scholarly journals Cyclic CH4 Injection for Enhanced Oil Recovery in the Eagle Ford Shale Reservoirs

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 3094 ◽  
Author(s):  
Yuan Zhang ◽  
Yuan Di ◽  
Yang Shi ◽  
Jinghong Hu
Keyword(s):  
Capillary Pressure ◽  
Enhanced Oil Recovery ◽  
Oil Recovery ◽  
Molecular Diffusion ◽  
Well Performance ◽  
Eagle Ford Shale ◽  
Eagle Ford ◽  
Well Production ◽  
Operation Parameters ◽  
Shale Reservoirs

Gas injection is one of the most effective enhanced oil recovery methods for the unconventional reservoirs. Recently, CH4 has been widely used; however, few studies exist to accurately evaluate the cyclic CH4 injection considering molecular diffusion and nanopore effects. Additionally, the effects of operation parameters are still not systematically understood. Therefore, the objective of this work is to build an efficient numerical model to investigate the impacts of molecular diffusion, capillary pressure, and operation parameters. The confined phase behavior was incorporated in the model considering the critical property shifts and capillary pressure. Subsequently, we built a field-scale simulation model of the Eagle Ford shale reservoir. The fluid properties under different pore sizes were evaluated. Finally, a series of studies were conducted to examine the contributions of each key parameter on the well production. Results of sensitivity analysis indicate that the effect of confinement and molecular diffusion significantly influence CH4 injection effectiveness, followed by matrix permeability, injection rate, injection time, and number of cycles. Primary depletion period and soaking time are less noticeable for the well performance in the selected case. Considering the effect of confinement and molecular diffusion leads to the increase in the well performance during the CH4 injection process. This work, for the first time, evaluates the nanopore effects and molecular diffusion on the CH4 injection. It provides an efficient numerical method to predict the well production in the EOR process. Additionally, it presents useful insights into the prediction of cyclic CH4 injection effectiveness and helps operators to optimize the EOR process in the shale reservoirs.

An Optimized Experimental Investigation of Foam-Assisted N2 Huff-n-Puff Enhanced Oil Recovery in Fractured Shale Cores

2021 ◽  
Author(s):  
Xiaofei Xiong ◽  
James Jia Sheng
Keyword(s):  
Enhanced Oil Recovery ◽  
Oil Recovery ◽  
Rapid Decline ◽  
Production Time ◽  
Experimental Conditions ◽  
Cycle Number ◽  
Injection Process ◽  
Matrix Permeability ◽  
Shale Reservoirs ◽  
Scale Matrix

Abstract Sustainable development of shale reservoirs and enhanced oil recovery have become a challenge for the oil industry in recent years. Shale reservoirs are typically characterized by nano Darcy-scale matrix, natural fractures, and artificially fractures with high permeability. Some of earlier studies have confirmed that gas huff-n-puff has been investigated and demonstrated as the most effective and promising solution for improving oil recovery in tight shale reservoirs with ultra-low permeability. Fractures provide an advantage in enhancing recovery from shale reservoirs but they also pose serious problems such as severe gas channeling, which led to rapid decline production from a single well. More studies are needed to optimize the process. This paper studies the method of foam-assisted N2 huff-n-puff to enhance oil recovery in fractured shale cores. The influence of foam on oil recovery was analyzed. The effect of matrix permeability, cycle number and production time on oil recovery are also considered. The shale core used in the experiment was from Sichuan Basin, China. For the purpose of comparation and validation, two groups of tests were conducted. One group of tests was N2 huff-n-puff, and the other was foam-N2 huff-n-puff. In the optimization experiment, matrix permeabilities were set as 0.01mD, 0.008mD and 0.001mD, cycle numbers ranged from one to five, the production time is designed to be 1 hour and 24 hours respectively. During the puff period of experiments, the history of oil recovery was closely monitored to reveal the mechanism. During a round of gas injection of fractured shale cores, foam-assisted N2 huff-n-puff oil recovery is 4.59%, which is significantly higher than that of N2 huff-n-puff is only 0.0126%, and the contrast becomes more obvious with the increase of matrix permeability. The results also showed that the cumulative oil recovery increased as the number of cycles was increased, with the same experimental conditions. There is an optimal production time to achieve maximum oil recovery. The cycle numbers, matrix permeability, and production time played important roles in foam-assisted N2 huff-n-puff injection process. Therefore, under certain conditions, foam-N2 huff-n-puff has a positive effect on oil development in fractured shale.

Nanopore Compositional Modeling in Unconventional Shale Reservoirs

2016 ◽  
Vol 19 (03) ◽  
pp. 415-428 ◽  
Author(s):  
Najeeb S. Alharthy ◽  
Tadesse W. Teklu ◽  
Thanh N. Nguyen ◽  
Hossein Kazemi ◽  
Ramona M. Graves
Keyword(s):  
Phase Behavior ◽  
Oil Recovery ◽  
Flow Behavior ◽  
Flow Characteristics ◽  
Gas Production ◽  
Eagle Ford ◽  
Compositional Modeling ◽  
Shale Reservoirs ◽  
Behavior Shift

Summary Understanding the mechanism of multicomponent mass transport in the nanopores of unconventional reservoirs, such as Eagle Ford, Niobrara, Woodford, and Bakken, is of great interest because it influences long-term economic development of such reservoirs. Thus, we began to examine the phase behavior and flow characteristics of multicomponent flow in primary production in nanoporous reservoirs. Besides primary recovery, our long-term objectives included enhanced oil production from such reservoirs. The first step was to evaluate the phase behavior in nanopores on the basis of pore-size distribution. This was motivated because the physical properties of hydrocarbon components are affected by wall proximity in nanopores as a result of van der Waals molecular interactions with the pore walls. For instance, critical pressure and temperature of hydrocarbon components shift to lower values as the nanopore walls become closer. In our research, we applied this kind of critical property shift to the hydrocarbon components of two Eagle Ford fluid samples. Then, we used the shifted phase characteristics in dual-porosity compositional modeling to determine the pore-to-pore flow characteristics, and, eventually, the flow behavior of hydrocarbons to the wells. In the simulation, we assigned three levels of phase behavior in the matrix and fracture pore spaces. In addition, the flow hierarchy included flow from matrix (nano-, meso-, and macropores) to macrofractures, from macrofractures to a hydraulic fracture (HF), and through the HF to the production well. From the simulation study, we determined why hydrocarbon fluids flow so effectively in ultralow-permeability shale reservoirs. The simulation also gave credence to the intuitive notion that favorable phase behavior (phase split) in the nanopores is one of the major reasons for production of commercial quantities of light oil and gas from shale reservoirs. It was determined that the implementation of confined-pore and midconfined-pore phase behavior lowers the bubblepoint pressure, and this, in turn, leads to a slightly higher oil recovery and lesser gas recovery. Also it was determined that the implementation of midconfined-pore and confined-pore phase-behavior shift reduces the retrograde liquid-condensation region, which in turn, leads to lower liquid yield while maintaining the same gas-production quantity. Finally, the important reason that we are able to produce shale reservoirs economically is “rubblizing” the reservoir matrix near HFs, which creates favorable permeability pathways to improve reservoir drainage. This is why multistage hydraulic fracturing is so critical for successful development of shale reservoirs.

scholarly journals Molecular-Scale Considerations of Enhanced Oil Recovery in Shale

Energies ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 6619
Author(s):  
Mohamed Mehana ◽  
Qinjun Kang ◽  
Hari Viswanathan
Keyword(s):  
Carbon Dioxide ◽  
Enhanced Oil Recovery ◽  
Oil Recovery ◽  
Energy Equation ◽  
Simulation Approach ◽  
Production Region ◽  
The World ◽  
Fluid Properties ◽  
Shale Reservoirs ◽  
Different Gases

With only less than 10% recovery, the primary production of hydrocarbon from shale reservoirs has redefined the energy equation in the world. Similar to conventional reservoirs, Enhanced Oil Recovery (EOR) techniques could be devised to enhance the current recovery factors. However, shale reservoirs possess unique characteristics that significantly affect the fluid properties. Therefore, we are adopting a molecular simulation approach that is well-suited to account for these effects to evaluate the performance of three different gases, methane, carbon dioxide and nitrogen, to recover the hydrocarbons from rough pore surfaces. Our hydrocarbon systems consists of either a single component (decane) or more than one component (decane and pentane). We simulated cases where concurrent and countercurrent displacement is studied. For concurrent displacement (injected fluids displace hydrocarbons towards the production region), we found that nitrogen and methane yielded similar recovery; however nitrogen exhibited a faster breakthrough. On the other hand, carbon dioxide was more effective in extracting the hydrocarbons when sufficient pressure was maintained. For countercurrent displacement (gases are injected and hydrocarbons are produced from the same direction), methane was found to be more effective, followed by carbon dioxide and nitrogen. In all cases, confinement reduced the recovery factor of all gases. This work provides insights to devise strategies to improve the current recovery factors observed in shale reservoirs.

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