Well completion method and apparatus

Wells – Processes – Cementing – plugging or consolidating

Reexamination Certificate

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Details

C166S289000, C166S154000

Reexamination Certificate

active

06464008

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to deep well completion and production procedures and apparatus. More particularly, the invention relates to completion procedures and apparatus that avoid a final cement plug drilling procedure and a corresponding tool change trip.
2. Description of the Prior Art
The process and apparatus by which deep production wells for fluids such as oil and gas are completed and prepared for production involves the step of sealing the production zone or earth strata from contamination by foreign fluids from other strata, above or below. Additionally, the tubing through which the produced fluid flows to the surface must be secured and sealed within the well bore. Often, the production zones are thousands of feet below the earth's surface. Consequently, prior art procedures for accomplishing these steps are complex and often dangerous. Any procedural or equipment improvement that eliminates a downhole “trip” is a welcomed improvement.
Consistent with prior art practice, production tube setting and opening are separate “trip” events. First, the raw borehole wall casing is secured by placing cement in the annulus between the raw borehole wall and the outer surface of the casing pipe. A string of fluid production tubing is then positioned where desired within the borehole and the necessary annulus sealing packers are set by a controlled fluid pressure increase internally of the tubing bore, for example. After the packers are set, a cementing circulation valve in the production tube assembly is opened by another controlled change in the tubing bore pressure. Cement is then pumped into the segment of annulus around the production tubing that extends upwardly from the upper production zone packer.
This prior art procedure leaves a section of cement within the tubing below the cementing valve that blocks the upper tubing bore from production flow. The cement blockage is between the upper tubing bore and the production screen at or near the terminal end of the tubing string. Pursuant to prior art practice, the residual cement blockage is usually removed by drilling. A drill bit and supporting drill string must be lowered into the well, internally of the production tubing, on a costly, independent “trip” to cut away the blockage.
SUMMARY OF THE INVENTION
An objective of the present invention, therefore, is to position well production tubing within the wellbore, secure the tubing in the well by suitable means such as cement or epoxy, and open the tubing to production flow in one downhole trip.
Another objective of the invention is a completion assembly having the capacity for complete removal of the cement tubing plug without drilling.
It is also an object of the present invention to provide a more expeditious method of well completion by the elimination of at least one downhole trip.
In pursuit of these and other objectives to hereafter become apparent, the present invention includes a production tubing string having the present well completion tool body attached above the upper production packer and the production screen. The completion tool body includes upper and lower pipe subs that are linked by concentric radially spaced tubular walls. The tubular walls are perforated by flow trans for ports. With the annular space between the concentric walls are a pair of axially sliding sleeve pistons. Both sleeve pistons may be axially displaced by fluid pressure within a central flow bore of the tool to close flow continuity through the flow transfer ports between the central flow bore and the surrounding well annulus. An elongated mandrel tube is secured to the internal bore surface of the tool body at a point below the flow transfer ports. From the tool body attachment point, the mandrel tube extends downwardly and concentrically within the production tubing. A retainer socket terminates the lower end of the mandrel tube. The mandrel tube wall is perforated along the upper portion of its length above the plug seat.
Also secured within the internal bore surface of the tool body at a point above the flow transfer port is an elongated dart transport tube having a dart seat at each distal end. The dart transport tube extends longitudinally within the internal bore of the perforated mandrel and is releasably secured to the internal bore surface of the tool body by a set of locking dogs. Proximate of its upper end, the dart transport tube is perforated for flow continuity with the flow transfer ports in the tool body tubular walls.
The completion assembly is placed downhole with all tubes open. When in place, a first closing dart is dropped along the production string bore from the surface to be transferred by gravity and/or pumping onto the closure seat at the downhole end of the dart transport tube. Closure of the downhole seat permits the internal bore of the tubing string to be pressurized independently of the of the production zone wall.
The normal procedural sequence provides for a relatively low tubing string pressure to set the zone isolation packers. A second and greater fluid pressure within the production tubing opens the flow transfer ports in the tool body by shifting one of the closure sleeves. Cement is then delivered down the tubing bore under a pressure head sufficient to discharge the cement through the dart transport tube perforation and flow transfer ports in the tool body into the annulus between the tubing string and the casing wall.
When the appropriate quantity of cement has been delivered into the production tubing, a second closure dart is placed in the tubing bore to cap the surface of the cement column standing in the tubing bore. A finishing fluid such as water is pumped against the second dart thereby completing the flow displacement of the cement remaining in the production tube. When the second dart engages the upper seat of the dart transport tube, all cement is displaced into the well annulus except that remaining in the dart transport tube between the dart seats. Upon closure of the upper transport tube seat, internal tubing bore pressure may be increased to shift the second sleeve piston in the tool body that simultaneously closes the flow transfer ports and releases the locking dogs from the dart transport tube. When released, the dart transport tube travels down the perforated mandrel taking all of the residual cement with it.
At the end of the perforated mandrel is a retainer socket that receives and engages a nose dart on the dart transport tubing. This retainer socket secures the dart transport tube within and along a lower segment of the mandrel. Above the dart transport tube, the perforated mandrel is preferably pierced by numerous large apertures to accommodate a free flow of formation fluid into the internal bore of the production tube.


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patent: 5746274 (1998-05-01), Voll et al.
patent: 5960881 (1999-10-01), Allamon et al.
patent: 6286594 (2001-09-01), French
patent: WO 97/15748 (1997-05-01), None

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