Monthly Archives: February 2012

Casing Wear Series – 1: How we got here?

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Prologue

Mr. Gefei Liu, president of Pegasus Vertex, Inc. (PVI), suggested that I write a series of short articles to discuss the empirical science of casing and riser wear. PVI incorporates this technology in their computer program – ‘CWPRO’. This program applies wear technology to predict casing and riser wear to be expected during drilling operations.

The observations and opinions expressed in these articles are based on my 20-year association with the subject of casing and riser wear. Much of this time was spent at Maurer Engineering, under the direction of Dr. W. C. Maurer. Much of the advances in the subject were the direct result of Dr. Maurer’s phenomenal knowledge of and insight into the technical challenges that were encountered during the development and application of casing and riser wear technology.

In the beginning

Casing wear was not recognized as a problem until the early 1960s. Vertical wells were being drilled deeper, and directional wells were being pushed out further. This required longer drilling times, and resulted in much greater exposure of the inner wall of the intermediate casing to the rotating tool joints of the drill string. Wear grooves appeared in the intermediate casing and progressed from noticeable to serious.

Up to this time, tool joint wear was the only wear problem being treated.

The universally accepted treatment to prevent tool joint wear was to coat the tool joints with an alloy containing tungsten carbide particles. This protected the tool joints, but was proving to be a bit hard on the intermediate casings.

Tungsten carbide coated tool joint (Field Applied)

Figure 1: Tungsten carbide coated tool joint (Field Applied)

The tungsten carbide coated tool joints were efficiently machining wear grooves into the inner walls of the intermediate casings. As these wear grooves deepened, they would seriously reduce the pressure capacities (burst & collapse), sometimes resulting in catastrophic failure.

Pressure test of worn casing

Figure 2: Pressure test of worn casing

These early findings resulted in the establishment of two distinct, but related, developments.

1. Experimental studies of casing wear; and

2. The development of casing-friendly tool joint coatings that would also protect the tool joints.

First of all, what are the basic elements of casing wear?

If boreholes were straight, casing wear would be much less of a problem. But, boreholes are not straight. As shown in Figure 3, tension in the drillstring pulls the rotating tool joints into the convex sides of the curved borehole. Since the tension in the drillstring may be several hundred thousand pounds force, the lateral loads forcing the tool joints into the convex wall of the intermediate casing may be several thousands of pounds force. The greater the curvature of the borehole, measured as `dogleg severity’, the greater will be the lateral load pushing the drill string into the intermediate casing wall. ‘Dogleg Severity (DLS)’, which is measured in degrees per 100 feet, can run as high as 5 deg/100 ft. or worse.

Drilling fluid which transports drill cuttings to the surface, flows past the tool joint/casing contact, and provides the abrasive needed to grind a wear groove into the inner wall of the intermediate casing.

Casing wear at a dogleg is shown in Figure 3, and a schematic of the resulting casing wear groove is shown in Figure 4.

The existence of the casing wear grooves indicates that there are many locations where epicyclic drillstring vibrations do not occur.

Elements of casing wear

Figure 3: Elements of casing wear

Casing wear groove

Figure 4: Casing wear groove

 



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Calgary – a beautiful oil city to be explored

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According to the 2011 annual ranking of the most livable cities in the world, compiled by the Economist Intelligence Unit, Calgary is the 5th place in the list. Vancouver remains the most livable city in the world.

The ranking scores 140 cities on 30 factors spread across five areas: stability, health care, culture and environment, education, and infrastructure. These numbers are then weighted and combined to produce an overall figure. Seven of the top ten cities are in Australia and Canada. Harare, the capital of Zimbabwe, is in 140th place. Somewhere between the extremes sit London and New York in 53rd and 56th places.

This list definitely makes all those folks in Calgary proud. A little bit surprised (pleasantly), I myself was happy to see it in the top 5, as it is also one of my favorite cities in the world, from both business and pleasure points of view.

Doing business in the oil and gas section of Calgary is easy because majority of oil and service companies are located within 10 by 10 blocks of downtown. These offices all have  “T2P” in their zip codes and most of them are all connected by the Plus 15 or +15 skyway network, the world’s most extensive pedestrian skywalk system with a total length of 9.9 miles and 59 bridges. The system is so named because the skywalks are approximately 15 feet above street level.

Because of the closeness of those companies in downtown, they do not use post masters for mails or packages. They use bicycle messengers (aka bike couriers). Courier companies use bike messengers because bicycle is less subject to unexpected holdups in city traffic jams, and is not deterred by parking limitations, fees or fines in high density development.  Benefits include environmental friendly business, predictable delivery time, etc.

We have been enjoying business association with quite a few companies in Calgary and Edmonton. Personally, I like Calgary so much that I found all excuses to visit the city.

Houston is too flat. As Mr. Jim Dech, one of our folks in Maurer Engineering 15 years ago, said: “If you stand on a can of Coke, you see everywhere.” Calgary is just the opposite, as it is located in an area of foothills and prairie, approximately 50 miles east of the Canadian Rockies. One could actually live in the Mountain and commute to work every day.

For me, not many things excite me more than driving to the Mountains after business meetings in Calgary and immersing myself in the beauties of mountains, lakes and hot spring.  Banff, Sulphur Mountain, Lake Louise, Jasper, etc. remind me one of a whole new world different in everyway from Houston. As the railroad builder William Cornelius Van Horne said, “If we can’t export the scenery, we’ll import the tourists.”

Once I became one of the imported tourists, Calgary has become one of my favorite cities.

Allow me to share some of the pictures taken in my previous trips.

Jasper - Fairmont

Lake Louise

Lake Louis



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“Being a deepwater well driller—what’s it like?”

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Source: excerpted from A Sea In Flames, published by Crown Publishers, New York.

On a recent trip to South Korea, I spent most of my time in the airplane reading Carl Safina’s non-fiction book “A Sea in Flame”. I liked it very much.  Among many things, the following section attracted my eyes, because it describes the deepwater drilling in a easy-to-understand format.

I contacted Carl Safina and got his permission to publish this section in our blog.

Pegasus

                                                                                                                                             

Being a deepwater well driller—what’s it like? To simplify, imagine pushing a pencil into the soil. Pull out the pencil. Slide a drinking straw into that hole to keep it open. Now, a little more complex: your pencil is tipped not with a lead point but with a drilling bit. You have a set of pencils, each a little narrower than the last, each a little longer. You have a set of drinking straws, each also narrower.

PencilYou use the fattest pencil first, make the hole, pull it out, then use the next fattest. And so on. This is how you make the hole deeper. At the scale of pencils-as-drills, you’re going down about 180 feet, and the work is soon out of sight. As you push and remove the pencils, you slide one straw through another, into the deepening hole. You have a deepening, tapering hole lined with sections of drinking straw, with little spaces between the hole and each straw, and between the sections of straw.

You have to seal all those spaces, make it, in effect, one tapering tube, absolutely tight. And here’s why: the last, narrowest straw pokes through the lid of a (very big) pop bottle with lots of soda containing gas under tremendous pressure. As long as the lid stays intact and tight, there’s no fizz. But only that long. Everyone around you is desperate for a drink of that pop, as if they’re addicted to it, because their lives depend on it. They’re in a bit of a hurry. But you have to try to ignore them while you’re painstakingly working these pencils and straws. And you’d better keep your finger on the top of the straw, or you’re going to have a big mess. And you’d better seal those spaces between sections of straw as you go down, or you’re going to have a big mess when you poke through that lid. And before you take your finger off the top of the straw, you’d better be ready to control all that fizz and drink all that pop, because it’s coming up that straw. And if, after poking a hole in this lid that’s been sealed for millions of years, you decide you want to save the soda for later, then you’d better—you’d better—have a way to stopper that straw before you take your finger off. And you’d better have a way to block that straw if the stopper starts leaking and the whole thing starts to fizz. If it starts to fizz uncontrollably, and you can’t regain control, you can get hurt; people can die.

The real details beggar the imagination of what’s humanly and technologically possible. Rig floor to seafloor at the well site: 5,000 feet of water, a little under one mile. Seafloor to the bottom of the well: about 13,360 feet—two and a half miles of drilling into the seabed sediments. A total of 18,360 feet from sea surface to well bottom, just under three and a half miles.

Equally amazing as how deep, is how narrow. At the seafloor—atop a well 2.5 miles long—the top casing is only 36 inches across. At the bottom it’s just 7 inches. If you figure that the average diameter of the casing is about 18 inches, it’s like a pencil-width hole 184 feet deep. Nine drill bits, each progressively smaller, dig the well. The well’s vertical height gets lined with protective metal casings that, collectively, telescope down its full length.

At intervals, telescoping tube of casing gets slid into the well hole. The upper casing interval is about 300 feet long. Some of the lower ones, less than a foot across, are 2,000 feet long. The uppermost end of each casing will have a fatter mouth, which will “hang” on the bottom of the previous casing. You will make that configuration permanent with your cementing jobs.

The casings and drill pipes are stored on racks, awaiting use. Casings are made in lengths ranging from 25 to 45 feet; the drill pipe usually comes in 30-foot joints. They are “stacked” in the pipe racking system. You assemble three at a time and drop approximately 90 feet in, and then repeat. When you get and drop approximately 90 feet in, and then repeat. When you get ready to put the casing in, you pull all the drill pipe out. Rig workers also remove the drill pipe from the hole every time the drill bit gets worn and needs changing or when some activity requires an open hole. Pulling the entire drill string from the hole is called “making a trip.” Making a trip of 10,000 feet may take as long as ten or twelve hours. When you want to start drilling some more, you have to reassemble the drill pipe and send it down.

                                                                                                                                                 



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Drilling Software: Get More Done by Doing Less

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More than a century ago, Italian economist Vilfredo Pareto noted the consistently lopsided relationship between inputs and outputs called “The 80/20 Principle”, which asserts that a small portion of inputs or efforts leads to a big portion of outputs or results. In 2008, self-confessed “lazy entrepreneur” Richard Koch explained this principle in great details in his best-seller book “The 80/20 Principle”.

Basically, if 2 sets of data, relating to causes and results are examined, the most likely result is that there will be a pattern of imbalance. The imbalance may be 65/35, 70/30, 80/20 or 95/5, or any set of portions in between. However, rarely 50% of inputs will account for 50% of outputs.

80/20 principleWhether we realize it or not, the principle applies to our work, social life, and personal matters.

In our personal life, 20% of our clothes will be worn 80% of the time. 20% of our carpet areas are likely to get 80% of the wear. If you have an alarm system, 80% of the false alarms will be set off by only 20% of the possible causes.

In society, 20% of motorists cause 80% of all accidents. 80% of the value of our relationships is derived from 20% of close relationships.

In business, 20% of products or customers are responsible for 80% of a company’s revenue. 80% of wealth increase in portfolios comes from fewer than 20% of the investments. In a study of the revenues and lifespan of 300 movies released over an 18-month period, they found 4 movies (1.3% of the total) earned 80% of box office revenue – a clear example of the rule of imbalance.

Similar analysis could be done to study our time allocation of our drilling engineers/managers. It will probably show the similar imbalance. Achievements should probably not be “99% perspiration and 1% inspiration”. Instead, they may come from the 20% of our work.

The key terms in the equation of imbalance may vary from person to person. But from our drilling engineers’ perspective, taking the advantage of drilling software is one of the ways to improve our efficiency, because we then can spend more time in analyzing/identifying potential problems, rather than doing the tedious calculation.

As a software vendor, majority of our time is spent on R&D and software development, so that our clients do not have to spend big chuck of their valuable time making spreadsheet calculation. This is a derivative of the 80/20 principle: if you are not many times better than others in certain areas, outsource the tasks.

Drilling software does not replace drilling engineering. It amplifies drilling engineers’ skills so that we can get more done by doing less.



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