Amir Reza Rahmani

Effects of Magnetic Field on the Motion of Multiphase Fluids Containing Paramagnetic Nanoparticles in Porous Media

When paramagnetic nanoparticles are adsorbed at the oil-water interface or dispersed in one of the fluid phases in reservoir rock pores, then exposed to an external magnetic field, the resultant particle movements displace the interface. Interfacial tension acts as a restoring force, leading to interfacial fluctuation and a pressure (sound) wave. Here we focus on the interface motion. We apply the theory of ferrofluids to the case of an interface in a cylindrical pore. The predictions are consistent with experiments with an aqueous suspension of iron oxide nanorods in which the interface motion is measured by optical coherence tomography. The relative densities of the fluid phases (air/aqueous and dodecane/aqueous in our case) strongly affect the displacement of the interface. Application of a magnetic field introduces pressure-like terms into the equation of fluid phase motion. We then recast the problem in terms of interface motion, extending a numerical interface-tracking model based on the level-set method to account for capillarity and magnetic pressures simultaneously. We use the model to illustrate the motion of an interface between inviscid fluids at the pore scale when magnetic forces are imposed on one fluid phase.

Control of magnetite primary particle size in aqueous dispersions of nanoclusters for high magnetic susceptibilities

Aqueous dispersions of iron oxide nanoparticles with a high initial magnetic susceptibility (χi) are of interest as contrast agents in electromagnetic tomography. Nanoclusters composed of iron oxide primary particles were formed by co-precipitation of Fe(II) and Fe(III) chlorides at alkaline conditions and high temperature of 95°C. Two-step addition of citrate was used to produce large primary particles and then stabilize the nanoclusters. The size of the primary particles was tuned from 5nm to 15nm by varying the citrate/iron precursor ratio during the normal phase hydrolysis reaction, while the second iteration of citrate stabilized the nanoclusters with hydrodynamic diameters of 30-75nm. The crystallinity of the iron oxide nanoparticles was promoted by annealing at 95°C and systematically studied with Superconducting Quantum Interference Device (SQUID), Vibrating Sample Magnetometer (VSM), Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD). The dependence of χi was examined over a range of low volume fractions (0.005<θ<0.02) to understand the magnetic behavior of dispersions. The χi of the dispersions increased markedly with the size and concentration of the constituent primary particles, reaching an unusually high value of 0.85 at 1.6% v/v for 15nm primary particles, which is 2-3 times higher than that for typical commercial ferrofluids. The high χi values are favored by the high crystallinity and the large magnetic diameter of 9.3nm, indicating a relatively thin surface nonmagnetic layer where the spin orientations are disordered.

Quasi-static analysis of a ferrofluid blob in a capillary tube

Ferrofluids have promising application potentials for biological, medical, subsurface, and many other industrial purposes. To bring the potentials to reality, it is of utmost importance to characterize the behavior of ferrofluids under different conditions, especially in the presence of more than one phase. In this study, the quasi-static behavior of a non-wetting incompressible and inviscid ferrofluid blob surrounded by a wetting non-magnetic fluid confined in a capillary tube is theoretically and computationally investigated when a uniform magnetic field is applied, assuming isothermal conditions. The effect of geometrical, hydrodynamic, and magnetic properties of the blob on its deformations when subject to a magnetic field is explained. Moreover, the effect of nonlinear magnetization on the ferrofluid blob evolution in the capillary tube is investigated in detail. In the case of a tube with constant circular cross-section, the behavior of the blob before the critical state of detachment is determined ...

Impedance Analysis as a Tool for Hydraulic Fracture Diagnostics in Unconventional Reservoirs

Production from unconventional reservoirs plays a key role in supplying hydrocarbon to the worlds increasing energy demand. Hydraulic fracturing is one of the most advancing technologies in producing hydrocarbon from low-permeability reservoirs, especially in tight and shale formations. The geometric properties of a hydraulic fracture affect significantly the production rate from these stimulated reservoirs. Therefore, it is of utmost importance to characterize the geometric features of hydraulically-induced fractures during stimulation processes. The geometric properties of a hydraulic fracture change with fracture evolution due to stress propagation along the cracks. We have modeled such a system based on the analogy between fluidic and electric circuits. The model takes into account the dynamic alteration of hydrodynamic impedance of the fracture. The hydrodynamic impedance controls the relation between the fracture fluid flow rate and pressure drop during stimulation process. The proposed model incorporates the effects of both hydrodynamic capacitance and resistance of the fracture and the wellbore to compute the fracture impedance. Downhole measurements of pressure and flow rate can explicitly determine the hydrodynamic impedance of the fracture. Fracture impedance can also be implicitly inferred from wellhead pressure and flow rate measurements. The pulsatile nature of hydraulic fracturing treatment makes it sensible to utilize the wellhead data for the purpose of impedance monitoring based on the electromagnetic transmission line theory. We have performed extensive sensitivity analyses on the most important parameters of a single hydraulic fracture for assessing fracture impedance. These parameters include fracture thickness, fracture radial extent, and fracture shape. Through sensitivity analyses results and real-time measurement of fracture impedance, we infer the basic geometric properties of a hydraulic fracture. This research has led to an analytical approach for evaluating hydraulic fractures geometric characteristics. The approach builds an intuition toward better understanding how to design hydraulic fractures in a more efficient fashion.