Carbon dioxide(CO_(2))flooding is a widely applied recovery method during the tertiary recovery of oil and gas.A high water saturation condition in reservoirs could induce a‘water shielding’phenomenon after the inje...Carbon dioxide(CO_(2))flooding is a widely applied recovery method during the tertiary recovery of oil and gas.A high water saturation condition in reservoirs could induce a‘water shielding’phenomenon after the injection of CO_(2).This would prevent contact between the injected gas and the residual oil,restricting the development of the miscible zone.A micro-visual experiment of dead-end models,used to observe the effect of a film of water on the miscibility process,indicates that CO_(2)can penetrate the water film and come into contact with the residual oil,although the mixing is significantly delayed.However,the dissolution loss of CO_(2)at high water-cut conditions is not negligible.The oil-water partition coefficient,defined as the ratio of CO_(2)solubility in an oil-brine/two-phase system,keeps constant for specific reservoir conditions and changes little with an injection gas.The NMR device shows that when CO_(2)flooding follows water flooding,the residual oil decreasesdnot only in medium and large pores but also in small and micro pores.At levels of higher water saturation,CO_(2)displacement is characterized initially by a low oil production rate and high water-cut.After the CO_(2)breakthrough,the water-cut decreases sharply and the oil production rate increases gradually.The response time of CO_(2)flooding at high watercut reservoirs is typically delayed and prolonged.These results were confirmed in a pilot test for CO_(2)flooding at the P1-1 well group of the Pucheng Oilfield.Observations from this pilot study also suggest that a larger injection gas pore volume available for CO_(2)injection is required to offset the dissolution loss in high water saturation conditions.展开更多
SF_(6)电气设备内部的分解组分可以通过可调谐吸收光谱技术进行检测,其中CO_(2)浓度反映了设备内部的绝缘缺陷情况。因此,通过准确测量CO_(2)浓度可以及时发现设备潜在的绝缘故障。为克服传统最小二乘法浓度反演模型稳定性较差的问题,...SF_(6)电气设备内部的分解组分可以通过可调谐吸收光谱技术进行检测,其中CO_(2)浓度反映了设备内部的绝缘缺陷情况。因此,通过准确测量CO_(2)浓度可以及时发现设备潜在的绝缘故障。为克服传统最小二乘法浓度反演模型稳定性较差的问题,文中基于改进的旗鱼优化算法(Improved Sailed Fish Optimizer,ISFO)与核极限学习机(Kernel Based Extreme Learning Machine,KELM)建立了ISFO-KELM气体浓度反演模型。利用多策略初始化方法、Levy随机步长、柯西变异和自适应t分布变异等技术提升了旗鱼优化算法寻优能力和跳出局部最优解能力。实验结果表明,该模型具有高精度和鲁棒性,并且在稳定性和泛化能力方面优于最小二乘法、极限学习机、反向传播(Back Propagation,BP)神经网络等传统方法,对评估SF_(6)电气设备运行状态具有重要意义。展开更多
With the increasing demand for petroleum,shale oil with considerable reserves has become an important part of global oil resources.The shale oil reservoir has a large number of nanopores and a complicated mineral comp...With the increasing demand for petroleum,shale oil with considerable reserves has become an important part of global oil resources.The shale oil reservoir has a large number of nanopores and a complicated mineral composition,and the effect of nanopore confinement and pore type usually makes the effective development of shale oil challenging.For a shale oil reservoir,CO_(2) flooding can effectively reduce the oil viscosity and improve the reservoir properties,which can thus improve the recovery performance.In this study,the method of non-equilibrium molecular dynamics(NEMD)simulation is used to simulate the CO_(2) flooding process in the nanoscale pores of shale oil reservoir.The performance difference between the organic kerogen slit nanopore and four types of inorganic nanopores is discussed.Thus,the effects of nanopore type and displacement velocity on the nanoscale displacement behavior of CO_(2) are analyzed.Results indicate that the CO_(2) flooding process of different inorganic pores is different.In comparison,the displacement efficiency of light oil components is higher,and the transport distance is longer.The intermolecular interaction can significantly affect the CO_(2) displacement behavior in nanopores.The CO_(2) displacement efficiency is shown as montmorillonite,feldspar>quartz>calcite>kerogen.On the other hand,it is found that a lower displacement velocity can benefit the miscibility process between alkane and CO_(2),which is conducive to the overall displacement process of CO_(2).The displacement efficiency can significantly decrease with the increase in displacement velocity.But once the displacement velocity is very high,the strong driving force can promote the alkane to move forward,and the displacement efficiency will recover slightly.This study further reveals the microscopic oil displacement mechanism of CO_(2) in shale nanopores,which is of great significance for the effective development of shale oil reservoirs by using the method of CO_(2) injection.展开更多
文摘Carbon dioxide(CO_(2))flooding is a widely applied recovery method during the tertiary recovery of oil and gas.A high water saturation condition in reservoirs could induce a‘water shielding’phenomenon after the injection of CO_(2).This would prevent contact between the injected gas and the residual oil,restricting the development of the miscible zone.A micro-visual experiment of dead-end models,used to observe the effect of a film of water on the miscibility process,indicates that CO_(2)can penetrate the water film and come into contact with the residual oil,although the mixing is significantly delayed.However,the dissolution loss of CO_(2)at high water-cut conditions is not negligible.The oil-water partition coefficient,defined as the ratio of CO_(2)solubility in an oil-brine/two-phase system,keeps constant for specific reservoir conditions and changes little with an injection gas.The NMR device shows that when CO_(2)flooding follows water flooding,the residual oil decreasesdnot only in medium and large pores but also in small and micro pores.At levels of higher water saturation,CO_(2)displacement is characterized initially by a low oil production rate and high water-cut.After the CO_(2)breakthrough,the water-cut decreases sharply and the oil production rate increases gradually.The response time of CO_(2)flooding at high watercut reservoirs is typically delayed and prolonged.These results were confirmed in a pilot test for CO_(2)flooding at the P1-1 well group of the Pucheng Oilfield.Observations from this pilot study also suggest that a larger injection gas pore volume available for CO_(2)injection is required to offset the dissolution loss in high water saturation conditions.
文摘SF_(6)电气设备内部的分解组分可以通过可调谐吸收光谱技术进行检测,其中CO_(2)浓度反映了设备内部的绝缘缺陷情况。因此,通过准确测量CO_(2)浓度可以及时发现设备潜在的绝缘故障。为克服传统最小二乘法浓度反演模型稳定性较差的问题,文中基于改进的旗鱼优化算法(Improved Sailed Fish Optimizer,ISFO)与核极限学习机(Kernel Based Extreme Learning Machine,KELM)建立了ISFO-KELM气体浓度反演模型。利用多策略初始化方法、Levy随机步长、柯西变异和自适应t分布变异等技术提升了旗鱼优化算法寻优能力和跳出局部最优解能力。实验结果表明,该模型具有高精度和鲁棒性,并且在稳定性和泛化能力方面优于最小二乘法、极限学习机、反向传播(Back Propagation,BP)神经网络等传统方法,对评估SF_(6)电气设备运行状态具有重要意义。
基金supported by the National Natural Science Foundation of China(No.52004303)Beijing Natural Science Foundation(No.3212020).
文摘With the increasing demand for petroleum,shale oil with considerable reserves has become an important part of global oil resources.The shale oil reservoir has a large number of nanopores and a complicated mineral composition,and the effect of nanopore confinement and pore type usually makes the effective development of shale oil challenging.For a shale oil reservoir,CO_(2) flooding can effectively reduce the oil viscosity and improve the reservoir properties,which can thus improve the recovery performance.In this study,the method of non-equilibrium molecular dynamics(NEMD)simulation is used to simulate the CO_(2) flooding process in the nanoscale pores of shale oil reservoir.The performance difference between the organic kerogen slit nanopore and four types of inorganic nanopores is discussed.Thus,the effects of nanopore type and displacement velocity on the nanoscale displacement behavior of CO_(2) are analyzed.Results indicate that the CO_(2) flooding process of different inorganic pores is different.In comparison,the displacement efficiency of light oil components is higher,and the transport distance is longer.The intermolecular interaction can significantly affect the CO_(2) displacement behavior in nanopores.The CO_(2) displacement efficiency is shown as montmorillonite,feldspar>quartz>calcite>kerogen.On the other hand,it is found that a lower displacement velocity can benefit the miscibility process between alkane and CO_(2),which is conducive to the overall displacement process of CO_(2).The displacement efficiency can significantly decrease with the increase in displacement velocity.But once the displacement velocity is very high,the strong driving force can promote the alkane to move forward,and the displacement efficiency will recover slightly.This study further reveals the microscopic oil displacement mechanism of CO_(2) in shale nanopores,which is of great significance for the effective development of shale oil reservoirs by using the method of CO_(2) injection.
