The precipitation of acid-resistant carbonate minerals through chemical interaction between injected fluids and leaking CO2 can act as an effective sealant for remediating CO2 leakage through faults and fractures in geological CO2 storage reservoirs. Magnesite is one of the most stable carbonate phases that can contribute to addressing the challenge of long-term plugging of CO2 leakage and the chemical mechanism that can catalyse its formation is of great interest and practical significance. This research provides new insights into the mechanism and kinetics of magnesite formation at mineral/fluid interfaces in a range of conditions and can help facilitate defining strategies to mitigate risks involved with underground CO2 leakage.
WP5 Impact mitigation and remediation
Outputs
D5.8 Report on kinetics of enhanced cementation reactions for CO2 leakage remediation and fault-healing processes
D5.7 Recommendations on how to minimise damage to cement sheath and surrounding rock during hydraulic fracturing and CO2 injection
This report considers three related aspects: firstly, we develop a field-scale model incorporating a well section with perforations, from which hydraulic fracture initiation is simulated. Secondly, we report on hydrate-related work that has a focus on first assessing the conditions favouring hydrate formation, rather than considering potential mechanical damage to the cement sheath during CO2 injection. The final part of this report describes experimental work on geochemical remediation through engineered precipitation.
D5.6 A physics-informed constrained optimisation workflow: maximising injection while constraining induced seismicity at Oklahoma waste-water injection sites
In this report, models and modelling strategies are calibrated by looking at waste-water injection events in Oklahoma, USA, which led to a surge of induced seismicity. The modelling strategy can be applied to any other site and activity in the subsurface and should be seen as a good practice to maximise injection while minimising induced seismicity. Multiple injection scenarios are tested, leading to the identification of an optimum theoretical scenario. The report shows that such a scenario would have prevented the rapid growth of the seismicity rate in 2015 in Oklahoma.
D5.5 Report on the small-scale processes occurring during engineered precipitation and models to assist in the upscaling
This report presents laboratory and modelling results pertaining to formulation and testing of new remediation fluids and upscaling fracture networks to field conditions. The remediation chemistries are designed to react with or withstand exposure to leaking CO2. Modelling presented in the report uses an advanced fracture simulator to recreate the fractures observed in well cement and surrounding sandstone and can be used to predict where to place remediation fluids, in case of detected leakage events.
D5.4 Guideline on ranking of various squeeze sealant materials with respect to ease of placement
Remediation fluids need to fill fractured cement and rock around wells. The challenge in designing such fluids lies in having them flow easily to penetrate fractures but then harden in situ into a solid mass. Fracture opening at depth is usually not large under high earth stresses, meaning that thick formulations may end up propagating the crack or creating new ones. In this deliverable we present a methodology to evaluate the performance of several simple fluids used for remediation in the laboratory. We show that, under field-like conditions and geometry, fluids performing satisfactorily in bench-top evaluation have a difficult time fulfilling their purpose.
D5.3 Report on remediation strategies for tubings and casings
This report addresses several potential casing and tubing failure mechanisms in CO2 and shale gas wells, and will describe remediation strategies to maintain well integrity. The objectives of this report are to:
- describe the most common well-barrier envelopes used for CO2 and shale gas wells, based on the NORDSOK STANDARD D-010 concerning well integrity
- review different casing and tubing failure mechanisms. The different mechanisms considered in the report during hydraulic fracturing in unconventional oil and gas operations:
- abrasion
- corrosion
- mechanical loads
- review different remediation methods and technologies for failure of tubing and casing
- outline planned laboratory testing to investigate tubing mechanical strength after remediation by cement squeeze: this activity will complement similar tests investigating cement fracturing and remediation, outlined in deliverable D5.1
D5.2 Report on experiment-based knowledge on acoustic emission characteristics of CCS and shale gas operations and suggestions on how to mitigate seismicity for both
This report reviews acoustic emission (AE) laboratory tests designed to investigate mechanisms by which microseismicity arises in CCS and shale gas operations. The differences between the two subsurface operations are reviewed, in terms of the stress path leading to rock failure and acoustic emission.
D5.1 Report on remediation strategies for tubings and cement sheaths
Well integrity is a relevant topic to the oil and gas industry and is equally important for CO2 storage projects. This report describes the well-barrier approach to well integrity using the NORSOK D-010 standard, reviews possible leakage scenarios for CO2 wells and uses the same approach to address possible leakage scenarios from shale gas wells. Remediation strategies and technologies that can be applied to failure of tubing, casing and cement sheath are reviewed, including:
- squeeze cementing
- alternative sealing materials
- casing and tubing repair
Finally, the novel aspects of this work related to leakage remediation and alternative sealing materials are discussed, along with the experimental plan for the combined tasks in WP2 on risk assessment strategies and WP5 related to leakage remediation and testing of alternative sealants.
The potential environmental impacts of geoenergy projects are always a consideration. These impacts relate to leakage from wells including CO2 and methane (CH4), naturally occurring permeable pathways or the potential for induced seismicity.
We will make use of a network of commercial, pilot and research-scale sites both in Europe and internationally in order to demonstrate best practice and investigate new methods for predicting, avoiding or reversing environmental impacts.
Our research will be underpinned by laboratory measurements, which will be used to model field-scale scenarios. We will look at pipeline integrity and resilience and ways to minimise damage to wells and rock, as part of geoenergy operations. The use of sealants and other remediation strategies will also be considered.