Method and apparatus for preventing debris build-up in underwater oil wells

An improved method and apparatus for preventing buildup of cuttings or debris in underwater oil wells. The apparatus includes a drilling tool in the form of a primary tubular member having an internal diameter a predetermined amount greater than the external diameter of a drill string which is run downwardly through a conventional riser pipe string and underwater wellhead assembly. The drilling tool preferably includes an external shoulder formed on the lower end portion thereof for engagement with a corresponding internal shoulder at the juncture of the riser pipe string and the wellhead assembly for supporting the tool independently of the drill string. An annular resilient seal can be included on the lower end portion of the tool for providing a fluid-tight seal between the lower end portion of the tool and the juncture of the riser pipe string and the wellhead assembly. The tool can include a second tubular member connected at its lower end to the lower end of the primary tubular member. An annular space, open at its upper end, can thus be provided between the two tubular members of the tool for trapping cuttings and debris which may settle out from circulating or non-circulating mud in the annulus between the drill string and the riser pipe string above the tool. The tool is adapted to be retrieved with the drill string upwardly through the riser pipe string to the water surface where any cuttings and debris trapped therein can be disposed of without falling back to the bottom of the borehole.

This invention relates generally to improvements in oil and gas well 
drilling and more particularly, but not by way of limitations, to 
improvements in mud systems and methods of their employment in oil and gas 
well drilling operations. 
A conventional technique employed in the drilling of underwater oil and gas 
wells involves the utilization of a riser pipe string to communicate 
between an underwater wellhead assembly, secured to the underwater floor, 
and the water surface at a drilling barge or platform. Ordinarily, the 
lengths of typical riser pipe strings range between 200 and 800 feet and 
the inside diameter of the riser pipe strings is generally in excess of 
sixteen inches. During drilling, cuttings from the bottom of the well are 
carried therefrom in a drilling mud solution which is pumped downwardly 
through the tubular drill string and circulated upwardly in the annulus 
between the drill string and the borehole, wellhead assembly and riser 
pipe string to the water surface. These cuttings and other debris from the 
bottom of the well can be delivered to the water surface provided the 
proper fluid velocity, mud weight and annulus areas are compatible. 
It has been determined by Applicant, however, that when the annulus area 
between the outer diameter of the drill string and the inner diameter of 
the riser pipe string is very large in comparison to the annulus between 
the exterior of the drill string and the wall of the borehole and inner 
surfaces of the wellhead assembly, the drilling mud can lose the desired 
velocity or flow rate in the annulus between the drill string and the 
riser pipe string necessary to convey the cuttings and debris upwardly 
through the riser pipe string to the water surface for removal from the 
drilling mud. The cuttings and debris carried by the mud in this area of 
reduced velocity are held in suspension in this area as long as mud 
circulation continues, as shown below in FIG. 6, FIG. 7, FIG. 7A and FIG. 
7B. When the mud pump stops and circulation is discontinued, the cuttings 
and debris can settle back to the bottom of the well. Further, when the 
drill string is removed and mud naturally falls within the wellbore to 
assume the space formerly occupied by the drill string, cuttings are 
pushed downwardly out of the riser pipe string into the wellbore. Although 
this problem in underwater well drilling appears to be universal. The 
predominant means currently used to combat this problem is the "piggyback 
system" as shown in FIG. 2 of U.S. Pat. No. 3,465,817 where an extra 
circulation system is employed to boost mud velocity in the riser annulus. 
However, such a system is cumbersome, requires extra motors or pumps, is 
inefficient and, as known to those currently drilling offshore wells, is 
not generally very effective. Junk baskets such as shown in U.S. Pat. No. 
3,102,600 are known for land wells, but the applicability of such devices 
to the riser annulus debris problem has not therefore been appreciated. 
Most often no countermeasures are taken and cuttings and debris fall from 
the riser and remain in the bottom of the well. Such materials may 
thereafter adversely affect testing and cementing programs subsequently 
performed in the well. Circulation employed during testing can be expected 
to cause cuttings or debris to foul various downhole tools causing testing 
misruns, and to severely damage tool parts, thereby materially increasing 
the costs incurred in well completions in offshore areas where new 
production is so urgently needed. As seen in U.S. Pat. No. 3,012,610, it 
has been known to support a wellhead assembly on a drill bit while 
lowering the assembly to a drop-off point, but such technology has not 
been applied to solving the problem of debris accumulation in riser pipes. 
The present invention contemplates a drilling tool for use with a drill 
string comprising a length of drill string, having at least one attachment 
means thereon for attaching the drilling tool, insertable within a riser 
pipe string in underwater drilling operations. The tool includes a first 
tubular member having an upper end portion, a lower end portion, an inner 
portion of a diameter greater than the outer diameter of a portion of the 
drill pipe and means, on said tool, for engaging said attachment means of 
said drill string to support said tool independently of said riser pipe 
string. The tool also includes means, on the lower end portion of the 
first tubular member, operatively engageable with the lower end portion of 
the riser pipe string for supporting the first tubular member within the 
lower end portion of the riser pipe string independently of the drill 
string. The inner diameter of said tool is sufficiently close in magnitude 
to the outer diameter of said drill string to create an annulus 
therebetween of a cross-sectional area sufficiently small to provide, at 
normal circulation rates, a flow velocity therethrough of a magnitude 
greater than the settling rate of said debris in said annulus. The tool 
can further include seal means for providing fluid-tight sealing 
engagement between the lower end portions of the first tubular member and 
the riser pipe string. 
The present invention further contemplates a method of trapping cutting 
debris in an underwater drilling operation wherein a tubular drill string 
having a drill bit on the lower end thereof extends downwardly from the 
water surface within a riser pipe which extends between the water surface 
and an underwater wellhead assembly on the underwater floor. The method 
includes the steps of: inserting a device into the riser string; 
positioning said device adjacent the lower portion of said riser string; 
passing the tubular pipe string downwardly through the riser pipe string 
and wellhead assembly into the borehole, so as to create an annulus 
between said tubular pipe string and said riser pipe, wellhead assembly 
and borehole; circulating a liquid downwardly through the pipe string and 
out the lower end thereof into said annulus; circulating said liquid 
upwardly through the portion of said annulus between the tubular pipe 
string and the borehole and through the portion of said annulus between 
the tubular pipe string and the wellhead assembly at a flow rate 
sufficient to cause said liquid to have an upward flow velocity faster 
than the settling rate of said debris in said liquid; and circulating said 
liquid upwardly from the interior of said wellhead and through said 
annulus between the riser pipe string and the tubular pipe string while 
simultaneously using said device to restrict at least part of said riser 
portion of said annulus to a cross-sectional area sufficiently small to 
cause said liquid to flow therethrough with an upward velocity in excess 
of said settling rate.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, a preferred underwater drilling installation 
constructed in accordance with the present invention is illustrated 
therein and is generally designated by the reference character 10. To 
facilitate illustration, the drilling installation 10 has been broken into 
three segments with the upper segment 12 thereof shown in FIG. 1, the 
intermediate segment 14 thereof shown in FIG. 2, and the lower segment 16 
thereof shown in FIG. 3. 
As shown in FIG. 1, the upper segment 12 of the drilling installation 10 
extends above the water surface 18 and terminates in the usual manner in 
an offshore drilling platform, barge or the like, which is not shown in 
the drawing. The upper portion of the drilling installation 10 includes a 
drilling mud circulation assembly comprising a shale shaker 20, mud tank 
or pit 22 communicating with the shale shaker 20 and a mud pump 24 having 
its inlet connected to the mud tank 22 via a conduit 26. The outlet of the 
mud pump 24 is connected to a conventional swivel 28 via a connecting 
conduit and stand pipe 30 in the usual manner. The outlet of the swivel 28 
communicates with a conventional tubular drill string 32 via a kelly 34. 
The drill string 32 extends downwardly through a riser pipe string 36, the 
upper end of which extends above the water surface 18. A conduit or mud 
return line 38 communicates between the upper end 40 of the riser pipe 
string 36 and the inlet of the shale shaker 20. 
Referring now to FIG. 2, the lower end 42 of the riser pipe string 36 is 
disposed beneath the water surface 18 and is sealingly engaged with the 
upper end 44 of an underwater wellhead assembly 46. The interior of the 
riser pipe string 36 communicates with a vertical passage 48 in the 
wellhead assembly 46. An upwardly facing annular shoulder 50 can be formed 
in the lower end 42 of the riser pipe string 36 adjacent the juncture 
between the wellhead assembly 46 and the riser pipe string 36. It should 
be understood that the upwardly facing shoulder 50 can, alternatively, be 
formed in the upper end 44 of the wellhead assembly 46 adjacent the 
juncture between the wellhead assembly and the riser pipe string. A 
suitable fluid-tight seal can be achieved between the lower end 42 of the 
riser pipe string 36 and the vertical passage 48 of the wellhead assembly 
46 by means of a suitable annular seal 52. 
The wellhead assembly 46 is suitably secured to the underwater floor and 
can be of conventional construction. The wellhead assembly 46 comprises a 
suitable connector 56 at the upper end 54 thereof for connection with the 
lower end 42 of the riser pipe string 36. A blowout preventer 58 
communicates with and is positioned below the connector 56. A gate 60, 
including pipe rams and shut-off rams, is positioned below the blowout 
preventer 58. The gate 60 communicates with a base column 62 positioned 
therebelow which extends downwardly therefrom through a base 64 supported 
on the underwater floor 54. The base column 62 preferably extends 
downwardly from the underwater floor 54 into a borehole 66 and is cemented 
therein as shown at 68. 
The drill string 32 extends downwardly from the base column 62 and 
terminates in a suitable bit 70 for drilling additional borehole 72 
beneath the lower end 74 of the base column 62. 
The drill string 32 is of conventional construction and comprises a 
plurality of joints of drill pipe intermediate the kelly 34 and can 
include an upper drill collar 76, and additional drill collars 78 
intermediate the upper drill collar 76 and the drill bit 70. It will be 
understood that the drill string 32 extends downwardly through the 
vertical passage 48 of the wellhead assembly 46. 
The underwater drilling installation 10 further includes a drilling tool, 
which can be a junk catcher 80, as shown in FIG. 2. The junk catcher 80 
comprises a first tubular member 82 having an upper end portion 84, a 
lower end portion 86 and a cylindrical inner surface 88 having a minimum 
inner diameter greater than the outer diameter of the drill pipe of the 
drill string 32 but less than the outer diameter of the uppermost drill 
collar 76. This minimum inner diameter could be made less than the 
diameter of surface 88 by use of one or more internal ledges (see FIG. 8). 
An annular wall 90 extends radially outwardly from the lower end portion 
86 of the first tubular member 82 and provides means on the lower end 
portion of the first tubular member for supporting the first tubular 
member on the upwardly facing shoulder 50 independently of the drill 
string 32. A second tubular member 92 is disposed concentrically around 
the first tubular member 82 and has an upper end portion 94, a lower end 
portion 96 secured to the annular wall 90, a cylindrical inner surface 98 
having a diameter greater than the diameter of the cylindrical outer 
surface 100 of the first tubular member 82 and a cylindrical outer surface 
102 having a diameter slightly less than the diameter of the inner 
cylindrical surface 104 of the riser pipe string 36. 
The junk catcher 80 further includes an annular resilient seal member 106, 
which may be suitably formed of an elastomeric or synthetic resinous 
material, secured about the lower end portion 86 of the first tubular 
member 82 providing seal means for achieving a fluid-tight seal between 
the lower end portion of the first tubular member and the juncture of the 
lower end portion of the riser pipe string 36 and the wellhead assembly 
46. It will be seen in FIG. 2 that the seal member 106 is preferably 
secured between the cylindrical outer surface 100 of the lower end portion 
86 of the first tubular member 82 and the downwardly facing annular 
surface or shoulder of the annular wall 90 by suitable means such as 
bonding. 
The junk catcher 80 further preferably includes a plurality of perforations 
108 extending between the inner and outer cylindrical surfaces 98 and 102 
of the second tubular member 92. The perforations 108 are sized to permit 
the drainage of drilling mud from the annular space 110 formed in the junk 
catcher 80 intermediate the cylindrical inner surface 98 of the second 
tubular member 92 and the cylindrical outer surface 100 of the first 
tubular member 82 while retaining cuttings and other debris from the 
borehole in the annular space 110 when the junk catcher 80 is removed 
upwardly through the riser pipe string 36. It will be noted in FIG. 2 that 
the upper end portion 84 of the first tubular member 82 extends a distance 
above the upper end portion 94 of the second tubular member 92. 
The outer diameter of the cylindrical outer surface 102 of the second 
tubular member 92 is preferably selected to provide sufficient clearance 
between the junk catcher 80 and the cylindrical inner surface 104 of the 
riser pipe string 36 to permit free passage of the junk catcher 80 
downwardly and upwardly through the interior of the riser pipe string 36 
while minimizing the possibility of cuttings and other debris settling in 
the annulus between the junk catcher 80 and the inner surface 104. The 
inner diameter of the cylindrical inner surface 88 of the first tubular 
member 82 of the junk catcher 80 is selected to provide sufficient 
clearance between the first tubular member 82 and the cylindrical outer 
surface of the drill pipe of the drill string 32 to provide a 
cross-sectional area in the annular space 112 between the first tubular 
member 82 and the drill string 32 to maintain the required mud velocity to 
allow heavy cuttings and debris to be circulated by the mud upwardly 
through the annular space 112 past the upper end portion 84 of the junk 
catcher 80. The overall length of the junk catcher 80 is preferably 
approximately twenty-eight feet. 
Alternatively, a compensator 114 could be used in place of junk catcher 80. 
Compensator 114 is a tubular conduit with an inner surface 116 of a 
primary inner diameter greater than the outer diameter of drill string 32. 
The primary inner diameter of compensator 114 is selected to provide an 
annulus 113 between surface 116 and the drill string 32 of sufficiently 
small cross section to maintain an upward mud flow velocity greater than 
the falling rate in drilling mud 118 of debris being circulated by said 
drilling mud 118. Compensator 114 extends upwardly through riser pipe 
string 36. Above riser pipe string 36, annulus 112 is communicted with mud 
return line 38 via mud outlet 120 so as to substantially avoid mud passage 
between compensator 114 and surface 104 of riser 36. The top of the riser 
36 could be sealed relative to the compensator 114 by means of a 
conventional system such as seen in at reference numbers 96, 97, 107 and 
108 of FIG. 9 of U.S. Pat. No. 3,137,348. Compensator 114 preferably 
includes a landing flange 122 to provide additional seating surface on 
shoulder 50 of riser pipe string 6 for added strength and better sealing. 
Compensator 114 could also be hung from a casing hanger at the top of the 
riser pipe, provided the lower end of compensator 114 is sufficiently 
close to the bottom of the riser pipe to prevent substantial debris 
accumulation. A rubber seal (not shown) or other sealing means could be 
added to flange 122 to provide better sealing, and to cushion contacts 
between shoulder 50 and compensator 114. Internal lugs 124 can be provided 
on inner surface 116 for positioning and retrieving compensator 114. 
A further alternate to junk catcher 80 is provided by latching junk catcher 
126, which is provided with collet fingers 128 or other suitable latching 
means such as a retractable slip or a ratchet mechanism to hold latching 
junk catcher 126 in position at the bottom of riser pipe string 36. Drill 
string 32 can include external lugs 130 cooperable with internal lugs 132 
of junk catcher 126 for raising and lowering junk catcher 126 above the 
lower end of riser pipe string 36, or any large diameter portion thereof, 
such as the drill bit, or a drill collar could be utilized in place of 
lugs 130. 
OPERATION 
Looking to FIGS. 6, 7, 7A and 7B, the prior art system has been realized by 
Applicant to contain an inherent problem. The increased annulus between 
the drill string 32 and the riser pipe string results in slower upward 
flow therethrough. In the case of aluminum cuttings 134, the falling rate 
of cuttings has been found to be greater in drilling mud than the reduced 
upward flow velocity through the riser pipe resulting in settling as in 
FIGS. 7, 7A and 7B into a mass of debris at the lower end of the riser 
pipe string. Applicant has therefore determined that to solve this 
problem, either the flow area must be more restricted through the riser 
pipe string 36 or the debris must be trapped and removed to prevent its 
falling back into the borehole. Otherwise an extra circulation system must 
be provided to boost riser annulus flow velocity. 
Once the wellhead assembly 46 and the riser pipe string 36 are placed in 
proper position, as illustrated in FIGS. 1, 2 and 3, in the well-known 
conventional manner, the drill string 32 may be run in the riser pipe 
string 36 and wellhead assembly 46 to form or extend the borehole 72. The 
drill string 32 is assembled with the drill bit 70 on the lower end 
portion thereof and with drill collars 76 and 78 spaced thereabove. The 
junk catcher 80 is then positioned about the first length of drill pipe 
secured above the drill collar 76. The junk catcher 80 is supported on the 
drill string 32 by the uppermost drill collar 76 or other means such as 
lugs 130 or drill bit 70 as illustrated in FIGS. 5 and 9. The drill string 
32 is lowered downwardly through the riser pipe string 36 and the wellhead 
assembly 46 through the addition of additional lengths of drill pipe 
thereto in a conventional manner. When the junk catcher 80 reaches the 
lower end portion of the riser pipe string 36, the resilient annular seal 
member 106 sealingly engages the upwardly facing annular shoulder 50 thus 
terminating the downwardly movement of the junk catcher 80 within the 
riser pipe string 36 and supporting the junk catcher 80 therein 
independently of the drill string 32. The junk catcher 80 preferrably can 
be latched or otherwise held in position as in FIG. 9. The drill string 32 
is lowered further within the riser pipe string 36 and the wellhead 
assembly 46 until the drill bit 70 contacts the bottom of the borehole 72. 
The weight of the junk catcher 80 bearing on the annular shoulder 50 
through the annular resilient seal member 106 preferably provides a 
fluid-tight seal between the lower end portion 86 of the first tubular 
member 82 of the junk catcher 80 and shoulder 50. 
When drilling commences, drilling mud 118 is circulated from the mud tank 
or pit 22 through conduit 26 to the mud pump 24 and through the conduit 
and stand pipe 30 to the swivel 28. Mud further passes downwardly from the 
swivel through the kelly 34 and drill string 32 and out the lower end 
portion thereof through the drill bit 70 to flush cuttings and debris from 
the bottom of the borehole 72 and circulate the cutting debris upwardly 
with the drilling mud through the annulus between the exterior of the 
drill string and the borehole 72 or casing upwardly to the wellhead 
assembly 46. The cutting and debris laden drilling mud circulates further 
upwardly through the annulus between the exterior of the drill string 32 
and the vertical passage 48 through the wellhead assembly 46 into the 
lower end portion of the riser pipe string 36. The mud and debris further 
circulates upwardly through the annular space 112 between the junk catcher 
80 or compensator 114 or latching junk catcher 126 and the exterior of the 
drilling string 32 when junk catcher 80 is used the mud continues upwardly 
beyond the upper end portion 84 of the first tubular member 82 of the junk 
catcher 80 into the annular space between the exterior of the drill string 
32 and the cylindrical inner surface 104 of the riser pipe string 36. 
Since the inner diameter of the cylindrical inner surface 88 of the first 
tubular member 82 is selected to provide the annular space 112 with a 
cross-sectional area sufficiently small to maintain the cuttings and 
debris in suspension in the circulating drilling mud, substantially all of 
the cutting debris will be circulated upwardly from the bottom of the 
borehole past the upper end portion of the junk catcher 80 into the 
annulus between the drill pipe and the riser pipe string. 
Since the length of the riser pipe string 36 can ordinarily be expected to 
range between 200 and 800+ feet between the wellhead assembly 46 and the 
water surface 18, and since the inner diameter of the riser pipe string 36 
is usually in excess of sixteen inches, cuttings and debris from the 
bottom of the borehole which have been carried upwardly in suspension in 
the drilling mud either remain in suspension in the drilling mud or begin 
to fall slowly downwardly since the cross-sectional area of the annulus 
between the drill string and the riser pipe string is very large in 
comparison to the annulus between the drill string and the borehole, 
casing, wellhead assembly and junk catcher 80, thus causing the 
circulating drilling mud to lose sufficient upward velocity to continue 
circulating the cuttings and debris upwardly through the riser pipe string 
to the upper end 40 thereof where the cuttings and debris may be removed 
from the drilling mud for passage through the shale shaker 20 and mud pit 
22 in the usual manner. 
It will be seen that the cuttings and debris which settle from the drilling 
mud in the annulus between the drill string 32 and the riser pipe string 
above the junk catcher 80 will be collected within the annular space 110 
in the junk catcher 80. Further, when the circulation of drilling mud is 
terminated, for purposes of replacing the drill bit or the like, cuttings 
and debris which were previously suspended in the drilling mud above the 
junk catcher 80 also settle into the annular space 110 of the junk catcher 
80, thus preventing the cuttings and debris from falling back through the 
wellhead assembly 46 to the bottom of the borehole in sufficient 
quantities to cause difficulties in testing and cementing operations. When 
the drill string 32 is withdrawn from the borehole upwardly through the 
wellhead assembly 46 and the riser pipe string 36, the uppermost drill 
collar 76, or drill bit 70, or lugs 130 or other suitable engagement means 
engages the lower end portion of the junk catcher 80, or suitable 
engagement means thereon as shown in FIG. 5, whereby the junk catcher 80 
is withdrawn upwardly through the riser pipe string 36 to the rig floor 
with the drill string 32. The perforations 108 in the second tubular 
member 92 of the junk catcher 80 permit the drainage of drilling mud from 
the annular space 110, thus minimizing the difficulty in disassembling the 
drill string 32 and junk catcher 80 at the rig floor. After the junk 
catcher 80 is emptied at the water surface, it can then be reinstalled on 
the drill string 32 and reinserted therewith into the riser pipe string 36 
for continued drilling operations. 
It will be understood that the junk catcher 80 may also be run with pipe 
strings which are to be employed for testing purposes, drilling purposes, 
or both. The use of the junk catcher 80 will be found to be advantageous 
at any time forward circulation of mud is to be employed with a pipe 
string in a riser pipe string and it is forseen that debris will be 
circulated out of the borehole by the mud, or might otherwise be present 
in the riser pipe which debris might be anticipated to cause various 
problems in drilling, testing or cementing operations if such debris were 
permitted to be returned to or remain in the borehole. 
It will also be apparent that the invention is equally applicable to oil 
well operations below lakes or rivers as well as offshore. 
From the foregoing it will be seen that the present invention provides 
method and apparatus providing distinct advantages over known mud systems 
which facilitate drilling, cementing and testing underwater oil and gas 
wells. Changes may be made in the combination and arrangement of parts or 
elements as heretofore set forth in the specification and shown in the 
drawings without departing from the spirit and scope of the invention as 
defined in the following claims.