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To improve the oil recovery and economic efficiency in heavy oil reservoirs in late steam flooding, taking J6 Block of Xinjiang Oilfield as the research object, 3D physical modeling experiments of steam flooding, CO2-foam assisted steam flooding, and CO2 assisted steam flooding under different perforation conditions are conducted, and CO2-assisted steam flooding is proposed for reservoirs in the late stage of steam flooding. The experimental results show that after adjusting the perforation in late steam flooding, the CO2 assisted steam flooding formed a lateral expansion of the steam chamber in the middle and lower parts of the injection well and a development mode for the production of overriding gravity oil drainage in the top chamber of the production well; high temperature water, oil, and CO2 formed stable low-viscosity quasi-single-phase emulsified fluid; and CO2 acted as a thermal insulation in the steam chamber at the top, reduced the steam partial pressure inside the steam chamber, and effectively improved the heat efficiency of injected steam. Based on the three-dimensional physical experiments and the developed situation of the J6 block in Xinjiang Oilfield, the CO2 assisted steam flooding for the J6 block was designed. The application showed that the CO2 assisted steam flooding made the oil vapor ratio increase from 0.12 to 0.16 by 34.0%, the oil recovery increase from 16.1% to 21.5%, and the final oil recovery goes up to 66.5% compared to steam flooding after perforation adjustment. Key words: heavy oil reservoir, three-dimensional physical simulation experiment, steam flooding, CO2 assisted steam flooding, steam chamber, steam (CO2) chamber overriding gravity drainage

It is necessary to establish effective communication between two horizontal wells during the preheating period of steam-assisted gravity-drainage (SAGD). However, the preheating time is usually very long, which results in high steam consumption and CO2 emissions. There is little research on the effects of different wellbore fluids during the preheating period. The heat transfer and heating characteristics of different wellbore fluids–water, heat-conduction oil, and air–were explored by using physical experiments and numerical simulations. In this study, the results indicated that the heat-transfer performance of heat-conduction oil is the best. The numerical simulation’s results indicated that compared with the wellbore saturated with water, the heat-conduction oil reduced the viscosity of crude oil, and energy consumption was not obvious during the preheating stage. The super-heavy oil flowed into the wellbore due to the solubility of the heat-conduction oil and its own gravity. As a result, the super-heavy oil content in the wellbore gradually accumulated, increasing the risk of coking. Those experiments showed that the use of electrical heating provides good potential to improve SAGD efficiency during the preheating period, and water is the best injection fluid for wellbores during the electrical heating process.

It is challenging to enhance heavy oil recovery in the late stages of steam flooding. This challenge is due to reduced residual oil saturation, high steam-oil ratio, and lower profitability. A field test of the CO2-assisted steam flooding technique was carried out in the steam-flooded heavy oil reservoir in the J6 block of the Xinjiang oil field (China). In the field test, a positive response to the CO2-assisted steam flooding treatment was observed, including a gradually increasing heavy oil production, an increase in the formation pressure, and a decrease in the water cut. The production wells in the test area mainly exhibited four types of production dynamics, and some of the production wells exhibited production dynamics that were completely different from those during steam flooding. After being flooded via CO2-assisted steam flooding, these wells exhibited a gravity drainage pattern without steam channeling issues, and hence, they yielded stable oil production. In addition, emulsified oil and CO2 foam were produced from the production well, which agreed well with the results of laboratory-scale tests. The reservoir-simulation-based prediction for the test reservoir shows that the CO2-assisted steam flooding technique can reduce the steam-oil ratio from 12 m3 (CWE)/t to 6 m3 (CWE)/t and can yield a final recovery factor of 70%.

Background Cuticular waxes cover plant surface and play important roles in protecting plants from abiotic and biotic stresses. The variations of wax deposition and chemical compositions under changing environments have been shown to be related to plant adaptations. However, it is still not clear whether the wax depositions could be adjusted to increase plant adaptations to stressed conditions. Methods In this study, exogenous methyl jasmonate (MeJA), the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and salicylic acid (SA) were applied to test their effects on cuticular wax deposition in two Brassica napus cultivars, Zhongshuang 9 (ZS9, low wax coverage ) and Yuyou 19 (YY19, high wax coverage). Next, we measured the water loss rate and the transcriptional expression of genes involved in wax biosynthesis as well as genes related to disease defense. Results Seven wax compound classes, including fatty acids, aldehydes, alkanes, secondary alcohols, ketones, and unbranched as well as branched primary alcohols, were identified in B. napus leaf wax mixtures. MeJA, SA and ACC treatments had no significant effect on total wax amounts in YY19, whereas ACC reduced total wax amounts in ZS9. Overall, hormone treatments led to an increase in the amounts of aldehydes and ketones, and a decrease of secondary alcohol in ZS9, whereas they led to a decrease of alkane amounts and an increase of secondary alcohol amounts in YY19. Concomitantly, both cultivars also exhibited different changes in cuticle permeability, with leaf water loss rate per 15 min increased from 1.57% (averaged across treatments) at 1.57% (averaged across treatments) at 15 min to 3.12% at 30 min for ZS9 (except for ACC treated plant) and decreased for YY19. MeJA-treated plants of both cultivars relatively had higher water loss rate per 15 min when compared to other treatments. Conclusion. Our findings that B. napus leaf wax composition and cuticle permeability are altered by exogenous SA, MeJA and ACC suggest that the hormone treatments affect wax composition, and that the changes in wax profiles would cause changes in cuticle permeability.

Through Laplace transform and Stehfest numerical inversion, this research established a mathematical model for constant temperature electric heating of dual-horizontal-well steam-assisted gravity drainage (SAGD) start-up. To verify the model, a finite element simulation based on a typical SAGD block was completed, which proved the excellent agreement between the model solution and simulation results. Moreover, by means of superposition principle, underground temperature distribution and energy-related parameters during the multiwell operation were obtained, as well as a computational method targeted at quantifying the conserved energy, water and fuel of electric heating against steam heating. A parametric sensitivity analysis of electric heating was undertaken, which proved that the start-up effect is most sensitive to heating temperature, featuring a nonlinear negative correlation. Additionally, start-up effect is positively linear-correlative to porosity, and negatively linear-correlative to wellbore radius and oil saturation. The proposed model can be employed to predict key indexes such as underground temperature distribution, energy-consumption parameters, and accumulated conserved amounts of energy, water and fuel versus steam heating. Under a specified terminal temperature, temporal and energy quantities required by the start-up can also be determined. Key words: dual-horizontal-well SAGD, constant-temperature electric heating, underground temperature distribution, energy consumption, energy conservation, water conservation, fuel conservation

Abstract: Based on the systematic summary of current research on oil bank, the definition of oil bank in the process of fire flooding and its quantitative indices were proposed; and a new one-dimensional positive dry-fire flooding model considering temperature gradient was established based on the steady flow theory of gas and liquid phases. Single factor analysis and orthogonal experiments were adopted to verify the reliability and reveal the formation mechanisms and the controlling factors of the oil bank. Then the optimal conditions for the oil bank to form were discussed. The study results show the formation of the oil bank is controlled by 3 factors: (1) Oil bank would come into being within a certain temperature interval and above a critical value of temperature gradient (absolute value), with temperature too high or too low and temperature gradient absolute value lower than the critical value, the oil bank couldn't form. (2) For fire flooding process in heavy oil reservoirs, the viscosity of oil influences the width of oil bank and the speed at which oil bank forms; the lower the oil viscosity is, the wider the oil bank is and the faster the oil bank forms. (3) Oil saturation could affect the developing temperature and speed of oil bank. The favorable temperature at which oil bank develops gets lower and the accumulating speed of oil gets faster when the oil saturation is higher. By orthogonal experiments with the model, the optimal combinations of reservoir conditions for forming oil bank during fire flooding in heavy oil reservoirs can be worked out. Key words: fire flooding heavy oil, oil bank, flow model, single factor analysis, controlling factor, orthogonal experiment

The mechanisms of oxygen-reduced air flooding (ORAF) and the explosion limit and the corrosion control approaches were studied based on the pilots of oxygen-reduced air flooding (ORAF) in the Dagang, Changqing and Daqing oil fields in China. On the foundation of indoor investigations and pilots, the explosion limits, oxygen reduction limits and corrosion control approaches were clarified. When the temperature of reservoir is equal to and higher than 120 °C, there is a violent reaction between oxygen and crude oil, that means the effect of low temperature oxidation would be fully taken use of to enhance oil recovery by air flooding directly; nitrogen dominated immiscible flooding with oxygen-reduced air should be applied in cases where reservoir temperature is below 120 °C with little oxygen consumption and little heat generated. The oxygen-reduced air flooding is suitable for 3 types of reservoirs: low permeability reservoir, water flooding development reservoir of high water-cut and high temperature and high salinity reservoir. In the process of development, in order to ensure safety, the oxygen reduction limits should be controlled fewer than 10%, while oxygen-reduced air can obviously reduce the corrosion rate of pipes; The surface pipelines and injection wells don't need to consider about oxygen corrosion with no water, special materials and structure of pipe or corrosion inhibitor can be applied to the surface pipelines and injection wellbores with water. Air/oxygen-reduced air is a low-cost displacement medium and it could be applied in many special conditions of low permeability reservoir for energy supplement, huff and puff and displacement, that means oxygen-reduced air flooding has become the most potential strategic technology in 20 years. Key words: oxygen-reduced air flooding, explosion limit, oxygen-reduction limit, low temperature oxidation, oxygen corrosion control

With the 3a pilot area in Block H1 of Xinjiang Oilfield as an example, a basic model for accurate numerical simulation of fire flooding is established combining with physical simulation and field performance, after oil components are divided reasonably, high temperature combustion formula is defined. This model is used to trace and simulate the fire flooding in Block H1. The main results are as follows: (1) secondary water generated after steam injection is mostly displaced by flue gas during initial combustion phase, and only a small fraction works for limited wet combustion; (2) the flooded reservoirs, from the gas injection well to the production well, are divided into burnt zone, fire wall, coking zone, high temperature condensed zone (added newly), oil bank, and residual oil zone; and (3) the fire flooding for reservoir after steam injection, unlike original reservoir, experiences a process of oil bank building and migration featuring “pit filled and bank built”, with bank shape related to the performance of adjacent production wells. Moreover, the field experiment indicates that the numerical simulation of fire flooding contributes to the prediction and management of flooding performance. Key words: heavy oil reservoir, fire flooding, numerical simulation, secondary water, oil bank, high temperature condensed zone

The propagating characteristics of combustion fronts and coke zones in the combustion assisted gravity drainage process were studied using 3D physical simulation experiments. The main mechanisms and factors affecting stable propagation of the combustion fronts were discussed. The experimental results show that the propagation of combustion front can be divided into startup stage, radial expands stage and moving forward stage. The top oil layer is ignited first at the startup stage. Ignition temperature, ignition time and air injection rate are the key parameters for successful ignition. At the radial expanding stage the combustion front grows in size and expands radically and downwards like a funnel, and the air injection rate should match the area of combustion front. After the combustion front propagates beyond the “toe” position, the burning zone would advance along the horizontal well at a certain angle. The controlled gas override and gas seal of the coke in the horizontal well contributes significantly to the overall stability of the process. In field pilot testing, well pattern, ignition parameters and regime of injection and production should be optimized to ensure the stable propagation of the combustion front. Key words: combustion assisted gravity drainage, horizontal well, combustion front, propagating characteristic, physical simulation