The Study And LBM Simulation Of Drag Reduction Mechanism Of Nanoparticles Adsorption Method In Microchannels

Drag reduction by hydrophobic nanoparticles (HNPs) adsorption in reservoirmicrochannels is a new technology to enhance oil recovery in low permeabilityoilfields. Its mechanism is that HNPs are adsorbed on porous walls and a micro-andnano-structure rough surface is formed, which has strong-or super-hydrophobicproperties, and can generate the water-flow-slip effects. Laboratory experiments haveverified this mechanism and played an important role in the development of thistechnology. However, because of the complexity of the petroleum reservoir rockmicrochannel, numerical simulation methods must be adopted in order to see thedetails of the fluid flow. Based on lattice Boltzmann method (LBM), numericalsimulations were made to simulate the mechanism of HNPs. The dynamics oftwo-phase flows inside a microchannel and porous was studied by using the LBM andthe Shan-Chen multiphase model in this thesis, flow regimes under different wallwettability and over smooth and grooved geometric surfaces were investigated, thereason of sliding was discussed as well. Furthermore, parallel codes for LBMsimulations have been developed to simulate the liquid transportation at meso-scale.The details and some accomplishments are presented as follows.1) Based on the investigation of the related literatures, theoretical models,experimental techniques, and numerical simulation methods of micro-flows weresummarized to provide a basis for numerical and experimental researches in thisthesis. A practical overview of Shan-Chen-type LBM and implementation details wereprovided.2) Micro-and nano-structured surfaces on cores were constructed by the HNPsadsorption method. The surfaces were observed by Scanning Electron Microscope andthe contact angles on them were tested. The results show that nanoparticles can adsorbon core surfaces and compose a new micro-and nano-structured surfaces，whose wettability is changed from strong hydrophilic to hydrophobic. The flow-pressurerelationship of water flow through the microchannels of core before and after theadsorption of nanoparticles was tested through core flow experiments. The resultsshow that, after the adsorption of nanoparticles, water flow rates throughmicrochannels were increased observably and flow resistance was reduced.3) The contact angle on plane and concave boundary were simulated using theShan-Chen-type multiphase model lattice Boltzmann method, and the relationshipbetween the contact angles and related parameters was obtained. The predictionmethod of the apparent contact angle is established, which can also explain the reasonof super-hydrophobic of pelleting of the nano powder.4) The wettability and particle geometrical characteristics (including the lengthand height of rough particles, as well as the distance between the rough particles) onthe flow features were discussed. Hysteresis phenomenon of dynamics contact anglewas analyzed during droplet movement in the microchannel. The results show that thedifferent value between the back angle cosine and the forward angle cosine isproportional to capillary number.5) The reason of sliding was discussed. Because of the wettability, a layer ofmuch less dense fluid (most probably gas) is induced between the dense liquid andsolid surface. Different from the macroscopic flows, the layer can’t be ignored inmicro/mesoscopic hydrodynamics. The weaker the wettability of wall is, the less thedense of the fluid at the surface is, and the less viscous shear force is, and the moresignificant slippage is.6) A method was proposed to impose controllable slip boundary conditions inLBM. Different from the macroscopic flows, the velocity slippage on solid wallsshould be considered in micro/mesoscopic hydrodynamics. The strength of slippagecould be adjusted by variation of parameters in the present method, and the validityand availability of the approach were verified. Using the relationship between the sliplength and contact angle, it is easy to estimate the slip length because the contact angle is a parameter that can be easily measured.7) The phenomenon of the flow in porous media was simulated in pore-scale.The characteristics of fluid flow in porous media were investigated. The LBM wasused to predict permeability of the core of microchannels before and after theadsorption of nanoparticles.