A Study of Wettability and Permeability Change Caused by Adsorption of Nanometer Structured Polysilicon on the Surface of Porous Media

Abstract

A nanometer (10-9m) structured particle material, generally so defined that the diameter of the particle is no more than 100nm, has some special physical efficacy in its surface, small size and other properties. One kind of polysilicon with sizes ranging from 10~500nm, and considered as nanometer or sub nanometer sized powder, was used in oilfields to enhance water injection by changing wettability of porous media. The mechanism of enhancing water injection is through improving relative permeability of the water-phase by changing wettability induced by adsorption of polysilicon on the porous surface of sandstone. On the other hand, the adsorption on the porous surface and plugging at the small pore throats of the polysilicon may lead to reduction in porosity and absolute permeability (K) of porous media for pore sizes from 100 to 1000,000nm. Thus the degree of success in well treatment is determined by the improvement of effective permeability of the water-phase. In this paper a mathematical model, which was combined with the study of experiments in the laboratory, is presented and a simulator is developed to simulate water injection dynamics under the conditions of polysilicon injection. The simulator can accurately simulate the process of migration and adsorption in the pore bodies and blocking at the pore throat of the polysilicon in the sandstone. A series of numerical simulation runs was conducted to study the effect of a wide range of parameters, such as the sandstone with different permeabilities, concentration of the polysilicon, injection volumes, and others. The effective permeabilities of the water-phase measured by a number of core flooding experiments are matched well by the numerical results. Since April 2000, nine well treatments with solvent slugs of suspended polysilicon particles in several oilfields in China was shown to be successful and the average injection rate increased 5 times after treatments. Introduction A nanometer particle, generally defined as its size from 1 to 100nm and invisible with the naked eyes or ordinary microscope, is referred to as a nanometer scaled ultra fine particle in its size which is larger than an atom cluster and smaller than ordinary micro-powder. Nanometer technology originated at the end of the 1980's and is developed into a new high technology, by which new materials can be formed by rearranging atoms or molecules. A nanometer structured particle material has some special physical effects in its surface, small size, quantum size and macro-quantum tunnel1. Nanometer particle material has a large specific surface area, which increases rapidly with the decrease in diameter of particle. The large surface area leads to an increase in the proportion of atoms on the surface of the particle, which results in an increase in surface energy. The deficiency of atomic coordination and high surface energy leads to the unsteady, high activity of atoms on the particle, the increase in tendency of combination with other atoms, and the appearance of active cores. Non-chemical equilibrium and coordination of non-integer numbers lead to considerable difference in chemical properties and chemical equilibrium systems for nanometer powder. Analogously, sand rock, which is composed of grains with different sizes, is porous media deposited under the combination of consolidation and compaction throughout a long geological period, and also has large specific surface area. Since the property of the surface of minerals determines the wettablity of porous walls, and the wettability of reservoir rock governs, to a great extent, the location, flow, and distribution of oil, water, and gas in a reservoir, the distributive characteristics, relative permeability of water and oil and flow dynamics of fluids in porous media can be changed by modifying the wettability of porous walls. Accordingly, the process of development of a reservoir can be improved by wettability modification.

Enhanced Oil Recovery by Nanoparticles Injection: Modeling and Simulation

“…Also, it is important to define the total surface area in contact with fluids for all the size intervals of the nanoparticles per unit bulk volume as follows [1,2],…”

“…Also, the permeability variation due to nanoparticles deposition on the pore surfaces or blocking of pore throats may be expressed as [2],…”

“…However, the nanoparticles can be adhered to the pore walls if the nanoparticles sizes are much less than the pore sizes. Ju et al [2] reported that when the suspension of the polysilicon nanoparticles of one nanosize is injected into an oil reservoir, it could change the wettability of porous surfaces of sandstone and consequently have effects on water and oil flows. Ju et al [2] and Ju and Dai [1] have founded their mathematical model of nanoparticles transport in two-phase flow in porous media based on the formulation of fine particles transport in two-phase flow in porous media provided in Refs.…”

The study on increase low permeability reservoir adsorption ability with nano-polymerisation emulsion

“…The natural cores, as shown in Figure 2, used for wettability measure (Ju et al, 2002), are sampled from the low permeability reservoir of Quan III horizon with 1,832.86~1,850.86 m depth in Daqing Oilfield. They are cylindrical, with a diameter of about 25 mm and a length of about 80 mm.…”

Modeling Formation Damage and Wettability Alteration Induced by Asphaltene Precipitation and Their Effects on Percolation Performances During Oil Production

“…Thus, considering Brownian diffusion effects in the process of asphaltene migration in porous media, the continuity equation for asphaltene in oil phase can be expressed as the following equation by modifying the equation [18] : Inasmuch as the asphaltene suspended is small enough in size, diffusion should be also considered.…”