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.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA nanometer (10 -9 m) 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 waterphase 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. 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.
The precipitation or block of asphalts, asphaltene and other organics in the porous media near the wellbole will reduce permeability due to change in temperature, pressure and compositions of reservoir oil. Injection of organic aromatic solvents and soaking is one feasible method to remove the precipitates. The objects of this paper are to confect economical and efficient solvents and optimize injected rate, volume and soak time of solvent. To obtain the objects, core flooding experiments by solvents are conducted to select optimum solvents and a simulator to remove the formation damages caused by organic deposition by soaking of aromatic solvents is developed. The influences of different injected rates, volume and soak time of solvent are simulated to improve the permeability of the damaged region. And the permeability is also predicted after soak. A project to remove organic formation damage near the wellbole by injection aromatic solvents started Nov, 1998 at an offshore oil field in China. And the production of the first well increased from 90t/d to 270t/d after injection solvent U-01 selected by core flooding experiments. The simulated results coincide well with the data from the oilfield. Introduction Asphaltenes have been defined as the n-heptane insoluble, but aromatic soluble fraction of crude oil with a condense F structure including significant N/S/O and alkyl groups1,2. And asphalts have been defined as the combination of asphaltenes and resins1. Under normal conditions in the reservoirs, asphaltenes exist in dispersion by the resins peptization. Any changes in temperature, pressure and composition can result in asphaltene precipitation and being deposited. During crude oil production, asphaltenes and asphalts preci-pitation may occur in the wellbore and the vicinity of the wellbore due to changes in temperature, pressure and composition. The problems caused by asphaltene and asphalt precipitation in the tube or wellbore can be easily eliminated by physical or chemical methods. However, the precipitation and deposition of asphaltenes and other organics in the sand will cause formation damage and reduce effective hydrocarbon mobility by a) blocking the pore throats, b) altering the formation wettability from water-wet to oil-wet due to adsorbing onto the rock surfaces and c) increasing hydrocarbon viscosity by nucleating water in oil emulsions3. To remove the asphaltene deposition problems occurred in the formation is rather difficult than those in the tube or wellbore for the paths of hydrocarbon flow in the formation are microporous media compacted and cemented by various minerals with different natures. In general, formation damage caused by asphaltene precipitation and operations such as drilling, completion, workover and stimulation, first occurs in the vicinity of wellbore. However the formation condition near the wellbore is very important where pressure drop of the oilfield mainly depletes. Although the drainage radius may be several hundreds of feet, the effective permeability close to the wellbore has a disproportionate effect on well productivity. According to Roland F. Krueger's study4 for the effect of permeability discontinuity on production performance near wellbore, if the permeability of the formation rock near the wellbore has been damaged to 20% of its original value by some operation to depth of 0.6m, a well treatment that restores the original permeability will increase well productivity by about 100%. On the other hand, if the region doesn't suffer from formation damage, a well treatment that increases the normalized permeability of this undamaged zone by 80% will only a minor effect (about 10%) on the well productivity. Thus, a removal of formation damage in the vicinity of wellbore has significance for improving well productivity. This is so-called elimination of "bottom efficiency" for the wells with formation damage during the production in oilfields.
The mathematical model of gravity drainage in naturally fractured reservoirs and singular perturbation analyses are presented which explore the effect of capillary, gravity, and wettability on oil saturation distribution and oil recovery in reimbibition. This study shows that wettability capillary end effect and fracture transmissibility appear to be most important factors in oil recovery. Numerical results are also presented which summarize and compare the effective saturation in nonequilibrium state with the actual saturation in equilibrium state. Based on this work, we believe reimbibition or capillary continuity in a stack of matrix blocks can not provide higher oil recovery than in continuity core. Introduction In recent years, growing attention has been focused on reimbibition and capillary continuity in gravity drainage. Reimbibition process is closely related to various forces (gravity, capillary, viscous, diffusive and relaxation). However, the experimental and theoretical research on gravity drainage mechanism in naturally fractured reservoirs is limited. Bogomolova and Glazova (1970) have observed the end effects and saturation discontinuities on the boundaries of unconsolidated porous media with some different permeability. Hagoort (1980) used the classical Buckley-Leverett theory to study the gravity drainage in homogeneous media, and indicated that oil relative permeability is a key factor in the gravity-drainage process. Barenblatt's work investigated the end effects in heterogeneous media. Recent experiments and observations by Firoozabadi and his co-worker (l992), Catalan and Dullien (1992) prompted us to reexamine the gravity drainage mechanism. This study has tried to examine from both a mathematical and a physical viewpoint the key features of gravity drainage in a stack of matrix blocks. P. 357^
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