Binshan Ju

ENHANCED OIL RECOVERY BY FLOODING WITH HYDROPHILIC NANOPARTICLES

In this paper, the mechanism of enhanced oil recovery using lipophobic and hydrophilic polysilicon (LHP) nanoparticles ranging in size from 10 to 500 nm for changing the wettability of porous media was analysed theoretically. A one-dimensional two-phase mathematical model considering the migration and adsorption of LHP and wettability change in reservoir rock was proposed, and a simulator was developed to quantitatively predict the changes in relative and effective permeability of the oil and water phases and the oil recovery in sandstone after water driving. Numerical simulations were conducted to study the distribution of the particle concentration, the reduction in porosity and absolute permeability, the LHP volume retention on pore walls and in pore throats along a dimensionless distance, and oil production performance. In conclusion, oil recovery can obviously be improved by flooding with hydrophilic nanometer powders though permeability declines for the retention of nanoparticles in porous media. It is suggested that an LHP concentration ranging from 0.02 to 0.03 is preferable to enhance oil recovery.

Experimental Study on Nanoparticles Transport and Its Effects on Two-Phase Flow Behavior in Porous Networks

A suspension of nanoscale polysilicon particles (NSPP) is injected into low permeable sand formations for reducing flow resistance of water. A set of instruments was assembled to get insights into the characteristics, adsorption and transport of the NSPP, wettability alteration, and its effects on two-phase flow performances in porous media. The TEM images show that the particles are approximate spheres with diameters from 10 to 200 nm. The NSPP could be adsorbed on the pore surfaces, and it looks like frost on the grains in the crossing section of sandstone. The wetting angle of water drop becomes far larger than 90o after the adsorption of the NSPP. It implies that the adsorption on pore surfaces leads to wettability alteration from water-wetness to oil-wetness. Wettability alteration is a major factor to change the percolation flow resistances of two phases, which has been verified by the change in relative permeabilities of the two phases. The flowable improvement of water results from the reduction in filtrational resistance of water in the sand formation.

Modeling CO2 miscible flooding for enhanced oil recovery

The injection of fuel-generated CO2 into oil reservoirs will lead to two benefits in both enhanced oil recovery (EOR) and the reduction in atmospheric emission of CO2. To get an insight into CO2 miscible flooding performance in oil reservoirs, a multi-compositional non-isothermal CO2 miscible flooding mathematical model is developed. The convection and diffusion of CO2-hydrocarbon mixtures in multiphase fluids in reservoirs, mass transfer between CO2 and crude, and formation damages caused by asphaltene precipitation are fully considered in the model. The governing equations are discretized in space using the integral finite difference method. The Newton-Raphson iterative technique was used to solve the nonlinear equation systems of mass and energy conservation. A numerical simulator, in which regular grids and irregular grids are optional, was developed for predicting CO2 miscible flooding processes. Two examples of one-dimensional (1D) regular and three-dimensional (3D) rectangle and polygonal grids are designed to demonstrate the functions of the simulator. Experimental data validate the developed simulator by comparison with ID simulation results. The applications of the simulator indicate that it is feasible for predicting CO2 flooding in oil reservoirs for EOR.

A Study to Prevent Bottom Water From Coning in Heavy-Oil Reservoirs: Design and Simulation Approaches

The coning problems for vertical wells and the ridging problems for horizontal wells are very difficult to solve by conventional methods during oil production from reservoirs with bottom water drives. If oil in a reservoir is too heavy to follow Darcy’s law, the problems may become more complicated for the non-Newtonian properties of heavy oil and its rheology. To solve these problems, an innovative completion design with downhole water sink was presented by dual-completion in oil and water columns with a packer separating the two completions for vertical wells or dual-horizontal wells. The design made it feasible that oil is produced from the formation above the oil water contact (OWC) and water is produced from the formation below the OWC, respectively. To predict quantitatively the production performances of production well using the completion design, a new improved mathematical model considering non-Newtonian properties of oil was presented and a numerical simulator was developed. A series of runs of an oil well was employed to find out the best perforation segment and the fittest production rates from the formations above and below OWC. The study shows that the design is effective for heavy oil reservoir with bottom water though it cannot completely eliminate the water cone formed before using the design. It is a discovery that the design is more favorable for new wells and the best perforation site for water sink (Sink 2) is located at the upper 1/3 of the formation below OWC. DOI: 10.1115/1.2955560

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

Asphaltene, which exists in crude oil, is a high molecular weight, polar component. It is widely believed that asphaltene may precipitate and plug pores of reservoir rock and induce wettability alteration for the changes in oil composition, reservoir pressure and temperature. Therefore, alphaltene precipitation in the pores of oil formation definitely leads to formation damage and wettability alteration. The mechanisms caused asphaltene precipitation have been researched in labs and the key factors to effect the precipitation have been well understood, but prediction for its quantitative damages for oil formation, wettability alteration and their effects on percolation performance are still uncertain. In this work, a mathematical model considering asphaltene precipitation and wettability alteration is presented and an oil field scaled numerical simulator is developed to predict for asphaltene precipitation problems in the development of oil field. The simulation results show that the porosity and permeability in the vicinity of production wellbore decrease dramatically for asphaltene precipitation. The water-cut increases for the increase in the effective permeability of oil phase and the decrease in the effective permeability of water for the wettability alteration induced by asphaltene deposition onto the pore surfaces. Introduction Asphaltene, which is the heaviest component in crude oil, is defined as n-heptane or n-pentane insolubles. In general, it is dissolved in the crude oil under the initial reservoir conditions. However, any changes in reservoir pressure, temperature, and composition during oil production may leads to precipitation from crude oil. Asphaltene precipitation from reservoir oil due to the changes of reservoir conditions such as pressure, temperature and compositions may lead to serious problems. On one hand, asphaltene precipitation can buildup at the production facilities such as pumps, wellbore, tube, flow lines and other surface facilities, which leads to operational problems, and increases in cost on remediation. On the other hand, Asphaltene precipitation and deposition on pore walls of oil formation can strongly lead to formation damages in forms of the reductions in porosity and permeability and influence production performances . In addition, asphaltene precipitation on pore walls will also lead to wettability alteration [11-13] of pore surfaces and have an effect on oil recovery. The study on asphaltene precipitation in laboratory mainly focuses on the onset of asphaltene deposition and permeability reduction caused by asphaltene adsorption on pore surfaces or asphaltene plug in the sandstone cores. Mansoori presented a mathematical model used for predicting asphaltene precipitation. However, the model is not capable of simulating the process of asphaltene deposition on pore walls and plugging in porous media. Ali and Islam developed a single-phase formation damage model for under-saturated oil based on Gruesbeck and Collins pathway approach. The model can deal with both asphaltene adsorption on pore surfaces and mechanical trapping in porous media. The permeability reduction was described by the Gruesbeck and Collins empirical expressions. More recently, M.Nikookar and M.R.Omidkhah developed a correlation for predicting for asphaltene deposition by using the experimental data. At present, published work regarding to comprehensive mathematical

Wettability Alteration and Its Effects on Production in Water Flooding

Abstract The experiments validate that the wettability of reservoir rocks changes from weak water wetness to strong water wetness during secondary oil recovery. The relative permeabilities of the oil and water show that the increase in water wetness results in an obvious decrease in the water permeability. A numerical simulator considering wettability alteration was developed to predict oil production. The simulation indicates the wettability alteration during water flooding has strong effects on the water cut and oil recovery. It is found that the increase in water wetness during water flooding leads to a higher oil recovery and less accumulated production water at a water cut.

A Practical Compositional Method for Simulation of CO2 Flooding in Porous and Fractured Petroleum Reservoirs

CO2 flooding is one of the most effective and used methods for enhanced oil recovery (EOR) approaches. The number of CO2 flooding projects has increased rapidly in China and around the world. Compositional simulation is required for evaluating CO2 flooding in EOR operations, especially for miscible or nearly miscible flooding when black-oil simulation is no longer adequate. The simulation method proposed here is a multi-dimensional, three-phase, and compositional modeling approach, which is applicable to both porous and fractured reservoirs. In the model formulation, a generalized multi-continuum approach is adopted to handle flow and transport in naturally fractured reservoirs and the mass flux of each mass component is contributed by advection and diffusion processes. In addition, precipitation of heavy oil components and absorption of CO2 on the solid grains are modeled based on reversible linear or nonlinear isotherms. The governing partial differential equations for conservation of each component are discretized using a finite volume method and the resulting discrete equations are solved fully implicitly by Newton-Raphson iteration. The equation of state (EOS) by Soave-Redlich-Kwong is used to calculate the physical properties of fluids. Research has shown that the flash calculations with EOS in compositional simulation are computationally intensive and may not be reliable at near critical conditions. Therefore, a K-value based approach, improved by Almehaideb et al. (2002), is used for partitioning of oil components and CO2 between oil and CO2 phases. In addition, the laboratory measured oil and CO2 phase compositional data can be used alternatively to account for compositional effect in this model. Two numerical examples are presented to show that the proposed modeling method is efficient for simulation of CO2 flooding processes in EOR operations. Introduction CO2 flooding has been used as a commercial process for enhanced oil recovery (EOR) for over 40 years and is the secondmost applied EOR process in the world (Jarrell et al., 2002). Both laboratory studies and field applications have established that CO2 can be an efficient oil-displacing agent. CO2 injection in mature hydrocarbon fields has also been considered as a favourable option to reduce accumulation of atmospheric CO2 and thus mitigate greenhouse effects on climate (Bradshaw and Cook, 2001). As the results, a number of CO2 flooding projects has increased rapidly in China and around the world. Numerical simulation is the most common technique in the oil industry to better understand, predict, design, and manage a CO2-EOR project. Miscibility between oil and CO2 will occur when pressure is high enough to compress the CO2 to a density at which it becomes a good solvent for the lighter hydrocarbons in the crude oil. Compositional simulation is required for modeling the complex interaction of flow in CO2-EOR operations, especially for miscible or nearly miscible flooding when black-oil simulation is no longer adequate. In recent years, we have seen more CO2 application in naturally fractured reservoirs. Due to the large permeability contrast between the matrix and the fracture in fractured reservoirs, injected fluids such as CO2 or water easily move toward the production well and result in bypassing of the matrix oil and poor sweep efficiency. Early gas or water breakthrough becomes problematic in the secondary oil recovery stage in most fractured reservoirs. Among the commonly used conceptual models for analyzing flow through fractured rock, dual-continuum models, i.e., doubleand multi-porosity, and dual-permeability, are perhaps the most popular approaches used in fractured reservoir modeling studies (Barenblatt et al., 1960; Warren and Root, 1963; Kazemi, 1969). A more general and efficient method for multi-continuum, named multiple-interacting-continua (MINC) method, was proposed (Pruess and Narasimhan, 1985; Wu and Pruess, 1988). The TOUGH2 family of multiphase flow numerical simulators (Pruess, 2004) has a long recognized record of