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Claims  |
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What is claimed is:
1. A method of operating a well in a generally horizontal,
petroleum-bearing subsurface formation, said well including a generally
horizontal section extending into the formation and a generally vertical
section extending to the earth's surface, comprising:
running a first tubing string down the well and substantially into the
generally horizontal section;
running a second tubing string down the well to terminate above the
generally horizontal section;
packing off the first and second tubing strings above the generally
horizontal section;
producing petroleum from the formation into the annulus between the first
tubing string and the wall of the generally horizontal section and thence
into and through the first tubing string; and flowing a clean petroleum
liquid down the second tubing string.
2. Apparatus for completing a well in a subsurface oil bearing formation,
the well including a lower, generally horizontal section which extends
into the formation; which comprises:
a dual packer set in the well above the formation;
a first tubing string extending down through a first passageway in the
packer and substantially into the generally horizontal section in the
formation; said first tubing string being closed at its lower distal end
and defining a plurality of perforations proximate the distal end;
a pump in the first tubing string above the packer operable to pump liquid
up the well; and
a second tubing string extending from the earth's surface down the well
through a second passageway in the packer and terminating below the
packer.
3. The apparatus of claim 2 which further comprises a landing nipple in the
second tubing string at the packer.
4. Apparatus for completing a well in a subsurface petroleum bearing
formation wherein the well has a generally vertical upper section, and a
generally horizontal lower section which extends into the formation which
comprises:
a dual packer positioned in the well above the generally horizontal
section;
a first tubing string extending from the earth's surface down through a
first passageway in the packer and then to a remote preselected point in
the formation, the first tubing string being closed at its lower end and
perforated near its lower end;
a pump in the first tubing string above the packer capable of pumping fluid
up the well to the earth's surface; and
a second tubing string extending from the earth's surface down through a
second passageway in the dual packer to terminate proximate the packer.
5. The apparatus of claim 4 further comprising a pump in the second tubing
string above the packer capable of pumping liquid down the well.
6. The apparatus of claim 4 further comprising a landing nipple in the
second tubing string adapted to land a retrievable orifice.
7. The apparatus of claim 6 further comprising an orifice in the second
tubing string at the landing nipple.
8. A well completion for a well penetrating a petroleum-bearing subsurface
interval, wherein the well includes a generally horizontal section
extending into the interval and a generally vertical section extending
upward from the generally horizontal section, which comprises:
a dual passageway packer positioned in the well above the generally
horizontal section;
a downhole pump in the well above the packer capable of pumping liquid up
the well;
a first conduit extending from the suction side of the pump through a first
passageway in the dual packer into the generally horizontal section to
define an annular space with the wall surface of the generally horizontal
section, the first conduit being closed at its distal end and perforated
proximate its distal end;
a second conduit extending from the pump up the generally vertical well
section; and
a third conduit extending down the well through a second passageway in the
dual packer.
9. The well completion of claim 8 which further comprises an orifice in the
third conduit.
10. The well completion of claim 9 in which the orifice is at the packer.
11. The well completion of claim 9 in which the orifice is at the top of
the well.
12. The well completion of claim 8 wherein the downhole pump is a
rod-actuated pump and the second conduct extends from the discharge of the
pump up the well.
13. The well completion of claim 8 wherein the downhole pump is a jet pump,
the second conduct is adapted to supply power fluid down the generally
vertical section to the jet pump, and the discharge of the pump discharges
into the generally vertical section.
14. The well completion of claim 8 which further comprises a landing nipple
in the third conduit at the packer and capable of landing a retrievable
orifice.
15. The well completion of claim 14 further comprising a retrievable
orifice landed in the landing nipple.
16. The well completion of claim 8 further comprising an uphole pump at the
top of the well connected to the third conduit to pump liquid down the
well.
17. A method of recovering oil from a subsurface oil-bearing formation by
means of a well which has a vertically disposed well section extending
down from the surface of the earth, and a laterally disposed well section
which extends into the formation generally along the bedding planes of the
formation to a distal end within the formation, comprising:
transmitting oil produced from the formation into the laterally disposed
section from the distal end of the laterally disposed section through a
first separate fixed passageway extending from the distal end of the
laterally disposed section to the earth's surface; and
transmitting fluid down a second separate fluid passageway from the earth's
surface to a point above the laterally disposed section.
18. The method of claim 17 in which the fluid is recovered oil.
19. The method of claim 18 in which the fluid is recovered oil which has
been treated to remove sediment.
20. The method of claim 17 in which the fluid is steam or hot water.
21. The method of claim 20 in which the transmittal of oil through the
first fluid passageway is restricted during at least a portion of the time
that hot water or steam is transmitted down the second passageway.
22. The method of claim 17 which further comprises injecting an
oil-displacing fluid into the oil-bearing formation toward the laterally
disposed well section from a second laterally disposed well section which
is spaced from the first-named laterally disposed well section.
23. The method of claim 22 in which the second laterally disposed well
section is spaced laterally from the first-named laterally disposed well
section.
24. The method of claim 22 in which the second laterally disposed well
section is spaced vertically from the first-named laterally disposed well
section.
25. Apparatus for producing oil from a subsurface oil-bearing interval,
which comprises:
a laterally disposed well section which extends from a proximal end to a
distal end within the subsurface, oil-bearing interval;
a vertically disposed well section which extends from said proximal end to
the earth's surface;
a first conduit within said laterally disposed section extending from a
distal end within the laterally disposed section to a proximal end within
the vertically disposed section said first conduit being closed at its
distal end and defining a plurality of perforations proximate its distal
end;
a second conduit disposed within the vertically disposed section configured
to receive fluid from the proxemal end of the first conduit and to convey
such fluid to the earth's surface; and
a third conduit disposed within the vertically disposed section capable of
conveying fluid from the surface of the earth down the vertically disposed
section.
26. The apparatus of claim 25 which further comprises a downhole pump
arranged to take suction from the proximal end of the first conduit and to
discharge into the second conduit.
27. The apparatus of claim 26 in which the vertically disposed well section
is cased, a dual packer is positioned within the vertically disposed well
section below the downhole pump, the first conduit passes through a first
passageway in the packer, and the third conduit passes through a second
passageway in the dual packer.
28. The apparatus of claim 27 in which the downhole pump is a rod-actuated
pump.
29. The apparatus of claim 27 which further comprises an orifice in the
third conduit.
30. The apparatus of claim 29 in which the orifice is positioned at the
dual packer.
31. The apparatus of claim 29 in which the orifice is positioned proximate
the earth's surface.
32. The apparatus of claim 26 which the vertically disposed well section is
cased and the second conduit comprises the well casing; the pump is a jet
pump; a dual packer is positioned in the vertically disposed well section
below the downhole pump; the first conduit passes through a first
passageway in the packer; and the third conduit is adapted to convey a
power fluid to the jet pump.
33. The apparatus of claim 25 further comprising a packing material within
the annular space between the first conduit and the laterally disposed
well section.
34. The apparatus of claim 25 which further comprises:
a second laterally disposed well section which is spaced from the first
laterally disposed well section, and which extends from a proximal end to
a distal end within the subsurface interval;
a second vertically disposed well section which is spaced from the first
vertically disposed well section, and which extends from the proximal end
of the secondlaterally disposed well section to the earth's surface; and
a fourth conduit disposed within the second vertically disposed well
section to convey fluid from the earth's surface to the second laterally
disposed well section.
35. The apparatus of claim 34 in which the fourth conduit extends at its
distal end into the second laterally disposed well section and said fourth
conduit is closed at its distal end and defines at least one set of
perforations within said second laterally disposed well section. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to the completion and operation of wells
drilled laterally into underground formations. The invention, more
especially, concerns a system of completing a horizontally disposed well
in a producing formation in a manner which promotes production from the
formation. The system also enables the well to be cleared of bridges and
the like which may occur in the well. The invention has particular
application to the production of oil and gas from subterranean formations.
2. Related Art
A continuing objective in the petroleum industry is to increase the
productivity of wells drilled into petroleum-bearing formations. Another
continuing objective is to minimize the need for expensive repair and
workover operations caused by the occurrence of bridges and like in
producing wells.
Once a well has been drilled into a petroleum bearing formation, it is a
common practice to stimulate the well by hydraulic fracturing, acidizing,
perforating, solvent treatments, and similar techniques. The general
purpose of such techniques is to increase the effective permeability of
the producing formation penetrated by the well. A related purpose is to
increase the effective volume of the formation which is drained by the
well. These purposes become especially important in instances where wells
are very expensive to drill. This is particularly true, for example, in
offshore locations where many wells may be drilled from a single offshore
island or platform. It is a common practice in drilling such offshore
wells to have them fan out laterally in many directions from the island or
platform. These wells, therefore, will frequently extend in a generally
horizontal direction into a formation.
The drilling of horizontally disposed wells is not limited to offshore
locations. Wells of this nature are also drilled onshore. The more general
practice onshore, however, is to drill vertical wells which extend down
through the producing zone. Any sand, silt or other solids with a high
density which may enter the well will then drop to the bottom "rat hole"
portion of the well and cause no difficulties in producing the well. In
this sense, vertical wells have had an advantage over horizontal or
lateral wells in that the latter wells have been very subject to bridging
The bridging material commonly consists of silt, formation particles, frac
proppant, and the like.
Horizontal wells do not have a rat hole into which silt, sand and other
particles may drop and accumulate. These materials, instead, accumulate
along the lower side of such wells where they tend to raft up into
barriers due to fluid flow. All too frequently, these barriers can
completely close off the flow passage, in which case no production can be
realized from behind the barriers.
SUMMARY OF THE INVENTION
The present invention springs in part from the realization that
petroleum-bearing formations characteristically have naturally occurring
vertical fractures, and that these fractures present the potential of
producing from a substantially rectangular volume of a formation. By way
of contrast, a vertical well drilled through such fractures results in
production from a generally elliptical shaped volume whose major axis lies
along the fractures, and whose minor axis is perpendicular to the
fractures. It follows that the volume of a formation exposed to production
is much greater in a horizontal or lateral well bore than a vertical well
bore. It will be recognized, of course, that this condition prevails in
those instances where the formation bedding planes are laterally disposed.
It will further be recognized that this is generally the case in petroleum
bearing formations.
The present invention is accordingly concerned with an improved system for
completing horizontally disposed wells in petroleum bearing formations.
The invention is especially concerned with a system which will reduce the
adverse effects on such wells caused by bridging and the like. The
invention is also concerned with a system for more effectively producing
petroleum bearing formations.
To this end, the invention comprises a system in which two strings of
tubing or similar conduits are installed in a well which includes a
vertically disposed upper section and a laterally disposed lower section.
A first string extends from the upper end of the well to the lower end of
the well. This string is perforated near its lower end--i.e., near the
distal end of the lateral section of the well. The second string extends
from the upper end of the well to a point generally above the lateral
section of the well. In a preferred form of the invention, a dual packer
is installed in the vertical section of the well above a producing
formation, zone or other interval of interest. The first tubing string
passes through one passageway in the packer to terminate within the
interval of interest. The second tubing string passes through the other
passageway in the packer and normally terminates just below the packer.
Assuming the well to be equipped with a suitable pump, the pump is located
in the vertical portion of the well above the packer. The pump is
installed in the string of tubing which extends into the horizontal or
lateral borehole to its far or distal end. As noted earlier, suitable
perforations in the form of holes, slots or the like exist in this tubing
proximate its distal end. Typically, the perforations will be located
within a few feet or yards of the distal end of the tubing. The distal end
of the tubing is closed. Formation fluids entering the horizontal section
of the borehole must enter the tubing through the perforations and then
through the tubing to the suction of the pump. From there, the pump may
deliver the formation fluids up the well to the earth's surface. In the
case where the pump is a rod-actuated pump, the fluids will normally flow
up the first tubing string--i.e., the production string--to the surface.
Alternatively, as in the case where the pump is a jet pump, the produced
fluids may be pumped up the well annulus around a tubing string which
delivers power fluid to the pump.
As noted earlier, a second string of tubing extends down the vertical
portion of the well through the second passageway in the dual packer. In a
preferred form of the invention, the second tubing string includes a
landing nipple at the packer. This latter arrangement makes it possible to
install a retrievable orifice or choke in the second tubing string. It is
thereby also possible to select a controlled flow rate of fluid through
the second tubing string while maintaining pump suction pressure in the
horizontal well bore.
The foregoing type of well completion makes possible a variety of
operations. A first such operation is directed at keeping the horizontal
borehole free of bridges and the like. To that end, a small, normally
regulated flow of clean crude or other oil is pumped down the second
tubing string, and then through the horizontal borehole annulus into the
far end of the first tubing string. From there the clean crude passes
through the second tubing string to the downhole pump, whence it is pumped
up to the surface of the earth. If a bridge develops in the horizontal
well bore, the level of clean oil in the second tubing string
automatically begins to rise and build up pressure in this string. By
proper selection of the clean oil flow rate and the diameter of the second
string, the pressure in this string will build up quickly to the pressure
in the producing formation. However, the pressure will continue to rise if
the bridge does not break at that point. As a consequence the bridge will
almost surely break, because very high differential pressures (between
pressures in the second string and the suction pressure below the downhole
pump) become available. Moreover, additional pressure beyond the head
pressure in the second tubing string can be exerted by increasing the flow
rate of the pump at the earth's surface which delivers clean oil to the
second string.
In accordance with an alternate embodiment of the invention, an orifice in
the second tubing string may be installed at the entrance to the string at
the earth's surface rather than at the dual packer. Bridging will now
cause the hydrostatic head in the second string to build up as before;
however, when the bridge breaks, clean oil flow will not be restricted
until the hydrostatic head in the second string has been depleted.
In accordance with another alternate embodiment of the invention, the dual
packer may be omitted in which case clean crude may be permitted to build
up in the well as far as the earth's surface. This embodiment, however,
lacks the control provided by the packer and retrievable choke.
In accordance with still another embodiment of the invention, various
fluids may be injected down the second (smaller) tubing string for the
purpose of stimulating production from the formation penetrated by the
horizontal well. Thus, production from the well can be shut in while a
fluid such as carbon dioxide, liquefied propane, hot water, steam or the
like is injected down the second string and into the formation. After
sufficient fluid has been injected to soak, or otherwise mix with,
formation fluids surrounding the well, the well can be placed on
production again with attendant increased flow of formation fluids from
the well.
In instances where more than one well has been completed in a given
formation, the invention may be used to advantage in producing formation
fluids from one well to another. Thus, assuming two laterally spaced wells
completed in accordance with the present invention, an oil displacing
fluid such as thickened water can be injected down the small tubing string
in one well and then forced toward the adjacent well by restricting
production from the original well in favor of production from the adjacent
well. Further, various flow patterns may be established between the wells,
such that improved sweep between the wells may be obtained.
In considering all of the above producing operations, it is important to
recognize that the presence of natural vertical fractures in a formation
greatly favors increased production. As explained earlier, the combination
of a horizontally drilled well and vertical fractures is a highly
beneficial one in making for better production rates.
The present invention also contemplates the placement of gravel, resin
coated sand and similar packing in the horizontally disposed annulus
between the walls of a horizontally drilled well and a length of
perforated tubing within the well. Placement of such materials can be
attained by pumping them down the second tubing string and into the
annulus to be deposited in the annulus. If a small diameter, retrievable
orifice is present in the second string through the dual packer, this
orifice may be removed prior to pumping the placement material down the
well.
In those instances where gas locking of the down hole pump may occur
because of low formation pressure or high gas/oil ratios of the fluids
produced, etc., it is contemplated that locking may be readily overcome by
venting the well through the second tubing string.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates in partial vertical section how the invention may be
applied to an existing vertical well.
FIG. 1A, is an enlarged detail view in longitudinal cross-section of a
landing nipple and orifice located at the dual packer.
FIG. 1B, is an enlarged, detail view in section of an orifice located in
the spaghetti string at the earth's surface.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, a horizontally disposed well section or borehole 12
has been formed in producing zone, formation or other interval 10 from a
vertically disposed well section 8. Casing 11 extends down the vertical
well 8 to a point somewhat above the lateral section 12. A dual packer 18
is set within the casing 11, and two strings of tubing 14 and 24 extend
through the dual passages in the packer. The larger tubing string 14
extends from a down hole pump 20 above the packer 18 to the remote or
distal end 16 of the well 12. The tubing string 14 is perforated by
perforations 34 proximate its closed distal end 32.
The second tubing string 24, normally smaller in diameter than string 14,
extends from a pump 36 at the surface of the earth down through the second
passageway in the packer 18. A landing nipple 26 is installed in this
packer passageway such that removable orifices of different sizes may be
placed in the second tubing string.
A tubing string 22 extends up the well 8 from the pump 20 to the surface of
the earth. This tubing string and tubing string 14 constitute, in effect,
a single string 14 through which pump 20 takes suction and delivers
produced fluids up the well to the surface. A wellhead ss not shown at the
top of the well 8; however, it will be recognized that the selection of a
suitable wellhead is within the state of the art.
The pump 20 shown in the drawing is typically a downhole rod-actuated pump,
although a jet pump may also be used as explained earlier in this
description. In the latter case, a jet pump would normally discharge fluid
into the annulus 21 and thence o the earth's surface.
In operation, the system shown in FIG. 1 enables fluids in the producing
formation 10 to flow into the annulus 30, from which the fluid | | |
