Wells – Processes – Separate steps of fracturing or attacking formation
Reexamination Certificate
1999-11-01
2001-05-29
Schoeppel, Roger (Department: 3672)
Wells
Processes
Separate steps of fracturing or attacking formation
C166S287000, C166S288000, C166S289000, C166S300000, C166S303000, C166S308400, C166S376000, C166S074000
Reexamination Certificate
active
06237688
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to apparatus and methods for completing subterranean wells and, in a preferred embodiment thereof, more particularly relates to the completion of a subterranean well using a pre-drilled casing section having plugged side wall apertures therein which may be opened downhole in conjunction with the process of communicating an adjacent subterranean formation with the interior of the casing section via its side wall apertures.
In a conventional completion process for a subterranean well, a well bore is extended through a subterranean formation, and a tubular casing structure is coaxially positioned within the wellbore to maintain the integrity of the wellbore, and facilitate subsequent placement of various downhole tools in the well. After placement of the casing within the well bore, the casing is laterally enveloped within a cement liner structure by forcing cement downwardly through the casing, outwardly through its lower end, and back up the well bore along the exterior surface of the casing. The resulting external cement liner on the casing serves to prevent undesirable vertical communication between various formations via the space between the exterior side surface of the casing and the side surface of the well bore.
Next, an explosive-based perforating gun structure is lowered into the cemented-in casing to a position vertically adjacent the formation to be perforated. Firing of the perforating gun detonates various shaped explosive charges thereon, with each of the detonated shaped charges sequentially penetrating an adjacent portion of the casing side wall, the adjacent cement lining, and a portion of the formation extending outwardly from the cement lining. This explosive penetration of the formation operatively communicates it with the interior of the now perforated casing so that production fluid from the formation may enter the casing for appropriate retrieval and transport to the surface in a well known manner.
This conventional use of a perforating gun carries with it the usual risks, inconveniences and unreliability associated with dealing with highly explosive materials. Moreover, when utilizing a perforating gun the operator must often contend with the deploying, dropping and recovering the perforation equipment.
As can readily be seen from the foregoing, a need exists for improved apparatus and associated methods for communicating the interior of a well casing with a surrounding subterranean formation. It is to this need that the present invention is directed.
SUMMARY OF THE INVENTION
In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, a subterranean well is completed using a specially designed tubular casing section having side wall apertures which are sealingly covered by plug structures that are removable downhole to re-establish communication between the interior of the casing section and its outer side via the side wall apertures.
According to one illustrated method, the plug structures are of a eutectic material, and a casing assembly, having a longitudinal portion defined by the apertured casing section, is positioned within a wellbore with the plugged casing side wall apertures adjacent a portion of a preselected subterranean formation. A sealing layer is formed outwardly around the positioned casing assembly by sequentially flowing a sealing material, representatively a cement material, downwardly therethrough, outwardly therefrom, and then upwardly between the exterior of the casing assembly and the surface of the wellbore.
The plugged side wall apertures are then re-opened by introducing a source of heat into the apertured casing section. The heat source is representatively a heated liquid flowed into the casing assembly, but could be another type of heat source, such as steam or an ignited propellant material, if desired. Introduction of such heat source into the casing section melts the plug structures and re-establishes communication between inner and outer side portions of the casing sections through its now re-opened side wall apertures. (In cases where the casing assembly is not cemented-in along the wellbore surface, this communicates the subterranean formation with the interior of the casing assembly via the opened side wall apertures).
Next, fracture areas are created which extend outwardly from the re-opened side wall apertures, through adjacent portions of the sealing layer, and outwardly into the formation. Preferably, this step is performed using a propellant-based stimulation tool, such as a stimulating gun or stimulating stick, lowered into the casing assembly and actuated after the casing side wall apertures are re-opened. Alternatively, an explosive-based stimulation tool could be utilized.
While the plug structures are representatively of a eutectic material, they could be of a variety of other materials, and other techniques could be alternatively utilized to remove them, downhole, from the casing side wall apertures which they sealingly block. For example, the plug structures could be of a frangible material which could be broken downhole, could be of a corrodible material which could be eaten away downhole by an acidic or highly basic liquid introduced into the casing section, or could be of a combustible material which could be ignited and combusted downhole.
In another illustrated embodiment of the completion method described above, a propellant-based stimulation tool lowered into the casing is used to simultaneously remove the casing side wall aperture plug structures and form the fracture areas that extend from the re-opened casing side wall apertures sequentially through the sealing layer and outwardly into the adjacent subterranean formation. The lowered propellant-based stimulation tool may be used to break the plug structures, or the plug structures may be formed from an ignitable propellant material which is ignited and combusted by the hot gases generated by activation of the stimulation tool. Alternatively, an explosive-based stimulation tool could be utilized.
REFERENCES:
patent: 5320178 (1994-06-01), Cornette
patent: 5355956 (1994-10-01), Restarick
patent: 5685372 (1997-11-01), Gano
Burleson John D.
George Flint R.
Halliburton Energy Service,s Inc.
Imwalle William M.
Konneker J. Richard
Schoeppel Roger
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