Nov-2024

Enhancing decarbonisation through tracer technology

Tracer technology can be effectively employed across various types of CCUS projects, regardless of the chosen storage method.

Roy Greig
RESMAN Energy Technology

Article Summary

Carbon capture (CC), including carbon capture and storage (CCS) and carbon capture, utilisation, and storage (CCUS), is a cornerstone technology for advancing global energy transition objectives. It is critical for cutting emissions from conventional energy sources that are challenging to decarbonise, and it serves as a key strategy for tackling the dual goal of mitigating climate change while also maintaining energy security during the shift towards a low-carbon economy.

The energy sector is experiencing a new-found excitement for CC, reflecting a global shift towards understanding it as an essential rather than an optional strategy. Earlier doubts about its cost and efficacy are slowly fading, replaced by acknowledgement of its critical role, especially as electricity demand continues to soar.

Nonetheless, while CCS/CCUS is set to play a leading role in the energy transition, its success depends on scaling up its implementation. To meet the ambitious emission goals, CC capacity needs to increase more than 100-fold over the long term. Any setbacks in rolling out CC technologies could have a substantial effect on future emissions. Hence, the quest for effective CC solutions has never been more critical, and central to these efforts is the need for precise monitoring and verification of carbon dioxide (CO₂) storage.

Tracer technology for CO₂ monitoring and verification
Tracer technology is at the forefront of advancements in environmental monitoring, offering significant benefits for the decarbonisation agenda. A tracer is a specific identifiable substance that follows a transport process in a reservoir in a predictable manner without affecting the transport process or being affected by the process. Tracers cause no degradation, sorption to rock, known phase partitioning, or natural occurrence in reservoir fluids (see Figure 1)

Tracers are unique, non-naturally occurring substances introduced into storage reservoirs to allow tracking of CO₂ movement. They serve as distinct markers for tracking CO₂ as it moves through geological formations, acting as unique fingerprints for CO₂ leakage identification. They are inert, non-radioactive, and safe with low toxicity, providing high benefits at a low cost.

Tracer technology application in offshore and onshore carbon capture projects
There is currently an ongoing industry debate regarding CCUS – is it more advantageous to use offshore or onshore aquifers vs depleted reservoirs? Tracer technology offers a valuable solution to this debate, as it can be effectively employed across various types of CCUS projects, regardless of the chosen storage method. In this article, we discuss two projects where tracer technology was applied successfully in different types of reservoirs.

K12-B gas field
Tracer technology has been applied in the K12-B gas field on the Dutch continental shelf to advance our understanding of CO2 storage and migration. This allows us to better appreciate its role in optimising CCUS efforts and ensuring the long-term integrity of CO₂ storage.

Background
The K12-B gas field, situated about 150km (about 93.21 mi) northwest of Amsterdam in the Dutch North Sea, has been central to research on CO₂ injection and storage. The project aims to evaluate the feasibility of injecting and storing CO₂ in depleted natural gas fields on the Dutch continental shelf towards developing a permanent CO₂ injection facility. This mature field has been producing natural gas since 1987.

Traditionally, the CO₂ separated from this gas was vented into the atmosphere, but recent efforts have redirected it into the same reservoir from which it originated, at a depth of around 4,000 metres (about 2.49 mi).

The initiative at K12-B is part of the Dutch government’s CRUST project, which aims to evaluate the feasibility of CO₂ injection in depleted natural gas fields and assess the associated environmental and legal aspects. This project, subsidised by the Dutch Ministry of Economic Affairs and operated by Gaz de France Production Nederland B.V., represents a pioneering effort in offshore CO₂ storage.

Challenge
The integration of CO₂ storage into existing gas fields presents several challenges. There are inherent uncertainties surrounding the long-term behaviour of CO₂, the effectiveness of enhanced gas recovery (EGR), and the potential environmental impacts of such storage solutions. Specifically, the challenge lies in accurately assessing the behaviour of injected CO₂, understanding its migration pathways, and ensuring that it remains securely stored without unintended leakage.

In this depleted gas reservoir nearing the end of its life, the objective was to track the movement of CO₂ and enhance the understanding of the reservoir’s behaviour. The study revealed that CO₂ exhibited similar behaviour to methane in certain areas of the reservoir but diverged significantly in other regions. This discrepancy introduced uncertainties, even though this mature reservoir was well-understood.

Solution
During the analysis of CO₂ breakthrough, tracer data was used in conjunction with analogue equipment from the well. CO₂ was injected into the same field from which it originated, with the aim of enhancing gas recovery while the field remained in production. A CO₂ tracer was incorporated to optimise the injection scheme and successfully identify the breakthrough of ​re-injected CO₂.

The tracers served multiple purposes:
○ Tracking CO₂ migration: By following the path of the tracers, the movement of CO₂ through the reservoir could be accurately mapped. This included measuring the CO₂ injection rate, composition, and the physical interaction between injection and production wells.
○ Assessing reservoir behaviour: Tracer data helped evaluate the sweep efficiency of the injected CO₂ and the overall flow behaviour within the reservoir.
○ Ensuring well integrity: The tracers also provided insights into the condition of the CO₂ injection tubing and the quality of the cement bond in the injection well.

Results
The application of RESMAN’s tracer technology at K12-B yielded valuable insights into the CO₂ storage process. Tracers detected the CO₂ as soon as it broke through, whereas traditional gauges did not register any change for months. The analogue equipment, with its lower resolution, detected the breakthrough with a delay compared to the tracers. This immediate detection by tracers provided a much clearer and more timely resolution of the CO₂ movement, highlighting the superior sensitivity and effectiveness of tracer technology in monitoring such processes.