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).    
www.google.com/patents?id=1z8aAAAAEBAJ     www.google.com/patents?id=QfkiAAAAEBAJ

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. 

Overview of Design.  See Figure 1 and 2 below.  

The main housing and operational action of this directional drilling “tool” is  shown in the Figures 1 and  2 below.   Any device installed in a drill pipe (string), such as this directional drilling device,  is called a “tool”  or a “sub.”  The numbers in the text henceforth refer to specific components of the tool as  labeled in Figures 1 and 2.

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 degrees).

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.  

 Major Problems:  

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.   

Solutions:  

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 2) above.

Problem  1)  was solved with  a third cylinder  10  inside the two outside housing cylinders 1 and 2.    Third cylinder 10  carries the pressurized mud fluid 20 through the center of the tool.   The internal cavities of the outer two cylinders 1 and 2  are sealed by seal positions 12 and 13  with the inner third cylinder 10.  This configuration  makes a hydraulic cylinder  11  that closes the two outer  cylinders 1 and 2 on themselves rather than expands them apart when mud pressure 20 is applied inside the assembly.

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?)

Achieving the “open widely” valve feature was my second  Eureka moment.    This was simply  a necessity that I had to invent or give up.  

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.”  

History:

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   www.wattenburg.us ).    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.