This is a story about a town located at the bottom of a deep valley.
The only road into town was steep and windy, barely hanging on to the steep mountain-side surrounding the town. Very often, cars traveling into town would get too close to the edge of the road and tumble into the valley. Over time, the town spent hundreds of thousands of dollars responding to wrecks and they got tired of going out to respond to the same thing over and over. The town’s people rendezvoused to discuss the matter and how to solve it. Some folks thought they should ignore what was happening and let people fend for themselves. Others thought they should continue to help the people who went off the road, but should charge them for the costs involved. A few suggested that they should just close the road so those strangers wouldn't cause them any more problems. The majority of the people quickly acknowledged that the road posed a risk for strangers but also for friends, family and the townspeople themselves. Since nobody agreed to a specific solution, one person suggested they put up a barrier on the edge where cars most often went off the road and everybody agreed and so they did. Over the years, the barrier cost the community far less than all the rescuing they had been doing for so many years. A simple barrier was the solution.
It's a simple story, but a great metaphor for prevention. Like the barriers on the road, for more than 6 decades, casing centralization has been established as being essential to efficient mud removal and therefore to a successful cementing job. Prior to a production it is very common for field engineers to spend time improving casing centralization using software, particularly for highly deviated wells. However today, while long lateral wells are being drilled, they become more challenging in getting the casing to bottom and achieving good zonal isolation. That is why casing centralizers play a key role in achieving these objectives and should be evaluated differently than they have been in the past.
Predicting casing standoff is essential since not knowing where to locate the centralizers and how many are needed can cause several problems. The main reason for centralization is to ensure a uniform distribution of cement around the casing. No centralization or poor centralization will cause channeling of the cement and therefore produce poor cement adherence.
What do centralizers prevent?
- When running a casing, the adequate use of centralizers reduces the chance of wall sticking.
- In deviated wells because of the increased amount of support, the casing requires to stay in the center of the hole – especially in build-up sections - a more dense distribution of centralizers is required than in straight holes.
There are two main types of centralizer:
- Spring (Bow) Centralizers
- Rigid Centralizers
Spring (bow) centralizers are often used for vertical and deviated wellbores and rigid centralizers are used for horizontal wellbores. The method of installation for both of these depends entirely upon the centralizer design. However, care must be taken to ensure the quality of the cementing job. Centralizer placement is synonym of prevention.
For this PVI developed CentraDesign software that optimizes the centralizer placement, predicts casing standoff and torque and drag for extended reach drilling and deviated wellbores.
CentraDesign also determines the number and placement of centralizers, hence providing both service companies and operators with a very sophisticated yet easy to use tool that will help prevent problems during the cementing process.
Prevention is like the barrier put up to keep cars from going over the edge and it works to keep unwanted things from happening in the first place.