By utilizing an innovative cementless technology, Total were able to reduce risk and increase operational efficiency for their Moho North field in The Congo.
The cementing process that isolates the various down hole formation zones as well as firmly fixing the casing in place has been core to the completion process since it was first used over a century ago. Despite its maturation as a completing technology is still presents a myriad of challenges to operators which has led them to seek new and better ways for zonal isolations.
During the drilling process, you will have to do several tests to make sure that you have correct pressure and a nonleaking well. Cementing is central to the discussion of zonal isolation and well integrity because cement typically provides at least one barrier in a well and is a component of the barrier envelope or barrier system during well construction and the operational phases of the well.
Three cementing challenges in deepwater
Part of the process of preparing a well for further drilling, production or abandonment, cementing a well is the procedure of developing and pumping cement into place in a wellbore. Most commonly, cementing is used to permanently shut off water penetration into the well. Part of the completion process of a prospective production well, cementing can be used to seal the annulus after a casing string has been run in a wellbore.
Additionally, cementing is used to seal a lost circulation zone, or an area where there is a reduction or absence of flow within the well. In directional drilling, cementing is used to plug an existing well, in order to run a directional well from that point.
Also, cementing is used to plug a well to abandon it. Deepwater is one of the most challenging cementing locations where operators face a triumvirate of challenges including low temperatures, low fracture gradient and shallow flow hazards.
A new way
That all changed last year when it was announced that Total had successfully utilized an innovative cementless completion technology in the Moho North Albian field that they had developed in partnership with Welltec.
The technology was Welltec Annular Isolation (WAI). Moho Nord is a deep offshore oil project situated 75 kilometers off the Congolese coast. It came on stream in March 2017 and is the largest oil project ever undertaken in the Republic of the Congo. The field will produce untapped reserves in the Moho-Bilondo license block, which covers an area of 320 kilometers and four reservoirs situated at water depths of 750 to 1,200 metres.
Given the challenges that cementing presents to operators they have long been searching for an alternative completion method that both reduces risk and saves operation expense. By using an innovative cementless technology it is possible for an operator to save up to $75 to $100m over a 15 to 20 wells deepwater field development plan can be achieved.
This solution is equally as viable for onshore and shallow offshore markets. Approaching it from a larger scale makes the value proposition more obvious. “We like to think that we work on solutions that are best for the well and the overall project,” Gbenga Onadeko, Senior Vice President, Welltec Africa, says.
“In most cases, our industry is integral to the economies of the oil and gas producing countries. We therefore believe that we are having a positive impact on the overall wealth of the nations we operate in.
“Total initially selected a cemented and perforated liner solution, the liner length was short and deep, implying the volume of cement was relatively small, which increases the operational risk of cementing the reservoir section.
Because of the potential of cement contamination and also to increase the success rate of placing it behind the liner, the volume of cement pumped was increased by enlarging the hole (under-reaming) and drilling deeper i.e. a longer rat hole section, which placed the toe of the well within less preferential sections of the formation increasing the drilling and production risks.
“With the liner deployed and cement in place, the WAB is expanded quickly under full surface control sealing against the formation rock, displacing the cement, providing a high integrity pressure isolation between zones. This in turn ensures that even if channels or micro-annulus are present in the cemented interval, effective isolation is still achieved within the annulus.”
The long road to adoption
Even under the long-term depressed state of the price of oil that has necessitated a drive to greatly improve operational efficiency the oil and gas sector is still risk averse when it comes to adopting innovative techniques.
The deployment of this project started four years ago when the Total team arrived in the Congo to prepare for the deployment. “Initially the Total team was not ready for a full cementless solution, so they used one of our products, which is called the WAB, in the wells in addition to the traditional cement,” Onadeko says.
“Normally, the WABs can be used without cement to isolate several sections of the well,but in this case, because they had some technical issues, they decided to go with the WABs for their isolation propertiesin addition to cement.
“For most of the wells on this project, we had already deployed the WABs. But then towards the end of 2017 amidst the height of the industry downturn when the sector was really feeling the low cost per barrel, Total realised that this project was costing far too much.
It had been sanctioned when the price of oil was much higher, and they urgently needed to cut costs, which provided us an opportunity to utilise this technology with its associated cost saving. In December 17 they invited all the service companies that had a contract with them on this project, to come and discuss how they could slash the well drilling costs by half.”
Another reason that Total had confidence to proceed with the cementless WAI solution came about by chance. “On one of the WAB operationsthey put it in a long zone and accidentally put it into a well section thereby shutting off the hydrocarbon instead of water,” Onadeko explains.
“Then they had to shoot some explosives into that hole to perforate it and the WAB was robust enough to withstand the shock; it did not impair their production. So that was another reason why they could go ahead and use the cementless solution, knowing now that they can perforate through and get a diversion.
“We develop cutting edge technologies and work extremely hard to convince our clients to deploy the value adding solutions. One of values we add to the industry is to assist our clients in overcoming their initial reluctance. We want to ensure that these technologies are included in their field development plans to avoid paying premiums later due to rush mobilizations. Including the technologies in their initial plans reduces the risk of budget variation.”
The WAB and the WAI
The WAI provides long length open hole zonal isolation, significantly reducing the free annulus space between the casing and the open hole. The removal of this annular space can be beneficial in highly layered reservoirs of varying permeability, where selective production, stimulation or water shut off is required.
Its metal expandable sleeve is hydraulically expanded, under full surface control using the rig pumps. Sealing on the open hole is achieved using a series of compliant, elastomeric seals, backed up by full circumferential metal to rock contact fins that prevent seal extrusion under high differential pressure.
While the WAI is suited to zonal isolation, the WAB for well completions can be utilised to provide solutions to many requirements throughout the completion phase of a well. Its leak rate capability, when set in cased hole, makes it ideal as a high-pressure production packer for both high pressure gas and oil well applications.
In addition to this it can rotate and reciprocate during installation and cementing operations, and then expand and seal, on demand. In horizontal applications this allows the WAB to be incorporated as a Rapid Set Liner Hanger, reducing both risk and complexity in these often-challenging applications.
“The WAB gives us a zone of isolation,” Onadeko adds. “What we mean by that is you have a seal between a liner and reservoir and then you have a distance between that packer and the well.
So, you have like an open anulus between these two packers for zonal isolation purposes. What the WAB gives you is seal integrity between the liner and the rock. Once you have established your seal then you are able to simulate, inject or produce into a certain zone.”
When cementing fails
The main competition to this technology has been cement, where liners are cemented in a well. The challenges are where the trajectories and the geometry of the wells become more difficult.
In these instances, it becomes very challenging to assure the seal when using cement, despite that the bulk of wells today are completed with cement. But because cement does not always deliver the optimum seal between the liner and the anulus it makes it very difficult to compartmentalize your well.
“What the WAI gives you is cement replacement,” Onadeko continues. “Instead of leaving either cement between the packers or an open anulus, then the WAI fills the anulus with confined compartments; each WAI will be a compartment that’s isolated from the next compartment. We have no open anulus, we have no cement, but the whole of the anulus is now compartmentalized.
With that achieved, you can then decide if you want to leave that compartment isolated, or whether you want to perforate it, stimulate it or produce it or inject into it. The WAI breaks down your reservoir into two metre compartments. And then you’ve got control over each two metre compartments. And each department has high integrity in relation to sealing.”
There are several things to consider when removing cement from the completion process. Cement has three functions that it is trying to achieve for the well. The first as we have already discussed is to provide sealing which is not always possible as the well geometry becomes more challenging.
For the Moho project Total had a tremendous challenge in ensuring the cement was going to seal. The second function of cement is to provide an anchor between the liner and the rock. Finally cement also supports the rock formations. If the formation is unconsolidated it provides a support to the rock to make sure it does not cave onto the liner.
“When we remove the cement, we need to be sure that we’ve addressed all three, the sealing, the anchoring and support of the rock,” Onadeko explains. “The WAB delivers two of those; it gives you the anchoring or sealing, but across the open anulus you are dependent on the rock having some sufficient mechanical properties that it won’t start to fall in onto the liner.
Where the WAI will give you the sealing and the anchoring, it also gives you this mechanical support to the rock. So, WAI is really cement replacement in its full entirety, without the risk of the challenges presented by the geometry.”
