Wells – Above ground apparatus – Moving tubing or cable into an existing well
Reexamination Certificate
1999-07-01
2001-06-19
Tsay, Frank S. (Department: 3672)
Wells
Above ground apparatus
Moving tubing or cable into an existing well
C166S385000
Reexamination Certificate
active
06247534
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to systems and methods for introducing cable and items connected thereto into a wellbore and, in certain particular aspects to a system with a capstan drive apparatus for facilitating the introduction of cable into a wellbore reducing or eliminating the need for added weight, e.g. sinker bars.
2. Description of Related Art
Various operations in a wellbore require the raising and lowering of various tools and equipment on a cable within the wellbore. For example, in wellbore logging operations a logging system is hung from a cable and moved into and out of the wellbore by raising and lowering the cable. In various prior art wellbore cable systems, the tools or equipment for introduction into and movement within a wellbore are connected to one end of the cable and the other end is connected to some type of winch or other raising/lowering system. In many systems, the cable is passed over one or more sheave wheels positioned between the winch and the wellbore. It is common for one such sheave wheel to be secured to a derrick or rig above the wellbore as well as one such sheave wheel mounted below on the ground or on a rig platform. Such systems typically employ a fluid pressure control system to counterbalance the pressure of fluid in the well which can oppose the introduction into the wellbore of the cable and items connected thereto. Often weight (e.g. sinker bars) is added to the items hung from the cable to counter upward fluid pressure in the wellbore and to pull the cable through the fluid pressure control system. This added weight requires a corresponding increase in height of a lubricator used above the wellhead between it and the sheave wheel(s). The lubricator is long enough to hold all of the tools going downhole, including the sinker bars.
In the prior art systems described above the height of an entire system above the rig platform can be substantial, e.g. forty-five or more feet. The problems associated with such high systems were addressed in U.S. Pat. No. 5,188,173 which discloses a cable system for use in well cable operations in association with a rig at the surface, the system having a pressure control device for counterbalancing the fluid pressure from the well; a high pressure chamber through which the cable passes; and a cable sheave wheel incorporating the chamber. By using the cable sheave wheel in its own pressurized chamber and pointing the chamber downward, an effort is made to reduce overall system height. The sheave wheel of the systems of U.S. Pat. No. 5,188,173 has a groove for receiving and holding the cable.
There has long been a need for an effective and efficient system for introducing cable into a wellbore whose overall height is reduced as compared to the height of prior art systems and which adequately moves the cable into the wellbore. There has long been a need for a system which pulls the cable through a pressure control device in high pressure wells and thus reduces or eliminates the need for sinker bars thereby reducing rig up height.
SUMMARY OF THE PRESENT INVENTION
The present invention, in certain aspects, provides a method and system for introducing cable and items connected thereto into a wellbore. In certain embodiments the system has a powered drive system with a rotatable capstan ring about which the cable is wrapped several times. The capstan drive system is positioned between a pressure control device or stuffing box (on one side and a lubricator system on the other) on one side and the wellbore on the other. The lubricator system is attached to a wellhead over the wellbore. The capstan drive system pulls the cable through the pressure control device. A motor rotates the capstan ring via appropriate gearing.
The pulling force generated by the capstan pulls the cable through the pressure control device overcoming the wellhead pressure times cable area force (wellhead pressure force) that seeks to blow the cable out of the pressure control device. In previous systems this wellhead pressure force was overcome by adding sinker bars (weights) to the tool. With systems according to the present invention, the need for the sinker bars is reduced or eliminated, reducing the length of lubricator needed, and thus reducing the height of the system.
In certain aspects the capstan's rotatable ring has a flat outer surface with no groove or grooves, unlike the sheave of many prior art systems (e.g. that of U.S. Pat. No. 5,188,173) which has one or more grooves. The flat capstan surface allows the cable to be wrapped around the capstan a plurality of times, and to slide across the face of the capstan ring, as it progresses through the plurality of wraps. Such a capstan is a tension multiplier. The amount that the capstan multiplies the tension is given by the following equation:
T
2
T
1
=
ⅇ
2
μπn
where:
T
1
is the initial tension caused by the weight of the logging tools
T
2
is the final tension—the tension in the cable being pulled through the stuffing box
&mgr; is the friction coefficient—usually about 0.18 for an oil wet environment
&pgr; is 3.14159
n is the number of wraps the cable makes around the capstan
For example, assuming a friction coefficient of 0.18 and the number of wraps as 4.5, the tension multiplication factor (T
2
/T
1
) is 162.3. Thus if the weight of the logging tools is 100 lbs, the driven capstan multiplies this tension to 16,230 lbs. Thus as much as 16,230 lbs of tension would be available to pull the cable through the pressure control device. The stator or scroll in the housing serves to guide the cable across the capstan face so that the cable does not cross over itself or become tangled in some way.
One of the critical parameters which is measured during a wireline operation is the hanging weight of the cable and tools in the well, typically referred to simply as “weight”. This weight measurement is typically measured with a load cell located either at the wireline reel or at a sheave at the base of the wellhead. The capstan in this invention will be changing the tension in the cable, so it will be difficult to measure the weight in these locations. Thus a small sheave wheel or roller is mounted on a load measuring device and located on the wellbore side of the capstan. A load is generated at this small sheave or roller by having the cable change its angle slightly around this sheave or roller. This change in angle causes a load in the sheave or roller which is proportional to the weight.
What follows are some of, but not all, the objects of at least certain preferred embodiments of this invention. In addition to the specific objects stated, other objects and purposes will be readily apparent to one of skill in this art who has the benefit of this invention's teachings and disclosures. It is, therefore, an object of at least certain preferred embodiments of the present invention to provide:
New, useful, unique, efficient, non-obvious systems and methods for introducing cable and items connected thereto into a bore or well;
Such systems and methods which employ a capstan drive;
Such systems which result in a significant reduction in rig-up height;
Such systems and method which employ a driven capstan without grooves about which the cable is wrapped; and
Such systems with a stator or scroll to guide the cable across the capstan.
Certain embodiments of this invention are not limited to any particular individual feature disclosed here, but include combinations of them distinguished from the prior art in their structures and functions. Features of the invention have been broadly described so that the detailed descriptions that follow may be better understood, and in order that the contributions of this invention to the arts may be better appreciated. There are, of course, additional aspects of the invention described below and which may be included in the subject matter of the claims to this invention. Those skilled in the art who have the benefit of this invention, its teachings, and suggestions will appreciate that th
CTES L.C.
McClung Guy
Tsay Frank S.
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