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Research Papers: Petroleum Engineering

The Influences of CO2 Injection Pressure on CO2 Dispersion and the Mechanism of CO2–CH4 Displacement in Shale

[+] Author and Article Information
Xidong Du

State Key Laboratory of Coal Mine
Disaster Dynamics and Control,
College of Resources and
Environmental Science,
Chongqing University,
No. 174 Sha Zheng Street,
Shapingba District,
Chongqing 400044, China
e-mail: xidongdu@126.com

Min Gu

State Key Laboratory of Coal Mine
Disaster Dynamics and Control,
College of Resources and
Environmental Science,
Chongqing University,
No. 174 Sha Zheng Street,
Shapingba District,
Chongqing 400044, China
e-mail: mgu@cqu.edu.cn

Shuo Duan

State Key Laboratory of Coal Mine
Disaster Dynamics and Control,
College of Resources and
Environmental Science,
Chongqing University,
No. 174 Sha Zheng Street,
Shapingba District,
Chongqing 400044, China
e-mail: 278444324@qq.com

Xuefu Xian

State Key Laboratory of Coal Mine
Disaster Dynamics and Control,
College of Resources and
Environmental Science,
Chongqing University,
No. 174 Sha Zheng Street,
Shapingba District,
Chongqing 400044, China
e-mail: xianxf@cae.cn

1Corresponding author.

Contributed by the Petroleum Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received May 22, 2017; final manuscript received August 5, 2017; published online September 12, 2017. Assoc. Editor: Daoyong (Tony) Yang.

J. Energy Resour. Technol 140(1), 012907 (Sep 12, 2017) (9 pages) Paper No: JERT-17-1239; doi: 10.1115/1.4037687 History: Received May 22, 2017; Revised August 05, 2017

The effects of CO2 injection pressure (PCO2) on CO2 dispersion and the mechanism of CO2–CH4 displacement in a shale sampled from Changning of China were studied. Results indicated that Coats–Smith dispersion–capacitance model gave a reasonable simulated result to the breakthrough curves of CO2 under different injection pressures. The shapes of CO2 breakthrough curves became more asymmetrical with the increase of CO2 injection pressure. A higher CO2 injection pressure caused early CO2 breakthrough and reduced the recovery of CH4 at CO2 breakthrough (Rpipeline-CH4), but improved the ultimate displaced CH4 amount (Rultimate-CH4). With the increase of CO2 injection pressure, dispersion coefficient (Kd) increased nearly exponentially. A larger Kd led to a lower Rpipeline-CH4 and a longer transition zone. With the increase of CO2 injection pressure, the flowing fraction (F) in pore space decreased nearly linearly and more CO2 diffused into stagnant region to replace adsorbed CH4 in a shale, which resulted in a larger Rultimate-CH4. The mass transfer coefficient (Km) between the flowing and stagnant regions increased with the increase of CO2 injection pressure, which led to a smaller F and larger Rultimate-CH4. CO2 diffusion provided major contribution to CO2 dispersion at lower injection pressure, and mechanical mixing of CO2–CH4 offered predominant contribution to CO2 dispersion at higher injection pressure. Larger mechanical mixing accelerated the mixing of CO2–CH4, which was unfavorable for Rpipeline-CH4. Lower CO2 injection pressure was conductive to gain higher Rpipeline-CH4.

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References

Figures

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Fig. 1

Breakthrough curves of CO2 and CH4 under different injection pressures

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Fig. 2

Variations of Fin-CO2 and CO2 breakthrough curves at injection pressures of: (a) 5.05 MPa, (b) 7.50 MPa, (c) 10.00 MPa, (d) 12.50 MPa, and (e) 15.00 MPa

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Fig. 3

CO2 storage capacity at tb (a) and CO2 storage rate (b) under different injection pressures

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Fig. 4

Simulated and experimental results of CO2 breakthrough curves at injection pressures of 5.05 MPa and 12.50 MPa

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Fig. 5

CO2 breakthrough curves and their simulated results at different injection pressures

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Fig. 6

Relationships of injection pressure and the parameters of: F (a), Kd (b), υ (c), and Km (d)

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Fig. 7

Distributions of CO2 concentrations at different locations in flowing region (a) and stagnant region (b)

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Fig. 8

Distributions of CO2 concentrations at different times in flowing region (a) and stagnant region (b)

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Fig. 9

Contributions of CO2 diffusion and the mechanical mixing of CO2–CH4 to CO2 dispersion

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