Wells – Processes – Placing or shifting well part
Reexamination Certificate
2000-05-18
2001-11-27
Neuder, William (Department: 3672)
Wells
Processes
Placing or shifting well part
C166S077200
Reexamination Certificate
active
06321848
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods of inserting tubing into a well bore and to well head apparatus for performing such methods and is useful for the insertion of continuous tubing, e.g. of plastic, and of coupled tubing sections into live well bores.
2. Description of the Related Art
One of the differences between running coil tubing and coupled tubing into a well head is typically the way the well head is configured. Because it is usually predetermined that coil tubing is going to be installed into the well instead of coupled tubing, a full opening closure is installed at the surface to the top of the casing of the well bore before the well is perforated. The closure installation is generally consistent with coupled tubing live well installations, with the difference typically but not always being the type of closure. The closure may vary in size and configuration from a standard valve to any suitable well control device, e.g. a blow out preventor. The closure is dependent on the well application, with a typical prerequisite being full opening consistent with the inside diameter of the well casing or the largest size of any tool or mechanism that may be installed within the well head assembly, e.g. the tubing hanger assembly.
Once the well has been perforated, the full opening closure is closed so as to maintain the well pressure below the closure. A well head which is designed to hang or suspend coil tubing may be installed on top of the casing, after or prior to perforating the well, and below the full opening closure, once again depending on the application, the closure therefore being located above or below the wellhead. The well head is generally much the same as any conventional well head, with typical outlets and valves on opposing sides to allow access to the annulus (i.e. the space between the tubing and the casing) as may be necessary to deal with any particular well. The well head may also have a sealing device incorporated into the body of the head to allow movement of the tubing while maintaining well bore pressure.
Most coil tubing installed into wells today is steel and is injected into the well with a hydraulically activated injector head that has two opposed rolling surface areas that effectively push the tubing into the well from above the well head, using friction to ensure control and movement of the tubing into the well bore and thereby exerting compressive forces on the tubing. This process is very expensive because of the cost of the steel tubing and also because it requires the use of elaborate and therefore expensive equipment.
Plastic tubing, which is very inexpensive compared to steel tubing, has been inserted into wells using the same apparatus, but is limited to use with low well bore pressures because of the risk of buckling and collapsing in response to the compressive forces acting on the plastic tubing.
Another factor with the use of coil tubing in well applications is the difficulties encountered with depth measurement relating to the leading end of the tubing. The tendency for coil tubing to remain in a semi-coiled state in the well bore because of residual memory, resulting from the tubing being installed from a round spool, and also surface contact friction encountered as the tubing lays against the walls of the well casing increase friction, thereby making insertion into the well bore more difficult, increasing the potential for buckling and making depth measurement very inaccurate.
BRIEF SUMMARY OF THE INVENTION
According to the present invention, there is provided a method of inserting tubing into a well bore which comprises the steps of supplying a leading end of a continuous length of well bore tubing from a coil of such tubing towards the well bore, providing on the leading end a piston, and supplying gas or fluid under pressure to the piston to thereby force the piston and the leading end downwardly into the well bore.
By the present invention, therefore, the tubing is pulled downwardly into the well bore by the piston on the leading end of the tubing and the tubing is subjected to tensile forces instead of the compressive forces which were exerted on the tubing in the above-discussed prior art method. This is particularly advantageous when plastic well bore tubing is employed.
Also according to the present invention, there is provided a method of inserting tubing into a well bore which comprises the steps of inserting the piston on a leading end of the tubing into a conduit above the well head and supplying gas under pressure from a compressed gas source above the piston to thereby force the piston and the leading end of the tubing downwardly into the well bore.
Preferably, a closure and flow regulating device, e.g. a pressure regulator or choke, is installed on a trailing end of the tubing intended for installation, and fluid displaced below the piston is allowed to flow upwardly through the tubing at a controlled rate corresponding to the displacement and pressure of the well bore. By allowing the fluid displaced below the piston to flow upwardly through the tubing, the fluid, which may be gas, in the well is prevented from being pushed back into the formation, which would have undesirable effects on the well (depending on the sensitivity of the well formation) and production.
By maintaining consistent and close to equal pressures between the inside and outside of the tubing, collapse of the tubing is prevented. With the use of plastic tubing the performance properties of the tubing are such that the tubing would otherwise allow only a relatively low external pressure before the well pressure forces would compress the exterior wall of the tubing to an undesirable point of collapse. By maintaining a pressure inside the tubing the external forces from the pressure of the well can be counteracted.
With equal pressures or moderate differential pressures on the internal and external surface of the walls of the tubing, remaining within the scope of the collapse performance of the tubing, the tubing can be installed into wells with much higher pressures than would otherwise be possible.
Once he tubing has reached the desired depth in the well, the closure at the trailing end of the tubing is closed and the tubing is then landed into the receiving well head while constantly maintaining pressure inside the tubing and thereby not allowing it to collapse.
The methods and apparatus according to the present invention thus address and prevent issues and restrictions incurred with the use of conventional methods and equipment while installing tubing into live well bores. The displacement and collapse issues with the use of plastic coil tubing, as well as buckling and depth measurement associated with tubing being inserted or hanging in a well, are eliminated. Another advantage to the present invention is that the tubing can be left in tension while suspended in the well by employing the piston at the leading end of the tubing and thereby pulling the tubing into the well bore. Hydrocarbons from the well are never introduced to equipment above the well head and are immediately displaced into the well bore followed by an inert fluid or gas above the piston, making the present method and apparatus much safer in the event of human error or equipment failure than prior art methods used today.
In a preferred embodiment of the invention, a wellhead assembly is installed above a closure and the closure is closed to maintain pressure in the well bore. The leading end of the tubing is then introduced together with the piston into a cylindrical tube, and gas under pressure, from a pressured vessel is introduced into a passage within the cylindrical tube either above and/or below the piston while the tubing is secured to prevent movement of the piston and the tubing. The pressures above and below the piston are thus equalized.
Further gas under pressure is then introduced into a passage above the piston to effect the forcing of the piston and the leading end of the tubing into and down the well bo
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