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, 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 all 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 ‘new’ greener energy resources and provides methods for safely storing them. It can elongate the life 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: thru-tubing or slimhole sidetracks, underbalanced drilling, high pressure wells which require specialist MPD/UBD, and remote operations.
The most commonly used BHA diameter for CTD is 3-1/8” with larger tools available with 5” OD and smaller tools available with 2-3/8” OD. The BHA sizes are limited to 5” or below due to the practical limits on the size of coiled tubing. The technique is most suited to smaller hole sizes such as 8-1/2” or below, with most wells drilled typically between 3-5/8” and 4-3/4”.
The benefits usually stem from re-entry drilling or shallow gas or 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 ‘cleanly’
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 as efficiently as possible.
Many are looking at developing new waves of technology to help with this process, but in order for new approaches to be adopted, cost-efficiency is absolutely crucial for success and more importantly crucial for the sustainability of the effort.
This is where CTD can make a major 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, of course is to ensure the planning is right. 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 which 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 can be located on very small pads so the pad size for each well should also be considered and permission to extend sought if required. A minimum pad size of 200ft x 300ft 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 mobilised, so that remedial cement jobs can be carried out if required. Ideally, casing pressure tests should also be carried out 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 finalised and the wells permitted.
So, with the right preparation you are securing the same productive gains as you would from a new well, 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 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 towards net-zero is cost. The ‘recycling’ of existing technology to revitalise existing wells means that multiple immediate costs are negated, helping companies to make an impact on the environment without having to make a huge 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 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.
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. Utilising existing technology such as CTD will allow organisations to have wells ready for hydrogen and carbon capture storage that will provide countries with the cleaner energy options and importantly a vital reserve securing their energy sovereignty.
Geothermal
Geothermal energy is being touted as one of the most advantageous sources of energy. It is environmentally friendly, present in many areas, is 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 burn fossil fuels means that geothermal energy which is potentially a key component to the journey towards net zero. The ability to create electricity with 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 large 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 well, even at the greater depth 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, 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 are realistic proposition.
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