transfer measured data from well outside to inside. Long-term trend in the measured pore pressure is consistent with a formation-testing-based estimate. On the other hand, the measured pressure and temperature show rather high oscillation in short-period scale, especially during shut-ins. Finite element (FE) modeling study is performed in order to understand this behavior. We find that the oscillation is caused mostly by thermal effects in the tubing, not by any abnormal formation pressure, during injection. The FE modeling study also shows that the thermally-induced pressure oscillation can be removed, and the formation pore pressure is recovered. Finally, the FE modeling study is extended to explore potential behavior of the pressure data when the system is installed in shale formation.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.77)
- Europe > Norway > North Sea > PL 169 > Block 25/8 > Breidablikk Field > Statfjord Formation (0.99)
- Europe > Norway > North Sea > PL 169 > Block 25/8 > Breidablikk Field > Lista Formation (0.99)
- Europe > Norway > North Sea > PL 169 > Block 25/8 > Breidablikk Field > Hod Formation (0.99)
- (6 more...)
Abstract Experimental study of a two cutters PDC bit-rock interaction shows that increase in the confining pressure reduces ROP through two mechanisms. The negative influences of confining pressure on the bit performance in addition to the rock strengthening under elevated borehole pressure (BHP), is the accumulation of crushed cuttings material in between the face of bit cutters and rock surface in the zone of penetration. The flow of crushed cuttings material on the surface of the PDC cutter causes additional confinement of the rock surface in the zone of the penetration due to friction. On the other hand, utilizing a bit with an appropriate jet flow significantly improves ROP. In order to maximize the positive effect of bottom hole cleaning on ROP, the jet velocity has been raised to achieve cavitation condition by reducing the pressure with a high flow velocity ahead of the nozzles. However, the experimental results indicate that there are optimal conditions for applying a high velocity jet flow ahead of the bit, which yields maximum ROP when the cutters penetrate the rock mainly under the chamfer. After the effective cuttings removal condition, further increase in jet velocity no longer assists the bit to penetrate the rock faster.
- North America > United States (0.94)
- North America > Canada > Newfoundland and Labrador (0.47)
- Well Drilling > Drilling Operations (1.00)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid management & disposal (1.00)
- Well Drilling > Drill Bits > Bit design (1.00)
Comparison of two Modeling Procedures to Evaluate Thermal-Hydraulic-Mechanical Processes in a Generic Salt Repository For High-Level Nuclear Waste
Blanco, Martín L. (Lawrence Berkeley National Laboratory) | Rutqvist, J. (Lawrence Berkeley National Laboratory) | Birkholzer, J.T. (Lawrence Berkeley National Laboratory) | Wolters, R. (Clausthal University of Technology) | Rutenberg, M. (Clausthal University of Technology) | Zhao, J. (Clausthal University of Technology) | Lux, K.-H. (Clausthal University of Technology)
Abstract The long-term thermal-hydraulic-mechanical response of a generic salt repository for high-level nuclear waste is investigated using the TOUGH-FLAC simulator, developed at Lawrence Berkeley National Laboratory, and the FLAC-TOUGH simulator, developed at Clausthal University of Technology. Although these sequential simulators rely on the same flow and geomechanics software, they are based on different numerical schemes. One of the aims of using two different approaches to model the same scenario is to gain reliability on the results obtained. The two simulators include state-of-the-art constitutive relationships and coupling functions. The generic scenario studied assumes in-drift emplacement of the waste packages and subsequent backfill of the drifts with crushed salt. The Lux/Wolters constitutive model for natural salt is used. The simulations are two-way coupled and include the stages of excavation, waste emplacement, backfilling and post-closure. This work has been performed within the framework of a collaboration effort between Lawrence Berkeley National Laboratory and Clausthal University of Technology. Although the predictions presented in this paper cover a post-closure period of 100 years, it is intended to continue the benchmark until 100,000 years. The results obtained so far provide confidence in the capabilities of the two simulators to evaluate the barriers integrity over the long-term.
- Europe > Germany (0.93)
- North America > United States > California (0.46)
- Water & Waste Management > Solid Waste Management (1.00)
- Government > Regional Government (1.00)
- Energy > Power Industry > Utilities > Nuclear (1.00)
- Energy > Oil & Gas > Upstream (1.00)
Abstract Hydraulic fracturing technique has been widely applied in the enhanced geothermal systems, to increase injection rates for geologic sequestration of CO2, and most importantly for the stimulations of oil and gas reservoirs, especially the unconventional shale reservoirs. One of the key points for the success of hydraulic fracturing operations is to accurately estimate the redistribution of pore pressure and stresses around the induced fracture and predict the reactivations of pre-existing faults. The fracture extension as well as pore pressure and stress regime around it are affected by: poro- and thermoelastic phenomena as well as by fracture opening under the combined action of applied pressure and in-situ stress. A couple of numerical studies have been done for the on this for the purpose of analyzing the potential for fault reactivation resulting from pressurization of the hydraulic fracture. In this work, a comprehensive analytical model is constructed to estimate the stress and pore pressure distribution around an injection induced fracture from a single well in an infinite reservoir. The model allows the leak-off distribution in the formation to be three-dimensional with the pressure transient moving ellipsoidcally outward into the reservoir with respect to the fracture surface. The pore pressure and the stress changes in three dimensions at any point around the fracture caused by thermo- and poroelasticity and fracture compression are investigated. Then, the problem of constant water injection into a hydraulic fracture in Barnett shale is presented. In particular, with Mohr-Coulomb failure criterion, we calculate the fault reactivation potential around the fracture. This study is of interest in interpretation of micro-seismicity in hydraulic fracturing and in assessing permeability variation around a stimulation zone, as well as in estimation of the fracture spacing during hydraulic fracturing operations.
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.58)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Renewable > Geothermal > Geothermal Resource (0.34)
Abstract We calculate the effective vertical and horizontal stresses in the Hejre field, North Sea with a Biot’s coefficient estimated from log data. We show that a drilling window (for a vertical well) calculated with these stresses is larger than if using a Biot’s coefficient of 1. We show a method to estimate Biot’s coefficient from logging data and find Biot’s coefficients between 0.8 and 1 for the Shetland chalk Group, 0.8 to 1 for the Tyne Group and 0.6 to 0.8 for the Heno sandstone formation. Biot’s coefficient is straight forward to estimate in formations with a stiff frame, whereas in formations such as shales caution has to be taken. We discuss the consequence of assuming "shale" to be a mineral rather than assuming shale to be composed of minerals and fluid.
- Europe > Denmark > North Sea > Danish Sector (0.85)
- Asia > Middle East > Qatar > Arabian Gulf (0.60)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.69)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (0.68)
- North America > United States > California > Sacramento Basin > 2 Formation (0.99)
- Europe > Norway > North Sea > Norwegian Sea > Tuxen Formation (0.99)
- Europe > Norway > North Sea > Norwegian Sea > Sola Formation (0.99)
- (21 more...)
Abstract Hydraulic fracturing re-distributes pore pressure and stresses inside rock and causing failure by fracture initiation and/or activation of discontinuities such as natural fractures or layering boundaries. The clear result of this process would be enhancement of the formation permeability. In this paper, poroelastic numerical method is employed to investigate interactions of hydraulic fractures and porous rock. Besides, evolution of potential failure (microseismic events) during hydraulic stimulation is studied. The model uses indirect boundary element method. Temporal variations and pressure-dependent leak-off, hydro mechanical response of porous matrix, fluid flow in matrix, couplings of matrix volumetric deformation and pore fluid dissipation, and hydraulic fractures interaction are taken into account. Results clearly show the modification/redirection of principal stresses around pressurized hydraulic fracture. It also shows that modified stresses cause failure around the fracture tip which generally covers a bigger area than the fracture itself and could results in an overestimation of the stimulated reservoir volume. Then, pressurization of multiple parallel fractures studied. As expected, it is found that fracture geometry and the distance between hydraulic fractures are the most important factors in modifying the stress state and pore pressure and consequently extent of failure region. It was also observed that the opening of a fracture induces shear stresses on adjacent fractures. The SIF for pressurized cracks was calculated for Mode I and Mode II, and it was shown that when the distance between hydraulic fractures increases, the Mode I SIF also increases and the Mode II SIF decreases.'ép.
- North America > Canada (0.68)
- North America > United States > Oklahoma (0.28)
Abstract In this study, a coupled poro-elasto-plastic Finite Element Method (FEM) is used to calculate a set of scenarios of fault reactivation which could occur. The potential for fault reactivation is estimated numerically for faults surrounding a well designed for drilling cuttings reinjection in offshore West Africa. This well is in a block bordered with 3 major faults. The results of these calculations on fault reactivation are used to design the injection pressure and further control the total volume of drilling cuttings which can be safely injected. Numerical results obtained with the FEM model include: distribution of equivalent plastic strain within the whole model, distribution of von Mises equivalent stresses, and the displacement field under a given pore pressure boundary condition at the bottom of the model. The plastic region is the area where the fault is being reactivated. In this way, results of both the location and the level of fault reactivation are obtained and visualized. The numerical results are shown for the plastic strain distribution at the stage where the plastic region is growing up to the top of the fault zone and the distribution of the von Mises stresses.
- North America > United States (0.95)
- Africa > West Africa (0.61)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology > Fault (0.88)
- Africa > Angola > South Atlantic Ocean > Lower Congo Basin > Area B > Block 0 > Greater Vanza Longui Area (GVLA) Field > Pinda Formation (0.98)
- Europe > United Kingdom > England > London Basin (0.91)