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Tavakoly A.A.,U.S. Army | Maidment D.R.,University of Texas at Austin | McClelland J.W.,University of Texas at Austin | Whiteaker T.,University of Texas at Austin | And 4 more authors.
Journal of the American Water Resources Association

This article presents a framework for integrating a regional geographic information system (GIS)-based nitrogen dataset (Texas Anthropogenic Nitrogen Dataset, TX-ANB) and a GIS-based river routing model (Routing Application for Parallel computation of Discharge) to simulate steady-state riverine total nitrogen (TN) transport in river networks containing thousands of reaches. A two-year case study was conducted in the San Antonio and Guadalupe basins during dry and wet years (2008 and 2009, respectively). This article investigates TN export in urbanized (San Antonio) vs. rural (Guadalupe) drainage basins and considers the effect of reservoirs on TN transport. Simulated TN export values are within 10 percent of measured export values for selected stations in 2008 and 2009. Results show that in both years the San Antonio basin contributed a larger quantity than the Guadalupe basin of delivered TN to the coastal ocean. The San Antonio basin is affected by urban activities including point sources, associated with the city of San Antonio, in addition to greater agricultural activities. The Guadalupe basin lacks major metropolitan areas and is dominated by rangeland, rather than fertilized agricultural fields. Both basins delivered more TN to coastal waters in 2009 than in 2008. Furthermore, TN removal in the San Antonio and Guadalupe basins is inversely related to stream orders: the higher the order the more TN delivery (or the less TN removal). © 2016 American Water Resources Association. Source

Saugier L.,Hilcorp Energy Company
Society of Petroleum Engineers - SPE Asia Pacific Oil and Gas Conference and Exhibition 2012, APOGCE 2012

This paper will present results from a modeling effort to derive best practices for the completion of hydraulically fractured horizontal Eagle Ford wells. The well, reservoir, completion/frac and production information used in this evaluation were provided by an operator from a five-county area in Texas. Hydraulically fractured horizontal completions pose significant modeling and evaluation challenges. This is primarily due to two issues: 1) lack of well-specific data about the reservoir/rock properties, and 2) improper assumptions used in the modeling process. As shown in this paper, a data-driven approach to modeling these completions provides a much needed pragmatic perspective, identifies high-impact parameters and provides direction about how to improve the effectiveness of these complex completions. Sensitivities performed on the predictive data model indicate that well-to-well variation in reservoir quality and geology has a dominant effect on Eagle Ford production. In addition, issues such as fracture spacing, frac volume, perforation distribution, proppant selection and wellbore length also affect well production and economics. A summary of completion and frac methodology for the Eagle Ford, in addition to a ranking of controllable (completion and frac design) and non-controllable (reservoir and geology) parameters that affect Eagle Ford production, will be included in this paper. The information contained in this paper will be useful to those interested in reservoir, completion and frac parameters that affect production from shales analogous to the Eagle Ford. Reservoir quality, completion and frac methodology effects on production results will be quantified in this paper. Copyright 2012, Society of Petroleum Engineers. Source

Birkedal K.A.,University of Bergen | Birkedal K.A.,ConocoPhillips | Freeman C.M.,Hilcorp Energy Company | Moridis G.J.,Lawrence Berkeley National Laboratory | Graue A.,University of Bergen
Energy and Fuels

Numerical tools are essential for the prediction and evaluation of conventional hydrocarbon reservoir performance. Gas hydrates represent a vast natural resource with a significant energy potential. The numerical codes/tools describing processes involved during the dissociation (induced by several methods) for gas production from hydrates are powerful, but they need validation by comparison to empirical data to instill confidence in their predictions. In this study, we successfully reproduce experimental data of hydrate dissociation using the TOUGH+HYDRATE (T+H) code. Methane (CH4) hydrate growth and dissociation in partially water- and gas-saturated Bentheim sandstone were spatially resolved using Magnetic Resonance Imaging (MRI), which allows the in situ monitoring of saturation and phase transitions. All the CH4 that had been initially converted to gas hydrate was recovered during depressurization. The physical system was reproduced numerically, using both a simplified 2D model and a 3D grid involving complex Voronoi elements. We modeled dissociation using both the equilibrium and the kinetic reaction options in T+H, and we used a range of kinetic parameters for sensitivity analysis and curve fitting. We successfully reproduced the experimental results, which confirmed the empirical data that demonstrated that heat transport was the limiting factor during dissociation. Dissociation was more sensitive to kinetic parameters than anticipated, which indicates that kinetic limitations may be important in short-term core studies and a necessity in such simulations. This is the first time T+H has been used to predict empirical nonmonotonic dissociation behavior, where hydrate dissociation and reformation occurred as parallel events. © 2014 American Chemical Society. Source

Odunowo T.O.,Texas A&M University | Moridis G.J.,Lawrence Berkeley National Laboratory | Blasingame T.A.,Texas A&M University | Olorode O.M.,Texas A&M University | And 2 more authors.
SPE Journal

Low- to ultralow-permeability formations require "special" treatments/stimulation to make them produce economical quantities of hydrocarbon, and at the moment, multistage hydraulic fracturing (MSHF) is the most commonly used stimulation method for enhancing the exploitation of these reservoirs. Recently, the slot-drill (SD) completion technique was proposed as an alternative treatment method in such formations (Carter 2009). This paper documents the results of a comprehensive numerical-simulation study conducted to evaluate the production performance of the SD technique and compare its performance to that of the standard MSHF approach. We investigated three low-permeability formations of interest-namely, a shale-gas formation, a tight-gas formation, and a tight/shale-oil formation. The simulation domains were discretized with Voronoi-gridding schemes to create representative meshes of the different reservoir and completion systems modeled in this study. The results from this study indicated that the SD method does not, in general, appear to be competitive in terms of reservoir performance and recovery compared with the more traditional MSHF method. Our findings indicate that the larger surface area to flow that results from the application of MSHF is much more significant than the higher conductivity achieved by use of the SD technique. However, there may exist cases, for example, a lack of adequate water volumes for hydraulic fracturing, or very high irreducible water saturation that leads to adverse relative permeability conditions and production performance, in which the low-cost SD method may make production feasible from an otherwise challenging (if not inaccessible) resource. Copyright © 2014 Society of Petroleum Engineers. Source

Freeman C.M.,Hilcorp Energy Company | Boyle K.L.,Lawrence Berkeley National Laboratory | Reagan M.,Lawrence Berkeley National Laboratory | Johnson J.,Lawrence Berkeley National Laboratory | And 2 more authors.
Computers and Geosciences

Few tools exist for creating and visualizing complex three-dimensional simulation meshes, and these have limitations that restrict their application to particular geometries and circumstances. Mesh generation needs to trend toward ever more general applications. To that end, we have developed MeshVoro, a tool that is based on the Voro++ (Chris H. Rycroft, 2009. Chaos 19, 041111) library and is capable of generating complex three-dimensional Voronoi tessellation-based (unstructured) meshes for the solution of problems of flow and transport in subsurface geologic media that are addressed by the TOUGH (Pruess, K., Oldenburg C., Moridis G., 1999. Report LBNL-43134, 582. Lawrence Berkeley National Laboratory, Berkeley, CA) family of codes. MeshVoro, which includes built-in data visualization routines, is a particularly useful tool because it extends the applicability of the TOUGH family of codes by enabling the scientifically robust and relatively easy discretization of systems with challenging 3D geometries.We describe several applications of MeshVoro. We illustrate the ability of the tool to straightforwardly transform a complex geological grid into a simulation mesh that conforms to the specifications of the TOUGH family of codes. We demonstrate how MeshVoro can describe complex system geometries with a relatively small number of grid blocks, and we construct meshes for geometries that would have been practically intractable with a standard Cartesian grid approach. We also discuss the limitations and appropriate applications of this new technology. © 2014 Elsevier Ltd. Source

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