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DRILLING WELLS FOR CARBON SEQUESTRATION IN SALT CAVERNS: A PROMISING APPROACH

The emphasis on environmentally responsible solutions in the oil and gas industry has surged in recent years. Salt caverns...


SALT CAVERNS: A SAFE ALTERNATIVE TO OILFIELD WASTE DISPOSAL

It is no secret that the drilling industry creates waste that requires proper disposal. Over the years, operators utilized different methods...

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Each basin presents its own unique drilling challenges. At Panther, we have the experience to manage them all. Learn more about how we do it. 

Steve Sonnier September 11, 2023

Drilling Wells for Carbon Sequestration in Salt Caverns: A Promising Approach

The emphasis on environmentally responsible solutions in the oil and gas industry has surged in recent years. Salt caverns, as previously discussed in our blog about their utility as a safe alternative for oilfield waste disposal, have emerged as a leading choice for underground storage. The Panther Companies, always at the forefront of innovative approaches, delves deeper into this subject, examining the feasibility of these caverns for carbon storage.

 

Drawing parallels with existing drilling techniques, we’ll explore how adapting these methods can lead to a sustainable carbon sequestration solution. Join us as we journey through the intricacies of salt drilling, solution mining, and its promising role in carbon storage, marrying our commitment to environmental preservation with cutting-edge engineering.


Carbon Storage: A Comparison with Current Salt Drilling


Historically, salt caverns have played a pivotal role in the storage of hydrocarbons like crude oil and natural gas. The process involves drilling a well into a salt formation and subsequently injecting water to dissolve the salt, thereby forging a massive underground cavern through solution mining. Depending on the specific salt formation, these caverns can span up to 1000 meters in depth and 100 meters in diameter.

 

Using this established drilling technique in salt formations as a reference, we can extrapolate its applicability to the promising realm of carbon sequestration. Still, certain nuances will likely need revisiting to safely and efficiently sequester carbon dioxide or CO2.

 

A groundbreaking initiative underscoring this potential is the pilot cavern for CO2 storage, set in motion offshore Brazil by the Research Center for Gas Innovation (RCGI). This center, a brainchild of Shell and the São Paulo Research Foundation, is headquartered at the esteemed Polytechnic School of the University of São Paulo. Their endeavor underscores the importance of ensuring that the CO2, once introduced, remains staunchly ensconced within the salt caverns.

 

Geotechnical engineering and intricate modeling will be paramount to deciphering the behavior of CO2 under the specialized conditions prevalent within these caverns. It’s equally imperative to confront challenges such as maintaining wellbore stability amidst supercritical CO2, understanding the physicochemical dynamics between the salt formation and CO2, and ensuring the cavern’s long-term structural integrity.


Drilling Salt Cavern Wells for Disposal: A Step-by-Step Process


Salt caverns, frequently used for crude oil storage, offer a compelling solution for underground disposal needs. Their formation process can be briefly outlined as follows:

  • Step 1. Solution Mining Initiation: A well is drilled into a salt dome formation.
  • Step 2. Water Injection: Massive volumes of fresh water are injected into the drilled well, dissolving the salt within.
  • Step 3. Brine Removal: As salt dissolves, it forms a brine which is then either transferred to disposal wells or channeled offshore, for example, into the Gulf of Mexico, ensuring environmental safety.
  • Step 4. Precision Control: The freshwater injection is carefully monitored, allowing for the creation of salt caverns with highly accurate dimensions. Notably, about seven barrels of raw water are required to create storage space for a single barrel of crude oil.


This method is not only cost-effective for long-term storage but is also environmentally secure due to rock salt’s unique properties, according to the U.S. Department of Energy. With low porosity, limited permeability, and self-healing attributes, rock salt ensures the cavern’s stability, sealing any microcracks that may emerge.

While this technique has been proven effective for oil storage like the Strategic Petroleum Reserve (SPR), its potential in carbon sequestration is an exciting avenue worth exploring, marrying environmental responsibility with innovative engineering.


Drilling Fluids: A Choice between WBM and OBM


Selecting the right drilling fluid, or “drilling mud,” is crucial in drilling operations. These fluids are essential for cooling and lubricating the drill bit, transporting cuttings to the surface, and stabilizing pressure in the well.

When drilling through salt formations, comprehensive strategies are developed by mud and drilling engineers. These strategies aim to prevent washouts during the drilling process within the salt formations. Three key components of these strategies are density, salinity, and rheology.

In salt formations, the choice arises between the environmentally friendly water-based mud (WBM) and the robust invert emulsion fluids, commonly referred to as oil-based mud (OBM). The decision depends on specific project requirements.

      WBM

In the realm of drilling, both deepwater and coastal onshore settings present unique challenges, especially when dealing with diapiric salt formations, a hallmark of salt structures earmarked by the SPR for oil storage. In offshore contexts, riserless pump and dump methods are often the go-to method, allowing for the drilling fluid to be replaced with the production zone fluid post the salt drilling phase. For the coastal onshore, techniques for drilling these salt structures can differ. These onshore methods generally parallel their offshore counterparts, but notably exclude the pump and dump approach.

WBMs, recognized for their environmental benefits, are a popular choice in top-hole drilling, both in offshore settings and around coastal diapiric structures. However, it’s essential to understand that these techniques, while commonly practiced, might vary depending on factors such as depth, local geology, and environmental regulations. The precise method adopted is tailored to the specific requirements and conditions of each drilling operation.

      OBM

In addressing the drilling of deeper salt formations, multiple regions come to mind, highlighting the diverse applications of OBM. One example is the regional

Prairie Salt formation in North Dakota, which forms a seal above certain portions of the Bakken shale. A similar preference for OBM is evident in the Gulf of Mexico, particularly in areas characterized by thick salt canopies. Here, the selection of OBM is driven by its effectiveness in maintaining borehole stability and its thermal stability. In both scenarios, once the drilling penetrates the salt layers, there’s a transition to the production zone fluid. Such strategic choices underline the adaptability of drilling techniques based on regional geology and project demands.

Given these considerations, the selection between WBM and OBM is determined by the unique requirements of each drilling operation, with an emphasis on performance, safety, and environmental considerations.

Constructing Salt Cavern Wells: Complying with Regulatory Standards

Drilling wells for conversion into salt caverns, especially for disposal, demands meticulous adherence to well construction standards. Here’s a breakdown of the key phases, ensuring the integrity, safety, and environmental protection:

  • Casing and Cementing: Essential for all salt cavern disposal wells, casings that reach the surface must be cemented to avert any fluid transfer to drinking water resources or freshwater reservoirs.
  • Injection Tubings: Injection tasks, barring the circulation of drilling fluids during construction, mandate the use of two concentric and removable tubings, which originate from the wellhead.
  • Well Annulus System Considerations: Every component of the well’s annulus system, including its outer tubing and packer, demands a regulatory permit or written approval from the executive director of the state’s environmental office. This ensures alterations to the original plan retain or surpass the safety standards set forth.
  • Logs and Tests: Comprehensive logs and evaluations are paramount during the drilling and edification phases. This suite of analyses, which covers geophysical logging, pressure testing, coring, and integrity validation, mandates expert interpretation.

By understanding and implementing these meticulous regulations, the potential of drilling salt wells for carbon sequestration could be realized while ensuring the utmost safety and minimal environmental impact.

Bringing It All Together: Salt Caverns and the Future of Carbon Sequestration

In the quest to offset carbon emissions, salt caverns hold immense promise for carbon sequestration, marrying innovation with geology’s gifts. Let’s recap:

  • Potential: Salt caverns, with their unique characteristics, offer high storage capacity, natural sealing, enhanced injectivity, and retrieval flexibility, emerging as a powerful solution for carbon storage.
  • Significance: With every successful drilling operation, we move a step closer to capturing and storing substantial amounts of carbon emissions. This process is crucial in mitigating the impact of carbon dioxide in our atmosphere, effectively helping to reduce our carbon footprint.
  • Efficiency: The Panther Companies’ fluid management system stands as a testament to efficiency and sustainability in salt drilling operations.
  • Future: Unprecedented developments and research opportunities in salt cavern carbon sequestration technology await us.

The future of the oil and gas industry hinges on solutions like these. Interested in learning more? Download The Panther Companies flyer for a deeper dive into our services and offerings.

Steve Sonnier

EVP of Operations

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