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Description  |
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BACKGROUND OF THE INVENTION
In the art of drilling wellbores for the purpose of producing hydrocarbon
bearing formations found downhole therein, it is often advantageous to
slant the lower marginal end of the borehole so that the pay zone is
penetrated substantially horizontally and at a considerable distance
radially away from the drilling rig. One of the advantages found in
slanting a borehole in this manner is to enable the pay zone to be entered
at a number of different locations radially spaced about the drilling rig
so that a plurality of the boreholes can be formed from a common drilling
location. This technique is especially advantageous when the cost of
moving the drilling rig is considerable, as for example, an offshore
drilling rig.
Another advantage derived from slanting the lower marginal end of the
borehole horizontally respective to the pay zone is that a tremendous
amount of surface area of the borehole is located directly in the pay
zone; and therefore, a greater number of perforations can be formed which
extend back up into the hydrocarbon bearing formation, thereby achieving a
much greater production rate from the pay zone.
Where the pay of the slanted borehole is located in an unconsolidated type
strata, the loose particles of the formation tend to flow through the
perforations and thereby bring about many undesirable and complicated
production problems which are difficult to overcome. Accordingly, it would
be desirable to be able to perforate a slanted borehole in such a manner
that the formation is penetrated only in a predominately downward
direction; and accordingly, flow of unconsolidated material must therefore
occur in an upward direction, thereby causing the solid matter which
constitutes the pay zone to tend to gravitate downwardly and remain insitu
respective to the formation, and this is the primary subject of this
invention.
SUMMARY OF THE INVENTION
Method for completing a lower slanted marginal end of a cased wellbore by
running a jet perforating gun downhole into proximity of the hydrocarbon
bearing formation to be completed, and orienting all of the jet charges of
the gun to fire in a downward direction so that production from the
perforated pay zone must flow upwardly through the perforations before
entering the slanted portion of the borehole.
More specifically, this invention comprehends a jet perforation gun having
the shaped charges thereof oriented to fire in substantially the same
direction radially away from the gun in a substantially narrow angle of
divergence respective to one another. Casing engaging means in the form of
a member which is attached to the gun housing and extends radially away
from the gun in opposition to the oriented shaped charges is included in
the invention. The length of the arm is of a value to cause the free end
thereof to extend into close proximity of the inside peripheral wall
surface of the casing. This expedient distributes the mass of the gun in
such a manner that the center of gravity thereof causes the gun to
gravitate into a position whereby the members thereof seek an upright
position, while the shaped charges thereof seek an inverted position, and
the shaped charges are accordingly aligned respective to the slanted
borehole such that when detonated they fire downwardly through the casing
wall and into the formation, rather than horizontally or upwardly
thereinto.
In one form of the invention, a tubing string is connected to a swivel, the
swivel is connected to a ported sub, with the sub being connected to a gun
firing head, while the gun firing head is connected to detonate all of the
shaped charges of the gun. A weighted object is circulated down through
the tubing string, through the swivel, and impacts against the gun firing
head, with circulation occurring down the tubing string, through the
ported sub, and back up the casing annulus. The impact of the weighted
object against the gun firing head detonates the individual shaped
charges. The gun includes a plurality of charge carriers which are
connected in series relationship so that a substantial length of the
slanted borehole can be perforated and production thereafter controlled to
avoid producing the unconsolidated material of the formation.
Accordingly, a primary object of the present invention is the provision of
a system by which an unconsolidated formation of a hydrocarbon producing
wellbore can be completed.
Another object of the invention is to disclose and provide a method for
completing a wellbore so that fluid can be produced from an unconsolidated
formation without producing solid material therefrom.
A further object of this invention is to disclose and provide a method by
which the shaped charges of a jet perforating gun are oriented to fire in
a predominantly downwardly direction when the gun is placed downhole in a
slanted borehole.
A still further object of this invention is to disclose and provide a
gravity oriented perforating system for a slanted wellbore by which the
perforations are caused to extend in a predetermined direction away from
the wellbore.
These and various other objects and advantages of the invention will become
readily apparent to those skilled in the art upon reading the following
detailed description and claims and by referring to the accompanying
drawings.
The above objects are attained in accordance with the present invention by
the provision of a combination of elements which are fabricated in a
manner substantially as described in the above abstract and summary.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 diagrammatically illustrates a cross-sectional view of a slanted
borehole having apparatus made in accordance with the present invention
associated therewith;
FIG. 2 is an enlarged, broken, part cross-sectional, elevational view of
part of the apparatus disclosed in FIG. 1;
FIG. 3 is an enlarged, cross-sectional view taken along line 3--3 of FIG.
1;
FIGS. 4, 5, and 6 diagrammatically illustrate various different exaggerated
configurations of the apparatus disclosed in FIG. 3; and,
FIG. 7 is a fragmented, enlarged, cross-sectional view of a casing of a
wellbore which has been perforated in accordance with the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 diagrammatically illustrates a wellbore 10 which has a casing 12
extending downhole into the earth. A tubing string 14 is more or less
concentrically arranged respective to the casing and also extends downhole
through the borehole and into proximity of a hydrocarbon containing
formation. The lower marginal end 16 of the borehole has been slanted, and
in the illustrative view of FIG. 1 it will be appreciated that the degree
of the slant has caused the lower end of the borehole to assume a path
which is essentially horizontal, while the upper end of the borehole is
essentially vertical.
As seen in FIGS. 1-3, a jet perforating gun 18, made in accordance with the
present invention, is located downhole in the slanted portion of the
borehole. The gun includes a charge carrier 20 within which there is
disposed a plurality of shaped jet perforating explosive-type charges. The
individual shaped charges are made in accordance with the prior art. A
plurality of other charge carriers 22 can be series connected with respect
to the charge carrier 20. The charge carrier is provided with the usual
threaded plugs 24 which form a closure member for a port formed
therewithin, through which the hot plasma jet exits whenever the gun is
detonated.
As seen in FIGS. 1 and 2, a sub 26 interconnects each of the charge
carriers. A sub 28 is provided with radially spaced apart ports 29 and is
connected to the lower end of the tubing string by means of a swivel 30.
The swivel 30 can take on a number of different forms so long as it
enables relatively low friction axial rotation between the charge carrier
and the tubing string.
Numeral 31 of FIG. 1 diagrammatically illustrates the bend of the borehole
which, of course, occurs over a length of several hundred feet as the
vertical upper marginal end of the borehole is slanted toward the
illustrated horizontal lower marginal end of the borehole. In this
respect, the term "slanted borehole", as used throughout this disclosure,
is intended to relate to a borehole which is sloped away from a vertical
position sufficiently to enable the gun apparatus of the present invention
to bear against the inside peripheral wall surface thereof with sufficient
gravitational force to cause the gun to be oriented into an upright
position. The term "upright position", as used herein, is intended to mean
that the shaped charges of the gun come to bear in a substantial downhole
direction as contrasted to an uphole direction.
The outer housing of the charge carrier is rigidly connected to an
outwardly directed member 34 and 36, which is affixed to the housing and
extends in opposition to the shaped charges, with the free outer end
portion of the member being sized such that it is located in close
proximity to the inside peripheral wall surface of the casing when the gun
is in the upright position.
In the illustration of FIGS. 1-6 of the drawings, the individual charge
carriers 20, 22 of the gun are illustrated as each having a forward and
rearward casing engaging member 34 and 36, 34' and 36' (not shown).
A gun firing head 38 is affixed to the forward or uphole end of the
uppermost charge carrier and is connected in affixed relationship to the
ported sub 28. The forward end 40 and rear end 41 of the orientating
members are preferably curved in order to avoid engagement with any
irregularity formed along the casing wall. A web 42 is rigidly affixed to
the charge carrier housing and supports a load bearing enlargement 43 at
the free end thereof.
In FIG. 1 the hydrocarbon bearing formation 25 has been penetrated at 44 by
the action of the jet charges. The shaped charges have penetrated the
plugs to produce a plasma jet of hot gases and vaporized metal which form
the tunnels 44 in the manner of FIGS. 1, 3, and 7.
In FIGS. 4, 5, and 6, the operation of the gravity orientating perforating
system of the present invention is illustrated. In particular, FIG. 4
discloses the position on the inside wall surface 46 of the casing 12
which is engaged by the casing engaging member 34 should the gun tend to
axially rotate respective to the tubing 14 as the gun is run downhole. As
seen in FIG. 4, should the gun tend to climb the sidewall of the casing,
enlargement 44 will be rotated into engagement with the casing wall at 46,
thereby preventing any further rotation. At the same time, the mass of the
gun tends to gravitate the gun back into the upright position seen
illustrated in FIGS. 1-3.
In FIG. 5 the gun has climbed the opposed sidewall of the casing, and the
outer enlargement 43 of the casing engaging member again has contacted the
inside peripheral wall surface of the casing at 46 whereupon the mass W of
the gun gravitates the apparatus in a manner such that it axially rotates
back into the upright position.
FIG. 6 illustrates that slight axial rotation of the gun has occurred as it
is located nearly on bottom dead center of the slanted portion of the
borehole. As seen in FIG. 6, should the gun for some reason or another
further axially rotate in either direction, the enlargement 43 of the
casing contacting member will engage the inside casing wall at 46 to
prevent further rotation thereof. Since the charges are aligned to
perforate in a downward direction in FIG. 6, the term "upright position"
applies to this geometrical configuration of the illustration therein.
In FIG. 1, a weighted object 48, in the form of a sinker bar, is circulated
downhole by means of pump P located on drilling platform 50.
In FIG. 3, prima cord 52 is illustrated as being looped through each of the
apertures located rearwardly within the shaped charges 54 in a
conventional manner. Detonating means 56 forms part of the firing head and
explodes the prima cord in response to the firing head being contacted or
impacted by the sinker bar 48 in accordance with my previously issued U.S.
Pat. Nos. 3,706,344 and 4,009,757.
In FIG. 7, the perforating gun of the present invention has been detonated,
thereby forming holes 58 through the aluminum plugs 24, thereby forming
the beforementioned tunnels 44. Upward flow of hydrocarbons from formation
25 is generally illustrated by the arrow at numeral 60. The unconsolidated
formation 25' will flow in the direction of arrow 60 should the individual
perforations of the pay zone be overproduced.
Looking again now to FIG. 6, numeral 62 indicates a vertical line taken
along the slanted portion 16 of the borehole. Numeral 64 indicates the
maximum acceptable angular displacement 72 of the casing engaging member
34 from a vertical plane 62. Numeral 66 indicates a horizontal plane taken
through the casing at 16, while numerals 24, 24' indicate the direction of
the hot gases which result from the detonated shaped charges, and numeral
68 indicates the minimum angle between one of the hot streams of gas from
one of the shaped charges and the horizontal. Numeral 70 is the angular
displacement between pairs of shaped charges when more than one shaped
charge is incorporated in radially spaced relationship in the illustrated
manner of FIG. 3, for example.
A packer 75 can be employed for completing the well in accordance with the
method of the present invention.
OPERATION
In carrying out the method of the present invention, a borehole having a
vertical, upper marginal end and a slanted, lower marginal end portion is
formed into the ground, and the casing 12 is cemented into place so that
the casing extends downhole through the formation 25 to be completed.
The gun is made up and attached to the tubing string 14 in the illustrated
manner of FIG. 1 so that the perforating apparatus can freely axially
rotate with a minimum of frictional resistance respective to the tubing.
The gun is run downhole on the end of the tubing string and positioned
adjacent to and within the formation to be completed. A sinker bar 48 is
pumped down the tubing string by connecting pump "P" to the uphole end of
the tubing string and pumping fluid down the string, out through ports 29,
up the casing annulus, and across the unset packer.
The sinker bar 48 impacts against the gun firing head 38, thereby
detonating the prima cord 52 and causing all of the shaped charges to
explode. The shaped charges penetrate the plugs, casing, and extend back
up into the formation in the illustrated manner of FIGS. 1, 3, and 7. The
gun can be removed from the borehole, and the well placed on production by
utilizing any number of different completion techniques.
Where deemed desirable, the unset packer 75 can be employed by setting the
packer immediately following perforation and the gun left downhole with
production occurring through ports 29 of the sub 28. Alternatively,
permanent completion techniques can be carried out in accordance with my
previously issued U.S. Pat. No. 3,706,344 in conjunction with the present
method.
The present invention enables an almost unlimited number of perforations to
be made along the slanted portion of a borehole, thereby effecting
communication over an extremely long length of borehole formed into the
formation 25, which advantageously enables a large production rate to be
achieved from relatively thin pay zones.
As seen in FIGS. 4-6, the gun is gravitated into the upright position
because of the distribution of mass respective to the casing engaging
member and the center of gravity of the gun. As particularly seen in FIG.
6, the gun is gravitated toward the upright position within the limits of
the angle indicated by numeral 72. The relative location of the pairs of
shaped charges are arranged respective to one another to penetrate the
formation along the indicated angle noted by numeral 70. Accordingly, when
the gun is at its maximum angle of rotation 72, there is always a minimum
angle 68 at which the tunnels extend back into the formation with respect
to the horizontal 66. Therefore, production must always occur from the pay
zone uphole into the casing.
In practicing the present invention, it is desired that the tunnels 44
extend downwardly from the casing so that any unconsolidated material 25'
remains insitu because it is held gravitated into its original position.
For this reason, a large number of perforations 44 are preferred so that
the aggregate rate of production of the sum of the flow through the
perforations is substantial, yet the flow is held to a value required to
avoid flowing any of the unconsolidated matter into the borehole.
The present invention provides an improved method of gravel packing the
formation contiguous to the casing since the gravel can be forced downhole
where it will gravitate into the downwardly directed tunnels 44.
The present invention can also be used in conjunction with a wireline,
wherein the wireline acts as the swivel 30, and with the gun being a
through tubing gun which is run through the tubing, downhole onto location
by pumping the gun with pump P. In this instance, the tubing 14 must be
considered representative of the wireline while the ported sub 28 is
eliminated since the gun is circulated down through the tubing with fluid
returning up through casing annulus. The gun is fired electrically using
known wireline techniques.
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Description |
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