Casing Wear Series – 4: Interpreting Casing Wear Test Data

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Casing wear test data consists of a series of wear groove depths and the elapsed test times at which they were obtained. A data set from one such test is pictured in Figure 1.

Wear groove depth VS Elapsed test time

Figure 1: Wear groove depth VS Elapsed test time

Since it is desired to use these test results to predict the performance of casing wear systems with dimensions other than those used in the laboratory test (Different casing ID and tool joint dimensions), a model which is independent of the casing and tool joint dimensions was needed. Such a model was proposed by Dr. W. C. Maurer. His model was: The casing wear groove volume per unit length of casing is proportional to the work done per unit length on the casing by the tool joint. The constant of proportionality, called `Wear Factor’, was to be evaluated at the end of the 8 hour casing wear test, as shown in Figure 2.

Casing Wear Groove Volume VS Work Done by Tool Joint

Figure 2: Casing wear groove volume VS Work done by tool joint

Here, the performance of the casing wear system is characterized by a single number – the wear factor. This describes the performance of the casing wear system (consisting of casing, tool joint, and drilling fluid ) as linear. Obviously, this is not the case.  But, the linear model greatly simplified the development of a mathematical procedure to predict the wear performance of a wear system in the field. This was the basis for several casing wear mathematical programs which are quite successful in predicting the casing wear to be expected in field drilling operations today. The difference between predictions based on the linear wear performance system and the real world non linear system is, in many cases, less than the uncertainty of wear data obtained in the field. Casing wear logs are costly and time consuming, and are not usually run on a routine basis.

CWPRO is a modern upgraded and improved descendent of these earlier casing wear programs.

Casing wear groove geometry

Figure 3: Casing wear groove geometry

Conversion from casing wear test data, ‘groove depth vs. elapsed time’, to ‘groove volume vs. frictional work’ is a straightforward mathematical operation based on the wear groove geometry shown in Figure 3.

From ‘groove volume vs. frictional work’ back to a ‘casing wear groove depth vs. rotating time’ is similarly straightforward, regardless of the geometry in the field operations.

Knowing the value of the wear factor, and applying the concept that casing wear groove volume is a universal function of frictional work done by the tool joint on the casing, allows us to convert from wear groove volume to wear groove depth for any combination of casing internal diameter and tool joint outside diameter.  When applying the wear model to field drilling operations, the frictional work done by the tool joint on the casing is first determined. Applying the mathematical model to this information, allows the casing wear groove volume to be determined. Knowing the wear volume, and the inside diameter of the casing and the outside diameter of the tool joint (see Figure 3) we have all the information needed to determine the depth of the casing wear groove.

When the complete description of the wear system performance is needed, the differential wear factor shown in Figure 4 is used. The differential wear factor is the slope (derivative) of the wear groove volume vs. work function curve.

Differential wear factor

Figure 4: Differential wear factor



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“Stay hungry, stay foolish” and other Steve Jobs’ quotes

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Steve Jobs, one of the fathers of the personal computing era and the founder of Apple, died on October 5th, 2011 at the age of 56. Throughout the years, he’s not only changed our lives with innovative products, but also with his charismatic personalities as colorful as his life and management style.

His life, work and words have inspired millions. Here are some of Steve Jobs’ quotes.

“When you’re a carpenter making a beautiful chest of drawers, you’re not going to use a piece of plywood on the back, even though it faces the wall and nobody will ever see it. You’ll know it’s there, so you’re going to use a beautiful piece of wood on the back. For you to sleep well at night, the aesthetic, the quality, has to be carried all the way through.” [Playboy, Feb. 1, 1985]

“It’s more fun to be a pirate than to join the navy.” [1982, quoted in Odyssey: Pepsi to Apple, 1987]

“Being the richest man in the cemetery doesn’t matter to me … Going to bed at night saying we’ve done something wonderful… that’s what matters to me.” [The Wall Street Journal, May 25, 1993]

“Innovation has nothing to do with how many R&D dollars you have. When Apple came up with the Mac, IBM was spending at least 100 times more on R&D. It’s not about money. It’s about the people you have, how you’re led, and how much you get it.” [Fortune, Nov. 9, 1998]

“We made the buttons on the screen look so good you’ll want to lick them.” [On Mac OS X, Fortune, Jan. 24, 2000]

“You can’t connect the dots looking forward; you can only connect them looking backwards. So you have to trust that the dots will somehow connect in your future. You have to trust in something — your gut, destiny, life, karma, whatever. This approach has never let me down, and it has made all the difference in my life.” [Stanford commencement speech, June 2005]

“Your work is going to fill a large part of your life, and the only way to be truly satisfied is to do what you believe is great work. And the only way to do great work is to love what you do. If you haven’t found it yet, keep looking. Don’t settle. As with all matters of the heart, you’ll know when you find it. And, like any great relationship, it just gets better and better as the years roll on. So keep looking until you find it. Don’t settle.” [Stanford commencement speech, June 2005]

“When I was 17, I read a quote that went something like: “If you live each day as if it was your last, someday you’ll most certainly be right.” It made an impression on me, and since then, for the past 33 years, I have looked in the mirror every morning and asked myself: “If today were the last day of my life, would I want to do what I am about to do today?” And whenever the answer has been “No” for too many days in a row, I know I need to change something.

“Remembering that I’ll be dead soon is the most important tool I’ve ever encountered to help me make the big choices in life. Because almost everything — all external expectations, all pride, all fear of embarrassment or failure — these things just fall away in the face of death, leaving only what is truly important. Remembering that you are going to die is the best way I know to avoid the trap of thinking you have something to lose. You are already naked. There is no reason not to follow your heart.” [Stanford commencement speech, June 2005]

“I didn’t see it then, but it turned out that getting fired from Apple was the best thing that could have ever happened to me. The heaviness of being successful was replaced by the lightness of being a beginner again, less sure about everything. It freed me to enter one of the most creative periods of my life.” [Stanford commencement speech, June 2005]

“No one wants to die. Even people who want to go to heaven don’t want to die to get there. And yet death is the destination we all share. No one has ever escaped it. And that is as it should be, because Death is very likely the single best invention of Life. It is Life’s change agent. It clears out the old to make way for the new. Right now the new is you, but someday not too long from now, you will gradually become the old and be cleared away. Sorry to be so dramatic, but it is quite true.

“Your time is limited, so don’t waste it living someone else’s life. Don’t be trapped by dogma — which is living with the results of other people’s thinking. Don’t let the noise of others’ opinions drown out your own inner voice. And most important, have the courage to follow your heart and intuition. They somehow already know what you truly want to become. Everything else is secondary.” [Stanford commencement speech, June 2005]

And One More Thing…

“Here’s to the crazy ones, the misfits, the rebels, the troublemakers, the round pegs in the square holes… the ones who see things differently — they’re not fond of rules… You can quote them, disagree with them, glorify or vilify them, but the only thing you can’t do is ignore them because they change things… they push the human race forward, and while some may see them as the crazy ones, we see genius, because the ones who are crazy enough to think that they can change the world, are the ones who do.” [Think Different, narrated by Steve Jobs]

Steve Jobs

The photo mosiac above was created by Charis Tsevis, a talented and creative artist/visual designer who has done work for a myriad of corporations, including Toyota, Fortune, Time, and the Los Angeles Times.  We got permission from Charis to use this artwork of his.  Thanks, Charis!  See more of his work in his website: http://www.tsevis.com



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Casing Wear Series – 3: Developing an Experimental Technology

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During the 15 years covered by these Drilling Engineering Association studies, more than 450 casing wear tests were run. Each test required an elapsed test operating time of 8 hours.  Each test would be interrupted after the first 15 minutes, then after elapsed time of 30 minutes, 2, 4, 6, and 8 hours to measure the width and depth of the casing wear groove. Such a casing wear groove is shown symbolically in Figure 2, and Figure 3 is a photograph of an actual casing wear groove. Tool joint wear was measured only after the conclusion of the 8 hour test time. Intermediate measures were not possible due to the very small amount of tool joint wear – usually 0.005 inches, or less, of diametrical wear. Measurement uncertainty was estimated to be ±0.0005 inches.

Casing and Tool Joint Samples

Figure 1: Casing and Tool Joint Samples

9 5/8 inch, 47 lb/ft. N-80 casing was chosen to be the baseline standard against which wear systems would be judged. At this time ( 1991 ), N-80 casing was the most commonly used tubular in oilfield operations. The standard tool joint was machined from AISI 4145 steel, and the baseline mud system was a 10 ppg, water-based mud carrying 7% by volume of Clemtex #5 sand.

All test operations were performed manually. Several attempts to automate test operations were unsuccessful. Satisfactory precision in the recorded data could not be achieved.

The original Drilco test machine was purchased by the National Oil company of China and a duplicate copy of the machine is now being operated by Ken Malloy of Mohr Engineering. Casing wear testing is available on a commercial basis from Mohr Engineering.

Casing and Tool joint Wear

Figure 2: Casing and Tool joint Wear

Casing Wear Groove

Figure 3: Casing Wear Groove



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Who was Derrick?

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Source: Cabot Specialty Fluids Limited

Tyburn-tree

Crowds gather to watch a hanging from the ‘Tyburn tree’ in 1696

The oil derrick is an industry ‘symbol’ typifying oilfields the world over. We’ve all seen them, but have you ever wondered how they got their name?

Derrick originated as a given (first) name in English and is derived from the Dutch “Diederik”, meaning ‘chief of the people’. There’s a certain irony in this, as the man who devised the first derrick was an Elizabethan Englishman by the name of Thomas Derrick, one of the country’s most famous hangmen. Not a popular profession at the time due to the threat of reprisals, many had to be coerced into the role. Derrick was convicted of rape and risked execution when Robert Devereux, the 2nd Earl of Essex, pardoned him on the condition that he become hangman at Tyburn, near the current location of Marble Arch in London.

Not content with the traditional rope over the beam method he invented a new structure using a movable beam and pulley system, and lent this new invention his name. Consequently, ‘derrick’ became synonymous with the support frame for the hangman’s noose from the 1600s and through general usage to cranes and derricks of today.

Derrick executed over 3,000 people during his prolific career, one of the most notable being his own pardoner, the Earl of Essex, for a botched coup d’état against the government of the day. Now there’s thanks for you.



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Casing Wear Series – 2: The Basics

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When it became apparent that casing wear was going to be a matter to be reckoned with, several organizations initiated experimental studies of this phenomenon. Among these were (1) Shell Oil Company, (2) Exxon, (3) Texas A & M, and (4) Drilco. All these operators discovered that experimental casing wear studies were both time consuming and expensive.

All of the casings wear studies involved building a machine that would simulate field conditions as closely as possible in the laboratory. Figure 1 is a symbolic presentation of a casing wear test machine that incorporates all of the parameters needed to simulate casing wear as it would occur under field conditions.

Elements-of-a-casing-wear-test-machine

Figure 1: Elements-of-a-casing-wear-test-machine

As shown in the Figure 1, the rotating tool joint sample is pressed against the inner wall of the casing sample with a constant force. The intersection of the casing and the tool joint is flooded with drilling fluid, which contains sand to simulate the drill cuttings which the mud transports to the surface in field operations.

In addition, the tool joint ( or the casing sample ) should be slowly reciprocated during the wear test to simulate drilling progress. Failure to include this reciprocation results in a significant reduction in the observed casing wear. It is believed that without reciprocation, the casing sample and the tool joint sample will `mate’ to each other, and the drilling fluid will then form a hydrodynamic lubricating layer between the two surfaces. This will greatly reduce the grinding effectiveness of the sand that is transported by the drilling fluid. Non-reciprocating wear tests may result in as little as 10% of the wear observed in tests where reciprocation is employed.

Such a casing wear test machine is pictured in Figure 2. This machine was built by Steve Williamson ( Drilco ) in the early 1980s, and was later purchased by Maurer Engineering for use in the Drilling Engineering Association ( DEA ) projects ( DEA – 8, DEA – 42, and DEA – 137 ). These projects covered the period from 1990 through 2002.

Drilco casing wear test machine

Figure 2: Drilco casing wear test machine

Most of the material presented in these articles was developed as a result of the work done using this machine.



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