The dynamic characteristics of carbonate sand under wave loads are very important for constructions on the ocean floor. The initial principal stress direction has been known to exert some influence on the dynamic char...The dynamic characteristics of carbonate sand under wave loads are very important for constructions on the ocean floor. The initial principal stress direction has been known to exert some influence on the dynamic characteristics of sand during cyclic loading. In an effort to investigate this aspect of the problem, several series of cyclic undrained tests were carried out on a saturated and loose sample of carbonate sand using a geotechnical static and dynamic universal triaxial shear apparatus. In this test apparatus, a hollow cylindrical sand specimen is subjected to a simultaneous application of both triaxial and torsional modes of shear stresses, which brings about the continuous rotation of principal stress axes. The test results indicated that the initial principal stress direction has a considerable influence on the dy- namic strength of loose carbonate sand and with the increase of initial orientation of principal stress, dynamic strength will be reduced, the cyclic pore pressure increased, but the residual pore pressure reduced.展开更多
Sand production is an undesired phenomenon occurring in unconsolidated formations due to shear failure and hydrodynamic forces. There have been many approaches developed to predict sand production and prevent it by ch...Sand production is an undesired phenomenon occurring in unconsolidated formations due to shear failure and hydrodynamic forces. There have been many approaches developed to predict sand production and prevent it by changing drilling or production strategies. However, assumptions involved in these approaches have limited their applications to very specific scenarios. In this paper, an elliptical model based on the borehole shape is presented to predict the volume of sand produced during the drilling and depletion stages of oil and gas reservoirs. A shape factor parameter is introduced to estimate the changes in the geometry of the borehole as a result of shear failure. A carbonate reservoir from the south of Iran with a solid production history is used to show the application of the developed methodology. Deriving mathematical equations for determination of the shape factor based on different failure criteria indicate that the effect of the intermediate principal stress should be taken into account to achieve an accurate result. However, it should be noticed that the methodology presented can only be used when geomechanical parameters are accurately estimated prior to the production stage when using wells and field data.展开更多
Sand particles textured with multi-walled carbon nanotubes (MWCNTs) can efficiently control the mobility and bioavailability of contaminants found in aquatic sediments. Adsorption measurements for a wide variety of aq...Sand particles textured with multi-walled carbon nanotubes (MWCNTs) can efficiently control the mobility and bioavailability of contaminants found in aquatic sediments. Adsorption measurements for a wide variety of aquatic contaminants (chlorinated hydrocarbons) on MWCNT-textured sand showed orders of magnitude increase in their sorption coefficients compared to traditional materials (sand) when used for physically separating contaminated sediments from overlying water. Molecular dynamics simulations performed on model experimental systems emphasize that the hydrophobic interactions of the MWCNT surfaces play a crucial role in driving the water molecules away, promoting such enhanced contaminant uptake. The MWCNT-textured sand significantly reduced the migration of contaminants from sediments to overlying water and possesses suitable parameters needed for contaminant sequestration and sediment remediation technologies. The single step and scalable procedure described here for synthesizing robust MWCNT-textured sand surfaces will provide important improvements in the field of remediation/aquatic environment restoration technologies.展开更多
文摘The dynamic characteristics of carbonate sand under wave loads are very important for constructions on the ocean floor. The initial principal stress direction has been known to exert some influence on the dynamic characteristics of sand during cyclic loading. In an effort to investigate this aspect of the problem, several series of cyclic undrained tests were carried out on a saturated and loose sample of carbonate sand using a geotechnical static and dynamic universal triaxial shear apparatus. In this test apparatus, a hollow cylindrical sand specimen is subjected to a simultaneous application of both triaxial and torsional modes of shear stresses, which brings about the continuous rotation of principal stress axes. The test results indicated that the initial principal stress direction has a considerable influence on the dy- namic strength of loose carbonate sand and with the increase of initial orientation of principal stress, dynamic strength will be reduced, the cyclic pore pressure increased, but the residual pore pressure reduced.
文摘Sand production is an undesired phenomenon occurring in unconsolidated formations due to shear failure and hydrodynamic forces. There have been many approaches developed to predict sand production and prevent it by changing drilling or production strategies. However, assumptions involved in these approaches have limited their applications to very specific scenarios. In this paper, an elliptical model based on the borehole shape is presented to predict the volume of sand produced during the drilling and depletion stages of oil and gas reservoirs. A shape factor parameter is introduced to estimate the changes in the geometry of the borehole as a result of shear failure. A carbonate reservoir from the south of Iran with a solid production history is used to show the application of the developed methodology. Deriving mathematical equations for determination of the shape factor based on different failure criteria indicate that the effect of the intermediate principal stress should be taken into account to achieve an accurate result. However, it should be noticed that the methodology presented can only be used when geomechanical parameters are accurately estimated prior to the production stage when using wells and field data.
基金ST acknowledges Southern Illinois University Car-bondale(SIUC)Office of Research and Development Administration for providing financial support through start-up funds and a seed grant.
文摘Sand particles textured with multi-walled carbon nanotubes (MWCNTs) can efficiently control the mobility and bioavailability of contaminants found in aquatic sediments. Adsorption measurements for a wide variety of aquatic contaminants (chlorinated hydrocarbons) on MWCNT-textured sand showed orders of magnitude increase in their sorption coefficients compared to traditional materials (sand) when used for physically separating contaminated sediments from overlying water. Molecular dynamics simulations performed on model experimental systems emphasize that the hydrophobic interactions of the MWCNT surfaces play a crucial role in driving the water molecules away, promoting such enhanced contaminant uptake. The MWCNT-textured sand significantly reduced the migration of contaminants from sediments to overlying water and possesses suitable parameters needed for contaminant sequestration and sediment remediation technologies. The single step and scalable procedure described here for synthesizing robust MWCNT-textured sand surfaces will provide important improvements in the field of remediation/aquatic environment restoration technologies.
