PRELIMINARY ESTIMATION OF THE RESERVOIR CAPACITY AND THE LONGEVITY OF THE BACA GEOTHERMAL FIELD, NEW MEXICO.

Data from open literature on the field are used to estimate the amount of hot water in place (reservoir capacity) and the length of time the reservoir can supply steam for a 50 MW power plant (reservoir longevity). The reservoir capacity is estimated by volumetric calculations using existing geological, geophysical and well data. The criteria used are described and the sensitivity of the results discussed

Coupled hydro-mechanical processes in crytalline rock and ininduratedand plastic clays: A comparative discussion

This paper provides a comparative discussion of coupledhydromechanical processes in three different geological formations:crystalline rock, plastic clay, and indurated clay. First, the importantprocesses and associated property characteristics in the three rock typesare discussed. Then, one particular hydromechanical coupling is broughtup for detailed consideration, that of pore pressure changes in nearbyrock during tunnel excavation. Three field experiments in the three rocktypes are presented and their results are discussed. It is shown that themain physical processes are common to all three rock types, but with verydifferent time constants. The different issues raised by these cases arepointed out, and the transferable lessons learned are identified. Suchcross fertilization and simultaneous understanding of coupled processesin three very different rock types help to greatly enhance confidence inthe state of science in this field

Uncertainty in the Maximum Principal Stress Estimated from Hydraulic Fracturing Measurements Due to the Presence of the Induced Fracture

Abstract The classical theory for hydraulic fracturing stress measurements assumes an ideal case with a linear elastic, homogenous, and isotropic medium; and a fracture that reopens distinctly when the minimum tangential borehole stress is exceeded. The induced fracture disturbs this ideal picture in several aspects, which are important for the evaluation of the maximum horizontal principal stress using the fracture reopening pressure. This disturbance can be attributed to the fracture normal stiffness and the initial hydraulic fracture permeability. In this paper, the hydraulic fracturing reopening test is studied by coupled hydromechanical modeling that takes into account an induced fracture that is incompletely closed. The result shows that with realistic equipment compliance, the apparent fracture reopening evaluated from the well-pressure is close to the magnitude of the minimum horizontal principal stress with little or no correlation to the maximum horizontal principal stress. This observation suggests that determination of maximum principal stress by hydraulic fracturing using the reopening pressure is very uncertain

Predicting the Severity and Prognosis of Trismus after Intensity-Modulated Radiation Therapy for Oral Cancer Patients by Magnetic Resonance Imaging

To develop magnetic resonance imaging (MRI) indicators to predict trismus outcome for post-operative oral cavity cancer patients who received adjuvant intensity-modulated radiation therapy (IMRT), 22 patients with oral cancer treated with IMRT were studied over a two-year period. Signal abnormality scores (SA scores) were computed from Likert-type ratings of the abnormalities of nine masticator structures and compared with the Mann-Whitney U-test and Kruskal–Wallis one-way ANOVA test between groups. Seventeen patients (77.3%) experienced different degrees of trismus during the two-year follow-up period. The SA score correlated with the trismus grade (r = 0.52, p<0.005). Patients having progressive trismus had higher mean doses of radiation to multiple structures, including the masticator and lateral pterygoid muscles, and the parotid gland (p<0.05). In addition, this group also had higher SA-masticator muscle dose product at 6 months and SA scores at 12 months (p<0.05). At the optimum cut-off points of 0.38 for the propensity score, the sensitivity was 100% and the specificity was 93% for predicting the prognosis of the trismus patients. The SA score, as determined using MRI, can reflect the radiation injury and correlate to trismus severity. Together with the radiation dose, it could serve as a useful biomarker to predict the outcome and guide the management of trismus following radiation therapy

A Semi-Analytical Solution for Large-Scale Injection-Induced PressurePerturbation and Leakage in a Laterally Bounded Aquifer-AquitardSystem

A number of (semi-)analytical solutions are available to drawdown analysis and leakage estimation of shallow aquifer-aquitard systems. These solutions assume that the systems are laterally infinite. When a large-scale pumping from (or injection into) an aquifer-aquitard system of lower specific storativity occurs, induced pressure perturbation (or hydraulic head drawdown/rise) may reach the lateral boundary of the aquifer. We developed semi-analytical solutions to address the induced pressure perturbation and vertical leakage in a 'laterally bounded' system consisting of an aquifer and an overlying/underlying aquitard. A one-dimensional radial flow equation for the aquifer was coupled with a one-dimensional vertical flow equation for the aquitard, with a no-flow condition imposed on the outer radial boundary. Analytical solutions were obtained for (1) the Laplace-transform hydraulic head drawdown/rise in the aquifer and in the aquitard, (2) the Laplace-transform rate and volume of leakage through the aquifer-aquitard interface integrated up to an arbitrary radial distance, (3) the transformed total leakage rate and volume for the entire interface, and (4) the transformed horizontal flux at any radius. The total leakage rate and volume depend only on the hydrogeologic properties and thicknesses of the aquifer and aquitard, as well as the duration of pumping or injection. It was proven that the total leakage rate and volume are independent of the aquifer's radial extent and wellbore radius. The derived analytical solutions for bounded systems are the generalized solutions of infinite systems. Laplace-transform solutions were numerically inverted to obtain the hydraulic head drawdown/rise, leakage rate, leakage volume, and horizontal flux for given hydrogeologic and geometric conditions of the aquifer-aquitard system, as well as injection/pumping scenarios. Application to a large-scale injection-and-storage problem in a bounded system was demonstrated

Characteristics of flow and transport in low-permeability fractured rock based on a channel network model

Discrete Fracture Network (DFN) models for evaluating flow and transport in low-permeability fractured rocks are important tools in safety assessments of nuclear waste repositories, and also important for other geoengineering and environmental applications. The well-known phenomena of flow channeling, arising from both intra-fracture and inter-fracture heterogeneities, is in general difficult to implement in these models. The present study uses the Channel Network Model (CNM) concept as a complementary approach to DFN models, with focus on channelized flow within fracture planes and in the fracture network. A method used to generate CNMs based on channels connecting centroids of fracture planes was implemented within a pychan3d library and applied to a 3D DFN model based on field data from Forsmark, Sweden. Three sets of realizations of the channel network are used to characterize the flow and transport system between deformation zones in the granitic host rock. The results indicate the significance of very low-conductivity fractures in providing critical flow connections in these rocks. It is shown that only a few (4 to 6 in our cases) key flow bridges within a network of 9000 or more fractures control its flow and transport. The use of CNMs together with DFN models enhances confidence in safety assessments for nuclear waste repositories and other applications, while providing valuable insights into complex flow and transport behavior in low-fracture-permeability rocks.</p

Simple Model Representations of Transport in a Complex Fracture and Their Effects on Long-Term Predictions

A complex fracture model for fluid flow and tracer transport was previously developed that incorporates many of the important physical effects of a realistic fracture, including advection through a heterogeneous fracture plane, partitioning of flow into multiple subfractures in the third dimension, and diffusion and sorption into fracture-filling gouge, small altered rock matrix blocks within the fracture zone, and the unaltered semi-infinite rock matrix on both sides of the fracture zone (Tsang and Doughty, 2003). It is common, however, to represent the complex fracture by much simpler models consisting of a single fracture, with a uniform or heterogeneous transmissivity distribution over its plane and bounded on both sides by a homogeneous semi-infinite matrix. Simple-model properties are often inferred from the analysis of short-term (one to a few days) site characterization (SC) tracer-test data. The question addressed in this paper is: How reliable is the temporal upscaling of these simplified models? Are they adequate are for long-term calculations that cover thousands of years? In this study, a particle-tracking approach is used to calculate tracer-test breakthrough curves (BTCs) in a complex fracture model, incorporating all the features described above, for both a short-term SC tracer test and a 10,000-year calculation. The results are considered the 'real-world'. Next, two simple fracture models, one uniform and the other heterogeneous, are introduced. Properties for these simple models are taken either from laboratory data or found by calibration to the short-term SC tracer-test BTCs obtained with the complex fracture model. Then the simple models are used to simulate tracer transport at the long-term time scale. Results show that for the short-term SC tracer test, the BTCs calculated using simple models with laboratory-measured parameters differ significantly from the BTCs obtained with the complex fracture model. By adjusting model properties, the simple models can be calibrated to reproduce the peak arrival time and height of the complex-fracture-model BTCs, but the overall match remains quite poor. Using simple models with short-term SC-calibrated parameters for long-term calculations causes order-of-magnitude errors in tracer BTCs: peak arrival time is 10-100 times too late, and peak height is 50-300 times too small. On the other hand, using simple models with laboratory-measured properties of unfractured rock samples for 10,000-year calculations results in peak arrivals and heights up to a factor of 50 too early and large, respectively. The actual magnitudes of the errors made by using the simple models depend on the parameter values assumed for the complex fracture model, but in general, simple models are not expected to provide reliable long-term predictions. The paper concludes with some suggestions on how to improve long-term prediction calculations