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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC Riverside Electronic Theses and Dissertations (2013)

The process of fracture propagation driven by the pressure of the fluid flow between the fracture surfaces has been of considerable interest for understanding natural geological phenomena such as the formation of volcanic dikes and developing hydraulic fracturing technologies for industrial applications. Man-made hydraulic fracturing has been most commonly used for stimulation of oil and gas reservoirs to increase hydrocarbon production, stimulation of geothermal reservoirs, remediation of soil and groundwater aquifers, injection of wastes, goafing and fault reactivation in mining, and measurement of underground in situ stresses.

Computational modeling and simulation of fluid driven fracture propagation in realistic geological formation has been a challenging problem because of various complexities including formation heterogeneities and the use of highly nonlinear engineered fluids. At present, one of the main obstacles for the robust industrial application of the simulating technology is the computational efficiency and stability. The objective of this study is to investigate the numerical efficiency and stability of various algorithms that can be potentially used in modeling of fluid driven fracture propagation. For simplicity, we have focused on fracture propagation in the plane strain condition. The fracture is assumed to in homogeneous linear

elastic medium and modeled using displacement discontinuity boundary element method (DDBEM). The nonlinear power-law fluid flow is modeled using conventional lubrication theory. The coupled equations are then discretized using zero order elements for its efficiency. The coupled equations become increasingly stiff and difficulty to solve when the power law indices become smaller. Various numerical algorithms such as Newton iteration

with line search, trust-region and quasi-Newton method are investigated and compared. We have also extended the model to the fluid driven non-planar fracture propagation. A numerical crack propagation criterion based on the minimum local shear stress under mixed loading condition is proposed and compared with conventional theoretical and numerical criteria. The new crack propagation criterion provides more accurate and smooth crack

initiation paths. Finally we have studied the geomechanics interaction between two simultaneous fluid driven fractures. The results provided some useful inputs for optimal design of multiple stage and multiple fracturing treatments along horizontal wells currently adopted

by the oil and gas industry for the economical recovery of unconventional resources such as shale gas and oil.

    Cover page: Modeling and Analysis of Fluid Driven Fracture Propagation Under the Plane Strain Condition
    • Article
    • Peer Reviewed
    UC San Francisco Previously Published Works (2007)
    There are many factors affecting the successful performance of CT colonography (CTC). Adequate colonic cleansing and distention, the optimal CT technique and interpretation with using the newest CTC software by a trained reader will help ensure high accuracy for lesion detection. Fecal and fluid tagging may improve the diagnostic accuracy and allow for reduced bowel preparation. Automated carbon dioxide insufflation is more efficient and may be safer for colonic distention as compared to manual room air insufflation. CT scanning should use thin collimation of < or =3 mm with a reconstruction interval of < or =1.5 mm and a low radiation dose. There is not any one correct method for the interpretation of CTC; therefore, readers should be well-versed with both the primary 3D and 2D reviews. Polyps detected at CTC should be measured accurately and reported following the "polyp size-based" patient management system. The time-intensive nature of CTC and the limited resources for training radiologists appear to be the major barriers for implementing CTC in Korea.
      Cover page: Fundamental Elements for Successful Performance of CT Colonography (Virtual Colonoscopy)
      • Article
      • Peer Reviewed
      LBL Publications (2024)
      In 2D noble metals like copper, the carrier scattering at grain boundaries has obscured the intrinsic nature of electronic transport. However, it is demonstrated that the intrinsic nature of transport by hole carriers in 2D copper can be revealed by growing thin films without grain boundaries. As even a slight deviation from the twin boundary is perceived as grain boundaries by electrons, it is only through the thorough elimination of grain boundaries that the hidden hole-like attribute of 2D single-crystal copper can be unmasked. Two types of Fermi surfaces, a large hexagonal Fermi surface centered at the zone center and the triangular Fermi surface around the zone corner, tightly matching to the calculated Fermi surface topology, confirmed by angle-resolved photoemission spectroscopy (ARPES) measurements and vivid nonlinear Hall effects of the 2D single-crystal copper account for the presence of hole carriers experimentally. This breakthrough suggests the potential to manipulate the majority carrier polarity in metals by means of grain boundary engineering in a 2D geometry.
        Cover page: Hole‐Carrier‐Dominant Transport in 2D Single‐Crystal CopperCreative Commons 'BY-NC' version 4.0 license
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