Badruzzaman, Ahmed (Pacific Consultants and Engineers / University of California, Berkeley) | Schmidt, Andrea (Lawrence Livermore National Laboratory) | Antolak, Arlyn (Sandia National Laboratories)
The porosity response of four proposed generator-based neutron tool concepts is studied using Monte Carlo simulation of the radiation transport. The objective is to examine, at a fundamental level, the potential of these sources to replace americium-beryllium (Am-Be) sources primarily in openhole applications and, briefly, in a through-casing application of interest to a number of operators. The accelerator-based sources include a dense-plasma focus (DPF) alpha-particle accelerator and deuterium-tritium (DT), deuterium-deuterium (D-D), and deuterium-lithium (D-7Li) neutron generators. The DPF uses the (a-Be) reaction to generate a neutron spectrum that is nearly identical to that from an Am-Be source. D-T and D-D neutron generators use compact linear accelerators and produce, respectively, 14.1 and 2.45 MeV neutrons. The D-7Li neutron spectrum resembles the Am-Be spectrum at lower energies, and has a neutron peak at 13.3 MeV
Simple spherical-geometry models that do not include tool and borehole are used to explore the basic physics. An openhole tool-borehole-formation configuration is used to explore key observations from the simpler model. In both models, the responses at various detectors are examined to understand the behavior of the ratios constructed. Sensitivity to formation conditions, such as lithology, presence of gas, low porosity and presence of thermal absorbers, and operational conditions, such as tool standoff, are examined. A casedhole configuration is also analyzed where neutron counts are the only method for zonal correlation.
The state of neutron-generator technology is discussed in terms of neutron yield, target properties, power demands etc., which are important considerations for implementing such generators in nuclear logging tools.
To better understand the factors contributing to electromagentic (EM) observables in developed field sites, we examine in detail through finite element analysis the specific effects of casing completion design. The presense of steel casing has long been exploited for improved subsurface interrogation and there is growing interest in remote methods for assessing casing integrity accross a range of geophysical scenarios related to resource development and sequestration/storage activities. Accurate modeling of the casing response to EM stimulation is recognized as relevant, and a difficult computational challenge because of the casing’s high conductivity contrast with geomaterials and its relatively small volume fraction over the field scale. We find that casing completion design can have a significant effect on the observed EM fields, especially at zero frequency. This effect appears to originate in the capacitive coupling between inner production casing and the outer surface casing. Furthermore we show that an equivalent ‘effective conductivity’ for the combined surface/production casing system is inadequate for replicating this effect, regardless of whether the casings are grounded to one another or not. Lastly, we show that in situations where this coupling can be ignored and knowledge of casing currents is not required, simplifying the casing as a perfectly conducting line can be an effective strategy for reducing the computational burden in modeling field–scale response.
Presentation Date: Tuesday, October 16, 2018
Start Time: 1:50:00 PM
Location: 213A (Anaheim Convention Center)
Presentation Type: Oral
Methods for the efficient representation of fracture response in geoelectric models impact an impressively broad range of problems in applied geophysics. We adopt the recently-developed hierarchical material property representation in finite element analysis (Weiss, 2017) to model the electrostatic response of a discrete set of vertical fractures in the near surface and compare these results to those from anisotropic continuum models. We also examine the power law behavior of these results and compare to continuum theory. We find that in measurement profiles from a single point source in directions both parallel and perpendicular to the fracture set, the fracture signature persists over all distances. Furthermore, the homogenization limit (distance at which the individual fracture anomalies are too small to be either measured or of interest) is not strictly a function of the geometric distribution of the fractures, but also their conductivity relative to the background. Hence, we show that the definition of "representative elementary volume", that distance over which the statistics of the underlying heterogeneities is stationary, is incomplete as it pertains to the applicability of an equivalent continuum model. We also show that detailed interrogation of such intrinsically heterogeneous models may reveal power law behavior that appears anomalous, thus suggesting a possible mechanism to reconcile emerging theories in fractional calculus with classical electromagnetic theory.
Presentation Date: Tuesday, October 16, 2018
Start Time: 8:30:00 AM
Location: 207A (Anaheim Convention Center)
Presentation Type: Oral
Pettitt, W.S. (Itasca International Inc.) | Hazzard, J. (Itasca International Inc.) | Riahi, A. (Itasca International Inc.) | Maxwell, S. (Itasca International Inc.) | Blankenship, D. (Sandia National Laboratories)
Reservoir simulations including induced and natural fractures have informed different initial conceptual designs for well geometries and stimulation strategies for the proposed Fallon FORGE site. The Distinct Element Method (DEM) has been used to run a suite of coupled three-dimensional Thermo-Hydro-Mechanical (THM) models that consider the geological site characterization, design concepts, and criteria for the project. Microseismicity is extracted from the models by observing the slip on existing fractures in the natural joint network. The aim is to convert the mechanical information observed in the numerical model into estimates of microseismic cloud dimensions and magnitude distributions that can inform the design of field monitoring for the Enhanced/Engineered Geothermal Systems (EGS) reservoir and the assessments of induced seismicity hazard for mitigation planning. Both hydraulic fracturing and hydraulic shearing ("hydro-shearing") were analyzed in the models using multi-stage stimulations along sub-horizontal laterals to assess design options on treatment strategy. The simulated microseismicity describes many of the features observed in field studies and is shown to be strongly dependent on the size and properties of the natural fractures combined with the fluid volume.
Presentation Date: Tuesday, October 16, 2018
Start Time: 1:50:00 PM
Location: 208A (Anaheim Convention Center)
Presentation Type: Oral
Tamayo-Mas, Elena (British Geological Survey) | Harrington, Jon (British Geological Survey) | Shao, Hua (Federal Institute for Geosciences and Natural Resources) | Dagher, Elias (Canadian Nuclear Safety Commission / University of Ottawa) | Lee, Jaewon (Korea Atomic Energy Research Institute) | Kim, Kunhwi (Lawrence Berkeley National Laboratory) | Rutqvist, Jonny (Lawrence Berkeley National Laboratory) | Lai, Shu-Hua (National Central University) | Chittenden, Neil (Quintessa Ltd.) | Wang, Yifeng (Sandia National Laboratories) | Damians, Ivan (Universitat Politecnica de Catalunya) | Olivella, Sebastia (Universitat Politecnica de Catalunya)
The processes governing the movement of repository gases through engineered barriers and argillaceous host rocks can be split into two components, (i) molecular diffusion (governed by Fick's Law) and (ii) bulk advection. In the case of a repository for radioactive waste, corrosion of metallic materials under anoxic conditions will lead to the formation of hydrogen. Radioactive decay of the waste and the radiolysis of water are additional source terms. If the rate of gas production exceeds the rate of gas diffusion within the pores of the barrier or host rock, a discrete gas phase will form (Wikramaratna et al., 1993; Ortiz et al., 2002; Weetjens and Sillen, 2006). Under these conditions, gas will continue to accumulate until its pressure becomes sufficiently large for it to enter the surrounding material. In clays and mudrocks, four primary phenomenological models describing gas flow can be defined, see Figure 1: (1) gas movement by diffusion and/or solution within interstitial fluids along prevailing hydraulic gradients; (2) gas flow in the original porosity of the fabric, commonly referred to as two-phase flow; (3) gas flow along localised dilatant pathways, which may or may not interact with the continuum stress field; and (4) gas fracturing of the rock similar to that performed during hydrocarbon stimulation exercises.
Kalinina, Elena (Sandia National Laboratories) | Hadgu, Teklu (Sandia National Laboratories) | Wang, Yifeng (Sandia National Laboratories) | Ozaki, Yusuke (Japan Atomic Energy Agency) | Iwatsuki, Teruki (Japan Atomic Energy Agency)
Its main purpose is providing a scientific basis for the research and development of technologies needed for deep geological disposal of radioactive waste in fractured crystalline rocks. The site hydrology is described in Iwatsuki et al., 2005 and Iwatsuki et al., 2015. A large amount of fracture data was collected in the Tono area. The fracture data analysis and development of the fracture models at the different scales is an ongoing effort. Bruines et al., 2014 described the development of the discrete fracture network models for 2 scales - local (9km x 9km) and site-scale (2km x 2km).
Hadgu, Teklu (Sandia National Laboratories) | Kalinina, Elena (Sandia National Laboratories) | Wang, Yifeng (Sandia National Laboratories) | Ozaki, Yusuke (Japan Atomic Energy Agency) | Iwatsuki, Teruki (Japan Atomic Energy Agency)
ABSTRACT: Experimental hydrology data from the Mizunami Underground Research Laboratory in Central Japan have been used to develop a site-scale fracture model and a flow model for the study area. The discrete fracture network model was upscaled to a continuum model to be used in flow simulations. A flow model was developed centered on the research tunnel, and using a highly refined regular mesh. In this study development and utilization of the model is presented. The modeling analysis used permeability and porosity fields from the discrete fracture network model as well as a homogenous model using fixed values of permeability and porosity. The simulations were designed to reproduce hydrology of the modeling area and to predict inflow of water into the research tunnel during excavation. Modeling results were compared with the project hydrology data. Successful matching of the experimental data was obtained for simulations based on the discrete fracture network model.
ABSTRACT: Helium and argon are represented by known amounts in air. Helium is 5.2 ppm by volume in the atmosphere and primarily the result of the natural radioactive decay of heavy radioactive elements. Argon is the third most abundant gas in the Earth's atmosphere, 9340 ppm; radiogenic argon-40, is derived from the decay of potassium-40 in the Earth's crust. The isotopic signature of noble gases found in rocks is vastly different than that of the atmosphere which is contributed by a variety of sources. Geogenic noble gases are contained in most crustal rock at inter and intra granular sites, their release during natural and man-made stress and strain changes represents a signal of deformation. When rock is subjected to stress conditions exceeding about half its yield strength, micro-cracks begin to form. As rock deformation progresses a fracture network evolves, releasing trapped noble gases and changing the transport properties to gas migration. Thus, changes in gas emanation and noble gas composition from rocks could be used to infer changes in stress-state and deformation. An experimental system we developed combines triaxial rock deformation and mass spectrometry to measure noble gas flow real-time during deformation. Geogenic noble gases are released during triaxial deformation and that release is related to volume strain and acoustic emissions. The noble gas release then represents a signal of deformation during its stages of development. Gases released depend on initial gas content, pore structure and its evolution, and amount of deformation imposed. Noble gas release is stress/strain history dependent and pressure and strain rate dependent. Sensing of gases released related to both earthquakes and volcanic activity has resulted in anomalies detected for these natural processes. We propose using this deformation signal as a tool to detect subterranean deformation (fracture).
Noble gases present in crustal rocks are derived from groundwater (atmospheric origins), magmatic activity (mantle origins), and radioactive decay of natural radioactive elements (e.g. U, Th, and K). Radiogenic noble gases are produced within minerals and retained to different degrees within the minerals. The composition of gases within the mineral phase is a function of the mineralogical composition, the rock matrix and the thermal, tectonic, erosional and depositional history of the formation. These gases migrate to the adjacent pore fluid and/or fracture networks over geological time periods via diffusion, recoil and chemical dissolution. Transport of gases occurs within the rock grain, along grain boundaries, in the pore fluid and within the micro to macro fracture network. The transport is a function of the stress state of the rock and its control on chemical processes and the physical configuration of the grain and fracture networks. The work we present investigates the release of these gases as a function of the systematic change in stress state by application of stresses sufficient to fracture the rock. We hope to use the noble gas release and subsequent detection to signal deformation.
ABSTRACT: Bayou Choctaw Cavern 20 is located near the edge of the salt dome. Its proximity close to the edge of the dome raises concerns about potential tensile failure in the surrounding rock near BC-20 induced by the cavern volume closure due to salt creep. The location of BC-20 in the salt dome is similar to the cavern involved in the Bayou Corne Sinkhole, which suggested that a risk of loss integrity of the sidewall of BC-20 should be investigated. This paper evaluates the structural instability in the salt between the dome edge and the cavern through a geomechanical analysis using a newly developed numerical model. The results from the analysis indicate that if we keep the new normal operation brine-side wellhead pressure, the edge pillar has no predicted risk of structural instability in the form of tensile failure and/or dilatant damage.
The U.S. Strategic Petroleum Reserve (SPR) stores crude oil in 60 caverns located at four sites located along the Gulf Coast. The reserve contains approximately 695 MMbbl (110 Mm3) of crude oil. Most of the caverns were solution mined by the U.S. Department of Energy (DOE). Bayou Choctaw Cavern 20 (BC-20) is located near the edge of the salt dome (Fig. 1). Its proximity close to the edge of the dome raises concerns about potential tensile failure in the surrounding rock near BC-20 induced by the cavern volume closure due to salt creep1. The location of BC-20 in the salt dome is similar to the cavern involved in the Bayou Corne Sinkhole shown in Fig. 2 suggested to us that a risk of loss integrity of the sidewall of BC-20 should be investigated. Due to the Bayou Corne cavern collapse, 150 homes had been evacuated for nine months since August 2012 . This paper evaluates the structural instability in the salt between the dome edge and the cavern (call ‘edge pillar’, indicated by yellow ovals in Fig. 1) through a geomechanical analysis using a newly developed numerical model [2, 3].
Ulrich, C. (Lawrence Berkeley National Laboratory) | Dobson, P. F. (Lawrence Berkeley National Laboratory) | Kneafsey, T. J. (Lawrence Berkeley National Laboratory) | Roggenthen, W. M. (South Dakota School of Mines & Technology) | Uzunlar, N. (South Dakota School of Mines & Technology) | Doe, T. W. (Golder Associates Inc.) | Neupane, G. (Idaho National Laboratory) | Podgorney, R. (Idaho National Laboratory) | Schwering, P. (Sandia National Laboratories) | Frash, L. (Los Alamos National Laboratory) | Singh, A. (Stanford University)
ABSTRACT: The EGS Collab project is focused on understanding and predicting permeability enhancement and evolution in crystalline rocks. To accomplish this, the project is creating a suite of intermediate-scale (~10-20 m) field test beds coupled with stimulation and interwell flow tests that will provide a basis to better understand the fracture geometries and processes that control heat transfer between rock and stimulated fractures. As part of the site characterization effort for the first experimental test bed, our team has worked on mapping the distribution, orientation, and nature of open and healed fractures exposed along the drift wall and within the eight bore holes drilled for this test bed. The fractures have been characterized through detailed description of continuous cores obtained from these boreholes, evaluation of televiewer logs, and mapping of fractures and seeps exposed along the drift wall. The fracture data are being compiled and interpreted for slip and dilation tendencies, and will be incorporated into coupled-process geomechanical flow and transport models to better constrain the planned flow and tracer tests.
The goal of the EGS Collab project (Kneafsey et al., 2018) is to establish a suite of intermediate-scale (~10-20 m) field test beds to host stimulation and interwell flow tests that will provide improved understanding of fracture stimulation methods, resulting fracture geometries, and processes that control heat transfer between rock and stimulated fractures for Enhanced Geothermal Systems (EGS). Our diverse team recently developed the first experimental test bed for conducting these experiments at the Sanford Underground Research Facility (SURF), the former Homestake gold mine, located in Lead, SD. Our experimental site is located on the 4850 level (1478 m below the surface) of SURF in the Precambrian Poorman Formation phyllite. The test bed consists of a stimulation/injection borehole, a production borehole, and six monitoring boreholes (Fig. 1). The borehole layout (Morris et al., 2018) was designed so that the axes of the injection and production boreholes are approximately parallel to Shmin, which will cause hydraulic fractures to be generated perpendicular to the boreholes. In this initial test bed, we will perform well-controlled and intensely monitored in situ experiments focused on creating a series of hydrofractures that connect the injection and production boreholes; these fractures will be used to evaluate fluid flow and heat transfer. However, the created hydrofractures may intersect permeable natural fractures, which may result in the cross well flow tests being in a fracture network rather than a single fracture. Thus, it is important to understand the distribution, orientation, and nature of existing fractures in the test bed prior to the hydraulic fracture stimulation and flow test experiments.