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Mudcake effects on wellbore stress and fracture initiation pressure and implications for wellbore strengthening

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Petroleum Science 2018年第2期15卷 319-334页

作者： Yongcun Feng Xiaorong Li K.E.Gray The University of Texas at Austin AustinTXUSA

Although a large volume of mudcake filtration test data is available in the literature, effects of mudcake on wellbore strengthening cannot be quantified without incorporating the data into a stress-analysis model. Traditional models for determining fracture initiation pressure （FIP） either consider a wellbore with an impermeable mudcake or with no mudcake at all. An analytical model considering permeable mudcake is proposed in this paper. The model can predict pore pressure and stress profiles around the wellbore, and consequently the FIP, for different mudcake thickness, permeability, and strength. Numerical examples are provided to illustrate the effects of these mudcake parameters. The results show that a low-permeability mudcake enhances FIP, mainly through restricting fluid seepage and pore pressure increase in the near- wellbore region, rather than by mudcake strength. Fluid loss pressure （FLP） should be distinguished from FIP when a mudcake is present on the wellbore wall. Fracture may occur behind the mudcake at FIP without mudcake rupture. The small effect of mudcake strength on FIP does not mean its effect on FLP is small too. Mudcake strength may play an important role in maintaining integrity of the wellbore once a fracture has initiated behind the mudcake.

关键词： Mudcake hoop stress Fracture initiation pressure Fluid loss pressure Wellbore strengthening

Quench characteristics and mechanical responses during quench propagation in rare earth barium copper oxide pancake coils

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Applied Mathematics and Mechanics(English Edition) 2021年第2期42卷 235-250页

作者： Mengdie NIU Jing XIA Huadong YONG Youhe ZHOU Key Laboratory of Mechanics on Disaster and Environment in Western China The Ministry of Education of ChinaLanzhou UniversityLanzhou 730000China Department of Mechanics and Engineering Sciences College of Civil Engineering and MechanicsLanzhou UniversityLanzhou 730000China Institute of Applied Physics and Computational Mathematics Beijing 100094China

Quench and mechanical behaviors are critical issues in high temperature superconducting(HTS)coils.In this paper,the quench characteristics in the rare earth barium copper oxide(REBCO)pancake coil at 4.2K are analyzed,and a two-dimensional(2D)axisymmetric electro-magneto-thermal model is presented.The effects of the constituent materials,background field,and coil size are analyzed.An elastoplastic mechanical model is used to study the corresponding mechanical responses during the quench propagation.The variations of the temperature and strain in superconducting layers are compared.The results indicate that the radial strain evolutions can reflect the transverse quench propagation and the tensile hoop and radial stresses in superconducting layers increase with the quench propagation.The possible damages are discussed with the consideration of the effects of the background field and coil size.It is concluded that the high background field significantly increases the maximum tensile hoop and radial stresses in quenching coils and local damage may be caused.

关键词： rare earth barium copper oxide(REBCO)pancake coil hoop stress quench characteristic mechanical response radial stress

Ionic Gravitation and Ionized Solid Iron Stellar Bodies

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Journal of High Energy Physics, Gravitation and Cosmology 2023年第2期9卷 414-437页

作者： Gurcharn S. Sandhu Independent Researcher Chandigarh India

A well-known but erroneous notion of electron degeneracy pressure has misled Astrophysics for nearly a century now. Because of their electrostatic interactions, the electrons can never exchange their momentum with positive ions through elastic collisions and hence can never provide the so-called electron degeneracy pressure in stellar cores to counter the effect of gravity. In situations of high core densities, when the mean separation distance between atoms or ions becomes less than the normal size of their parent atoms, their electrostatic repulsion will force them into a lattice gridlock, leading to a solid state. All degenerate stellar cores constitute a solid state and the radial and hoop stresses induced by self-gravitation are proportional to the square of radius (r2). As the size of a solid iron stellar core grows, its peripheral region will experience extreme compression and will get partially ionized due to the phenomenon of pressure ionization. All so-called Neutron Stars and Black Holes are in fact Ionized Solid Iron Stellar Bodies (ISISB). The presence of ions in the peripheral regions of the ISISB will be associated with the circulation of degenerate electrons around the surface, thereby producing strong magnetic fields. A positive excess of ionic charge in all ISISB becomes a source of Ionic Gravitation through the process of polarization of neutral atoms and molecules in stellar bodies. These ISISB are the primary constituents of AGN and are the source of all non-stellar radiation and Jets of ionized matter.

关键词： Solid Core Ionic Gravitation hoop stress Magnetic Field Black Holes AGN

Problem of Circular Hole in Thermopiezoelectric Media with Semi-permeable Thermal Boundary Condition

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Transactions of Nanjing University of Aeronautics and Astronautics 2014年第2期31卷 152-158页

作者：宋豪鹏胡巍高存法 State Key Laboratory of Mechanics and Control of Mechanical Structures Nanjing University of Aeronautics & Astronautics

The semi-permeable boundary condition is proposed to discuss the influence of the thermal conductivity acting on the stress and heat flow around the hole.Based on the Stroh formalism,the closed form solutions are derived,the stress and heat flow around the hole are discussed.The results show that the thermal boundary condition has significant influence on the hoop stress and heat flow around the hole.The hoop stress decreases dramatically with the increasement of the thermal conduction coefficient.

关键词： thermopiezoelectric thermal conductivity hoop stress heat flow