Estimates of CO2 leakage along abandoned wells constrained by new data

Geological carbon storage is an effective method capable of reducing carbon dioxide (CO2) emissions at significant scales. Subsurface reservoirs with sealing caprocks can provide long-term containment for the injected fluid. Nevertheless, CO2 leakage is a major concern. The presence of abandoned wells penetrating the reservoir caprock may cause leakage flow-paths for CO2 to the overburden. Assessment of time-varying leaky wells is a need. In this paper, we propose a new semi-analytical approach based on pressure-transient analysis to model the behavior of CO2 leakage and corresponding pressure distribution within the storage site and the overburden. Current methods assume instantaneous leakage of CO2 occurring with injection, which is not realistic. In this work, we employ the superposition in time and space to solve the diffusivity equation in 2D radial flow to approximate the transient pressure in the reservoirs. Fluid and rock compressibilities are taken into consideration, which allow calculating the breakthrough time and the leakage rate of CO2 to the overburden accurately. We use numerical simulations to verify the proposed time-dependent semi-analytical solution. The results show good agreement in both pressure and leakage rates. Sensitivity analysis is then conducted to assess different CO2 leakage scenarios to the overburden. The developed semi-analytical solution provides a new simple and practical approach to assess the potential of CO2 leakage outside the storage site. This approach is an alternative to numerical methods when detailed simulations are not feasible. Furthermore, the proposed solution can also be used to verify numerical codes, which often exhibit numerical artifacts.

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Early detection of brine and CO2 leakage through abandoned wells using pressure and surface-deformation monitoring data: Concept and demonstration

Advances in Water Resources ◽

10.1016/j.advwatres.2013.06.008 ◽

2013 ◽

Vol 62 ◽

pp. 555-569 ◽

Cited By ~ 53

Author(s):

Yoojin Jung ◽

Quanlin Zhou ◽

Jens T. Birkholzer

Keyword(s):

Early Detection ◽

Surface Deformation ◽

Deformation Monitoring ◽

Monitoring Data ◽

Co2 Leakage ◽

Abandoned Wells

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Numerical Simulation of CO2 Leakage through Abandoned Wells: Model for an Abandoned Site with Observed Gas Migration in Alberta, Canada

Energy Procedia ◽

10.1016/j.egypro.2009.02.158 ◽

2009 ◽

Vol 1 (1) ◽

pp. 3625-3632 ◽

Cited By ~ 19

Author(s):

Rajesh J. Pawar ◽

Theresa L. Watson ◽

Carl W. Gable

Keyword(s):

Numerical Simulation ◽

Gas Migration ◽

Co2 Leakage ◽

Abandoned Wells

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Subsea Re-Abandonment Strategies for High-Risk Wells to Minimize Leakage Risk in a Depleted Field for CO2 Storage

10.2118/207944-ms ◽

2021 ◽

Author(s):

Parimal A Patil ◽

Debasis P. Das ◽

Pankaj K. Tiwari ◽

Prasanna Chidambaram ◽

Renato J. Leite ◽

...

Keyword(s):

High Risk ◽

Co2 Storage ◽

Horizontal Stress ◽

Leakage Rate ◽

Storage Site ◽

Co2 Leakage ◽

Well Integrity ◽

Abandoned Wells ◽

Fracture Gradient ◽

Maximum Horizontal Stress

Abstract CO2 storage in a depleted field comes with the risk that is associated with wells integrity which is often defined as the ability to contain fluids with minimum to nil leakage throughout the project lifecycle. The targeted CO2 storage reservoir in offshore Malaysia has existing abandoned exploration/appraisal, and development wells. With a view of developing such CO2 storage sites, it is vital to maintain the integrity of the abandoned wells. High-risk characterized wells need to be analyzed and remedial action plan to be defined by understanding the complexity involved in restoring the integrity. This will safeguard CO2 containment for decades. Abandoned exploration/appraisal wells in the identified field are >40 years old and were not designed to withstand CO2 corrosion environment. Downhole temperature and pressure conditions may have further degraded the wellbore material strength elevating corrosion susceptibility. The reservoir simulation predicts that the CO2 plume will reach to these abandoned wells during the initial phase of total injection period. Single well was selected to assess the loss of containment through the composite structure along the wellbore and to determine the complexity in resorting the well integrity. CO2 leakage rates through all possible pathways were estimated based on numerical models and the well is characterized for its risk. For unacceptable leakage risk, the abandoned well needs to be re-entered to restore the performance of barriers. Minimum plug setting depth (MPSD) and caprock restoration considers original reservoir pressure(3450psia) anticipating the pressure buildup upon CO2 injection and is derived based on fracture gradient and maximum horizontal stress. This paper elaborates unique challenges associated with locating abandoned wells that are submerged below seabed. Top and side re-entry strategies are discussed to overcome challenges. Based on past abandonment scheme, leakage rate modeling calculates estimated leakage rate of ~460SCFD at higher differential pressure of around 3036psia at shallowest barrier and ~15SCFD for differential pressure of 1518psia at deepest barrier. Sensitivity analysis has been carried out for critical barrier parameters (cement permeability, cracks, fractures) to the containment ability and improving understanding of quality of barriers, uncertainties, and complexities for CO2 leakage risk. The paper proposes two(2) minimum plug setting depths (3550ft & 3750ft) derived based on fracture gradient and maximum horizontal stress. Perforate-wash-cement (PWC) and section milling were compared for operational efficiencies to achieve caprock restoration. for MPSD out strategic options to restore well integrity by remediating casing/cement barriers at by performing best fit abandonment technique to contain CO2 in the reservoir. Well integrity risk is assessed for existing plugged and abandoned (P&A) wells in a carbon storage site. Optimized remedial actions are proposed. Quantification of all the uncertainties are resolved that may affect long-term security of CO2 storage site.

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Numerical Simulation of CO2 Leakage through Abandoned Wells during CO2 Underground Storage

Springer Series in Geomechanics and Geoengineering - Clean Energy Systems in the Subsurface: Production, Storage and Conversion ◽

10.1007/978-3-642-37849-2_17 ◽

2013 ◽

pp. 197-210 ◽

Cited By ~ 1

Author(s):

Mingxing Bai ◽

Kurt M. Reinicke

Keyword(s):

Numerical Simulation ◽

Underground Storage ◽

Co2 Leakage ◽

Abandoned Wells

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Development of a Novel Method To Evaluate Well Integrity During CO2 Underground Storage

SPE Journal ◽

10.2118/173000-pa ◽

2015 ◽

Vol 20 (03) ◽

pp. 628-641 ◽

Cited By ~ 9

Author(s):

Mingxing Bai ◽

Kaoping Song ◽

Yang Li ◽

Jianpeng Sun ◽

Kurt M. Reinicke

Keyword(s):

Composite System ◽

Leakage Rate ◽

Cement Matrix ◽

Underground Storage ◽

Co2 Leakage ◽

Storage Reservoir ◽

Well Integrity ◽

Abandoned Wells ◽

Defect Dimension ◽

Cement Sheath

Summary A safe and ecologic underground storage of carbon dioxide (CO2) requires long-term integrity of the wells affected by the injected CO2, including both active wells and abandoned wells. In line with other investigators, technical integrity is assumed if there is no significant leak in the subsurface system from the storage reservoir. The evaluation of integrity of abandoned wells over a long time frame during CO2 underground storage can only be performed indirectly and requires a comprehensive understanding of relevant thermal/hydraulic/mechanical/chemical processes affecting well integrity. This paper presents an integrated approach coupling qualitative features, events, and processes (FEPs) and scenario analysis with quantitative-model development and consequence analysis. The qualitative analysis provides a solid and comprehensive study on all the FEPs that affect well integrity. The mechanical model presents the stress distribution of the casing/cement/rock composite system and provides a quantification of the defect dimension caused by different load conditions. The defect dimension can be used to compute equivalent permeability of the cement sheath by use of empirical correlations, which is an important input parameter for the following CO2-leakage simulation, provided it is considered that CO2 can only migrate through the defects instead of the cement matrix. When integrity is compromised, the storage reservoir will leak CO2. For this leakage, a numerical model is presented to simulate the flow of CO2 along abandoned wellbores during the storage period, such as 1,000 years. It is found from the FEP analysis that the most-critical system components are caprock, casing/cement/rock composite system, and abandonment elements. By building a geomechanical model and a leakage model, it is also found that in the simulated scenarios the CO2-leakage rate is very small except for when using cement sheaths of very poor quality, which can lead to a leakage rate exceeding the maximum-allowable value. The sensitivity analysis shows that the vertical permeability of the cement sheath plays the most critical role. In comparison with previous studies, this method is comprehensive and easy to implement.

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