Papers by Keyword: Fracture

Abstract: Pore, fracture and vugs consist of the main reservoir space of carbonate reservoirs. Fracture is an important seepage channel. The causes, fracture geometry, filling and situation will further affect the stress sensitivity of reservoir. By means of contrast experimentation, researching the stress sensitivity of natural fracture and artificial fracture samples, with and without solids invasion fracture samples, with and without acid etched fracture samples, connected and disconnected double vugs. The results including 8 groups show that the average stress sensitivity coefficient are respectively 0.64,0.75,0.52,0.18,0.73,0.50,0.33 and 0.73, and the degree of stress sensitivity is respectively medium to strong, strong, medium to strong, weak, strong, medium to weak, weak and strong. It showed that the stress sensitivity of natural fracture stronger than artificial fracture, solids invasion and acid etch strengthen the stress sensitivity, the connection of double vugs weaken the stress sensitivity of fractured samples.

Abstract: Due to the characteristics of the ultra-low permeability, facture system becomes the key to the deployment of shale gas, and the following stress sensitivity damage will restrict the engineering effect. The essay takes the Niutitang group of black shale as the research object, which carried out for natural fracture rock sample and artificial fracture rock sample study of stress sensitivity evaluation in order to compare differences between them. The experimental results show that the natural fracture rock sample is medium to strong stress sensitivity, while the artificial fracture rock sample is from strong to the extreme strong stress sensitivity. Natural fracture is more flattening than the artificial fracture formation because of leaching action. The processed SEM image can reflect structure information on the two-dimensional surface. Its surface structure conforms to the fractal structure characteristics. Whats more, fracture it can also reflect the three-dimensional information of the fracture surface through grey value, which provides a new imaging method for the research of surface microstructure for fracture.

Abstract: The quest for the advanced functional material of superior functionality for advanced structure is being driven in various fronts of engineering materials. One of such front is metal matrix composite (MMC) which has already been proven as one of the most productive field in that respect. With the advance of technology, now it is possible to reinforce the MMCs with nanosized particles compared to conventional micron-sized ones. However, the addition of nanoparticle in the MMC to improve its mechanical properties is not unconditional. To achieve positive gain by adding nanoparticles in the MMCs, all the influencing factors should be taken into consideration. The present paper reviews the failure mechanisms of nanoparticles reinforced MMCs in light of its strengthening mechanisms.

Abstract: As most of sedimentary rocks are anisotropic, it is significant to research the impact of the anisotropy of strength on wellbore stability in drilling engineering. Particularly, in the Kuqa piedmont exploration area, the anisotropy of strength caused by various jointed surfaces, fracture surfaces and fault planes in formation cause the formation of several groups of weak low-intensity planes traversing borehole . These weak planes will become failure earlier than the rock body in the context of strong stress and high pore pressure, causing chipping, breakouts and sticking. If fractures have good permeability and drilling fluid column pressure is greater than pore pressure, loss may occur. The loss pressure would not be controlled by fracturing pressure and horizontal minimum principal stress, but it depends on the relationship between fracture occurrence and triaxial stress state. In the event of loss, the drilling fluid will flow into these weak structural planes, causing the decrease of friction between rocks and increase of wellbore instability. As a result, for strongly anisotropic formation, the collapse pressure and leakage pressure of weak planes are key factors for evaluating well drilling stability. In this study, according to the stability evaluation on the transversely isotropic rock mechanics in Keshen zone of Kuqa piedmont, the impacts of fracture development on wellbore instability is analyzed; relevant suggestions on engineering geology for the special pressure window in strong anisotropic formation are also put forward.

Abstract: The fabrication process and fracture characterization of 35 and 65 vol% SiCp particulate-reinforced Al matrix (SiCp/Al) composites have been investigated. SiCp composites having different volume fractions of the n-SiCp were synthesized via by pressureless-infiltration at near-net-shape route and were uniaxially tested at room temperature. The SiC particles were mixed with silicasol as an inorganic binder in distilled water. The mixtures were consolidated in a mold by pressing and dried in two step process, followed by calcination at 1000 °C. The SiCp/Al composites were fabricated by the infiltration of Al melt into SiC performs. The experimental results show that volume fraction of reinforced particles in SiCp/Al composites had a significant influenec on fracture section surface characterization in tensile tests. Composite with 45 vol% SiCp, fracture was firstly happen in Al matrix, shallow dimples and intergranular fractures were seen in all the fractographs. With increasing of vol% SiCp, fracture was more brittle in appearance in the composites and the fracture surfaces were flat and less plastic deformations.

Abstract: This paper discusses the development of acoustic emission tomography to identify structural discontinuities in concrete. An algorithm was developed to reconstruct velocity tomographs of the interior of the material. Both theoretical analysis and experimental data were used to determine best sensor array geometry. Experiments on a concrete block with artificial fracture indicate that the technique can be used to identify structural discontinuities.

Abstract: approximate analysis formula for the water flow of single fracture and variable water temperature has been deduced considering the impact of water temperature to rock fracture seepage. Following conclusions were drawn: (1) The water head and the hydraulic gradient in single-fissure have nonlinear relation. Seepage curve was convex curve if water flows from higher temperature areas to lower temperature area. On this condition, the water head slants low under liner seepage simplification. On the contrary, Seepage curve is convex curve if water flows from lower temperature areas to higher temperature areas, and the water head slants high. (2) In a single fracture, the hydraulic gradient is smaller in the higher temperature zone and is larger in the lower temperature zone. The higher the mean water temperature of fracture was, and the faster the flow velocity was.

Abstract: Based on a system of macro & micro fracture appearance observation, energy spectrum analysis and metallurgical structure inspection, the cause of sample crack of Q345 steel were obtained. The results showed that the specimen occurred fatigue crack under alternating load, the crack source was a line source, the middle area of the fracture was the relatively flat topography and relatively narrow fatigue striations, the rear area of the fracture was the relatively uneven topography and relatively large fatigue striations, and a certain yield occurred at the crack tip.

Abstract: The effects of aggregate size and fiber volume fraction on the flexural behavior of 70MPa high strength steel fiber-reinforced concrete (SFRC) were investigated in this work. Test variables consist of fiber volume fraction (0, 1 and 2 %) and maximum aggregate size (8, 13 and 20 mm). The prism for flexural test was 100 x 100 x 400 mm and was tested under four points loading. Flexural toughness index was measured using ASTM C 1018 procedure. Test results indicated that the addition of steel fiber to 70MPa high strength concrete improves flexural and post-cracking behaviors. This phenomenon is remarkable for SFRC mixture with higher fiber content and smaller aggregate size. Also, the flexural toughness of high strength SFRC depends primarily on fiber content. The maximum aggregate sizes were secondary in importance.

Abstract: Failure reason of boiler extraction steam pipe was discussed by means of macro-observation, chemical composition analysis, metallurgical and SEM microstructure examination and EDS analysis. Results showed that the crack initiated from original corrosion flaw on outer wall of the extraction pipe, propagated rapidly under large pressure caused by water-hammer due to no drainage design in the unit pipe system until final bursting.