U.S. patent application number 15/812009 was filed with the patent office on 2019-05-16 for method of detecting methane in the bore of a blowout preventer stack.
The applicant listed for this patent is Benton Frederick Baugh. Invention is credited to Benton Frederick Baugh.
Application Number | 20190145256 15/812009 |
Document ID | / |
Family ID | 66433236 |
Filed Date | 2019-05-16 |
United States Patent
Application |
20190145256 |
Kind Code |
A1 |
Baugh; Benton Frederick |
May 16, 2019 |
Method of detecting methane in the bore of a blowout preventer
stack
Abstract
The method of sensing methane type gases in the bore of a subsea
blowout preventer stack comprising collecting a sample of the
fluids in the blowout preventer stack into a vacuum chamber,
expanding the volume of the chamber to allow the methane type gases
in the sample to evaporate either expand or evaporate, and then
measuring the change in pressure before and after the expansion to
determine the characteristics of the sample.
Inventors: |
Baugh; Benton Frederick;
(Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Baugh; Benton Frederick |
Houston |
TX |
US |
|
|
Family ID: |
66433236 |
Appl. No.: |
15/812009 |
Filed: |
November 14, 2017 |
Current U.S.
Class: |
166/250.01 |
Current CPC
Class: |
E21B 49/0875 20200501;
E21B 33/064 20130101; E21B 33/076 20130101; E21B 49/086 20130101;
E21B 34/04 20130101 |
International
Class: |
E21B 49/08 20060101
E21B049/08; E21B 33/064 20060101 E21B033/064; E21B 33/076 20060101
E21B033/076; E21B 34/04 20060101 E21B034/04 |
Claims
1. The method of sensing gas in the bore of a subsea blowout
preventer stack, comprising collecting a sample of the fluids in
said blowout preventer stack into a chamber, expanding the volume
of said chamber to allow said gas in said sample to evaporate
either expand or evaporate, and measuring the change in pressure
before and after said expanding to determine the characteristics of
said sample.
2. The method of claim 1 further comprising comparing said
characteristics with the characteristics of known fluids and gases
to determine what gases gasses are present in said sample.
3. The method of claim 1 further comprising alternately drawing
said sample of fluids into a test chamber and expelling said sample
of fluids from said test chamber.
4. The method of claim 3 further comprising providing a piston to
alternately draw said sample of fluids into a test chamber and
expelling said sample of fluids from said test chamber.
5. The method of claim 3 further comprising drawing said sample of
fluids through a filter and expelling said sample of fluids through
the same filter to clean said filter.
6. The method of claim 1 further comprising drawing said sample of
fluids through a first check valve and expelling said sample of
fluids through a second check valve causing said sample of fluids
to be at least partially refreshed on each cycle.
7. The method of claim 6 further comprising opening a third check
valve with the movement of a piston in a first direction.
8. The method of claim 6 further comprising closing said third
check valve with the movement of said piston in a second direction
allowing a vacuum to be drawn by further movement is said second
direction.
9. The method of claim 1 further comprising said gas is a methane
type gas.
10. The method of claim 1 further comprising said gas is
methane.
11. The method of sensing methane type gases in the bore of a
subsea blowout preventer stack, comprising collecting a sample of
the fluids in said blowout preventer stack into a chamber;
expanding the volume of said chamber to allow said methane type
gases in said sample to evaporate either expand or evaporate, and
measuring the change in pressure before and after said expanding to
determine the characteristics of said sample.
12. The method of claim 11 further comprising comparing said
characteristics with the characteristics of known fluids and gases
to determine what gases gasses are present in said sample.
13. The method of claim 11 further composing alternately drawing
said sample of fluids into a test chamber and expelling said sample
of fluids from said test chamber.
14. The method of claim 13 further comprising providing a piston to
alternately draw said sample of fluids into a test chamber and
expelling said sample of fluids from said test chamber.
15. The method of claim 13 further comprising drawing said sample
of fluids through a filter and expelling said sample of fluids
through the same filter to clean said filter.
16. The method of claim 11 further comprising drawing said sample
of fluids through a first check valve and expelling said sample of
fluids through a second check valve causing said sample of fluids
to be at least partially refreshed on each cycle.
17. The method of claim 16 further comprising opening a third check
valve with the movement of a piston in a first direction.
18. The method of claim 16 further comprising closing said third
check valve with the movement of said piston in a second direction
allowing a vacuum to be drawn by further movement is said second
direction.
19. The method of claim 11 further comprising said gas is a methane
type gas.
20. The method of claim 1 further comprising said gas is methane.
Description
TECHNICAL FIELD
[0001] This invention relates to the method of detecting methane or
other gases in the bore of a subsea stack before they enter the
lower pressure drilling riser and begin to dangerously expand,
tending to blow the drilling mud out of the riser.
BACKGROUND OF THE INVENTION
[0002] When drilling an oil or gas well into the seafloor, drilling
mud is circulated down a central drill pipe, goes through a drill
bit at the bottom where the hole is being drilled, and then
circulates back up through the annular area between the central
drill pipe and the hole. The hole consists of a lower portion which
is the size of the drill bit doing the drilling, up the slightly
larger bore of the last casing string landed, through the
considerably larger bore of the subsea blowout preventer stack at
the seafloor, and finally up the slightly larger drilling riser all
the way to the surface. The outer diameter of the central drill
pipe is relatively consistent above a short group of oversize drill
collars at the bottom. The velocity of the drilling mud slows each
time the hole it is in becomes larger, and the pressure is reduced
as the depth is decreased. What this generally means is that free
gas can travel up quickly to the area of the seafloor blowout
preventer slack, and then slowly moves up to the surface.
[0003] When a substantial volume of methane type gases enters the
wellbore during the drilling process and arrive up to the level of
a seafloor blowout preventer stack, they can be so small as to not
be noticeable in most cases.
[0004] If you take the case of a blowout preventer stack in 10,000
feet depths and presume a volume of gas the size of a ping pong
ball (1.57'' diameter) is in the bore. When the gas gets to the
ocean surface it's volume will be 20% bigger than two basketballs
(9.4'' diameter each), given a typical drilling mud weight.
[0005] As the drilling mud travels up the bore of the drilling
riser above the seafloor blowout preventer stack, additional gases
may come out of solution and both the gas already out of solution
and that which comes out of solution expand rapidly. What coming
out of solution is can be easily seen by a soft drink bottle or a
bottle of champagne. An unopened bottle will show no gas bubbles,
and is under some pressure inside. When opened and the pressure is
thereby reduced, suddenly some gas bubbles appear.
[0006] As if gas expanding from the size of one ping pong bails to
more than twice the size of a basketball isn't bad enough, gas
coming out of solution basically expands from nothing to
potentially a very large size.
[0007] This has been a problem as long as oil and gas wells have
been drilled. The best detection method presently is watching the
level of the drilling mud pits at the surface. During drilling you
would expect the mud to circulate down and back up at generally the
same volume, considering that you are drilling a deeper hole all
the time which takes additional drilling mud to fill. But you know
how fast you are drilling and can compensate for that. If your mud
pit level is increasing, it will tell you that something is
entering the well bore, with a good chance that it is gas. If your
mud pit is falling more than what is expected from your deepening
the hole, you are "losing circulation", generally meaning drilling
mud is seeping into the formations. As almost every blowout will
tell you, including the 2009 Macondo blowout in the Gulf of Mexico,
there was not an adequate system for detecting problems.
Additionally, when the mud pits have increased enough to detect it,
a high volume of gas has already entered the drilling riser. Means
for earlier detection have long been needed.
BRIEF SUMMARY OF THE INVENTION
[0008] The object of this invention is to provide a method of
detecting free gas within the drilling mud at subsea locations such
as a seafloor blowout preventer stack before it has a chance to
expand and can be directed out the higher pressure choke or kill
lines.
[0009] A second object of this invention is to provide a method of
defecting whether gas in solution the drilling mud at subsea
locations such as a seafloor blowout preventer stack will come out
of solution at the lower pressures seen as the drilling mud moves
up towards the surface of the ocean.
[0010] A third object of this invention is to regularly monitor
this situation in a why which can be reported in real time to the
personnel at the surface and/or on land.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a view of a system of subsea equipment utilizing a
sensor of this method.
[0012] FIG. 2 is a half section of a portion of the blowout
preventer stack of FIG. 1 showing the basic components of the
sensor.
[0013] FIG. 3 is a graph showing the anticipated pressures within
the vacuum chamber of the sensor generally under the conditions of
no methane in the bore and with methane in the bore.
[0014] FIG. 4 is a half section similar to FIG. 2 showing the
sensor with a vacuum drawn on tire vacuum chamber and being
monitored as illustrated on FIG. 2.
[0015] FIG. 5 is a half section similar to FIG. 4 showing the
sensor with the vacuum having been collapsed.
[0016] FIG. 6 is a half section similar to FIG. 5 showing the
sensor showing the tested charge of fluid being at least partially
removed.
[0017] FIG. 7 is a half section similar to FIG. 6 showing the
sensor showing the new charge of fluid starting to be drawn.
[0018] FIG. 8 is a half section similar to FIG. 7 showing the
sensor showing the new charge of fluid having been fully drawn.
[0019] FIG. 9 is a half section similar to FIG. 8 showing the
sensor with the new vacuum having been drawn and the vacuum being
monitored, making it identical to FIG. 4.
DETAILED DESCRIPTION OF THE DRAWINGS
[0020] Referring now to FIG. 1, a view of a complete system for
drilling subsea wells 20 is shown in order to illustrate the
utility of the present invention. The drilling riser 22 is shown
with a central pipe 24, outside high pressure fluid lines 26, and
cables or hoses 28.
[0021] Below the drilling riser 22 is a flex joint 30, lower marine
riser package 32, lower blowout preventer stack 34 and wellhead 36
landed on the seafloor 38.
[0022] Below the wellhead 36 it can be seen that a hole was drilled
for a first casing string 40, that first casing string 40 was
landed and cemented in place, a hole drilled through the first
string for a second string, the second string 42 cemented in place,
and a hole is being drilled for a third casing string by drill bit
44 on drill string 46.
[0023] The lower blowout preventer stack 34 generally comprises a
lower hydraulic connector 48 for connecting to the subsea wellhead
system 36, usually 4 or 5 ram style blowout preventers, an annular
preventer, and an upper mandrel for connection by the connector on
the lower marine riser package 32, which are not individually shown
but are well known in the art.
[0024] Below outside high pressure fluid line 26 is a choke and
kill (C&K) connector 50 and a pipe 52 which is generally
illustrative of a choke or kill line. Pipe 52 goes down to valves
54 and 56 which provide flow to or from the central bore of the
blowout preventer stack as may be appropriate from time to time.
Typically, a kill line will enter the bore of the blowout
preventers below the lowest ram and has the general function of
pumping heavy fluid to the well to overburden the pressure in the
bore or to "kill" the pressure. The general implication of this is
that the heavier mud cannot be circulated into the well bore, but
rather must be forced into the formations. A choke line will
typically enter the well bore above the lowest ram and is generally
intended to allow circulation in order to circulate heavier mud
down the drill pipe into the well to region pressure control of the
well. Normal circulation is down the drill string 46, through the
drill bit 44, up the annular area between the drill pipe and the
casing, and up the choke line.
[0025] In normal drilling circulation the mud pumps 60 take
drilling mud 62 from tank 64. The drilling mud will be pumped up a
standpipe 66 and down the upper end 68 of the drill string 46. It
will be pumped down the drill string 46, out the drill bit 44, and
return up the annular area 70 between the outside of the drill
string 46 and the bore of the hole being drilled, up the bore of
the casing 42, through the subsea wellhead system 36, the lower
blowout preventer stack 34, the lower marine riser package 32, up
the drilling riser 22, out a bell nipple 72 and back into the mud
tank 64.
[0026] During situations in which an abnormally high pressure from
the formation has entered the well bore, the thin walled central
pipe 24 is typically not able to withstand the pressures involved.
Rather than making the wall thickness of the relatively large bore
drilling riser thick enough to withstand the pressure, the flow is
diverted to a higher pressure choke line or outside fluid line 26.
It is more economical to have a relatively thick wall in a small
pipe to withstand the higher pressures than to have the
proportionately thick wall in the larger riser pipe.
[0027] When higher pressures are to be contained, one of the
annular or ram Blowout Preventers are closed around the drill pipe
and the flow coming up the annular area around the drill pipe is
diverted out through choke valve 54 into the pipe 52. The flow
passes up through C&K connector 50, up pipe 26 which is
attached to the outer diameter of the central pipe 24, through
choking means illustrated at 74, and back into the mud tanks
64.
[0028] Valve 54 which would be called a choke or kill valve
(probably called choke in that position) is shown mounted on the
side 90 of lower blowout preventer stack 34 and having a bore 92
communicating with the bore of the blowout preventer stack. On the
opposite side of the tower blowout preventer stack another similar
communicating bore 94 is provided and the methane sensor assembly
96 is installed in this bore 94. Blowout preventer stack 34 has an
internal bore 98.
[0029] Referring now to FIG. 2, blowout preventer stack 34 is shown
with side 90 and bore 98, communicating bore 94, and seal ring 100
sealingly engaging flange 102 of methane sensor assembly 96. Filter
106 is held in place by retainer ring 108. The general circulation
path through methane sensor assembly 96 is illustrated by arrows
110-122 as will be further described.
[0030] Filter 106 restricts particle size coming into the methane
sensor assembly at arrow 110 and is continually cleaned by the
reverse flow at arrow 120. Bore 124 leads to check valve 126, bore
128 leads to check valve 130 which checks the flow in the opposite
direction as check valve 126. Check valve 130 leads to vacuum
chamber cavity 132 which leads to bore 134, leading to check valve
136, leading to bore 138, leading to bore 140, and back to filter
106. Drilled hole 142 leads to pressure transmitter 144. Piston 146
is part of cylinder 148, with suitable fittings 150 for
operation.
[0031] Referring now to FIG. 3, a graph is shown which generally
shows the objective of the methane sensor assembly. The numbers 4-9
at the bottom indicate the figure numbers which follow as the
operations proceed in one full cycle from that shown in FIG. 4 to
FIG. 9. Area 160 between indicates the normal pressure in the
blowout preventer stack 34. Area 162 indicates the anticipated
pressure in the vacuum chamber cavity 132 read by pressure
transmitter 144 when there is no methane type gases in the bore,
and is likely the pressure signature of the water in the drilling
mud. Area 164 indicates the anticipated pressure in vacuum chamber
cavity 132 when methane type gases are in the bore. Areas 166 and
168 are transitional pressures while the vacuum is being pulled.
Areas 170 and 172 are simply continuations of lines 162 and 164
into the next cycle of operations. Areas 174 and 176 are
transitional pressures as the vacuum is being released. The
distinction in the pressure signatures will be utilized to
determine that something different is happening in the fluids
within the blowout preventer stack 34.
[0032] The reason for this distinction in the pressures of the
water in the water based drilling muds and the invading methane gas
is that water boils and starts to put off pressures when it boils
at 212 degrees F. or 100 degrees C. Methane boils and starts to put
off significant pressures at -257 degrees F. or -162 degrees C. The
vapor pressure of methane at 70 degrees F. or 21 degrees C. is
4,641 p.s.i, or 32,000 kPa. This means pure methane will not be a
gas at all until the drilling mud is less than that pressure in
typical drilling mud that would be (4641 p.s.i.)/(0.465 lb/ft
gradient times 1.33 heavier mud)=7487 feet. That means that pure
methane will not evaporate before that depth, which is a little
deeper than the 6000 feet for the Macondo blowout. Other potential
gases can come out at higher or lower pressures and depths.
[0033] Referring now to FIG. 4, methane sensor assembly is shown
with a vacuum puked and simply reading the pressure in vacuum
chamber cavity 132 for a period of time, likely a couple of
minutes. There is no flow occurring within the methane sensor
assembly 96, however, flow 180 continues within the bore 98 of
blowout preventer stack 34. Piston 146 is moved to the right
against a hard stop 182.
[0034] Referring now to FIG. 5, piston 146 has moved to the left to
contact the end 190 of check valve 130 in making this movement, the
vacuum is collapsed but nothing else has happened. This is
illustrated by areas 174 and 172 of FIG. 3. The left side of FIG. 6
shows an end view of the methane sensor assembly 96 as it would be
seen from inside the bore of the lower blowout preventer stack 34
having a central filter 106 and two securing bolts 192. Dashed
lines show the hidden location of check valves 126, 130, and
136.
[0035] Referring now to FIG. 6, piston 146 has continued to move to
the left pushing check valve 130 open and expelling the tested
fluids along arrows 116 to 122 through filter 106, cleaning filter
106 as it flows in this direction.
[0036] Referring now to FIG. 7, the movement of piston 146 is being
reversed in the opposite direction and beginning to draw fresh
drilling fluids into the methane sensor assembly along arrows 110
and 112 through filter 106. At this time check valve continues to
be mechanically held open by piston 146 and check valve 126
automatically opens by the flow.
[0037] Referring now to FIG. 8, piston 146 has moved to the right
until the check valve 130 is closed and so the maximum amount of
new drilling fluids have been pulled into the cavity.
[0038] Referring now to FIG. 9, piston 146 moves to the right
against hard stop 182 and a fresh vacuum has been drawn in vacuum
chamber cavity 132, or is in other words in the same condition as
FIG. 4. The pressure differential between the blowout preventer
stack bore pressure is now held back by check valves 130 and
136.
[0039] By following this process, a fresh batch of drilling mud is
drawn into the methane sensor assembly, tested, documented, and
expelled as frequently as desired. The data is communicated to the
surface for monitoring and analysis, with appropriate alarms
sounding and sent when a change occurs.
[0040] The particular embodiments disclosed above are illustrative
only, as the invention may be modified and practiced in different
but equivalent manners apparent to those skilled in the art having
the benefit of the teachings herein. Furthermore, no limitations
are intended to the details of construction or design herein shown,
other than as described in the claims below. It is therefore
evident that the particular embodiments disclosed above may be
altered or modified and all such variations are considered within
the scope and spirit of the invention. Accordingly, the protection
sought herein is as set forth in the claims below.
* * * * *