Monthly Archives: September 2014

An Illustration and A Twisted Finger

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Let’s illustrate in an easier way what torque and drag is:

Hold your index finger tightly in the fist of your other hand.

Now twist your finger.

Twist Your Finger and You Feel The Pain

 

 

 

 

 

 

Do you feel how your finger does not want to twist?

Yes!

You know why?

Because it's not built to be twisted.

The pain you feel is because of the torque you are putting on the joints.  - That's torque.

Do you feel how your finger resists the pull because you have a good grip on it with your fist? - That's drag.

Torque and drag can have a dramatic increase in horizontal and extended-reach wells and can become the limiting factor in determining the horizontal length or extended-reach of a well. For this reason, precise calculations of torque and drag are necessary for drilling operations. Torque and drag are the results of friction caused by a moving pipe inside the wellbore: torque occurs when rotating the pipe along the wellbore and drag occurs when moving the pipe.

When drilling horizontal or extended-reach wells, excessive torque and drag may become troublesome both in the drilling operations and later in the completion operations. Estimating torque and drag is very important, but the calculation of drag in the build section of a well is complicated by the effect of the axial force (tensile or compressive) on the lateral contact force which produces the sliding drag and in turn causes changes to the axial force itself. The axial force has a great effect on the torque and drag calculations in the build section. When the axial force (tension or compression) becomes large enough to let the pipe contact only one side of the wellbore, the torque and drag in the build section will increase proportionally with the increase in the axial force.

The most common way to calculate approximate torque and drag values in the build section involves monotonous numerical calculations: dividing the build section into many small pieces, assuming the axial force remains constant in those small pieces, calculating the friction factor for each of the pieces, and then summing these values to get the total drag over the entire build section. This process is both time-consuming and difficult for field engineers.

The analysis of torque and drag is made easier by today’s technology. There is a comprehensive torque and drag software in the market that removes many of the risks during the drilling process. This software was developed by PVI and it’s called TADPRO (Torque and Drag).

TADPRO - torque and drag

This software comes with features that help users to:

  • Calculate hookload and surface torque
  • Identify potential buckling
  • Perform sensitivity analysis
  • Determine side force
  • Analyze forces downhole
  • User-friendliness and graphical outputs

Illustrations have always been a great learning method and today we have learned two things:

  1. Fingers were not made to be twisted.
  2. Likewise a pipe is not built to be twisted, but the torque and drag inevitably occurs during horizontal drilling, but with the help of TADPRO, torque and drag can be calculated and predicted, therefore the risks are reduced.

A Phrase of Being Stuck

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Jill Scott said:

“I need to find a creative diversity because if I get stuck, I get unhappy.”

At times we all find ourselves stuck in different aspects of our lives.  Maybe not for the same reason; sometimes it could be fear, guilt, nostalgia and even boredom, but the result is the same.

We’re stuck.

But then, how can we get out of it? How do we get unstuck? The answer is very simple: “we find the problem and along with it, we find the solution”. Let’s take this example and apply it to the drilling process.

During a drilling operation, if a pipe cannot be freed from the hole without causing any damages to the pipe and without exceeding the drilling rig’s maximum hook load this is considered a stuck pipe. Pipe sticking can be classified under two categories:

  1. Differential pressure pipe sticking
  2. Mechanical pipe sticking

When having complications due to a stuck pipe this can be nearly half of the total cost of the well, making stuck pipe one of the most expensive problems that can occur during a drilling operation and is a serious risk in high-angle and horizontal wells.

Drilling through depleted zones, where the pressure in the annulus surpasses that in the formation, might cause the drillstring to be pulled against the wall and embedded in the filter cake deposited there. The internal cake pressure diminishes at the point where the drillpipe contacts the filter cake, causing the pipe to be held against the wall by the differential pressure. In high-angle and horizontal wells, the gravitational force contributes to prolonged contact between the drillstring and the formation.

What are some of the mechanical causes for stuck pipe?

  • Keyseating
  • Packoff from poor hole-cleaning
  • Shale swelling
  • Wellbore collapse
  • Plastic-flowing formation (i.e., salt)
  • Bridging

What are some of the signs that need to be monitored to prevent stuck pipe?

  • Increasing in torque and drag
  • Excessive cuttings loading
  • Tight spots while tripping
  • Loss of circulation while drilling

Depending on what the suspected cause of sticking is, it is necessary to act properly and urgently.

There is a tool developed by PVI Called StuckPipePro, which is a stuck pipe analysis that every operator should have to reduce the risks of pipe sticking to the minimum. This effective tool is equipped with great features, for example: stuck chance calculation, free point calculation, back-off force calculation, stuck pipe mechanism, which assist in determining the mechanism that is actually behind the stuck pipe situation and which technique should be used to free the pipe. It also comes with a decision flow chart that guides users through a series of questions to find the cause of pipe sticking.

StuckPipePro - Stuck-pipe-analysis

StuckPipePro - Stuck Pipe Analysis

Just like the phrase of being stuck said by Jill Scott; once we find the problem, we’ll find the solution, in this case, with StuckPipePro.

Like The Barriers on The Road

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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 Risk of Not Keeping Risks Under Control

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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.