Wells – Processes – Cleaning or unloading well
Reexamination Certificate
2002-02-25
2004-07-06
Schoeppel, Roger (Department: 3672)
Wells
Processes
Cleaning or unloading well
C166S175000, C166S223000
Reexamination Certificate
active
06758276
ABSTRACT:
FIELD OF THE INVENTION
The invention relates, generally, to new and improved methods and apparatus using mechanical separation between the drilling fluid and the displacement fluids, and specifically, to the use of swab cups and/or metal brushes to mechanically separate the drilling fluid from the displacement fluids, in combination with a casing scraper to remove debris from the inner wall of the casing or other tubular members. The method and apparatus can also be used to clean up downhole fluids, and can be used to wipe and brush well casing and completion risers clean, even with varying internal diameters.
BACKGROUND OF THE INVENTION
It is well known in the art of the completion and/or the workover of oil and gas wells to displace the drilling fluid with a completion fluid or a workover fluid. A workover fluid will typically be either a surface cleaning fluid, such as an acid, to clean out the perforations in the casing, or a formation treating chemical which can be used with proppants to prop open the formation. The completion fluid will typically be a clear, heavy brine such as calcium chloride, calcium bromide or zinc bromide, or various combinations of such heavy brines. The density of such clear brines is generally selected and controlled to ensure that the hydrostatic head or pressure of the fluid in the wellbore will match the hydrostatic pressure of the column of drilling fluid being displaced.
Displacement “spacers”, as they are commonly named, are used between the drilling fluid and the completion fluid, and these are typically formulated from specific chemicals designed for the specific base drilling fluid being displaced, and will typically include weighted or unweighted barrier spacers, viscous barrier spacers, flocculating spacers, and casing cleaning chemicals, as desired.
It is well known in this art that complete displacement of the drilling fluids is critical to the success of completion and/or workover operations. It is extremely important that the brines not be mixed with the drilling fluid itself.
In the prior art, there are two principal displacement methods, viz., direct and indirect. The choice between direct and indirect has depended upon casing-tubing strengths, cement bond log results, and exposure of the formation of interest. If the cement bond logs and the casing strength data indicate that the casing would withstand a calculated pressure differential, i.e., that the casing would not rupture, and that the formation of interest is not exposed, the conventional technique has been that of indirect displacement.
In a typical indirect displacement, large volumes of sea water are used to flush the drilling fluid out of the well. When applying the flushing method, however, it is very important that the pressure of the salt water flush not exceed the pressure which would burst the casing being flushed.
Direct displacement of the drilling fluid, used by those in this art whenever there are pressure problems or the formation of interest is exposed, uses chemical agents and weighted fluids to clean the wellbore and to separate the drilling fluid from the workover/completion fluid. Because a constant hydrostatic pressure is maintained, pressure problems are eliminated. Direct displacement is normally used when (1) casing and tubulars cannot withstand the pressures associated with the indirect displacement procedure; (2) when the formation of interest is exposed; (3) if a source of flushing water, typically salt water, is not readily available; or (4) in the event of disposal and discharge restraints being imposed on the particular well or group of wells.
A common element to both the direct and indirect displacement procedures is the use of barriers and cleaning chemicals (“spacers”) for effective hole cleaning and separation between the drilling fluid and the completion/workover fluid. The primary purpose of a barrier spacer is to provide a complete separation between the drilling fluid and the completion/workover fluid. In such prior art systems, the spacer fluid must be compatible with both the drilling fluid and the workover/completion fluid.
However, to the best of applicant's knowledge, the prior art has not had the ability to displace the drilling fluid with a workover/completion fluid without using a spacer fluid between the drilling fluid and the workover/completion fluid.
It is also well known in this art to use casing scrapers to clean-off the interior wall of a downhole casing, but typically, cannot use the same tool in cleaning casing strings or other tubular members of varying diameters. The following prior art United States patents show various combinations of casing scrapers and/or swab cups, but none of such patents, taken alone or in combination, show or suggest the combination of the present invention.
PRIOR ART
Gibson U.S. Pat. No. 2,362,198: This shows a casing scraper (brush) in combination with swab cups
17
in
FIG. 1
, and the flow of various fluids (water, circulation fluid or cement) through the hollow rod
10
. This device is meant to vertically reciprocate to clean the interior of casing, but does not suggest using the swab cups as a mechanical separation of the drilling fluid and the completion fluid.
Hodges U.S. Pat. No. 2,652,120: This shows a casing scraper
22
and a seal ring
23
(an inflatable packer instead of a swab cup) and a reciprocating rod
15
to create a suction which cleans out the perforations
12
in the casing (see Col. 3, lines 48-68 concerning its operation). The patent does not suggest the concept of mechanical separation of the fluids.
Hodges U.S. Pat. No. 2,687,774: This is related to Hodges U.S. Pat. No. 2,652,120, discussed above, and is of no additional relevance.
Keltner U.S. Pat. No. 2,825,411: This shows a swabbing device which includes a typical chemical cleaning process in conjunction with the reciprocating swabbing process. (See Col. 6, lines 1-11 for the chemical cleaning process.) There is no suggestion of mechanically separating the completion fluid from the drilling fluid.
Maly, et al., U.S. Pat. No. 3,637,010: This is of very little, if any, relevance, showing packers
66
and
68
(see
FIG. 2
) in a gravel packing operation in horizontal wells.
Jenkins U.S. Pat. No. 4,838,354: This shows a casing scraper with blades
18
and a packer
76
supported by a tubing string
12
having a drill bit
48
at its lower end, all within the casing
68
. The production packer
76
is apparently anchored to the casing wall independently of the downward movement of the tubing string
12
. This patent does not suggest the concept involving the mechanical separation of the fluids. In fact, as the pumped fluid exits the drill bit, the fluid returns back through the annulus
82
between the tubing string
12
and the inner tubular member
66
passing through the interior of the packer
76
.
Stafford U.S. Pat. No. 4,892,145: This shows chevron packings
22
and
23
, on opposite sides of a cavity “AC” (see FIG.
2
). Knife blade
34
functions as a scraper between the chevron packings
22
and
23
. Once the chevron packings have isolated the perforations in the casing, fluid is pumped out of openings
27
in the mandrel
11
to clean out the perforations.
Caskey U.S. Pat. No. 4,921,046: This shows a cleanup tool for cleaning the interior of a casing string having a packer cup
18
for sealing the tool to the casing wall, and which pumps clean out fluid out through the port
84
into the casing below the packer cup. The debris is then picked up by the pumped fluid and pumped into the lower end of the mandrel
70
and pumped back to the earth's surface. This does not suggest a mechanical separation of the completion fluid and the drilling fluid.
Jenkins U.S. Pat. No. 5,076,365: This is the same disclosure as U.S. Pat. No. 4,838,354, discussed above, and the same comments apply.
Ferguson et al. U.S. Pat. No. 5,119,874: This well clean out system is used to pump sand and other debris out of the bottom of a producing well, but aside from using swab cups, has essentially no relevance to the present i
M-I L.L.C.
Schoeppel Roger
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