Zonal isolation: In any well, in any type of reservoir

The WAB® is designed to address a number of the industry’s biggest challenges. Besides being a primary barrier, as discussed in the first part of the interview, the WAB also allows operators to establish zonal isolation with inflow control, as it facilitates cement assurance. Johnny Bårdsen, a specialist in completion technology, explains how operators can benefit from this latest innovation within completion technology and gain significant time-savings and increased production.

The WAB serves several purposes. What can operators gain by applying WAB’s for zonal isolation?

It’s in the word. Operators can gain reliable zonal isolation that will be engineered to the whole solution. It’s simply about splitting the reservoir into compartments. And this can be done with very high ΔP capability that allows you to accommodate a wide range of fluid types, which other products cannot.

For example, if you plan to perform an acid stimulation job, you will need to be able to handle the high ΔPassociated with the high pressure injection down the annulus as well as the exposure to the acid itself. The developed solution would then be engineered for the injection phase, but also, it needs to be capable of functioning for the life of the well during the operational phase.

This means maintaining the zonal isolation, as well as the compartmentalization, when the pressure of the reservoir is now higher than that in the annulus. The WAB’s can deliver this solution. This now gives the operator access to a much larger footprint of a well’s reservoir exposure when drilling and completing a well.

In addition, completing a well by setting WAB’s and WFV’s (well flow valves) in the open hole provides tremendous time savings versus a double skin completion or a single skin with cement and perforations.

 

Today’s wells need zonal isolation

We will get back to the topic of inflow control in a second. But first, can zonal isolation be established in any well or are there limitations?

In general, you can establish zonal isolation in any well and in any different kind of reservoir. And a lot of the world is now going for the so-called ‘hard oil’, where you more or less need zonal isolation on every single well.

The effectiveness of the solution will depend on the homogeneity of the reservoir though. With high homogeneity of the reservoir you typically have the same pore pressure, production porosity and permeability across the reservoir. In such cases, you can support and guide the production flow to a very great extent. Also, you can potentially isolate if you have water or gas coning, allowing you to optimize and extend the production over a longer time.

If you have low homogeneity of the reservoir it will impact the overall production, but in practice, having controllable ‘compartments’ allows the operator to mitigate his risks by allowing control of discrete portions of the well. Heel toe effects can be minimized and excessive water production or undesired gas breakthroughs can be shut-off. So yes, in general, zonal isolation makes sense and can be used in every type of reservoir and in the vast majority of wells. It’s a matter of engineering the right solutions for their well.

 

Full control of flow

Inflow control is a distinctive part of zonal isolation. Why is inflow control needed?

Inflow control is about being able to control your zonal production. There’s no point in creating a zone if you cannot control the flow from that zone. That’s why you have the well flow valve available, which you can position in the zone with a given production flow area through the valve.

Within a zone there can be one valve or a vast number of valves, depending on the flow rate desired. But what it gives you is the ability to control your flow area, which means you can either chose to hold back on production in a specific zone or not. If needed, you can actually close in that zone completely and maintain another one so that you can actively drain your different compartments.

And off course, the flow valves will always be designed for the application in question, giving the client optimal conditions for zonal isolation and increased recovery.

 

Mechanical foundation when cement is required

That WAB can also be used for cement assurance as a way of strengthening barriers. How does this work and what can operators gain from it?

We define the Welltec® Annular Barrier as a primary barrier and we have the background to support that. However, a barrier may be defined differently by the regulators in the different areas you are working in. So in the cases where cement is a 100% required due to regulatory matters, we offer a mechanical solution that can assist to anchor and secure the casing.

In such cases, the WAB’s provide a foundation for the cement. For example, if you want to do a stage cement job, one of the biggest challenges is to actually spot and get the cement where you want it. In such a case, the WAB can be used as a cement diverter, which basically forms the foundation of the cement. Here, you expand the WAB, get a pressurized barrier against your reservoir, but you put a cement port collar above the WAB. From here, you open that collar up then force cement outside, with the WAB as the foundation.

For many operators, this will be a very good solution where cement is needed to anchor and support the casing. Potentially, the operators can also have the WAB as the primary barrier, while at the same time not actually defining or referring to it as a primary barrier because of the regulatory guideline and rules.

 

Enabler for new wells

What other challenges do operators struggle with that the WAB can help solve?

When operators develop the fields, they may require water injection or gas injection or other reservoir management objectives. This means that the parameters of the formation that you drill through in order to penetrate the reservoir changes during the life of the well. Many times you actually have pressure regimes that have changed so much over time that you can’t drill anymore because you can’t isolate and support it with cement.

In cases like this, the WAB can provide the defense against surface annulus pressure. [edt: Read how the WAB as a primary barrier addresses the challenge of sustained annulus pressure in the first part of the interview: Rethink your completion strategy]. Basically, with regards to developing old fields, or maintaining production from them, the WAB is an enabler for being able to drill the additional wells and isolate the potential inflow zones that have appeared over the producing life of the wells. In this way, the WAB is not just a barrier for surface annulus pressure; it can also be an enabler for new wells.

 

Proven technology

Is the market ready to adopt this technology?

The market is in a flux given the downturn. Some operators will not be open for new ideas. But you have technology strong markets like in the North Sea – a really technology driven market geared to maintaining and getting as much out of the formations as you potentially can, which have and will continue to drive new solutions such as this one.

And based on all our testing qualifications and our track record, the WAB technology is not new anymore. It has been accepted and adopted by many clients, including most of the IOC’s and many NOC’s.

So now it’s as much a matter of helping the operators to change their thinking a little bit, and above all, to assist them in looking at what potential value the solutions can give them in all the different variations of their challenges. With this new and proven technology we offer, we can help operators prepare to take on the decision of changing the structure of their wells and to enable new wells in the future.

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JOHNNY BÅRDSEN

Johnny has extensive experience within the oil and gas industry. Among others, he worked several years for Baker Hughes and Statoil before joining Welltec in 2012 as Sales director for Well Completion Solutions in Scandinavia. Recently, Johnny won the Best Presentation Award at SPE Bergen, focusing on the WAB® and the Flex-Well® concept.