U.S. patent application number 10/598966 was filed with the patent office on 2008-01-03 for multizone stimulation using wax balls.
Invention is credited to Matthew Marcantonio, Vincent Marcantonio.
Application Number | 20080004190 10/598966 |
Document ID | / |
Family ID | 32117968 |
Filed Date | 2008-01-03 |
United States Patent
Application |
20080004190 |
Kind Code |
A1 |
Marcantonio; Vincent ; et
al. |
January 3, 2008 |
Multizone Stimulation Using Wax Balls
Abstract
A diverter for use in multizone stimulation processes and
characterised in that it comprises a ball consisting of wax with an
appropriate melting point, size and specific gravity for use in the
stimulation process.
Inventors: |
Marcantonio; Vincent; (West
Caister, GB) ; Marcantonio; Matthew; (West Caister,
GB) |
Correspondence
Address: |
WORKMAN NYDEGGER
60 EAST SOUTH TEMPLE
1000 EAGLE GATE TOWER
SALT LAKE CITY
UT
84111
US
|
Family ID: |
32117968 |
Appl. No.: |
10/598966 |
Filed: |
March 17, 2005 |
PCT Filed: |
March 17, 2005 |
PCT NO: |
PCT/GB05/01131 |
371 Date: |
June 13, 2007 |
Current U.S.
Class: |
507/200 |
Current CPC
Class: |
E21B 33/138
20130101 |
Class at
Publication: |
507/200 |
International
Class: |
E21B 21/00 20060101
E21B021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 18, 2004 |
GB |
0406123.0 |
Claims
1-6. (canceled)
7. A diverter for use in multizone stimulation processes, the
diverter comprising a ball being comprised essentially of wax
having an appropriate melting point and a specific gravity for use
in the stimulation process, the wax ball being sized such that it
is forced into a perforation in a wall of a well by the application
of pressure and hence forms a seal.
8. The diverter according to claim 7, comprising wax and an
appropriate diluent, wherein the diluent is used to adjust the
specific gravity of the ball such that it is at least similar to
the specific gravity of the chemical fluids to be used in the
stimulation process.
9. The diverter according to claim 7, wherein the diverter is
spherical.
10. The diverter according to claim 9, wherein the diameter of the
spheres are in the range 16 mm to 22 mm.
11. A method of producing a diverter suitable for use in multizone
stimulation processes, wherein, a) the process used to produce the
diverters is an injection moulding process; b) the material used in
the process is comprised essentially of wax with or without a
diluent and having a melting point and specific gravity appropriate
to the intended use; and c) the mould cavities defining the shape
of the moulded products are ball-shaped and sized to form a ball
which fits into a perforation in a wall of a well, by the
application of pressure, and hence forms a seal.
12. A multizone stimulation process comprising the steps of: a)
chemically treating an area to improve the flow of oil or gas
through rock strata; b) sealing the chemically treated area by
insertion under pressure of diverters into perforations in the wall
of a well; and c) subsequently releasing the diverters to allow oil
to flow; wherein the use of diverters which comprises essentially
of wax (with or without a diluent) balls of an appropriate size,
specific gravity and melting point that, on release of the sealing
pressure, they melt as they are carried upwards in the oil flow,
the wax balls being sized such that they enter into the
perforations in the wall of the well by the application of
pressure, and hence seal the perforations.
Description
FIELD OF THE INVENTION
[0001] The invention relates to improvements in multizone
stimulation processes used in the oil and gas industry.
REVIEW OF THE ART
[0002] During the production of oil (or gas) a process known as
multizone stimulation is often used. This process involves drilling
an elongate shaft also known as a well which is then sealed at one
end. A down-hole tool, known as a perforating gun, is used to
generate perforations in the side walls of the shaft, at a pre-set
point. Chemicals are then pumped into the surrounding rock to break
down the structure of the rock strata, such that oil can
subsequently be more efficiently removed from the surrounding
strata (or area).
[0003] Sealants such as polypropylene balls or small flat wax
frits--known in the industry as `diverters` or `Frac Balls`--are
then passed into the chemicals being used) under pressure such that
they pass into the perforations and so seal off the well shaft from
the surrounding area. The perforation process is then repeated at
further points within the shaft, chemicals introduced as required
and the other points sealed off in the same way if required. When
oil production is started/resumed from the area, if polypropylene
spheres have been used then they are forced out of their seating
positions (by the release of the retaining pressure) and carried
with the flow of the oil to a point where known means are present
to enable their removal. If wax frits are used then, due to the
increased ambient temperature at the normal depth at which oil
wells are located, the frits are released from their sealing
position (by the release of the retaining pressure) such that they
are melted by the hot oil and so do not require removal from the
resulting flowing oil.
[0004] Another process carried out in the oil/gas industry uses the
same chemicals to unblock strata, via previously made perforations,
which have become blocked during oil production. Polypropylene
balls or wax frits (sealants) are also used in this case but they
result in the blockage of the perforations into which the chemicals
initially flow such that the subsequent flow of chemicals is
directed to other perforations and hence other blocked strata
areas. In this way a number of previously blocked areas of strata
can be treated before the pressure is released which is keeping the
sealants in place, resulting in a resumption of the flow of oil
from the area.
[0005] However, due to the small size of the frits used in these
processes and their non-uniform shape, they are not readily
transported to the area which is required to be sealed off and the
process requires a build up of the frits in the perforations (some
frits pass through the perforation) thus resulting in the need to
use large quantities of the frits to seal off the perforations.
[0006] There are also problems associated with the transfer of the
frits down the apparatus used to deliver them to the relevant area.
Due to their irregular shape they tend to block the transfer lines
used in the transfer process.
[0007] There therefore exists a requirement for a material which
can be used in the aforementioned sealing processes which has the
shape and resulting flow characteristics of the polypropylene
spheres currently used in combination with the beneficial melting
properties associated with the use of wax frits. The current
invention seeks to provide a solution which addresses these
issues.
SUMMARY OF THE INVENTION
[0008] In a first aspect, the invention provides a diverter for use
in multizone stimulation processes and characterised in that it
comprises a ball consisting of wax with an appropriate melting
point, size and specific gravity for use in the stimulation
process. Diverters are also known as Frac Balls.
[0009] Preferably the diverter comprises wax and an appropriate
diluent.
[0010] Preferably the diverter comprises a ball which is
spherical.
[0011] In a second aspect, the invention provides a method of
producing a diverter suitable for use in multizone stimulation
processes, the method being characterised by the features,
[0012] a) that the process used to produce the diverters is an
injection moulding process;
[0013] b) that the material used in the process is wax with or
without any necessary diluent, of a melting point and specific
gravity appropriate to the intended use; and
[0014] c) that the mould cavities defining the shape of the moulded
products are ball-shaped.
[0015] In a third aspect the invention provides a multizone
stimulation process comprising the steps of: [0016] a) chemically
treating an area to improve the flow of oil or gas through rock
strata; [0017] b) sealing the chemically treated area by insertion
under pressure of diverters into the walls of a well shaft; and
[0018] c) subsequently releasing the diverters to allow oil to
flow;
[0019] characterised by the use of diverters in the form of wax (or
wax-based) balls of an appropriate size, specific gravity and
melting point that, on release of the sealing pressure, they melt
as they are carried upwards in the oil flow.
[0020] Included within the scope of the invention is a diverter for
use in multizone stimulation processes substantially as described
herein with reference to and as illustrated by any appropriate
combination of the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a perspective view of one of the stainless steel
block halves that makes up a two-part mould suitable for forming
wax spheres.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] In this embodiment, wax spheres are produced by injecting
into a two-part mould a wax with an appropriate melting point. The
spheres described herein are 5/8 of an inch (16 mm) or 7/8 of an
inch (22 mm) in diameter and this particular embodiment uses
paraffin wax with a melting point of 155.degree. F.
[0023] It will be appreciated by those skilled in the art that
other waxes with appropriate melting points could also be used such
as vegetable waxes and other manufactured and naturally occurring
waxes with appropriate melting points. Paraffin wax typically
comprises solid saturated hydrocarbons with the molecular formula
C.sub.nH.sub.2n+2. Wax is used in the current application as it is
inert with respect to the acidic chemicals used in the multizone
stimulation process described herein and additionally is soluble in
crude oil which is at a temperature above the melting point of the
wax.
[0024] The mould half of FIG. 1, and its mirror-image complementary
half (not illustrated) mould to be used in the process described
herein is treated with an appropriate agent to promote release of
wax spheres produced, preferably before the two-part mould used
herein is assembled.
[0025] The mould, when assembled, defines one or more (in practice,
many) rows of hollow spheres formed within two blocks of stainless
steel. Channels (13) are provided within the blocks such that each
hollow sphere 12 is connected to its immediately adjacent
neighbouring spheres.
[0026] Molten wax is forced into the mould under pressure via a
single inlet (11) leading into a sphere (15) defined in a central
portion of the mould. The wax is then forced by applied pressure
along the channels (13) to adjacent hollow spheres. In this way the
hollow spheres fill with wax, from the side to which the inlet is
connected, to the opposite side which incorporates a series of
channels forming outlets (14) through which air contained in the
mould is forced out as the molten wax fills the mould. It is
important that there are no air pockets in the formed wax
spheres.
[0027] The wax is then allowed to cool and the wax spheres then
contained within the mould are released by separating the two
blocks that form the mould.
[0028] These wax spheres when used in the process of multizone
stimulation are required to have a specific gravity similar to or
the same as the chemicals used to break down the rock structure.
The reason for this is that as the spheres used must be transported
with the chemicals being used, if they have a lower specific
gravity they will float in the chemical (gel/liquid), if they have
a higher specific gravity they will sink in the chemical
gel/liquid. In either of these cases a problem will be generated in
that the spheres are not readily transported to the required areas.
The result of this is that larger quantities of wax spheres must be
used to seal off the broken down rock structure before starting the
multizone stimulation at other points.
[0029] By making the density of the spheres the same as or similar
to the chemical fluids being used the spheres are readily
transported by the chemicals being used. The specific gravity of
the fluids normally used is 0.9, 1.1, 1.2 or 1.3 relative to water
at 25.degree. C. Spheres of the appropriate specific gravity are
produced by first mixing the wax used with appropriate quantities
of diluents such as calcium carbonate and/or talcum powder which
are used in a powdered form. The appropriate ratio of diluent to
wax can be determined.
[0030] The reason for using these particular diluents is that they
are inert with respect to the paraffin wax used herein. Various
other materials could be used as diluents such as other
aluminosilicates, potassium carbonate, calcium chloride and the
like.
[0031] The current process uses a vertically mounted mould which is
filled from top to bottom via the inlet (11).
[0032] In use, the size of the spheres used is determined by the
diameter of the perforations created by the perforating gun in the
well wall. A suitable quantity of wax spheres (typically 150-200)
is injected into the flow of the chemicals being used (treatment
fluid) by means of a transfer/injection gun.
[0033] The wax spheres are transported into the perforations in the
wall of the well using the chemicals being used to break down the
rock strata, the temperature in the well and immediate area having
been reduced below the melting point of the wax being used by the
flow of the stimulation chemicals used. The wax spheres are forced
into the perforations in the wall of the well under pressure and
form a seal such that the multizone stimulation process can be
repeated elsewhere--or alternatively, other processes can be
carried out. Positive pressure is applied to keep the spheres in
place until the multizone stimulation process or other processes
are complete. Release of the applied pressure results in the flow
of oil/gas up the drilled shaft. The temperature within the shafts
rises as a result of this to a point in excess of the melting point
of the wax. The molten wax then dissolves in the oil such that
there is not the previous need to manually recover the known
propylene spheres from the flow of oil/gas.
[0034] The paraffin waxes used in the embodiment described herein
can be obtained from the following suppliers:
[0035] Paraffin waxes with melting points of 155.degree. F.,
180.degree. F. can be obtained from the following suppliers;
[0036] AUBIN Chemical Solutions, Aberdeen (GB);
[0037] RAW Chemical Distribution Limited, Great Yarmouth (GB);
and
[0038] EGGAR & Co (Chemicals) Limited, Reading (GB) who are the
distributors for Eastman Chemical Company in the USA.
[0039] Paraffin waxes with a melting point of 220.degree. F. are
available from RAW Chemicals (GB) and EGGAR & Co (Chemicals)
Limited (GB).
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