Claims
- 1. In a method of drilling a well bore by means of a drill string through which drilling fluid is circulated, the step of causing at least a portion of the well bore from one location beneath the earth's surface to another point therebeneath which other location is displaced both horizontally and vertically with respect to the one location, to approximate the catenary curve that would be assumed by the drill string upon the application of a tension having a preselected horizontal component to thereby cause the drill string to move away from the side of the well bore.
- 2. In a method of drilling a well bore comprising the steps of predetermining the catenary curve that the drill string would tend to assume when an upward force having a preselected horizontal component is exerted thereon, and drilling the well bore along said predetermined catenary curve so that in the event the lower end of the drill string becomes stuck in the well bore, said upward force on the drill string will cause the drill pipe to tend to assume said predetermined curve which will move at least a substantial portion of the drill string out of engagement with the wall of the well bore to substantially reduce the friction between the wall of the well bore and the drill string and thereby increase the portion of the upward force exerted on the stuck portion of the drill string.
- 3. In a method of drilling a well bore from a point on the earth's surface to a final depth point below the earth's surface that is displaced horizontally a preselected distance from a vertical line extending through the surface point at a preselected vertical distance below the earth's surface wherein the weight of the bottom hole assembly, the weight of the drill pipe per unit length, the unit weight of the drilling mud, and the maximum desired angle of the well bore from the vertical at the final depth point are known comprising the steps of assuming a horizontal component of the total tensile force that would be exerted at a point at or adjacent the surface by the drill string if the drill string followed a catenary curve that extended from said point through the final depth point, calculating the angle of the catenary curve at said final depth point, raising or lowering the assumed total horizontal component as required to obtain the catenary curve having the desired angle of curvature at the final depth point, and drilling a well bore from said first point to said final depth point along a path that follows substantially the catenary curve that gave the desired angle from the vertical for the well bore at said final depth point.
- 4. The method of claim 3 in which the well bore is drilled between a plurality of selected points on said catenary curve along a radius of curvature between said points.
- 5. The method of claim 4 in which the radius of curvature sections are drilled by locating a bit stabilizer adjacent the drill bit and a string stabilizer spaced above the bit stabilizer, placing a predetermined weight on the section of the drill string between the stabilizer to bend the section between the stabilizer to cause the bit to tend to build the angle of the well bore at a predetermined rate.
- 6. The method of claim 3 in which the well bore is drilled between a plurality of calculated points on said catenary curve by increasing the angle of the well bore between said points at an increasing rate that approximates the change of curvature of said catenary curve.
- 7. The method of claim 6 in which said sections of the well bore between said points are drilled by locating a bit stabilizer adjacent the bit, locating a string stabilizer in the drill string a preselected distance above the bit stabilizer, locating a telescoping joint in the drill string between the two stabilizers that will allow the length of the drill string between the stabilizer to increase a predetermined distance as the bit deepens the well bore, and causing a pressure drop in the drilling mud flowing through the telescoping joint that will exert a compressive force on the section of the drill string between the telescoping joint and the stabilizer to cause the bit to tend to increase the angle of the well bore as the length of the drill string between the stabilizer increases due to the expansion of the telescoping joint and lowering the drill string to close the telescoping joint each time it reaches the end of its outward movement.
- 8. Apparatus for drilling between two points a well bore that is inclined from the vertical and has a substantially constantly increasing dip angle using a drill bit at the lower end of a drill string, comprising a bit stabilizer located in the drill string adjacent the drill bit, a string stabilizer located in the drill string a preselected distance above the bit stabilizer, a telescoping joint located in the string between the two stabilizers to allow the length of the drill string between the two stabilizers to increase as the bit continues to drill, and means in the telescoping joint to produce a pressure drop in the drilling mud pumped through the telescoping joint that produces a preselected compressive force in the drill string between the two stabilizers to provide the desired weight on the bit and to cause a preselected bending of the drill string between the stabilizers to cause the bit to tend to increase the dip angle of the well bore as the distance between the stabilizers increases and the bending increases.
- 9. A method of recovering substances from a subsurface earth formation, comprising: drilling a borehole along a catenary curve into said formation from a location horizontally and vertically displaced from said formation, and withdrawing substances from said formation.
- 10. A method of drilling a borehole into a subsurface earth formation, comprising: drilling a borehole into said formation from a location horizontally and vertically displaced from said formation and along a path at least a portion of which is defined by the curve of a catenary, and extending said borehole further through said formation along a substantially horizontal path of travel.
- 11. A well drilling method comprising: drilling a borehole into said formation along a path at least a portion of which is defined by the curve of a catenary, extending said borehole further through said formation along a substantially horizontal path of travel, and generating a driving force for the drill bit in said horizontal path in response to mud pressure.
- 12. A method of drilling a well into a subsurface earth formation, comprising: drilling at least a portion of a borehole from a location horizontally and vertically displaced from said formation along the curve of a catenary until the bedding plane of the formation is intersected, and extending said borehole from the catenary curve to and along the bedding plane of the formation to a maximum extent within the bedding plane, and withdrawing substances from said formation.
- 13. A well drilling method, comprising: drilling at least a portion of a borehole along the curve of a catenary until the bedding plane of the formation is intersected, extending said borehole to and along the bedding plane of the formation to a maximum extent within the bedding plane, and generating a driving force for the drill bit in the bedding plane in response to mud pressure.
Parent Case Info
This is a continuation-in-part of application Ser. No. 19,175, filed Mar. 9, 1979, and entitled "Drilling Method and Apparatus", now abandoned.
This invention relates to well drilling generally. In one of its aspects, it relates to a method of and apparatus for drilling a directional well, or a portion thereof, along a preselected path from the surface to a preselected point that is displaced horizontally from a vertical line extending through the starting point on the surface. It is another aspect of this invention to provide a method of and apparatus for urging the drill bit to tend to drill a well bore that has an increasing rate of change of angle to the vertical.
Many oil and gas wells, and most of those drilled offshore, are drilled at an angle to the vertical to locate the bottom of the well bore at some point displaced horizontally from a line extending vertically into the earth below the drilling rig. The coordinates of the final depth point of the well bore are selected prior to the well being drilled. These coordinates will include the vertical depth of the final depth point, the horizontal displacement, and the compass direction or bearing of this point from the drilling rig. The most common technique used by directional drillers to drill such wells is to gradually increase the dip angle, i.e., the angle between a vertical line and the longitudinal axis of the well bore, until the longitudinal axis of the well bore is pointing at the preselected final depth point, then drill the hole straight at the target--the final depth point. Usually, when the dip angle of a well bore is changed, it is done at a constant rate, which results in the well bore following a radius of curvature.
The drilling assembly or drill string for drilling a well bore includes the drill bit at the bottom of the drill string, a plurality of drill collars directly above the bit, and the drill pipe that extends from the drill collars to the surface. A drill collar is a thick-walled tubular member and a sufficient number of such collars are placed in the drill collar section to provide the desired weight on the bit. Preferably, the drill pipe is in tension during the drilling operations. Also, preferably, the neutral point, that is the point in the string where the stress changes from tension to compression, is located below the top of the drill collars.
The most common problem encountered while drilling a well bore is the sticking of the drill string somewhere along the well bore. This can occur well above the bottom of the hole. For example, where the hole is curved along a radius of curvature, the upward force required to support the pipe string can pull the pipe into the upper side of the curved portion of the hole to the extent that the frictional force between the pipe and the wall of the well bore is such that the pipe cannot be moved. The places in a well bore where this type of sticking is likely to occur are referred to as "key seats".
Usually, however, when a pipe string sticks in a well bore, it involves the drill collars and in most cases is the result of what is known as "differential pressure sticking". This occurs when the drill collars are laying against a porous formation that contains a fluid at a lower pressure than the hydrostatic pressure of the drilling fluid in the well bore. This creates a differential pressure equal to the difference between the formation pressure and the hydrostatic pressure of the drilling fluid that acts across the area of the drill collars in engagement with the formation. The large normal force thus created will produce a frictional force between the drill collars and the well bore that will require a substantial tensile force to overcome. In a conventional, directionally drilled well bore, when the drill collars are stuck against the well bore by differential pressure, the large upward force on the drill pipe required to free the pipe causes the drill pipe to move into frictional engagement with the high side of the well bore, which increases the frictional drag of the pipe against the well bore and the total force required to free the pipe. In other words, in such situations the harder the pull the higher the frictional forces to be overcome, with the result that pulling on the pipe is self defeating.
The primary object of this invention is to provide a method of drilling a well bore that substantially reduces the likelihood of the drill string becoming stuck because of a key seat in the well bore and that reduces the frictional force between the drill string and the well bore when a section of the drill string is held against the wall on the well bore by differential pressure so that most of the upward force applied to the drill string will be available to pull the stuck section away from the wall.
In accordance with my invention, the drill string is treated like a portion of a chain or other flexible line of uniform weight per unit of length, which, when suspended at both ends, assumes a "catenary" curve. Thus, I propose to drill a well bore along the path of a catenary curve based on a preselected horizontal component of the total force required to support the drill string, if it extended the full length of the catenary. Consequently, if the pipe becomes stuck in the well bore, and upward pull sufficient to produce the preselected horizontal component may be applied to the pipe to cause the pipe to tend to assume the same catenary curve as that of the well bore. This will cause the pipe string to tend to move to the center of the well bore away from its wall. So positioned, the upward pull of the pipe and/or the upward and downward shock of jars will be transmitted substantially undiminished to the portion of the pipe string that is stuck, greatly increasing the chances of freeing the pipe string.
A further advantage of drilling a well bore along a preselected catenary curve is that, as the drilling progresses, an increasing portion of the upper end of the drill string will have sufficient tension therein to tend to move away from the wall of the well bore, thereby decreasing the frictional forces between the drill string and the wall of the well bore that resist movement of the drill string in the well bore ahd reduce the wear on the casing in the upper end of the well bore by the rotating drill string.
The use of the two stabilizers is a known technique for causing a drilling bit to increase the dip angle of a well bore. One stabilizer is located just above the bit and the other is located some distance above the bit stabilizer. The drill collars between the two stabilizers, being at an angle to the vertical, will tend to bend in the vertical plane due to their own weight. The weight of the drill collars above the upper stabilizer acting on the bent section of collars between the stabilizers cause it to bend more. The bit stabilizer will pivot, due to the bending of the collars between the stabilizers and rotate the bit face toward the horizontal causing it to tend to "build angle".
The rate that the angle of the well bore actually increases is a function of many variables such as weight on the bit, hole angle, and the distance between the stabilizers. The dip of the formation being penetrated also affects the rate of change of the dip angle of the well bore. But for a given down hole assembly and weight on the bit, the bit will tend to build angle at a fairly constant rate.
This is fine for building angle along a radius of curvature. To approximate a catenary curve, however, as in my method, it is preferable to build angle at an increasing rate, and it is an object of this invention to provide apparatus for and a method of accomplishing this. This object is accomplished in accordance with my invention, by increasing the distance between the stabilizers, as the bit drills a section of the well bore. This increases the deflection of the collars and the angle the bit face makes with the vertical, as the bit moves away from the upper stabilizer.
It is yet another feature of this invention to provide an improved method and apparatus that is especially useful in drilling sub-surface boreholes in a substantially horizontal direction.
It is another feature of this invention to provide apparatus that can exert a force on a drill bit causing it to drill ahead along any dip angle.
US Referenced Citations (10)
Continuation in Parts (1)
|
Number |
Date |
Country |
| Parent |
19175 |
Mar 1979 |
|
Patent Grant
4440241
