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Numerical Modeling of Gas Migration through Cement Sheath and Microannulus
Mustafa Al Ramadan1,2, Saeed Salehi3, Murtada S Aljawad1,2
1College of Petroleum Engineering and Geosciences, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia.
ACS Omega
|December 29, 2021
Summary
Cement sheath integrity is crucial for well safety. This study models gas leakage, finding microannulus gap size and cement permeability significantly impact leakage time, not cement porosity.
Area of Science:
- Petroleum Engineering
- Materials Science
- Geosciences
Background:
- The cement sheath is a critical barrier in well integrity.
- Cement sealability is vital, but porous nature and flaws like microannuli can cause leakage.
- Complex casing/cement/formation interactions hinder complete fluid migration modeling.
Purpose of the Study:
- To develop a numerical model for gas flow in cement sheaths, including microannulus flow.
- To perform a parametric study on variables affecting leakage time.
- To analyze leakage scenarios considering casing/liner overlap and microannuli.
Main Methods:
- Numerical modeling of gas flow through cement sheath and microannuli.
- Parametric study varying microannulus gap size, cement permeability, cement column length, and cement porosity.
- Simulation of leakage scenarios with different casing/liner overlap lengths.
Main Results:
- Cement matrix permeability, microannulus gap size, and cement column length significantly influence leakage time.
- Cement porosity has a minimal effect on leakage time.
- Leakage detection requires casing/liner overlap of at least 300 ft and a pressure duration exceeding 30 min.
Conclusions:
- Gas leakage through cement sheaths is influenced by material properties and structural flaws.
- Effective well integrity requires careful consideration of cement properties and casing design.
- The developed model provides insights for predicting and mitigating wellbore leakage risks.
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