No description available.

Fractured reservoirs are commonly simulated using the Dual Porosity model, but for many major fields, the model does not match field results. For these cases, it is necessary to perform a more complex simulation including either individual fractures or pseudofracture groups modeled in their own grid blocks. Discrete Fracture Modeling (DFN) is still a relatively new field, and most research on it up to this point has been done with Delaunay tessellations. This research investigates an alternative approach using Voronoi diagrams, yet applying the same DFN principles outlined in previous works. Through the careful positioning of node points, a grid of Voronoi polygons can be produced so that block boundaries fall along the fractures, allowing us to use the DFN simulation methods as proposed in the literature. Using Voronoi diagrams allows us to use far fewer polygons than the Delaunay approach, and also allows us to perfectly align flow so as to eliminate grid alignment errors that plagued previous static systems. The nature of the Voronoi polygon further allows us to simplify permeability calculations due to orthogonality and, by extension, is more accurate than the commonly used cornerpoint formulation for non-square grid blocks.

A biostimulation field trial was conducted to determine the effect of nutrient addition on microbial populations in a fractured rock environment. The ultimate goal of this research is to induce bioclogging in rock fractures as a method of in situ containment and remediation of contaminated groundwater. This trial focused on biostimulation of indigenous bacteria in a single fracture through the addition of bioavailable carbon, nitrogen and phosphorus sources. Bench-scale experiments were conducted to determine the optimal source and concentration of nutrients for microbial growth. The final mixture selected for the field trial consisted of sodium lactate plus two liquid fertilizers, resulting in a 100:9:4 molar solution of bioavailable carbon, nitrogen, and phosphorus with a carbon source concentration of 8.9 g/L. The field trial was conducted in an uncontaminated area adjacent to an abandoned quarry in southern Ontario, Canada. The geology of the site consists of flat-lying dolostone pervaded by bedding plane fractures, with minimal overburden. An arrangement of three boreholes isolated a single fracture at a depth of 17m using straddle packer systems. A groundwater recirculation system was created with groundwater withdrawal at BH7 and reinjection of amended water at BH9. Throughout the three-week biostimulation experiment, general groundwater parameters, including temperature, dissolved oxygen and electrical conductivity, were monitored frequently. Geochemical and microbiological conditions including available electron acceptors, biochemical oxygen demand, heterotrophic plate counts, and microbial diversity were evaluated before and after the experiment. Monitoring results for the withdrawal well confirmed that nutrient delivery was occurring, albeit with substantial mass loss due to incomplete flow field development. Numerical modelling of the system estimated a nutrient mass loss of 29%. Geochemical monitoring of key electron acceptors suggested that redox conditions in the isolated fracture were greatly affected by nutrient addition. Biological data indicated significant changes in the microbial populations, with heterotrophic plate counts increasing significantly in the isolated fracture. Changes in microbial diversity were also observed through 16S rDNA analysis. Denaturing gradient gel electrophoresis results indicated substantial diversification and growth of the microbial community following biostimulation. Further research will investigate the potential for bioclogging at a NAPL-contaminated fractured bedrock site. / Thesis (Master, Civil Engineering) -- Queen's University, 2008-09-17 12:37:48.16

The objective of this study was to examine the effect of heat on the growth of a biofilm in a parallel glass plate fracture table. Groundwater was collected from a limestone aquifer and amended with a nutrient mixture to stimulate the indigenous microbial population. The amended water was heated to approximately 30oC in an upgradient reservoir attached to the fracture table and recirculated through the 2-m long, 0.6-m wide, parallel glass plate fracture having an approximate fracture aperture of 2000 μm. The fracture was maintained at approximately 10oC to simulate natural in situ groundwater temperature and the upgradient reservoir maintained at 30oC. Geochemical parameters and bacterial counts were measured regularly throughout the biostimulation to monitor biofilm growth in the fracture. Hydraulic tests and tracer experiments completed before and after the biostimulation were used as the primary indicators of the successful bioclogging of the fracture. Geochemical parameters measured throughout the trial revealed an increasingly reducing environment capable of supporting the development of a diverse biofilm. Direct and indirect bacterial counts revealed the dominant bacteria within the system included common groundwater bacteria pseudonomads, enteric, and slime-forming bacteria. Heterotrophic bacteria were also present in significant concentrations. Visible clusters of biofilm were observed on Day 2 of the trial with a fully-connected biofilm observed by Day 7. The biofilm impacted the groundwater flow through the fracture resulting in an approximately 2.75-hour delay in the tracer’s breakthrough during the tracer experiment completed on Day 13 of the trial compared to an experiment conducted during the initial stages of biofilm development. Based on the results of the tracer experiment, the biofilm growth reduced the velocity of the groundwater by 9.8%, the fracture aperture by 37.8%, and increased the bulk dispersivity to 50mm. Recommendations for future work include the application of heated biostimulation at the field scale in a well-characterized, isolated fracture. / Thesis (Master, Civil Engineering) -- Queen's University, 2011-08-01 12:33:25.286

An analytical model is presented for the interpretation of pumping tests conducted in a fractured rock aquifer. The solution accommodates multiple horizontal fractures intersecting pumping and observation wells with interconnecting vertical fracture features. The uppermost horizontal fracture is connected via this fracture network to a free surface boundary. Wellbore storage is included at the pumping and observation wells using an approximate superposition technique and the solution is derived using the Laplace transform method. Evaluation is performed by numerical inversion using the Talbot algorithm. Sensitivity of the model to the governing hydraulic parameters for both pumping and observation well data is presented for a realistic range of values for fractured rock. A field example is given to demonstrate the application of the model and to explore the uniqueness of the interpreted values. Based on the results obtained using the present analytical model, estimation of unique values of the vertical hydraulic parameters in a sedimentary rock setting may not be possible using pumping test results. Subsequently, measuring aquifer properties from various testing methods was investigated to explore the significance of fracture heterogeneities relative to tested volumes and to determine which testing methods were capable of producing reliable parameter estimates. The hydrogeological study was performed in a fractured sedimentary rock aquifer using four different field testing methods: constant head tests, pulse interference tests, 12-hour isolated interval pumping tests and 48-hour open-hole pumping tests. Particular emphasis was placed on the reliable estimation of vertical hydraulic parameters in this setting. The evaluation of the pumping test data was performed using the analytical model derived earlier to determine whether the new pumping test model could produce confident estimates of vertical hydraulic parameters. While estimates of horizontal hydraulic conductivity measurements were not affected by test method, open-well pumping tests do not appear able to predict values of vertical hydraulic conductivity and specific yield. Alternatively, pulse interference tests may be a less time-intensive option to constant head injection tests for determining vertical parameters in a sedimentary rock setting. / Thesis (Master, Civil Engineering) -- Queen's University, 2012-09-14 11:28:14.466

Induction logging is a well-developed geophysical method with multiple applications. It has been used extensively in academic research as well as in industry. Induction logging is a controlled-source electromagnetic (CSEM) exploration method. It characterizes geologic formations through the measurements of induced magnetics fields. The purpose of this research project is to better understand induction logs and the effects fractured geologic formations have on them. Computer modeling is used to generate synthetic logs for analysis in this research project. The original program required certain modifications to fit this research project’s goals. The computer program, Seatem is based on the finite element method. It is able to use a layered Earth model that is the basis for the synthetic log analysis. The geologic layers in this model are assigned various conductivities and also have the option of being assigned a geologic roughness value. The geologic roughness parameter is used to simulate fractured rocks in the subsurface. The synthetic logs generated by the modified Seatem program produce some encouraging results. In a thinning bed analysis, it is shown that as a conductive bed is thinned in a step-size procedure, the resulting induction log underestimates the actual conductivity of the layer. It also shows that the boundary layers around the thinned layer are better characterized in the log. The next synthetic log was calculated for a fractured resistive layer. This log shows that as the layer becomes more fractured, there is an increase in the underestimation of the actual conductivity. This layer is then thinned down and another synthetic log is calculated. The resulting log shows similar traits to the thinning bed analysis and shows an underestimation of the apparent conductivity. The same procedure is performed for a fractured conductive layer. The analysis produce similar results; however, that are much more drastic changes in the induction logs. As the unit becomes more fractured, the apparent conductivity is lower then the actual conductivity, as in the resistive case. However, smaller increases in the roughness parameter produced more severe underestimations than larger increases in the roughness parameter did for the resistive layer.

Characterization of field-scale transport in bedrock aquifers is necessary due to the preponderance of groundwater contamination in these settings, and the increasing attention paid to these sites by regulatory bodies. However, as a result of the inherent complexity, and the consequent uncertainty in the dominant transport processes, large-scale transport in fractured rock is poorly understood. In this study an investigation of large-scale transport was accomplished in part by conducting a radial-divergent tracer experiment in a 15 m thick section of aquifer with observations over a 245 m distance, using a novel tracer detection method capable of detecting breakthrough in individual fractures. The tracer experiment was conducted at a well-characterized field site in Smithville, Ontario, which is underlain by several large-scale bedding plane fractures, and used a submersible fluorometer to detect tracer arrival in-situ and to obtain vertical fluorescence profiles (VFPs) from observation boreholes. To complete the investigation, hydraulic characterization data and VFPs were used to approximate the dominant transport pathways and a numerical model which solves for flow and transport in discrete fracture features (HydroGeoSphere) was used to simulate the tracer experiment. The results of the experiment and the modeling exercise were compared to those from a large-scale single fracture tracer experiment conducted previously at the same site, for which the modeling was revisited. The experimental results of the fracture network experiment (FNE) were markedly more heterogeneous than those of the previously conducted single fracture experiment (SFE), with multiple peaks in the breakthrough curves, and scale dependent changes in breakthrough character. The VFPs illustrate that differences in the observed transport arise due to tortuous transport pathways within individual fracture features, and the combined effect of this tortuosity in the numerous fractures contributing to transport in the fracture network. For the observation boreholes closest to the source (< 55 m), both the FNE and SFE models were capable of fitting the data using parameters within the range of values determined from prior lab and field experiments at the site. These fits became poorer over increased transport distances however, where the models used could not account for the increased effects of tortuosity. / Thesis (Master, Civil Engineering) -- Queen's University, 2008-08-25 02:48:16.066

No description available.

Experiments exploring transport and bio-containment of contaminants in fractured rock were completed using fractured-limestone samples obtained in eastern Ontario, Canada. Three single-fracture samples, a fracture-intersection sample and a fracture-network sample were set into vertical flow systems. Three phases of experiments focused on the transport and hydraulic properties of each sample, the effects of biobarriers on diffusion processes in fracture rock, and methods of improving biobarrier stability and survivability. Hydraulic apertures were determined from constant-flow measurements and transport properties were interpreted from Lissamine and KBr tracer experiments with velocities of up to 8500 m/d for all five samples. At Re > 16, linear to non-linear transitions were observed in enlarged single fracture A and the fracture intersection samples. Reversible increases in aperture were observed at Reynolds numbers (Re) of 7, 4, and 3 for single fractures A and B, and the fracture-network, respectively. Non-linear effects were not observed in these samples over the range of velocities studied (up to Re = 20). Results from the 1-D analytical transport model overestimated values of matrix porosity, suggesting that diffusion from dead zones and slow-flowing regions are also contributing to observed breakthrough curves. Methods of improving biobarrier stability in fractured rock were studied in two single-fracture samples and the fracture-network sample by stimulating naturally-occurring groundwater bacteria. Survivability was improved with successive cycles of feeding and starving and stimulating growth at lower temperatures. Modeled values of matrix porosity decreased by up to 50%, indicating that diffusion processes are strongly influenced by biofilm development. Back diffusion of Lissamine was measured using one single-fracture sample and the fracture-intersection sample. Lissamine was allowed to diffuse into the matrix of each sample and, following a suitable loading period, the back-diffusion of residual Lissamine concentrations were measured from the outflow. This was done in the presence and absence of biofilm, and following the introduction of biofilm onto the fracture surfaces, diffusion was no longer a governing process affecting transport and only advective transport was observed. Experiments were interpreted using a 3-D finite difference model with a three-layer porosity approach, and indicated a decrease in aperture and porosity following biostimulation. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2012-11-22 11:23:24.065

A common problem in science and engineering applications deals with finding information about a system where only limited information is known. One example of this problem is determining the geometry of an aquifer or oil reservoir based on well tests taken at the site. The Conditional Coding Method attacks this type of problem. This method uses the Simulated Annealing Algorithm in conjunction with a probability model which generates possible solutions based on a uniform random number list. The Annealing Algorithm generates a conditional probability distribution on all possible solutions generated by the probability model, conditioned on the observed data set. The problem is attacked by sampling from this distribution. This method accounts for the noise inherent in the data set as well as the uncertainty due to the limited amount of data available.