Huff-n-Puff gas injection is a method originally used in heavy oil reservoir to reduce oil viscosity, increase mobility and displacement efficiency to enhance oil recovery. Now this method has been applied to enhance unconventional oil recovery in shale or tight reservoirs in recent years and proved to be effective in experiment study. N2, C1, CO2 or other rich gases are used in shale oil EOR. The purpose of this paper is to compare the EOR potential of different gas and provide a guide to choose gas based on the Wolfcamp shale oil reservoir. The composition of crude oil from Wolfcamp was analyzed by Gas Chromatography (GC). First, the core plugs from Wolfcamp with diameters of 1.5 inches were saturated with crude oil. Then gas huff-n-puff experiments using N2, C1, and CO2 were conducted in the laboratory with the same injection pressure of 2000 psi. Based on laboratory results, a compositional model is built and used to analyze the performance of gas huff-n-puff. The EOR capacity of gas mixture (N2, C1, CO2) and some solvents such as C3-CO2 mixture, the separator gases C1 to C4 from the field production were investigated using the simulation method. From the experiment results of the three kinds of gas injections, the oil recovery in the first two injection cycles were large. The incremental oil recovery decreased as the increase in number of injection cycles. Comparing the three kinds of gas EOR effects on Wolfcamp core samples, CO2 EOR result was the best, followed by N2 and C1. Coupling the equation of state method with GC analysis, 24 components of crude oil were achieved and then lumped into 5 pseudo components for simulation. The EOR effects of other gas mixture and solvents are investigated using the field model. The results show that the EOR effect of mixture of C1, C2 and C4 is the most favorite, followed by CO2-C3 mixture, produced gas, C1-CO2 mixture, and N2-CO2 mixture. Combined all of these results with economic factors, a comparison of gas capacity is proposed. This investigation is focused on injection gas selection for shale oil production and helps to provide us a screening criterion to choose effective and convenient gas when conducting huff-n-puff gas injection in shale oil development. Cheaper gas with higher EOR potential will reduce the production cost and bring huge economic benefits to oil company especially in this low oil price period.
The manipulation of a nanoconfined fluid flow is a great challenge and is critical in both fundamental research and practical applications. Compared with chemical or biochemical stimulation, the use of temperature as controllable, physical stimulation possesses huge advantages, such as low cost, easy operation, reversibility, and no contamination. We demonstrate an elegant, simple strategy by which temperature stimulation can readily manipulate the nanoconfined water flow by tuning interfacial and viscous resistances. We show that with an increase in temperature, the water fluidity is decreased in hydrophilic nanopores, whereas it is enhanced by at least four orders of magnitude in hydrophobic nanopores, especially in carbon nanotubes with a controlled size and atomically smooth walls. We attribute these opposing trends to a dramatic difference in varying surface wettability that results from a small temperature variation.
A unified model for gas slip flow through circular and angular pores in both single phase flow and two-phase flow conditions is developed, and the effect of water saturation on gas slippage factors in different pore shapes are revealed. For circular pores, the water saturation retains as thin film binding on pore surfaces without changing the shape of the cross section, and the hydraulic diameters continuously reduce as water saturation increases, directly leading to an increase in the slippage factor. However, for angular pores, the water saturation retains as both films at boundaries and condensations at corners, and the film-water and corner-water gradually change their cross-section shape (from sharp corners to round corners), which further affects the gas slip behavior. Due to the presence of round corners, the ratio of the cross-sectional area and perimeter, which can also be regarded as the reciprocal of a specific surface area, can even increase at a low water saturation condition. Thus the collisions between gas molecules and pore boundaries weaken, resulting in a slight reduction in the gas slippage factor. This interesting finding in the angular pore case directly explains the contradiction of the published experimental results with the general knowledge (i.e., the gas slip factor always increases as water saturation increases). Thus, the validity of the common assumption regarding actual porous media as capillaries with a circular cross-section must be considered more carefully.
The present study examined the antioxidant activity of black tea theaflavins and catechin derivatives in canola oil. Oxidation was conducted at 95°C by monitoring the oxygen consumption and decreases in the linoleic and α-linolenic acids of canola oil. All were tested at a concentration of 0.5 mM. Catechins, including (-)-epicatechin, (-)-epicatechin gallate, (-)-epigallocatechin, and (-)-epigallocatechin gallate (EGCG), were more effective than theaflavins, namely, theaflavin-1, theaflavin-3-gallate, theaflavin-3′-gallate, and theaflavin-3,3′-digallate (TF 3 ), against the lipid oxidation of canola oil. Among the four theaflavins, TF 3 was the most effective, whereas among the four catechins, EGCG was the most potent. Under the same conditions, all theaflavins and catechins were more powerful than BHT as an antioxidant in heated canola oil. Little or no difference in antioxidant activity was observed between each catechin and epimer pair. Methylation of the 3′-OH led to a significant loss of antioxidant activity of the catechins.
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