From the Designing

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.

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.

Casing Centralizer Series – 5: Are We Using Too Many or Too Few?

Our industry is blessed with many talented and experienced engineers. We also have centralizer vendors producing the very best and top quality products. It is critical that we maximize the engineering potential while selecting the proper types of centralizers and placements. A software package like CentraDesign should be an integral part of the total approach of the centralizer placement optimization.

Theories and equations determining the casing deflection between centralizers are well established, even though a hand calculation for a deviated well is impractical.

Experience plus software technology enable both centralizer vendors and operators to conduct centralizer optimization prior to field execution.

Fig. 1. Total Approach of Centralizer Placement

Fig. 1. Total Approach of Centralizer Placement

When optimizing the centralizer placement, consider the following:

  • Each well is different. Our previous experience may not apply to the next well.
  • Operators aim to obtain a satisfactory standoff with less centralizers.
  • Similarly centralizer vendors aim to obtain a satisfactory standoff to sell more units.
  • Software like CentraDesign optimizes the centralizer placement and usage.
  • Computer modeling reduces risks and costs.

Centralizer placement can make or break a good cementing job. Computer modeling is not only an easy but also a necessary step to achieve optimization of centralizer usage.  So, if you ask me the question: “Are we using too many or too few centralizers?” I would say: “If we all use readily available software to check the standoff profile for a specified spacing and optimize the placement, then we would probably use the correct number of centralizers.”

Casing Centralizer Series – 1: Types of Centralizers

Casing centralizer is a mechanical device secured around the casing at various locations to keep the casing from contacting the wellbore walls. As a result of casing centralization, a continuous annular clearance around the casing allows cement to completely seal the casing to the borehole wall.

Casing centralization is one of the key elements to ensure the quality of a cementing job by preventing mud channeling and poor zonal isolation. Centralizers can also assist in the running of the casing and the prevention of differential sticking.

Centralizer’s usage is extensive! It is estimated that 10 million centralizers are manufactured and used every year globally. Centralizer manufacturers likely want to increase the demand for centralizers. However, operators on the other hand, may wonder: “Should we use that many?”

While centralizers are used extensively, wellbore problems continue to arise due to poor cementing jobs. Centralizer properties and placements directly or indirectly affect the quality of the cementing job.

The challenge that both operators and service companies face is to choose the right type of centralizers and place the right amount at the optimum positions on the casing to achieve a good standoff profile.

There are 4 types of centralizers (Fig. 1): bow-spring, rigid, semi-rigid, and mold-on; each with its own pros and cons.

Types of Centralizers | Illustration from Pegasus Vertex, Inc. - Drilling Software

Fig. 1. Types of centralizers

1. Bow-Spring

Since the bow springs are slightly larger than the wellbore, they can provide complete centralization in vertical or slightly deviated wells. Due to the flexibility of bows, they can pass through narrow hole sections and expand in the targeted locations.

The shape and stiffness of the bows determine the restoring force, which is defined as the resistance force when a bow is compressed by 1/3 of its uncompressed height. The effectiveness of this type of centralizer is heavily dependent on the restoring force.

When the casing is heavy and/or the wellbore is highly deviated, they may not support the casing very well. For example, on a riser tieback casing string, a helically buckled casing could create a side force of 50,000 to 100,000 lbf (222 to 445 kN), well beyond the capabilities of the spring-bow centralizer. A solid centralizer would be able to meet the requirements.

2. Rigid

Rigid centralizers are built out of solid steel bars or cast iron, with a fixed blade height and are sized to fit a specific casing or hole size. This type is rugged and works well even in deviated wellbores, regardless of the side force. They provide a guaranteed standoff and function as bearings during the pipe rotation, but since the centralizers are smaller than the wellbore, they will not provide a good centralization as the bow-spring type centralizers in vertical wells.

3. Semi-Rigid

Semi-rigid centralizers are made of double crested bows, which provide desirable features found in both the bow-spring and the rigid centralizers. The spring characteristic of the bows allows the semi-rigid centralizers to compress in order to get through tight spots and severe doglegs. The double-crested bow provides restoring forces that exceed those standards set forth in the API specifications and therefore exhibits certain features normally associated with rigid centralizers.

4. Mold-On
The mold-on centralizer blades, made of carbon fiber ceramic materials, can be applied directly to the casing surface. The blade length, angle and spacing can be designed to fit specific well applications, especially for the close tolerance annulus. The non-metallic composite can also reduce the friction in extended reach laterals to prevent casing buckling.

The Risk of Not Keeping Risks Under Control

American writer and best-selling author Denis Waitley said:

“Life is inherently risky. There is only one big risk you should avoid at all costs, and that is the risk of doing nothing.”

Risks are everywhere. I was watching a documentary on earthquakes and hurricanes and it got me thinking about how there are risks in everything that surrounds us, but that doesn’t stop us from improving and moving forward. We have to acknowledge that risks exist. Taking risks is in our human nature and when something goes wrong we work towards being more prepared in the future.
Some people are reluctant to take risks because they’re somewhat afraid, but the reality is that taking risks can:

  • Open people up to new challenges and opportunities.
  • Empower people to establish new limits in their minds.
  • Stimulate people to become more creative.
  • Result in positive outcomes.
  • Help people to clearly define what they’re trying to achieve.
  • And once they have become accustomed to taking risks, they break free from the average way of thinking.

In the drilling industry every step and every decision has to be made, yet it is necessary to drill for oil. As a nation on the wheel, the usage of petroleum has become an everyday thing not only for the United States but for the rest of the world as well. So basically it’s all about risk control for every aspect of life including the drilling industry, and in this case it is all about a well done cementing job.

For drilling engineers, cementing seems to be more of an art than a science or technique. Cementing is the process of displacing cement to the annular space between the well-bore and casing or to the annular space between two successive casing strings. With the latest technologies and analytical software such as CentraDesign and CEMPRO developed by PVI, cementing engineers can use these types of software to ensure a complete and proper cement displacement.

A successful cementing job is one of the most important factors in the productive life of any well. However, challenges are always coming along as the wellbore goes deeper and to the places that are harder to reach. It’s already prevalent to predict a cementing job by computing the downhole temperature and pressure. If the cementing job is well done, all the risks are under control; a longer life of the wellbore and a higher productivity is promised.
We are living in a world where technology is advancing quickly. As PVI developers we are trying our best to develop more advanced software to meet the new needs. That’s why we developed CEMPRO+, the ultimate enhanced version of PVI’s mud displacement model, CEMPRO®.

CEMPRO+ - CEMPRO with displacement efficiency

Designed for land, offshore, conventional and/or foamed operations, CEMPRO+ uses advanced numerical methods to solve momentum and continuity equations on 3D grids and calculates the fluid concentration as well as the displacement efficiency. It accounts for many factors that can affect the efficiency of displacement jobs, including fluid properties, pumping rates, casing standoff and complex wellbore geometry.

3D Plot of Velocity Profile - CEMPRO+

Although taking risks requires some blind trust in most cases, with a well done cementing job, drilling does not need to be a problem, but the complete opposite. We’ll never know what we can accomplish until we take the risks, and we can always get the best rewards by finding the right solutions or tools to keep the risks under control.

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?

Buried Jewelry: Casing Centralizers

People in ancient time had different burial customs that they believed were necessary to ensure their immortality after death. For example, the ancient Egyptians followed some rituals and protocols which included mummification, casting of magic spells and burial with specific grave goods thought to be needed in the Egyptian afterlife.

The ancient Chinese believed that the afterlife was a continuation of life on earth. Therefore, it was very important that all things they needed were buried with them in their tomb, including their jewelry.

Incidentally, in the oil well cementing business, people sometimes refer to the centralizers as “the cementing jewelry”, probably because they are installed on a casing string in a way similar to a bracelet on the wrist.

Centralizer On Casing

Centralizer On Casing

Casing centralizer is a mechanical device secured around the casing at various locations to keep the casing from making contact with the wall. As a result of casing centralization, a continuous annular clearance around the casing allows cement to completely seal around the casing to the borehole wall.

Because of the cementation of casing with centralizers underground, casing centralizers are literally buried jewelry.

Unlike those real jewelry buried in tombs, these centralizers provide a vital function in zonal isolation. Without centralizers, the casing touches the wellbore. In this case, cement slurry will have difficulty displacing mud in the narrow side of an eccentric annulus during a cementing job. This will lead to incomplete displacement of mud or mud channel as shown in the following picture.

Mud channel left on the narrow side of the annulus “Macondo incident – Chief Counsel’s report, 2011”

Mud channel left on the narrow side of the annulus “Macondo incident – Chief Counsel’s report, 2011”

Mud channel weakens the cement bond between the casing and the formation. The good news is that with a computer software like CentraDesign, it is easier than ever to choose the right centralizer type with certain properties and place them strategically along the casing for a particular well path.

Each well is different and centralizer types and properties vary. It is best to perform a standoff analysis for each casing before a cementing job. Note that the total number of centralizers required and their placement on the casing are equally important.

Cloud Computing for Cementing Lab

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!

CEMLab-Cement_Lab_Data_Management_Software

What Can We Do in 3 Minutes?

There are millions of answers to this question. What I want to share with you is a story I learned in Dubai Museum.

At Dubai Creek in the early 20th century, pearl diving was a way to make a living. There were about 300 pearl diving dhows with over 7000 sailors on board. The divers made very deep dives, with only a nose clip, a leather finger protector, a basket made of rope, a stone weighing about 5kg to pull them down and a rope to pull them up again. About 50 dives were made a day, each about 3 minutes long.

There was hard life. The museum display board has the following description summarizing the story: “50 daily dips in the sea, with all their associated difficulties made the joy of returning home more precious than the pearls collected by the captain in his ornate.”

Resituating-Sustainability

The 3-minute diving made me wonder what we can do in the same period of time.

Cementing engineers can finish a mud displacement operation in a few hours. However, preparing a cementing job takes much longer than that, from slurry design, computer modeling to equipment arrangement. We have developed CEMPRO (mud displacement model) to reduce the time spent on job design stage. With CEMPRO, a cementing engineer can finish a job simulation within 3 minutes if he or she has necessary input data in hand.

Computer simulators like CEMPRO have allowed far better understanding of the cementing job than was previously possible. Many potential problems can be identified prior to the job and appropriate modification can be made.

CEMPRO-Mud_displacement_model

CEMPRO - Mud displacement model

Computer program such as PVI software have amplified our skill and time so we can finish more tasks, such as completing cementing job modeling in 3 minutes.