MEASUREMENT AND ANALYSIS OF HYDROMECHANICAL EFFECTS IN FRACTURED ROCK

Fractures in rock hold important stores of water and petroleum, and slight changes in fracture aperture accompanying drawdown from pumping wells play a key role in recovering these resources. Four accomplishments are described that advance insight into the behavior and characterization of fractured crystalline rock. First was the development of two removable borehole extensometers that enable small axial displacements to be measured during hydraulic well tests. The extensometers consist of four major components: 1.) a pair of anchors; 2.) a displacement transducer 3.) a registration system, and; 4.) a temperature-compensated reference rod. One extensometer uses an axial reference rod with multiple, low-profile anchors, whereas another uses an offset reference rod with a single pair of anchors. Both designs can be readily mobilized and are capable of resolving sub-micron displacements in boreholes. Second, hydromechanical well tests were developed using the extensometers to measure the axial displacement of borehole walls during conventional slug and constant-rate pumping tests. These displacements were dominated by changes in fracture aperture. Results from well tests in fractured gneiss near Clemson, SC, were characterized by maximum head changes up to 10m and accompanying maximum aperture changes ranging from 0.4 μm to 14.0 μm. Plotting the aperture change as a function of drawdown yielded plots having distinctly different shapes for different formation properties. Third, a numerical model that couples elastic deformation and fluid flow in a single fracture was used to predict aperture changes and pressures resulting from well tests. Analytical solutions for pressure were used to validate the model for idealized conditions. Model predictions of displacement for idealized fractures provided fundamental insights that were used to understand the response of more complicated formations found in the field. Fourth was the development of procedures to estimate subsurface properties. Field measurements of pressure and displacement, obtained using the extensometer, were used to infer hydraulic, mechanical, and geometric properties of the subsurface formations. Analytical methods were used to obtain initial estimates, which were then refined using an optimization software package together with the numerical model. The results indicated the characterization of hydraulic well tests in fractured rock could be improved by measuring and interpreting displacements along with pressure changes

Energy Harvesting from Atmospheric Variations - Theory and Test

The last two decades have offered a dramatic rise in the use of digital technologies such as wireless sensor networks that require small isolated power supplies. Energy harvesting, a method to gather energy from ambient sources including sunlight, vibrations, heat, etc., has provided some success in powering these systems. One of the unexplored areas of energy harvesting is the use of atmospheric temperature variations to obtain usable energy. This paper investigates an innovative device to extract energy from atmospheric variations using ethyl chloride filled mechanical bellows. The apparatus consists of a bellows filled with ethyl chloride working against a spring in a closed and controlled environment. The bellows expand/contract depending upon the ambient temperature and the energy harvested is calculated as a function of the bellows’ length. The experiments showed that 6 J of energy may be harvested for a 23 degree Celsius change in temperature. The numerical results closely correlated to the experimental data with a deviation of 1%. In regions with high diurnal temperature variation, such an apparatus may yield approximately 250 uW depending on the ambient temperature range

The development and application of autonomous, low-cost, 3D printers

Low-cost 3D printers have empowered individuals to create customized printed parts, but they have yet to be as user friendly as a vending machine. The purpose of this research project is to develop an autonomous, low-cost, 3D printing Vending Machine that would increase access to this technology. This research with 15 students is divided into two teams. One team is responsible for the design concepts required of an additive manufacturing vending machine and the other team is responsible for printing and prototyping the parts using a low-cost 3D printer. The teams have produced printed objects from original designs using kits they built, implemented basic communications, developed design concepts for the vending machine and training strategies to increase access. This multi-disciplinary research provides educational opportunities for students to pursue their interests in the emerging field of additive manufacturing emerging field of additive manufacturing and it addresses critical challenges in wide-spread implementation of this technology across campus

Device to measure axial displacement in a borehole

A device to measure minute displacement in rocks, including anchor deployment means, anchor registration means, and frame release means. Further including anchor units comprising a fixed anchor point, a reversible anchor actuator and a deployable anchor face capable of being deployed with a force of up to 2000 lbs

Regional Flow Simulation in Fractured Aquifers Using Stress-Dependent Parameters

A model function relating effective stress to fracture permeability is developed from Hooke's law, implemented in the tensorial form of Darcy's law, and used to evaluate discharge rates and pressure distributions at regional scales. The model takes into account elastic and statistical fracture parameters, and is able to simulate real stress-dependent permeabilities from laboratory to field studies. This modeling approach gains in phenomenology in comparison to the classical ones because the permeability tensors may vary in both strength and principal directions according to effective stresses. Moreover this method allows evaluation of the fracture porosity changes, which are then translated into consolidation of the medium.Comment: 10 pages, 7 figures, submitted to Ground Water 201

Air-slug low-pressure straddle-packer system to facilitate characterization of fractured bedrock

Straddle-packer tests are used for determining aquifer properties in fractured rock, but packer tests are often avoided because they can be expensive. We have developed a simple, inexpensive, lightweight air-slug straddle packer system that can measure transmissivity as well as head variations along boreholes. The air-slug packer system was used at a site in Clemson, South Carolina to evaluate the transmissivity and head distributions in a borehole. The results show that transmissivity in the aquifer range from 10-7 to 10-4m2/s. Transmissivity distributions show three permeable intervals (T≈10-4m2/s) at depths of 24, 34, and 50m separated by relatively low permeability material (T ≈ 10-7 m/s). Upward vertical head gradients of 0.013 and 0.0016 were measured in the well. Similar results were obtained with standard, high-pressure packers.Sponsored by: Georgia Environmental Protection Division U.S. Geological Survey, Georgia Water Science Center U.S. Department of Agriculture, Natural Resources Conservation Service Georgia Institute of Technology, Georgia Water Resources Institute The University of Georgia, Water Resources Facult

Transient changes in fracture aperture during hydraulic well tests in fractured gneiss

The influence of deformable fractures on aquifer tests is studied by the development of a technique to measure and analyze in-situ changes in fracture aperture. A high-resolution borehole extensometer is used to measure the axial displacement of a borehole during packed-off hydraulic well tests in fractured rock. The extensometer yields repeatable displacements ranging from less than 0.5 microns/(meter of head) to 5 microns/meter depending on the testing location. The field measurements are interpreted using a theoretical analysis that couples elastic deformation and fluid flow in the fracture. Basic measurements from a single well can be interpreted to estimate transmissivity and storativity as functions of depth.Sponsored by: Georgia Environmental Protection Division U.S. Geological Survey, Georgia Water Science Center U.S. Department of Agriculture, Natural Resources Conservation Service Georgia Institute of Technology, Georgia Water Resources Institute The University of Georgia, Water Resources Facult

Multidisciplinary Research Projects as a Pathway for Undergraduate Skill Development: A Pilot Study

This poster presents research in progress that is looking to explore the value of multidisciplinary, hands-on research projects within undergraduate mechanical engineering education programs. Developing programs to expand the skills of engineering graduates in order to better meet the needs of industry has become a recent topic of attention for many national organizations as well as education researchers. The overall goal of this research study is to identify outcomes associated with participation in multidisciplinary projects. This study has collected pilot data from students involved in a two year Creative Inquiry project at Clemson University. The multidisciplinary team of mechanical engineering, bioengineering, nursing, and marketing students aspired to develop a stabilization process for pediatric patient’s arms during venipuncture procedures, such as drawing blood. Pilot interviews were conducted with past team members who had since graduated and were either employed or pursuing further education. Pilot participants articulated direct links between the skills they developed from the project and their roles in their current careers. The findings of this pilot study have motivated future investigation into the implications of multidisciplinary research as a supplement to traditional mechanical engineering education

Combining periodic hydraulic tests and surface tilt measurements to explore in situ fracture hydromechanics

International audienceFractured bedrock reservoirs are of socio-economical importance, as they may be used for storage or retrieval of fluids and energy. In particular, the hydromechanical behavior of fractures needs to be understood as it has implications on flow and governs stability issues (e.g., microseismicity). Laboratory, numerical, or field experiments have brought considerable insights to this topic. Nevertheless, in situ hydromechanical experiments are relatively uncommon, mainly because of technical and instrumental limitations. Here we present the early stage development and validation of a novel approach aiming at capturing the integrated hydromechanical behavior of natural fractures. It combines the use of surface tiltmeters to monitor the deformation associated with the periodic pressurization of fractures at depth in crystalline rocks. Periodic injection and withdrawal advantageously avoids mobilizing or extracting significant amounts of fluid, and it hinders any risk of reservoir failure. The oscillatory perturbation is intended to (1) facilitate the recognition of its signature in tilt measurements and (2) vary the hydraulic penetration depth in order to sample different volumes of the fractured bedrock around the inlet and thereby assess scale effects typical of fractured systems. By stacking tilt signals, we managed to recover small tilt amplitudes associated with pressure-derived fracture deformation. Therewith, we distinguish differences in mechanical properties between the three tested fractures, but we show that tilt amplitudes are weakly dependent on pressure penetration depth. Using an elastic model, we obtain fracture stiffness estimates that are consistent with published data. Our results should encourage further improvement of the method