March 2024
SPECIAL FOCUS: Sustainability

Coiled tubing drilling’s role in the energy transition

Coiled tubing drilling is an excellent example of how existing technology can help move the oil and gas sector towards net zero.
Toni Miszewski / AnTech Ltd.

The energy transition is something that continues to dominate not just our sector, but much of wider society, too. It has moved into everyday life and mainstream media and can influence political and voting decisions. The COP28 conference has further pulled it into the mainstream.  

Although some of the headlines about the hosts and the effectiveness of the agreements made at the conference were not necessarily all positive, it did ensure that that the focus of the world was very much on the sector and efforts being made to move it towards a greener future. With businesses and governments around the world looking to ensure that they and their supply chains are as green as possible, finding ways to use existing technology to help that happen will be critical. 

Coiled tubing drilling (CTD) can provide the technology to allow many to move along the road towards net zero. It provides a solution to gain access to key greener energy resources and provides methods for safely storing them. It can elongate the lives of depleted wells and provide controls that allow the safe management of often difficult to control energy resources. It can achieve all of this with acceptable levels of investment, especially when compared to locating and drilling new sites. 

Why use coiled tubing drilling? The reasons for using CTD vary, depending on the application, but the main reasons are: 1) thru-tubing or slimhole sidetracks; 2) underbalanced drilling; 3) high-pressure wells that require specialist MPD/UBD; and 4) remote operations. The most commonly used BHA diameter for CTD is 3 1/8-in., with larger tools available with 5-in. OD and smaller tools available with 2 3/8-in. OD. The BHA sizes are limited to 5-in. or below, due to the practical limits on the size of coiled tubing. The technique is most suited to smaller hole sizes, such as 8½-in. or below, with most wells drilled typically between 3 5/8-in. and 4¾-in. The benefits usually stem from re-entry drilling or shallow gas and oil wells. An alternative way to think about CTD is that it is a reservoir drilling technology, so the closer to the reservoir, the more advantageous CTD will be.  

Producing, transporting and storing hydrocarbons with less emissions. One of the key factors in the energy transition is for the oil and gas sector to find ways to ensure that hydrocarbons are produced, transported, stored and used as cleanly and efficiently as possible. Many are looking at developing new waves of technology to help with this process, but for new approaches to be adopted, cost-efficiency is crucial for success and, more importantly, crucial for sustainability of the effort. 

Coiled tubing drilling’s contribution. Extracting the last drops from existing assets by re-entering and drilling laterals in existing wells is a prudent and economically advantageous strategy. This approach, rather than drilling a new well, does not mean that you are getting less productive gains either; in fact, they are very comparable. The key to success is to ensure the planning is accurate. The following is an example planning process, based on a mature field when the original reservoir has been depleted. 

In this scenario, the operator may choose to sidetrack, to access areas of virgin pressure away from the existing wellbores or can access other productive formations that are behind pipe. The formations between the casing exit and the reservoir need to be well-understood. If there are particular zones that are troublesome, then now is the time to assess whether the kickoff point can be lowered to avoid the zone, or if operational controls will need to be in place in the drilling program.  

The expected drilling fluids system should also be assessed at this stage, as it defines the equipment requirements and has a significant impact on the well budget (more on this later). This is also the time to evaluate the completion requirements with a particular focus on zonal isolation. For example, are there zones above that need to be isolated from the reservoir and, if so, can they be isolated with a swellable packer or is cementing required? Each consideration has a knock-on impact into the suitability of using CTD in either a managed pressure or underbalanced set-up.  

Once this initial planning is done, ensuring that the existing wells are suitable for sidetracking is the next key step. These wells need to be screened for integrity, current oil and gas production, location, casing/tubing size, and ability to reach directional targets. Once the initial list of wells has been created, then the available logs for each of the donor wells should be reviewed.  

Some older wells are situated on very small pads, so the pad size for each well should also be considered, and permission to extend needs to be sought, if required. A minimum pad size of 200 ft x 300 ft is desirable, but there is some flexibility, depending on the equipment to be used. In some cases, it may simply be that the pad has not been maintained to its boundaries, but the rights are in place and, therefore, it just needs to be prepared for the operation. 

The casing and cement integrity are both critical for successful operations. If a cement evaluation log is not available, then it should be planned to be carried out well before the CTD spread is to be mobilized, so that remedial cement jobs can be carried out if required. Ideally, casing pressure tests should also be conducted at this time, to verify the integrity of the casing where the exit will be. Once the donor wells have been selected, the trajectories can be finalized, and the wells permitted.  

CTD reduces NPT/waste. So, with the right preparation, you are securing the same productive gains as you would from a new well, and you also can quickly set up with minimal waste. There is very little site prep needed. No mass transportation of large amounts of new equipment is required, and so even at the first step, some energy savings have been made. The use of CTD also has an impact on the work environment, reducing noise levels, exhaust emissions and drilling waste. Although these are relatively small contributions to the energy transition, they are important and clearly show an advantage over the drilling of new sites. 

Cost. One of the major barriers facing those moving toward net-zero is cost. The recycling of existing technology to revitalize existing wells means that multiple immediate costs are negated, helping companies to make an impact on the environment without having to make a significant investment. CTD also has other economic advantages that can encourage companies to move forward with such an environmentally friendly approach. Advantages include: 

  • Low mobilization 
  • Ability to deal with lost circulation 
  • Tripping speed 
  • Minimum time from decision to new barrels 
  • Hybrid overbalanced/underbalanced. 

Such economic factors can make a real difference to decision-making, when it comes to the implementation of CTD. If one can prove the prominence of environmental factors alongside financial ones, there should be few barriers left. 

CTD influencing cleaner energy. CTD can make a real difference in areas that are crucial for the use of cleaner energy. CTD technology can be used for drilling wells for hydrogen (Fig. 1) and carbon capture storage (Fig.2), both crucial elements in the energy transition. The Royal Society released a report last year that stated that unless the UK government kick-starts the construction of large-scale hydrogen storage facilities immediately, it will not be able to meet legally binding net zero targets by 2050. It also stated that although an electricity system with significant wind and solar contributions offers the lowest-cost electricity, it will be crucial to have large-scale energy stores that can be accessed quickly, which will help to ensure energy security and sovereignty. 

Fig. 1. Hydrogen storage process.
Fig. 2. Carbon capture storage process.

All of this points to the hydrogen and carbon capture storage wells being absolutely critical for a move towards energy transition over the coming years. Utilizing existing technology, such as CTD, will allow organizations to have wells ready for hydrogen and carbon capture storage that will provide countries with cleaner energy options and, importantly, a vital reserve securing their energy sovereignty. 

Geothermal applications. Geothermal energy is being touted as one of the most advantageous sources of energy. It is environmentally friendly, present in many areas, not weather-dependent (unlike wind and wave), and can outperform even some of the more conventional sources of energy in many aspects. Extracted from the earth without having to burn fossil fuels means that geothermal energy is potentially a key component for the journey towards net zero. The ability to create electricity by having to rely on fossil fuels, does however, come with some challenges. 

The nature of the high temperatures needed to produce electricity from geothermal sources makes this an incredibly difficult and expensive task.  Finding new, deeper areas for geothermal sources adds to the technical and financial implications. The deeper geothermal resources are often found in harder geologic formations, certainly when compared to conventional hydrocarbon reservoirs. 

A substantial percentage of project costs can be spent at the exploration and drilling stages, making it less easy to justify. However, CTD can take the cost and risk away from the drilling of geothermal wells, even at greater depths and more challenging geologic formations. As CTD enables you to drill faster and bring the well on to production in a shorter period of time, you are immediately reducing cost and time to ROI.  

One of the main issues associated with geothermal drilling is lost circulation. This causes delays and drives up drilling costs. Lost circulation sees a total or partial loss of drilling fluids or cement in high-permeability zones, and natural or induced fractures. The high temperatures associated with geothermal wells also create challenges for maintaining drilling fluids. Despite lost circulation being widely studied and discussed, it remains a barrier for some. However, again, CTD can help. As CTD allows for easy control of pressures, it reduces the chances of lost circulation, helping save time and money, making the establishment of geothermal wells a realistic proposition. 

Collaboration, not competition. CTD can help the energy transition in several ways, including sidetracking from existing wells, without the need to drill for new resources. It can help with the storage of carbon and hydrogen after capture, as well as producing geothermal wells, negating many of the risks associated with this route to what many consider the cleanest route to net zero. 

However, the key to long-term success of the energy transition is that the wheel does not need to be reinvented here. CTD is just one proof point highlighting the fact that much of the needed tech is already in existence within the sector. There does not need to be a wholesale, mass, new investment to find cleaner tech to move towards net zero.  

Instead, the industry needs to look at existing technology, such as CTD, and “recycling,” utilizing the innovative design to move towards net zero. Dismissing technology already used within the oil and gas sector, because it is assumed it can only be used in relation to fossil fuels, is naïve and will, frankly, slow down the journey to net zero. Not taking into account existing technology, such as CTD, also makes it prohibitively expensive for many to consider looking at options that include carbon capture storage or geothermal wells.  

Another factor that has to be taken into account is if the energy transition is to be successful, then collaboration, not competition, holds the key to progress. Groups that largely want the same end result seem to be on opposite sides, instead of working together towards net zero. They are pulling apart, making the journey longer, more expensive and at worst, impossible. 

There has to be acknowledgement that moving towards net zero is a good thing for the planet. At the same time, a similar acknowledgement needs to be made that if the world is to hit the carbon reduction targets by 2050, then oil and gas will need to remain part of the energy mix, just at 20% of their current levels. There can be no solution where one approach is turned off and another turned on—overlap is critical, if the energy transition is to be a success.  

Through collaboration, accepting oil and gas will remain a critical role in a net zero world. By ensuring that we look at existing technology in the oil and gas sector to help with the transition, there can be a real move towards a greener future. 

About the Authors
Toni Miszewski
AnTech Ltd.
Toni Miszewski is founder and managing director at AnTech Ltd, where he has led the company’s entry in the underbalanced coiled tubing drilling market. Before founding AnTech, he worked for Schlumberger, both in the field and in engineering development. Mr. Miszewski has a BS degree in mechanical engineering from Imperial College, London, and holds several patents for downhole technology.
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