7 Basic Ideas

In completion of oil and gas wells, cement separates the wellbore, prevents casing failure, and keeps wellbore fluids from contaminating freshwaters. The basic factors engineers and operators must consider for successful cementing jobs are summarized in seven basic ideas:

  1. Condition the Drilling Fluid
  2. Use Centralizers
  3. Move the Pipe
  4. Increase the Displacement Rate
  5. Design Slurries for Proper Temperature
  6. Select and Test Cement Components
  7. Select a Proper Cementing System

1. Condition the Drilling Fluid

The drilling fluid condition is the most important variable in achieving very good displacement during a cementing job. As the workers pull the drill pipe, run the casing, and prepare for cementing operations, the drilling fluid in the wellbore basically remains static and hardens. Pockets of mud commonly exist after a wellbore is drilled and they make displacement difficult. These pockets of gelled fluid must be broken up. Regaining and maintaining good fluid mobility after running the casing is essential.

2. Use Centralizers

Centralizers are effective mud displacement helpers. Centralizers make easier the removal of gelled-mud and allow better cement bond with the wellbore. Centralizers are designed to serve various needs, for instance, they help with well control, provide increased mud-removal benefits, optimize drilling-fluid displacement. When a casing is poorly centralized the cement bypasses drilling fluid by following the path of least resistance. Good pipe standoff helps ensure uniform flow patterns around the casing. Centralizers also change fluid flow patterns and promote better mud displacement and removal.

3. Move the Pipe

Moving the casing before and during cementing breaks up the gelled pockets and it loosens the cuttings trapped in the gelled mud. Pipe movement allows high displacement efficiency at lower pump rates by keeping the drilling fluid flowing.

Movement compensates partially for poorly centralized casing by changing the flow path and allowing the slurries to circulate completely around the pipe. In some instances, some liner hangers and mechanical devices prevent casing movement, which must be considered during the cement displacement design.

4. Increase the Displacement Rate

High-energy flow in the annulus is more effective in ensuring good mud displacement. Turbulent flow around the casing circumference is desirable, but not necessarily essential. The best cementing results are obtained when the spacers and cement are pumped at maximum energy, the spacer is appropriately designed to remove the mud, and a more proficient cement is used.

5. Design Slurries for Proper temperature

Operators can optimize the slurry design if they know the actual temperature the cement will encounter. Bottomhole cementing temperatures affect the slurry thickening time, set time, rheology and the compressive-strength development. Operators tend to overestimate the amount of materials required to keep cement in a flowing for pumping, which can result in unnecessary cost and well-control problems. They can optimize cost and displacement efficiency by designing the job on the basis of actual wellbore circulating temperatures, obtained from a downhole temperature sub recorder.

6. Select and Test Cement components

Operators are encouraged to design cement slurries for specific applications, with good properties to allow placement in a normal period of time. The ideal cement slurries have no measurable free water, provide adequate fluid-loss control, have adequate retarder to ensure proper placement, and maintain a stable density to ensure hydrostatic control.

Before performing the job, they should check the cement reaction and actual location mix water to ensure that the formulation will perform as it is expected. Contaminants in the mix water can produce large variances in thickening time and compressive strength.

Organic materials and dissolved salts in mix water can affect the slurries setting time.

Cement dehydration from the loss of filtrate to permeable formations can cause bridging and increased friction pressure, viscosity, and density. Pump pressures can increase and additives can be used to provide fluid-loss control when is necessary to compensate for dehydration.

7. Select a Proper Cementing System

Operators select cement systems based on job objectives and well requirements.

Cement is basically inflexible. Cementing systems are similar in many ways, but sometimes they vary, for instance, in their capability to provide good zone isolation in changing environments. The cement selection has always been on the basis that higher compressive strengths result in higher cement sheath quality. Research has proven that the ability of cement to provide good zonal isolation is better defined by other mechanical properties. Good isolation does not necessarily require high compressive strength. The real competence test is whether the cement system in place can provide zone isolation for the life of the well.

For all these situations PVI has developed a series of software such as:

CentraDesign - Centralizer Placement Software

CentraDesign - Centralizer Placement Software

MUDPRO - Drilling Mud Reporting Software

MUDPRO - Drilling Mud Reporting Software

StuckPipePro - Stuck Pipe Analysis Software

StuckPipePro - Stuck Pipe Analysis Software

that can help engineers and operators to perform a better quality job and avoid any potential problems that can put at risk the production.

Knowledge and Diderot’s Philosophy

There are three principal means of acquiring knowledge... observation of nature, reflection, and experimentation. Observation collects facts; reflection combines them; experimentation verifies the result of that combination.
Denis Diderot (French Philosopher)

Knowledge is defined as a familiarity, awareness or understanding of someone or something, for instance the facts, information, descriptions, or skills, which is acquired through experience or education by perceiving, discovering, or learning of a subject.

In the past century technology went through many advances giving knowledge the opportunity to be more accessible to humanity. For drilling technology, literatures, books, computer programs and other sources have been put together by the brightest minds of drilling professionals; however while this technological know-how has notably driven the industry forward, some individuals are at times overwhelmed by the vast amount of information they receive from different sources of media.

The internet is loaded with drilling engineering information, but this information is scattered around in such a way that can lead to generate different answers to just one question.

The demand has been to create an all-in-one type of information and knowledge base software; a digital toolbox that is quick-to-access, reliable, accurate and interactive among other things. For this, PVI has developed a comprehensive collection of drilling engineering tools in a simple-to-learn and easy-to-use software package - Dr. DE.

Dr. DE - Drilling Engineering Toolbox

The software covers more than 180 functions ranging from the fundamentals of drilling engineering to an advanced well path design and 3D visualization of the wellbore; a resource made for every drilling engineer and technician to get the job done right while also making their engineering and sales efforts easy and efficient.

Dr. DE’s engineering features include:

  • Daily used drilling engineering problems and solutions
  • Extensive and expandable tubular, centralizer and fluid database
  • Survey data up to 5000 points
  • 3D wellbore visualization
  • Intelligent 2D well path design
  • Detailed illustrations
  • Support fraction input of tubular sizes

In the beginning of the article we quoted from Dennis Diderot, a person who strongly believed and promoted that all humans have the right to acquire knowledge because it’s in our nature to learn and that the best way of acquiring it, is through experimentation and the exercise of reasoning. With this in mind is how we developed Dr.DE and how our fellow drilling engineers and technicians can benefit from using it to accomplish their daily tasks.

Can You Afford Not To Use Drilling Software?

We decide to buy things based on the benefits those things may bring to us. Those benefits can be either tangible or intangible. If the tangible benefits are greater than the price, the decision process is easy, or if the benefits give us a perception of peace then we will most likely make the purchase.

Drilling software, in particular, is a product packed with advanced engineering calculations. One can say it is a condensed result of research, an interactive digital toolkit or an expert who never gets tired. It normally takes years of development by a well-trained team.

Setting prices for software packages is challenging because there are many uncertainties involved, such as market size, other similar products, etc. One thing is certain in any drilling software, if successfully used in pre-drilling analysis, it will most likely bring more benefits than the money spent on purchasing it. The cost of drilling an oil and gas well is so high that any non-productive time prevention (NPT) is well worth the spending.

Drilling software provides a good way of identifying potential problems in a drilling design and making good recommendations.

Take an example of casing centralizer placements, the purchase of centralizers is to provide a good casing standoff (>70%) to be better prepared for a cementing job. The standoff profile of a casing in a directional well depends on many parameters such as well path, casing weight, fluid densities, top of cement (TOC), centralizer properties and placement. Our past work experiences can help us select the proper types of centralizers and placement, but for a given well condition, it is best to use computer model to make recommendations for the centralizer usage. The following picture shows the resulting standoff profile with a designed centralizer spacing.

Standoff vs Measured Depth - Pegasus Vertex, Inc.

Standoff vs Measured Depth - CentraDesign

Thomas Edison once said: “I shall make electricity so cheap that only the rich can afford to burn candles.”

Nowadays, drilling software has become commonplace. Applying the latest drilling technology includes using the available solutions. Drilling software is like the electricity to light our understanding and design of drilling operations. Can you afford not to use it?