Abstract:CO2 flooding has gained momentum in the oil and gas industry and might be suitable for approximately 80% of oil reservoirs worldwide based on the oil recovery criteria alone. In addition to miscibility, production performance needs to be optimized to achieve higher sweep efficiency and oil recovery. Although many techniques have been made available for production optimization in the upstream oil and gas industry, it is still a challenging task to optimize production performance in the presence of physical and… Show more
“…Our new findings on CO 2 rates optimization mechanisms support and extend already exciting opinions proposed by many researchers (Chen et al, 2010; Chen and Reynolds, 2016). They thought CO 2 rates optimization increases the oil recovery mainly by improving the sweep efficiency, but didn't give the quantitative evidences.…”
The CO2 flooding with superior displacement efficiency and high injectivity is an efficient enhanced oil recovery method. However, due to the unfavorable sweep efficiency particularly for strong heterogeneous reservoirs and immiscible flooding, the oil recovery on site is not all favorable. Multi-well rates optimization is one of common measures improving sweep efficiency with easy implement and low cost There are many rates optimization methods have been proposed by now. In this research, we first introduced the multi-agent deep deterministic policy gradient (MADDPG) algorithm to the multi-well rates optimization of CO2 flooding, and the new rates optimization method was built. The MADDPG adopts the centralized training and decentralized execution algorithm framework, and overcomes the defect that the single-agent reinforcement learning cannot deal the multi-well rates optimization well and also avoids the dimensional disaster problems. We treated each well as an agent, and each agent has its own reward, state and action. We chose the net present value (NPV) as the reward, the injection-production rate change range as the action element, and the production time, the bottom hole pressure, the oil production rate, and the gas-oil ratio as the state elements. The simulation results show that the optimal case obviously improves the NPV compared with the base case, and the simulation case with strong heterogeneity and immiscible flooding can also converge to the optimal target, which prove the effectiveness and robustness of the rates optimization method respectively. This research provides recommendations that improving the oil recovery by increasing the sweep efficiency to increase the income, and reducing the invalid CO2 injection to decrease the cost can achieve the optimal NPV. Reservoir heterogeneity seriously impairs the rates optimization performance, and rates optimization makes little difference to extreme strong interlayer heterogeneity for serious interlayer influence.
“…Our new findings on CO 2 rates optimization mechanisms support and extend already exciting opinions proposed by many researchers (Chen et al, 2010; Chen and Reynolds, 2016). They thought CO 2 rates optimization increases the oil recovery mainly by improving the sweep efficiency, but didn't give the quantitative evidences.…”
The CO2 flooding with superior displacement efficiency and high injectivity is an efficient enhanced oil recovery method. However, due to the unfavorable sweep efficiency particularly for strong heterogeneous reservoirs and immiscible flooding, the oil recovery on site is not all favorable. Multi-well rates optimization is one of common measures improving sweep efficiency with easy implement and low cost There are many rates optimization methods have been proposed by now. In this research, we first introduced the multi-agent deep deterministic policy gradient (MADDPG) algorithm to the multi-well rates optimization of CO2 flooding, and the new rates optimization method was built. The MADDPG adopts the centralized training and decentralized execution algorithm framework, and overcomes the defect that the single-agent reinforcement learning cannot deal the multi-well rates optimization well and also avoids the dimensional disaster problems. We treated each well as an agent, and each agent has its own reward, state and action. We chose the net present value (NPV) as the reward, the injection-production rate change range as the action element, and the production time, the bottom hole pressure, the oil production rate, and the gas-oil ratio as the state elements. The simulation results show that the optimal case obviously improves the NPV compared with the base case, and the simulation case with strong heterogeneity and immiscible flooding can also converge to the optimal target, which prove the effectiveness and robustness of the rates optimization method respectively. This research provides recommendations that improving the oil recovery by increasing the sweep efficiency to increase the income, and reducing the invalid CO2 injection to decrease the cost can achieve the optimal NPV. Reservoir heterogeneity seriously impairs the rates optimization performance, and rates optimization makes little difference to extreme strong interlayer heterogeneity for serious interlayer influence.
“…As a nongradient-based method, genetic algorithm (GA) is applied to minimize the objective function in this study. GA is categorized as a global search heuristic method that can be used to find exact or approximate solutions to optimization and search problems. , Although GA may take hundreds of iterations to converge because its convergence rate is not very fast, no gradient information or derivative computation is required for the calculation processes. Details and theory of GA can be found elsewhere. − …”
A generalized
methodology has been developed and successfully applied
to determine diffusion coefficient of alkane solvent–CO2–heavy oil systems with consideration of swelling effect.
Theoretically, a one-dimensional and one-way mass transfer model incorporating
the volume translated Peng–Robinson equation of state (PR EOS)
has been developed to describe the mass transfer from alkane solvent–CO2 mixture to heavy oil, which accounts for the oil swelling
effect resulted from gas dissolution. The heavy oil sample has been
characterized as three pseudocomponents, while the binary interaction
parameter (BIP) correlations are tuned with the experimentally measured
saturation pressures. Both apparent diffusion coefficients for gas
mixtures and individual diffusion coefficient of each component of
a mixture are determined once the discrepancy between the measured
and calculated dynamic swelling factors of heavy oil has been minimized.
The volume translated PR EOS with the three characterized pseudocomponents
and the tuned BIP correlations is able to accurately predict the phase
behavior of alkane solvent–CO2–heavy oil
systems. Compared to the apparent diffusion coefficient, better agreements
between the measured and calculated dynamic swelling factors have
been obtained by use of the individual diffusion coefficients. Addition
of C3H8 into CO2 stream is found
to not only diffuse faster into heavy oil than CO2 but
also contribute to a larger degree of oil swelling, leading to a faster
and enhanced swelling effect of C3H8–CO2–heavy oil system in comparison with the CO2–heavy oil system.
“…Numerous attempts exist to improve optimization routines, including, but not limited to, Bayesian optimization [50], parametric sensitivity analysis [51,52], genetic algorithms for derivative-free optimization [53,54], and particle swarms approach [55,56].…”
Section: Discrete Fracture Network Models and Limitationsmentioning
Closed-form solution-methods were applied to visualize the flow near hydraulic fractures at high resolution. The results reveal that most fluid moves into the tips of the fractures. Stranded oil may occur between the fractures in stagnant flow zones (dead zones), which remain outside the drainage reach of the hydraulic main fractures, over the economic life of the typical well (30-40 years). Highly conductive micro-cracks would further improve recovery factors. The visualization of flow near hypothetical micro-cracks normal to the main fractures in a Wolfcamp well shows such micro-cracks support the recovery of hydrocarbons from deeper in the matrix, but still leave matrix portions un-drained with the concurrent fracture spacing of 60 ft (~18 m). Our study also suggests that the traditional way of studying reservoir depletion by mainly looking at pressure plots should, for hydraulically fractured shale reservoirs, be complemented with high resolution plots of the drainage pattern based on time integration of the velocity field.
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