Supporting the development of CO2 storage sites through technology-driven solutions

INGRID HULDAL and JAMES YARD, Expro 

Carbon capture and storage (CCS) is recognized as a pivotal process in the global transition towards reducing greenhouse gas emissions and achieving net zero targets by 2050. 

The International Energy Agency (IEA) notes that, despite the growing momentum for CCS, with over 500 projects in various stages worldwide, the current deployment rate is still significantly below what is needed to achieve net zero emissions by 2050. 

For companies with experience in the hydrocarbon sector, CCS presents opportunities across the entire value chain, but it also introduces a raft of new challenges and considerations. How can the industry move at the pace required to meet government targets? What are the technical gaps and how to close them? How will the supply chain manage the new demand? How can efficiencies be improved, and costs reduced? 

In focusing on CO₂ storage, there are obvious synergies with the oil and gas industry. The project lifecycle follows a similar path, starting with exploration and appraisal, moving into the field development phase, following with the operational period and concluding with abandonment and decommissioning. This process is well established in the oil and gas sector. 

Although CCS development has its specific nuances—such as governmental time pressures, extended operational periods and post-injection reservoir monitoring requirements—license holders and service companies are still responsible for executing operations and managing the field. Many practices within this cycle are directly transferable to CCS, but there are also new challenges that require unique technologies and alternative approaches. 

EXPLORATION AND APPRAISAL OF SALINE AQUIFERS 

Accurately appraising CO₂ storage reservoirs—particularly saline aquifers—is crucial for characterizing pore space in CCS projects. Saline aquifers hold the highest potential for CO₂ storage, but they are geologically under-characterized and require extensive evaluation to assess their effectiveness as CO₂ sinks. 

Currently, there are no standard approaches for appraising saline aquifers for CO₂ storage. Operators are evaluating different well testing methods, such as production testing, injection/fall-off testing, or a combination of both. Enhanced data acquisition is critical for understanding subsurface and reservoir properties. Greater clarity through comprehensive appraisal can help mitigate challenges, such as injection performance, enabling timely project delivery, and ensuring that injection rates stated at the outset of a campaign are achieved. 

Fig. 1 – The Northern Lights project, located in the Norwegian Sea

Northern Lights success. Regardless of the appraisal method, each reservoir requires a unique testing solution. For example, a leading provider of energy services, Expro, delivered an integrated well testing solution for the flagship Northern Lights (Fig. 1) project in the Norwegian North Sea, where test data provided critical contributions to the field development plan and final investment decision. 

A key challenge for the Northern Lights project was designing a well testing and Drill Stem Test (DST) system for an underpressured formation that would not flow naturally to surface and managing the produced fluids on the semisubmersible rig ahead of the injection test. As the integrated service provider, Expro designed a solution that included downhole/DST tools; fluid sampling and analysis apparatus; surface well testing equipment and subsea well access capabilities; incorporating design flexibility to account for evolving objectives and operational challenges as the project progressed. 

Expertise in traditional well testing and close collaboration with the operator and partners ensured all data-gathering objectives were met. Dynamic DST data—including near-wellbore formation and fluid identification, quantification of gas-in-water solution, information on heterogeneities confirming reservoir connectivity and flowing and injectivity data—supported the creation of geological, injection and storage simulation models for future operations. 

Following the successful project, the operator was able to formulate, confirm and submit its development plan on schedule for a parliamentary review, ultimately supporting a positive final investment decision (FID). 

Key products and technologies used in appraising aquifers include artificial lift systems to stimulate flow; advanced downhole and surface fluid sampling and analysis systems to evaluate reservoir fluids and flow properties; and wireless downhole gauges for reservoir data collection post-abandonment. 

WELL CONSTRUCTION FOR LONG-TERM INTEGRITY 

 The significance of long-term well integrity cannot be overstated. With the threat of accelerated corrosion, cold thermal cycling and increasing pressure over time, maintaining mechanical integrity in the completion, casings and cement is paramount. To combat the potentially acidic and corrosive downhole environments of carbon storage wells, corrosion-resistant alloy (CRA) tubulars are often installed. These must be handled and run carefully, as impressions, marks and cuts from make-up and handling can accelerate corrosion failures, which in turn may compromise the integrity of the wellbore. Expro has developed a line of non-marking tubular handling and running technologies that eliminate these risks and enhance the long-term integrity of CO₂ storage wells. 

The company’s Fluid Grip^® Tong and Collar Load Support (CLS^™) (Fig. 2) tools are designed to eliminate surface impressions. By avoiding front-end damage to the CRA tubing and casing, these tools help preserve the durability and reliability of these barriers during the injection period and long-term post-abandonment. This is critical for meeting the permanent storage objectives of these projects. 

Fig. 2 – Fluid Grip.

Other challenges during well construction include ensuring reliable cement jobs for casings and liners, as these form primary barriers. Modern stabbed-in inner string cementing technologies, such as Expro’s SeaCure^® system, provide optimal cement placement and support operational efficiencies, as well as solutions for circulating fluids into the annuls to further improve bonding. 

REPURPOSING DEPLETED OIL AND GAS FIELDS  

Reusing depleted fields for CO₂ storage may seem a logical solution and is being investigated in multiple projects worldwide. The key risk is the integrity of legacy wells in the field, as any issues could result in CO₂ migration and leakage outside of the confining zone, into the overburden and, in the most extreme cases, into the atmosphere. 

For legacy wells that are accessible, there are usually three options to consider: conversion to an injector well, conversion to a monitoring well or plug and abandonment. Whichever pathway is chosen, a rigorous assessment of the well’s integrity will be a pre-requisite. 

Traditional cased hole logging services—including cement bond logs, wall thickness tools, calipers and spectral noise logs—will be run as standard. However, new specialized well intervention systems exist to push the boundaries of what is possible. Expro delivers novel slickline-enabled distributed fibre optic sensing (DFOS), to provide distributed acoustic and temperature sensing (DAS and DTS) logs of the entire well in a single intervention.  

Combined with ultrasonic inspection tools that can see through multiple casings and cement, these technologies optimize solutions to maximize data collection and improve survey results. Additional solutions, such as Expro’s Octopoda™ annulus intervention system, manage sustained casing pressures and annular integrity issues. The company’s CoilHose™ hydraulic intervention system offers a lightweight alternative to coiled tubing for fluid displacement. These technologies provide alternative methods to fully evaluate wellbores and formations and remediate identified issues. 

LIFE OF FIELD SERVICES FOR CO₂ STORAGE 

There are inherent uncertainties with CO₂ injection that will not be fully understood until projects come online and injection rates are optimized. These include injectivity performance, phase changes, temperature profiles, corrosion, salt formation, thermal cycling and hydrate formation. Designing wells with contingencies in mind will be the key to successful delivery if plan A fails.  

Well intervention will be needed for routine logging, wellbore remediation, maintenance and emergency conditions, which requires systems to be qualified for CO₂ environments. Expro has initiated a study to this end, aiming to enable safe and reliable intervention services to enable projects to succeed. 

RESERVOIR MONITORING IN SUSPENDED OR ABANDONED WELLS 

Fig. 3 – CaTS EMX Wireless Monitoring System

Providing reservoir data from abandoned and suspended wells is a unique method for long-term monitoring. Challenges faced in CCS include CO₂ plume migration and pressure front tracking within the injection zone, leak detection, and monitoring behind the casing. Expro’s latest CaTS™ wireless downhole technology (Fig. 3) delivers extended battery life, greater data volumes, improved resolution, and simpler integration with other monitoring systems. In addition to its value during field appraisal, gauges can be installed in abandoned wells to convert them into high-value data assets, to continue data collection for many years into the future, supporting the overall Measurements, Monitoring and Verification (MMV) strategy. 

WELLS AND SURFACE FLOW MANAGEMENT TO ADVANCE CCUS  

Expro has 20 years of experience in supporting CCS projects globally, providing solutions across the well lifecycle in well construction, well flow management, well intervention and integrity and subsea well access. The company has supported multiple campaigns worldwide since 2004 and has notably been involved in Northern Lights (Norway) and Gorgon (Australia), Fig. 4. This experience has provided excellent learning opportunities and has helped identify key areas for future investment and technology development, particularly in well integrity and MMV. 

Fig. 4 – Gorgon Surface Flow Management

Expro is committed to fostering a low-carbon future through leveraging its technologies and expertise to reduce emissions and unlock new sources of cleaner, lower-carbon energy, ultimately playing its part as a true citizen of the world. Development of downhole sensing technologies, surface metering and integrity evaluation tools is already underway, with the objective of fast-tracked commercialization to provide new and alternative options for this critical sector. Expro continues to believe that through expanding its portfolio and delivering optimized solutions, the CCS sector will be a key enabler in supporting its own and clients’ net zero goals. 

INGRID HULDAL is a distinguished leader in the energy sector and currently holds the position of director of Sustainable Energy Solutions at Expro, which she joined in 2019. In her role, she is at the forefront of developing a dynamic portfolio offering and propelling the company's growth in line with the energy transition agenda.  She is currently pursuing an MBA in Sustainable Energy Futures at the University of Strathclyde. 

JAMES YARD is the CCUS Development manager for Expro and works in the Sustainable Energy Solutions department. He has 15 years of experience in the oil and gas industry, with expertise in downhole monitoring, wireless technologies and CCUS. He graduated from the University of Bristol with a master’s degree in geology.