Tag Archives: cement slurries

From the Designing

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Cementing operations represent one of the more crucial aspects regarding well integrity. Despite the vast amount of research and the large number of operations throughout the years, well integrity problems, during and after cementing jobs, is something the industry still faces. These problems have been experienced by the petroleum industry globally and can occur at any moment of the well’s life cycle. Well integrity issues have been categorized according to the moment at which they happen:

  1. During the cement displacement in the wellbore.
  2. After the cement placement.
  3. After the cement has been cured.

The first category may result in very serious well-control problems, including blowouts. During the period between 1992 and 2006, the leading cause for blowouts was cementing. These problems usually occur because of improper design of the cementing operations due to hydrostatic pressure of the cement slurries, failure when mixing the slurries to obtain the desire density, and lost circulation during the cement displacement.

The second category is normally associated with the loss of hydrostatic pressure of the cement slurries during the initial hydration period. This also can cause we-control problems, pressure build up in the annulus between the casing strings and zonal isolation problems eventually and the remedial solutions for this are normally expensive and difficult.

The last category refers to long-term problems normally caused by poor cementing jobs. Defective drilling mud removal during the cement slurry displacement in the annulus, insufficient cement height that may lead to casing leakage and corrosion problems are some of the factors that can contribute to long-term well integrity failures and the cost to fix these problems are highly expensive.

PVI has taken into consideration these types of problems and has created two great software for these situations: CEMLab and CEMPRO+.

CEMLab - Cement Lab Data Management Software

CEMLab - Cement Lab Data Management Software

This integrated database management application formulates slurries and calculates lab amounts for all ingredients such as cement, dry and liquid additives, salts and water. It also generates weigh-up sheets, stores API test results and generates lab reports. CEMLab allows quick access to all slurry formulations and testing statuses from anywhere, anytime.

CEMPRO+ : Mud Displacement Software

CEMPRO+ : Mud Displacement Software

This mud displacement program has the capability of displacement efficiency modeling. Designed for land, offshore, conventional and/or foamed operations, CEMPRO+ accounts for many factors that can affect the efficiency of a displacement job including fluid properties, pumping rates, casing standoff and complex wellbore geometry. CEMPRO+ is the must have software for cementing operations.

Before designing your next well, keep these two models in mind to help you achieve, from the designing of the slurries to the mud displacement, a successful cementing operation.

Step One: Preparation

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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.

Casing Centralizer Series – 3: Modeling

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We are going to study on the 5 parameters affecting casing standoff.

1. Well trajectory

Well trajectory is expressed in terms of survey data, consisting measured depth, inclination and azimuth angles. It defines the shape of the well path and thus has great impact on the direction and magnitude of the side forces that pull the casing string to the wellbore. Fig. 5 shows the magnitude and direction of the side force distribution on a casing in a horizontal well.

Fig. 1. Side Force Profile

Fig. 1. Side Force Profile

For a casing section in a build-up or horizontal section of wellbore, the weight of pipe pulls the casing toward to the lower side of hole. The blue lines indicate that the casing touches the lower side of wellbore. The upper section of the casing string has to sustain the weight of lower casing sections. This creates tension force along the casing string.  Wellbore doglegs cause the resultant force to pull the casing toward the upper side of the hole, as indicated by the red lines. Therefore, casing string in a deviated or horizontal well always touches the wellbore, upper or lower side.

Fig. 2. Side Forces with Casing Positions

Fig. 2. Side Forces with Casing Positions

Generally speaking, horizontal or extended reach wells require more support from centralizers to maintain a good standoff profile.

2. Casing size and weight

Casing weight determines the gravitational force which pulls the pipe toward the lower side of the borehole. The heavier the casing string is, more or stronger centralizers are required.

3. Fluids inside casing and in annulus

The buoyancy force calculation is further complicated by the multi-fluid configuration during a cementing job. When heavy cement slurries are inside the casing and light drilling mud in the annulus, the effective weight of casing is at its greatest. On the other hand, when cement slurries are in place and displacement fluid inside the casing, the buoyancy is at its peak and the effective weight of the pipe is the least.

When we design the centralizer placement for the scenario of cement slurries in place, it favors us to have less effective casing weight, pulling the casing string downward; but when the cement slurries are inside the casing during the displacement, the lower standoff could cause mud channeling problems. It is better to study standoff for all the situations.

4. Centralizer properties

Not all centralizers are created equal.  Centralizer manufacturers are striving to improve the performances of their products.

For solid centralizers including mold-on type, the blade OD is the key parameter as far as the casing centralization is concerned.

For bow-spring centralizers, the restoring force is the measurement of the strength of a centralizer. It is defined as the side force to deflect the bow by 1/3 or its original height.

5. Centralizer placement

Once the well is planned, casing designed, cementing procedure prepared and centralizer type selected, we do not have many options other than placing the centralizers strategically to achieve the desired standoff. However, this is also a great leverage.

Poor spacing will result in poor standoff even with the best centralizers in the market.

Cloud Computing for Cementing Lab

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In just 2 decades, the internet has fundamentally changed the way people interact with computers and each other. Everyone is now talking about “the cloud.” Business applications are moving to the cloud. The shift from traditional software models to the Internet has steadily gained momentum over the last 10 years. It is no longer a fad; it is the future.

Cloud computing is the use of computing resources (hardware and software) that are delivered as a service over a network (typically the Internet). The name comes from the use of a cloud-shaped symbol as an abstraction for the complex infrastructure it contains in system diagrams.

In cloud computing, users access cloud-based applications through a web browser while the software and user's data are stored on servers at a remote location. The idea is to share resources to achieve coherence and economies of scale similar to a utility (like the electricity grid) over a network.

These innovations in cloud computing are making our business (drilling software) more mobile and collaborative.

For example, the design and test of the slurry are the integral parts of every cementing job. This process is time-consuming and expensive because of the variability of the conditions between wells. Traditionally, cementing engineers and lab technicians used paper forms to record test results. With the introduction of MS Office Excel, people began to take advantage of electronic filing. This has greatly enhanced the reporting quality and filing. However, the part critically missing with this approach is organizing numerous reports and searching for specific data.

A stand-alone software with database backbone may solve the above problems, but we chose a more advanced approach: a web-based cementing lab database management.  CEMLab, our latest release provides solution to problems many cementing lab manager and technicians face today:

•           Difficulty of designing cement slurries

•           Waste of resources to repeat similar tests

•           Lack of prove while job problems occur

•           Non-standard practices at various labs within a company

Our goal was to make this cementing lab database management system CEMLab the daily platform to design slurry, record and store test results, create lab reports, and perform searches. This integration will free lab managers and technician to focus on their core business.

CEMLab is completely web-based, allows you to login from anywhere. You do not need to download a heavy desktop program, just visit your assigned server site from any computer worldwide.

CEMLab does not force lab staff to abandon their beloved workflow. In fact, features in CEMLab such as user management, job tracking and remote submission of test requests make workflow easier than ever. Workflows will become more streamlined. The search function featuring various and combined criteria is flexible enough to make the time-consuming task easy and simple.

2000 years ago, Chinese philosopher Lao Zi said:”A journey of a thousand miles begins with a single step.” We have taken the first step toward streamlining cement slurry design and testing.  Looking ahead, we are excited to see how this application, the first of its kind, brings happiness to many cementing lab managers and technicians along their journey!

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