Cross-section of rock formation with drilling mud and CO2 bubbles

Well Integrity Under Pressure: How CO2 Reactions Impact Mud-Affected Rocks

Soraya Malik in Climate & Environment December 2025 • 4 min read.

"A deep dive into how drilling fluids alter the porosity and stability of well barriers when exposed to CO2, crucial for safe carbon storage."

Leakage from CO2 storage reservoirs poses a significant threat to the success of Carbon Capture and Storage (CCS) initiatives. Abandoned or active wells are prime leakage pathways, emphasizing the need to maintain well integrity throughout their entire lifecycle. Understanding how CO2 interacts with well components like rock and cement is critical.

The reactivity of CO2 isn't straightforward. It's influenced by the presence of other fluids within the well. Drilling fluids, used during well construction, play a crucial role. These fluids can alter the properties of both rock and cement before CO2 exposure, creating a complex interaction that impacts long-term stability.

This article delves into how drilling fluids affect the way rock and cement respond to CO2 exposure. By examining samples with and without drilling fluid contamination before and after CO2 exposure, we'll uncover critical insights into porosity changes and their implications for well integrity and storage safety.

Drilling Mud's Impact on CO2-Rock Interactions: A Porosity Puzzle

Cross-section of rock formation with drilling mud and CO2 bubbles

To investigate the impact of drilling mud on CO2 reactivity, three rock types common in potential CO2 storage reservoirs were analyzed: Castlegate sandstone, Saltwash North sandstone, and Mons chalk. Cylindrical samples of each rock type were prepared, one kept pure as a reference and the other soaked in oil-based drilling mud (OBM) to simulate wellbore conditions.

In addition to the rock samples, cement samples were also prepared using Portland G oil-well cement, both pure and mixed with oil-based mud before hardening. All samples underwent detailed X-ray tomography characterization before and after exposure to CO2 under controlled conditions (13 bar, 66°C for 10 days) to assess changes in their porosity.

The study revealed key changes in porosity after CO2 exposure:

Saltwash North Sandstone: Porosity decreased at the edge and center of the sample.
Castlegate Sandstone: Porosity increased at the center but decreased at the edge.
Cement Sample with Mud: Showed a higher porosity than the pure cement sample.

These findings highlight that drilling fluids significantly alter how CO2 interacts with rock and cement. The presence of mud can either increase or decrease porosity depending on the rock type. Understanding these complex interactions is vital for predicting leakage risks and ensuring long-term CO2 storage safety.

Securing CO2 Storage: Why Understanding Mud-Rock Interactions is Key

This research underscores the importance of understanding how drilling mud affects the long-term integrity of CO2 storage wells. The study demonstrates that drilling fluids can significantly alter the reactivity of rocks and cement when exposed to CO2, leading to unpredictable changes in porosity.

The findings emphasize the need for careful consideration of mud removal techniques during well construction to minimize potential leakage pathways. Further research is needed to fully understand the chemical processes involved and to develop strategies for mitigating the risks associated with mud-affected well barriers.

By gaining a deeper understanding of these complex interactions, we can improve the safety and reliability of CO2 storage, paving the way for a more sustainable future. Further studies using chemical analysis could reveal which minerals are most affected by CO2 and mud.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1016/j.egypro.2017.03.1644, Alternate LINK

Title: Porosity Changes In Mud-Affected Rock And Cement Upon Reaction With Co2

Subject: General Medicine

Journal: Energy Procedia

Publisher: Elsevier BV

Authors: Ragnhild Skorpa, Jelena Todorovic, Malin Torsæter

Published: 2017-07-01

Everything You Need To Know

How do drilling fluids influence the behavior of rocks like Castlegate sandstone when exposed to CO2 in carbon storage wells?

When CO2 interacts with rock formations like Castlegate sandstone or Saltwash North sandstone, its reactivity isn't consistent. It's significantly influenced by the presence of drilling fluids used during well construction. These fluids alter the properties of the rock, causing varying porosity changes when exposed to CO2, ultimately impacting the well's long-term stability and potentially leading to CO2 leakage.

In what ways do oil-based drilling muds impact the porosity of different rock and cement types after exposure to CO2?

Drilling muds, specifically oil-based drilling mud (OBM), interact differently with various rock types when CO2 is introduced. For example, Saltwash North sandstone experienced a decrease in porosity, while Castlegate sandstone saw an increase at the center but a decrease at the edge. Cement samples mixed with oil-based mud also showed higher porosity than pure cement after CO2 exposure. These changes are vital to understand because they directly influence the effectiveness of CO2 storage and the potential for leakage pathways to develop.

Which rock types and wellbore materials were analyzed in the study, and what additional factors could be monitored to enhance the understanding of well barrier performance?

The study examined three rock types: Castlegate sandstone, Saltwash North sandstone, and Mons chalk, as well as Portland G oil-well cement, both pure and mixed with oil-based drilling mud. Samples were subjected to CO2 under controlled conditions, and X-ray tomography was used to assess porosity changes. Monitoring other factors like permeability and mineralogical changes before and after CO2 exposure would provide a more comprehensive understanding of well barrier performance.

Why is understanding CO2 and drilling fluid interactions vital for the success of Carbon Capture and Storage (CCS) projects?

Leakage poses significant risks to the success and safety of Carbon Capture and Storage (CCS) initiatives. Abandoned or active wells serve as potential leakage pathways, underscoring the need to maintain well integrity throughout their lifecycle. Understanding how CO2 interacts with well components like rock and cement, especially when drilling fluids are present, is crucial to preventing leaks and ensuring the long-term effectiveness of carbon storage.

What are the broader implications of this research on drilling mud and rock interactions for ensuring the long-term safety and effectiveness of CO2 storage?

This research highlights the critical need to understand how drilling muds affect the long-term integrity of CO2 storage wells. The findings demonstrate that drilling fluids can significantly alter the reactivity of rocks and cement when exposed to CO2, leading to unpredictable changes in porosity. This understanding is crucial for predicting leakage risks, designing better well completion strategies, and ensuring the long-term safety and effectiveness of CO2 storage projects. Further research into different drilling fluid types and their specific interactions with various geological formations is necessary to refine risk assessments and improve well integrity management.