Dr. Willard H. (Bill) Wattenburg
Down Hole Directional Drilling Tools whose angular position can be controlled and measured from the well head.
Dr. Bill Wattenburg
Many people have asked me to explain the downhole
directional drilling tools patented in 1995 and 1997, patent
numbers 5,445,230 and 5,673,765 (licensed to
Sperry Sun, part of Dresser Industries, later
purchased by Halliburton).
The 1997 patent is an improvement on the 1995 design to make the tool more useful for small bore drilling, down to 2 inch diameter flexible coiled drill pipe. The 1997 design has the same main features, but somewhat simplified from the standpoint of manufacturing ( in other words what I learned after nine prototypes and field testing in Houston).
See the last section below for the
history of this adventure.
Referring to Figures 1 and 2
below, the main housing of the tool consists of an upper
cylinder 1 in which a lower cylinder 2 slides and
rotates. The upper drill pipe 3 is rigidly attached to the
upper cylinder 1 at a small fixed bend angle 4 ( X
The lower drill string 5 is
rigidly attached to the lower cylinder 2 at the same angle 4 (X
degrees) as the upper drill pipe 3. In Figure 1
below, the effective bend angle 6 between the center
line of the drill pipe 3 and the center line of the drill
pipe 5 can thus be changed from zero degrees to 2 times X degrees
by rotating the lower cylinder 2 inside of and with respect to the
upper cylinder 1.
Pressurized mud fluid 20 which drives the drilling motor 30 (mud motor) flows down inside the drill pipe 3 through the directional drilling tool to the drill pipe 5 connected to the mud motor 30 and then out onto the annulus 21 of the well bore.
The main operational mode of this tool that allows drillers at the well head to change the bend angle in the down hole drill pipe is the following: The effective bend angle in the drill pipe is changed each time upper cylinder 1 is raised a short distance up from lower cylinder 2 which is connected to the heavy mud motor and drill bit. This releases an internal rotational locking mechanism that locks cylinder 1 and cylinder 2 when they are closed together. When the drill string is lowered again at the well head, cylinder 2 is pushed back up inside cylinder 1. As cylinder 2 comes back up into cylinder 1, an internal ratcheting mechanism causes cylinder 2 to rotate a fixed amount (say, 45 degrees). This changes the effective bend angle in the drill string by one increment (45 degrees) as it passes through the nested cylinders 1 and 2 of this tool. Once the drill string is lowered in place at the well head, mud pressure is brought up to drilling levels and drilling commences with the new bend angle for the drilling bit.
The ratchet movement to change angular position is accomplished when cylinder 1 is raised only about 6 inches and then lowered back on cylinder 2. This “up and down” action to change the bend angle down hole is very easy for drillers to execute at the well head. They simply shut off all mud fluid pressure in the annulus of the drill string to stop drilling and eliminate fluid pressure in the tool. Then they raise the drill string a short distance to change the bend angle by one increment (45 degrees). This new bend angle is locked in by lowering the drill string which closes up cylinders 1 and 2 (cylinder 2 fully inside cylinder 1). When cylinders 1 and 2 are closed together in the drilling mode, the cylinders are locked in a fixed rotational position with respect to each other so that the bend angle does not change during drilling operations.
Figure 2 shows the upper 3 and lower 5 fixed bend sections oriented in the same direction (zero degrees net bend angle for the drill pipe). In this orientation the cylindrical tool is nothing more than a small offset 7 or “kink” in the drill pipe. The center line 8 of the upper drill section 3 and the center line 9 of the lower drill pipe section 5 are parallel with an offset of distance 7. The drill bit is now pointed straight down with no effective angular deviation.
However, when the upper and lower fixed bend sections 3 and 5 are oriented in opposite directions, as in Figure 1, the effective bend angle 6 in the drill pipe passing through the tool is maximum at 2 times the fixed bend angle of X degrees. Continued rotation of the cylinders another 180 degrees with respect to each other brings the effective drill string bend angle back to zero degrees as shown in Figure 2.
1) The two-cylinder housing wants to blow apart.
The two- cylinder housing described so far is totally impractical in a down hole tool that carries highly pressurized fluid such as the mud fluid in a drill string at thousands of psi. It is obvious that the cylinders 1 and 2 will experience enormous hydraulic force to push them apart. Internal locking mechanisms strong enough to hold them together are cumbersome. Any failure of such a locking mechanism means that the lower drill string and the drilling motor and bit are lost when cylinder 2 is blown out of cylinder 1 down hole. That is why the industry had abandoned downhole drilling tools that used concentric cylinders as for the main housing of the tools.
2) How to confirm the down hole bend angle at top side?
There must be some way for drillers at top
side to measure and confirm the bend angle in the drill string
down hole, no matter how easy it is to change the bend angle.
Within the cylindrical housings 1
and 2 of this directional drilling tool, there are two main
subassemblies that solve the two “show stopper” problems 1) and
The third cylinder idea was the “Eureka” moment for me (third prototype, one year too late) that many others had missed for decades. This is what made a working cylindrical tool possible.
My first working prototype with the third internal cylinder 10 was shipped to their main testing lab in Houston. I did not tell the Dresser engineers about the third internal cylinder 10. They thought my device was still an ordinary dual cylinder tool and that I had built an ordinary (the latest) ill-fated cylinder locking mechanism inside to keep the cylinders from exploding apart under high internal pressure. To tease them, I started the test with the cylinders 1 and 2 extended fully apart. When internal mud pressure reached a mere 10 psi, the tool (cylinders 1 and 2) actually closed on itself. The cylinders 1 and 2 stayed closed when the internal mud fluid 20 pressure reached 500 psi. The engineers in attendance were in absolute disbelief. I remember one of the senior engineers storming out of the testing lab shouting “this is a goddamn fraud.” But the boss, Exec. VP Jim Bryan, was there. (He was the one who got me into this project when he bet me that I could not build a downhole direction drilling tool that could be controlled from the well head. We were in London in 1991 helping the Kuwait Oil Company put out their 500 oil well fires. See History section below. )
Jim Bryan looked around and ordered the test technicians to raise the mud fluid pressure to max, about 6000 psi. Other company engineers were leaving the testing floor. They were certain that my 10 inch diameter tool was going to blow apart with pieces flying out the walls. They believed that the two nested cylinders they could see on the outside were experiencing 150,000 lbs of force to blow them apart. I went over and leaned on the tool as the pressure came up. Jim Bryan looked at his assistant and announced: “I don’t know what this clever bastard has done, but give him the money to build one of these that we can put downhole and do some real drilling. If it works like this, give him some more money.”
2) The second essential component in the tool is an internal pressure relief valve 25 that solves problem 2. This valve is unique in that it opens widely shortly after the opening threshold pressure is reached. This unique pressure relief valve in line with the mud fluid pathway made it possible to measure the bend angle in the tool down hole. This pressure relief valve is designed to open at preset low pressures corresponding to the relative angles (ratchet positions) of the drill string downhole that are set by the up and down motion of the drill string as described above.
When the relief valve 25 opens, it allows initial mud fluid 20 to flow at the well head topside. The pressure when mud fluid flow first begins at topside is easily measured. There are eight preset pressure relief valve thresholds. These eight pressure thresholds correspond to the eight angular positions of the drill string that can be set by the tool down hole. These pressure thresholds when mud flow first begins to flow are clear signals at the wellhead (topside) that measure the effective drill angle of the tool down hole. Operators only need to note the pressure at which mud flow first begins as they bring up the mud fluid pressure (eventually to thousands of psi) to begin drilling after picking up the drill string and setting it back down to set a new drill bit angle.
I took prototype #6 to
Houston to demonstrate this topside drill angle measuring
scheme with the variable pressure relief valve. As I was
bragging about the successful test, the company engineers
informed me that pressure relief valves “of any sort are
forbidden in a down hole drill pipe. They just knew they had me
with another “gotcha.” Any experienced valve designer
would have known why. A normal spring loaded pressure
relief valve only opens a small amount such that the high
velocity flow through the valve creates a pressure drop that
keeps the valve open. This creates a large flow
restriction that is intolerable in a drill string. Worse yet,
the narrow fluid passageway at the valve seat is
rapidly eroded by high velocity mud fluid such that the
valve is eaten away. (I was one depressed person on
the flight back from Houston. How could I have been so
stupid as not to have realized that flaw in my design?)
Again, the internal third cylinder 10 scheme saved me. It let me design another hydraulic cylinder assembly between the third cylinder 10 and the upper outer cylinder 1 that supports the relief valve plunger. This cylinder mechanism pushes the valve head back and widely opens the valve after the valve first opens and gives a clear signal of the drill bit angle to the topside. (The details of this valve design are fully explained in great detail in the patent specifications.)
I demonstrated prototype #7 with the “opens widely relief valve” in the test lab at Houston. When the flow rate at full mud fluid pressure was not decreased with my valve in the drill pipe annulus, I got the same reaction. The company engineer who proudly told me earlier that “relief valves are not possible in drill pipes” demanded that my prototype be taken apart before his eyes. He was sure that somehow I had locked the internal relief valve widely open before the test. I made him a small wager that he would find the valve normally closed under no pressure. Of course, he could not see how or why it worked under real pressure when the tool housing was closed. He paid for the steak dinner that night while bugging me for how it worked. I told him I would send him a copy of the patent disclosure and application so he could see it first hand.
Exec VP Jim Bryan came to see my design tested one more time with both of the “show stopper” problems overcome. He agreed to buy a license for the patents and pay for all my expenses over the last four years. But never again will I shoot my mouth off about “how easy something will be.” That is what I had done in 1991. I had confidently told Jim Bryan, “when we get these oil well fires in Kuwait out I will design a downhole directional drilling tool for you that you can control from the well head.”
I got involved in this project to design and build a down hole directional drilling tool because I shot my mouth off to a famous driller while working on the Kuwait oil well fires in April 1991 (see Kuwait oil well fires section at ). Jim Bryan was the executive vice president of Dresser Industries, a major international oil well supply and service company. He came to help with the Kuwait oil well fires. His vast experience in the drilling business and his knowledge of the oil well equipment that we were trying to rescue in Kuwait was invaluable. And he was a great guy as a friend and mentor.
One night over dinner, I asked him what sort of technology he dreamed about having for his drilling operations. He told me about the great cost and difficulty of changing the direction that a drill bit goes down in a well hole. He explained how the driller had to pull up the entire drill pipe (“trip the string”) to insert a bend angle in the drill pipe (a “bent sub” ) just before the drill bit so that the drill bit would begin drilling at an angle instead of straight down. Then when the drill bit had drilled far enough in a new direction, the driller had to trip the string again to replace the bent sub with another one of a different angle ( or a straight ). Pulling out the entire drill pipe (tripping the string) for a well that could be 5000 ft deep was very costly and time consuming. He told me that every driller dreamed of having a tool in the drill pipe far down hole that could change the drilling angle without having to trip the string each time. And the tool had to be adjustable from the well head -- and the tool had to tell the driller at top side what the down hole angle of the tool was at anytime.
I thought about the drilling problem for a few minutes. I told him about some of the exotic things we had designed for underground nuclear testing over the years at the Lawrence Livermore National Laboratory. I told him that I thought what he wanted would not be difficult -- when I had time.
Jim Bryan calmly took out a piece of paper from his coat pocket and spent a few minutes writing out something for me. He handed it to me. It was a handwritten check for $50,000 drawn on a Houston bank. The conditions were: “This check can be cashed by Dr. Bill Wattenburg when he delivers to Dresser Industries an operational down hole directional drilling tool that can be programmed at the well head within one hour to change the drill bit direction down hole without tripping the string and the tool successfully operates for more than 100 hours at a depth of 1000 feet or more.” I smiled. I was confident that I would need only a few weeks when I got back to the Livermore Lab to collect this $50,000.
Thus began an adventure in frustration that eventually required nine different prototypes, six different tests in Houston, and over half of my time for the next three years before I won the bet. By that time I had expended many times the $50,000 out of pocket. Fortunately for me, the final tool that I delivered worked far better than Jim Bryan or any of his company engineers had expected. And they were very interested in some features of my tool that could be used in other downhole tools, such as the way the cylinders of the housing close under pressure and the “opens widely pressure relief valve.”.
Jim Bryan offered to license the patents on the design. I was delighted to turn a loser into a decent profit and leave it with them. I took a lump sum payment for a non-exclusive license of the patents and moved on to other problems for which I could offer some expertise.
Before this adventure was over, I learned that whenever the old timers in any field have not solved a very serious and expensive problem in their business, it is not necessarily because they are incompetent. You will have to work pretty hard to beat them at their own game.