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

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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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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Safeguarding CO2 Storage by Restoring Well Integrity Using Leakage Rate Modeling LRM along Wellbore in Depleted Gas Fields Offshore Sarawak

10.2118/205537-ms ◽

2021 ◽

Author(s):

Parimal A. Patil ◽

Prasanna Chidambaram ◽

M Syafeeq B. Ebining Amir ◽

Pankaj K. Tiwari ◽

Mahesh S. Picha ◽

...

Keyword(s):

Action Plan ◽

Co2 Storage ◽

Leakage Rate ◽

Dispersion Modeling ◽

Storage Site ◽

Remedial Action ◽

Well Integrity ◽

Gas Fields ◽

Remedial Action Plan

Abstract Ensuring long-term integrity of existing plugged and abandoned (P&A) and active wells that penetrated the selected CO2 storage reservoir is the key to reduce leakage risks along the wellpath for long-term containment sustainability. Restoring the well integrity, when required, will safeguard CO2 containment for decades. Well integrity is often defined as the ability to contain fluids with minimum to nil leakage throughout the project lifecycle. With a view to develop depleted gas fields as CO2 storage sites in offshore Sarawak, it is vital to determine the complexity involved in restoring the integrity of these P&A wells as well as the development wells. Leakage Rate Modeling (LRM) was performed to identify and evaluate the associated risks for designing the remedial action plan to safeguard CO2 storage site. The P&A wells in the identified depleted gas fields were drilled 35–45 years ago and were not designed to withstand high CO2 concentration downhole conditions. Corrosive-Resistant Alloy (CRA) tubulars and CO2 resistant cement were not used during well construction and downhole pressure and temperature conditions may have further degraded the material strength and elevated the corrosion susceptibility. As a proof of concept, single well was selected to assess the loss of containment along the wellbore and to determine the complexity in resorting the well integrity, multiple scenarios were considered in LRM and composite structure and barrier parameters were assigned to estimate possible leakage pathways. Detailed numerical models were simulated for estimating leakage from reservoir to the surface through possible leakage pathways. Risks were identified and remedial action plan was designed for restoring well integrity. Post remedial plan covers Marine CO2 dispersion modeling to design comprehensive monitoring and mitigation plan for potential CO2 leakage in the marine environment. This study summarizes the unique challenge associated with estimating well integrity and re-entering existing P&A wells. Leakage rate modeling along these wells involves uncertainties but when carried out with realistic parameters, it can be used as a predicting tool to determine the nature and complexity of leakage. Integrating with site survey results for any indication of gas bubbling, decision can be made to restoring the well integrity. The paper outlines the detail strategic options to safeguard CO2 storage by restoring well integrity using LRM and integrating with marine CO2 dispersion modeling. Assessing well integrity of P&A wells on individual basis, risk is assessed and identified. Proper remedial actions are proposed accordingly. Quantification of all the uncertainties involved needs to be conducted that may affect long-term security of CO2 storage site.

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Semi-Analytical Solution to Assess CO2 Leakage in the Subsurface through Abandoned Wells

Energies ◽

10.3390/en14092452 ◽

2021 ◽

Vol 14 (9) ◽

pp. 2452

Author(s):

Tian Qiao ◽

Hussein Hoteit ◽

Marwan Fahs

Keyword(s):

Analytical Solution ◽

Storage Site ◽

Co2 Leakage ◽

Transient Pressure ◽

Flow Paths ◽

Abandoned Wells ◽

Diffusivity Equation ◽

Carbon Dioxide Co2 ◽

Good Agreement

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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Fracture mapping using seismic amplitude variation with offset and azimuth analysis at the Weyburn CO2 storage site

Geophysics ◽

10.1190/geo2011-0075.1 ◽

2012 ◽

Vol 77 (6) ◽

pp. B295-B306 ◽

Cited By ~ 17

Author(s):

Alexander Duxbury ◽

Don White ◽

Claire Samson ◽

Stephen A. Hall ◽

James Wookey ◽

...

Keyword(s):

Cross Sections ◽

Co2 Storage ◽

Horizontal Stress ◽

Storage Site ◽

Fracture Zones ◽

Amplitude Variation ◽

Amplitude Variation With Offset ◽

Seal Integrity ◽

Cap Rock ◽

Weyburn Field

Cap rock integrity is an essential characteristic of any reservoir to be used for long-term [Formula: see text] storage. Seismic AVOA (amplitude variation with offset and azimuth) techniques have been applied to map HTI anisotropy near the cap rock of the Weyburn field in southeast Saskatchewan, Canada, with the purpose of identifying potential fracture zones that may compromise seal integrity. This analysis, supported by modeling, observes the top of the regional seal (Watrous Formation) to have low levels of HTI anisotropy, whereas the reservoir cap rock (composite Midale Evaporite and Ratcliffe Beds) contains isolated areas of high intensity anisotropy, which may be fracture-related. Properties of the fracture fill and hydraulic conductivity within the inferred fracture zones are not constrained using this technique. The predominant orientations of the observed anisotropy are parallel and normal to the direction of maximum horizontal stress (northeast–southwest) and agree closely with previous fracture studies on core samples from the reservoir. Anisotropy anomalies are observed to correlate spatially with salt dissolution structures in the cap rock and overlying horizons as interpreted from 3D seismic cross sections.

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Reservoir Characterization for Uncertainty Analysis and Its Impact on CO2 Injection and Sequestration in a Depleted Offshore Carbonate Gas Field

10.2118/205706-ms ◽

2021 ◽

Author(s):

Debasis P. Das ◽

Parimal A. Patil ◽

Pankaj K. Tiwari ◽

Renato J Leite ◽

Raj Deo Tewari

Keyword(s):

Co2 Storage ◽

Assessment Process ◽

Rock Properties ◽

Co2 Injection ◽

Storage Site ◽

Reservoir Pressure ◽

Gas Field ◽

Well Integrity ◽

Seismic Anomalies

Abstract The emerging global climate change policies have necessitated the strategic need for prudent management of produced contaminants and, with cold flaring being no more the best option, Carbon Capture Utilization & Storage (CCUS) technology provides opportunity for development of high CO2 contaminant fields. A typical CO2 sequestration project comprises capturing CO2 by separating from produced hydrocarbons followed by injection of CO2 into deep geological formations for long term storage. While injection ofCO2 may continue over tens of years, the long-term containment needs to be ascertained for thousands of years. Several geological and geophysical factors along with the existingwells need to be evaluated to assess the potential risks for CO2 leakage that maychallenge the long-term containment. This study considers a depleted carbonate field located offshore Sarawak as a possible long-term CO2 storage site. Elements that may lead to possible leakage of CO2over time are the existing faults or fractures, development of new fractures/faults during injection, caprock failure due to pressures exceeding fracture pressure during/after injection and possible leakage through existing wells. The risk assessment process includes identification and mapping of faults and fracture networks, mapping of seals, evaluation of seismic anomalies and gas while drilling records, pore-pressure analysis, laboratory experiments for analyzing changes in geomechanical & geochemical rock properties and well integrity of existing wells. All these parameters are cross correlated, and qualitative risk categorization is carried out to determine the robustness of the reservoir for long term CO2 storage. The evaluation of available data indicates less frequent faulting occur only towards the flank with no seismic anomalies associated with them. Some seismic anomalies are observed at shallower levels, however their impact on the reservoir and overburden integrity is assessed to be minimum. There are four shale dominated formations mapped in the overburden section, which will act as potential seals. Estimated fracture pressures for the potential seals ranges between 6200-9280 psia for the deepest seal to 2910-4290 psia for the shallowest. Therefore,it is interpreted that if the post injection reservoir pressure is kept below the initial reservoir pressure of 4480 psia, it would not hold any threat to the caprock integrity.Leakage rate riskalong the existing wells was determined based on well log data. Well integrity check of legacywells helped identify two abandoned wells for rigorous remediation to restore their integrity. The subsurface risk analysis is critical to ascertain the long-term containment of injectedCO2. The integrated subsurface characterization and well integrity analysis approach adopted in this work can be applied to any other field/reservoir to validate its robustness for long-term CO2 injection and storage.

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Modeling of Carbon Dioxide Leakage from Storage Aquifers

Fluids ◽

10.3390/fluids3040080 ◽

2018 ◽

Vol 3 (4) ◽

pp. 80 ◽

Cited By ~ 2

Author(s):

Parvaneh Heidari ◽

Hassan Hassanzadeh

Keyword(s):

Driving Forces ◽

Mechanistic Model ◽

Co2 Storage ◽

Transport Processes ◽

Saline Aquifers ◽

Storage Site ◽

Geological Storage ◽

Co2 Leakage ◽

Deep Saline Aquifers ◽

The Impact

Long-term geological storage of CO2 in deep saline aquifers offers the possibility of sustaining access to fossil fuels while reducing emissions. However, prior to implementation, associated risks of CO2 leakage need to be carefully addressed to ensure safety of storage. CO2 storage takes place by several trapping mechanisms that are active on different time scales. The injected CO2 may be trapped under an impermeable rock due to structural trapping. Over time, the contribution of capillary, solubility, and mineral trapping mechanisms come into play. Leaky faults and fractures provide pathways for CO2 to migrate upward toward shallower depths and reduce the effectiveness of storage. Therefore, understanding the transport processes and the impact of various forces such as viscous, capillary and gravity is necessary. In this study, a mechanistic model is developed to investigate the influence of the driving forces on CO2 migration through a water saturated leakage pathway. The developed numerical model is used to determine leakage characteristics for different rock formations from a potential CO2 storage site in central Alberta, Canada. The model allows for preliminary analysis of CO2 leakage and finds applications in screening and site selection for geological storage of CO2 in deep saline aquifers.

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Modeling of time-lapse seismic monitoring using CO2 leakage simulations for a model CO2 storage site with realistic geology: Application in assessment of early leak-detection capabilities

International Journal of Greenhouse Gas Control ◽

10.1016/j.ijggc.2018.06.011 ◽

2018 ◽

Vol 76 ◽

pp. 39-52 ◽

Cited By ~ 10

Author(s):

Zan Wang ◽

William P. Harbert ◽

Robert M. Dilmore ◽

Lianjie Huang

Keyword(s):

Co2 Storage ◽

Time Lapse ◽

Leak Detection ◽

Seismic Monitoring ◽

Storage Site ◽

Co2 Leakage ◽

Detection Capabilities

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Injection of a CO2-Reactive Solution for Wellbore Annulus Leakage Remediation

Minerals ◽

10.3390/min9100645 ◽

2019 ◽

Vol 9 (10) ◽

pp. 645 ◽

Cited By ~ 1

Author(s):

Laura Wasch ◽

Mariëlle Koenen

Keyword(s):

Large Scale ◽

Co2 Storage ◽

Leakage Rate ◽

Mitigation Measures ◽

Co2 Leakage ◽

Field Scale ◽

Mineral Precipitation ◽

Rock Interaction ◽

Wellbore Integrity ◽

Co2 Diffusion

Driven by concerns for safe storage of CO2, substantial effort has been directed on wellbore integrity simulations over the last decade. Since large scale demonstrations of CO2 storage are planned for the near-future, numerical tools predicting wellbore integrity at field scale are essential to capture the processes of potential leakage and assist in designing leakage mitigation measures. Following this need, we developed a field-scale wellbore model incorporating (1) a de-bonded interface between cement and rock, (2) buoyancy/pressure driven (microannulus) flow of brine and CO2, (3) CO2 diffusion and reactivity with cement and (4) chemical cement-rock interaction. The model is aimed at predicting leakage through the microannulus and specifically at assessing methods for CO2 leakage remediation. The simulations show that for a low enough initial leakage rate, CO2 leakage is self-limiting due to natural sealing of the microannulus by mineral precipitation. With a high leakage rate, CO2 leakage results in progressive cement leaching. In case of sustained leakage, a CO2 reactive solution can be injected in the microannulus to induce calcite precipitation and block the leak path. The simulations showed full clogging of the leak path and increased sealing with time after remediation, indicating the robustness of the leakage remediation by mineral precipitation.

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