Step One: Preparation

Cementing a well is the procedure of developing and pumping cement into a wellbore. Although it is used for various reasons, cementing protects and seals the well. Very frequently, cementing is used to permanently block out water from penetrating the well. Cementing is also used to seal the annulus after the casing string has been run in the wellbore. In addition, cementing can be used to seal a lost circulation zone, or a specific area where there is a reduction or absence of flow inside the wellbore. When it comes to directional drilling, cementing is used to plug an existing well, in order to run a directional well from that point.

Cementing is performed when the cement slurries are placed into the well by pumps, displacing the drilling fluids that are still located in the well, and replacing them with the cement. The cement slurries flow to the bottom of the well through the casing, which will later be the pipe through which the hydrocarbons flow to the surface. From there it starts filling the space between the casing and the wellbore, and hardens. This permanently positions the casing in place and seals the wellbore so that outside materials cannot enter.

Preparing the Cement

When preparing a well for cementing, it’s very important to be certain of the amount of cement required for the job. This is done by measuring the diameter of the borehole along its depth. Also, to know the required properties of the cement is very essential before beginning any cementing operation. The proper set cement is good to be determined, including the density and viscosity of the material, before actually pumping the cement into the hole.

Special mixers are used to combine dry cement with water to create the wet cement that is also known as slurry. The cement used in the well cementing process is Portland cement, and it is calibrated with additives to form one of eight different API classes of cement. Each is employed for various situations.

Additives can include accelerators, which shorten the setting time required for the cement, as well as retarders, which do the opposite and make the cement setting time longer. In order to decrease or increase the density of the cement, lightweight and heavyweight additives are added. Additives can be added to transform the compressive strength of the cement, as well as flow properties and dehydration rates. Extenders can be used to expand the cement in an effort to reduce the cost of cementing, and antifoam additives can be added to prevent foaming inside the well. In order to plug lost circulation zones, bridging materials are also added. However, the critical part missing here is the management of numerous reports and search function.

Without an efficient lab database, we will face the following situations:

  1. Difficulty of designing cement slurries.
  2. Waste of resources to repeat similar tests.
  3. Lack of prove while job problems occur.
  4. Non-standard practices at various labs within a company.

To streamline the cement lab operation, PVI developed CEMLab:CEMLab - Cement Lab Data Management SoftwareThis software is an integrated database management application that:

  • Formulates slurries.
  • Calculates lab amounts for all ingredients, such as cement, dry and liquid additives, salts and water.
  • Generates weigh-up sheets.
  • Stores API test results.
  • Generates lab reports.

CEMLab, is a web based application that allows quick access to all of your slurry formulations and testing statuses from anywhere, at any time. The advanced search function allows users to find the formula and test quickly and brings the previous jobs to their screen in no time. It’s a great tool for preparation.

Like The Barriers on The Road

This is a story about a town located at the bottom of a deep valley.

The Vally

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:

  1. Spring (Bow) Centralizers
  2. 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 (Centralizer Placement)

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.

The Best is Yet to Come

The following is told by an American lady:

“My grandmother always used to tell us, “keep your forks.” when the main dishes were being cleared from the table. It was my favorite part of dinner, because I knew that something wonderful was coming… like a velvety chocolate cake or a deep-dish apple pie.”

A similar expression would be “You have not seen anything yet.” or as my 8-year old daughter told me, “I am not done yet!” when I gave her an applause after she sang the song from the movie “Frozen”.

Life is a simple and normal routine. Everyone has the same number of hours in a day and the same number of days in a year. It is up to us to make our daily routines more interesting, to fill our time doing things that will make us grow in every aspect of our lives, to make the most of our time. We cherish the hope that our present situation is not our final destination. The best is yet to come.

For us software developers, we are continuously enhancing the drilling software that is being developed. We certainly can’t add more hours to our day, but we can make our development more efficient. We will probably spend the same amount of time as we did last year, but we will have better products in 2014.

The latest release of our cementing software CEMPRO+ is a milestone. Why? Because this is the first time we address the displacement efficiency during the multi-fluid displacement operations such as cementing or wellbore cleanup. Before CEMPRO+ we used to assume that the drilling mud was completely displaced by the cement slurry with the use of a piston. This convenient assumption makes the hydraulics relatively easy, but it fails to predict the mud channeling which occurs due to many factors such as, differences in the cement properties and mud flow rates, and the casing centralization. A typical illustration of mud channeling is shown here:

Mud channel left on the narrow side of the annulus

Mud channel left on the narrow side of the annulus (Macondo incident-Chief Counsel’s report, 2011)

CEMPRO+ can help predict the mud fractions in the annulus during a cementing job. The following picture is a snap shot from the program. It looks neat. Graphics are more significant, because they show what really happens in the wide and narrow sides of the annulus.

Displacement Efficiency Illustration in CEMPRO+

Displacement Efficiency Illustration in CEMPRO+

If our CEMPRO has been on your software menu, keep your forks, because the best is yet to come.