Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR MONITORING
$HE DENSITY OF A LIQUID
Field of the Invention
~ he present invention relates generally to
methods and apparatus for monitoring the density of
liquids, and more particularly, to methods and
S apparatus for monitoring the density of well drilling
li quids.
ac~ground of the Invention
It is frequently useful to monitor the density
of a liquid used in industrial proce~ses. For
instance, during drilling operations of a well bore,
drilling mud is circulated through the drill pipe and
the annulus of the well bore. The drilling mud serve~
several purposes in the drilllng process, including
lubrication and cooling of the drill bit and the
removal of cuttings resulting from the penetration of
the subsurface formation~ Additionally, the weight of
the drilling mud in the well bore exerts hydro~tatic
pressure on the subsurface formations that acts to
contain the subsurface pressure encountered during
drilling operations. These subsurface pre~sures may be
extremely high, such as 8,000-10,000 p~i, or the
equivalent of two ~2) pound~ per square inch per foot
of depth. If the hydrostatic pressure of the drilling
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mud at the depth at which the sub~urface pre~ure i8
encountered i8 not equal to or greater than the
sub~urface pres~ure, tbe reservoir fluld will emerge
from the subsurface formation and travel to the surface
through the well bore. This is known as a blow out and
creates extremely dangerous conditions as the
pressurized format~on fluid generally containing gas
rapidly expands a~ it approaches the surface and
atmospheric pressure. However, if the drilling mud
hydrostatic pressure i8 too high, the subsurface
formations may be fractured resulting in extensive loss
of the relatively expensive drilling mud into the
formation~ surrounding the well bore. Thus, the
density of the drilling mud must be monitored and
adjusted if necessary, to malntain it within a desired
range during drilling operations. Another constraint
on the denslty of the drilling mud is that an increase
in the density tends to reduce the penetration of the
drill bit.
Drilling mud is a liquid composition, u~ually
utilizing oil or water a3 a base to which various
sub~tances are added depending on the propertles
desired in the drilling operatlons, the subsurface and
environmental conditions, a8 well as other factors as
are known in the art. Typically, the additives include
solid particulates or clay~ to promote the formatlon of
a filter cake on the wall~ of the well bore and to
assist in suspending the cuttings until the drilllng
mud containing the cuttlngs re~ches the surface, and
weighting materials such a~ barites, to control the
density of the drilling mud. After circulation through
the well bore, the drilling mud is filtered to remove
the cuttings carried from the bottom of the well bore
and then stored in a mud pit for sub3equent use.
Under conventional drilling techniques, a
small sample of the drilling mud i5 perlodlcally
~ 2 ~ ~
obtained as lt i8 deposited in the mud pit. The
density of the sample i~ measured and a determinatlon
made whether or not to ad~u~t the density of the
drilling mud being u~ed in the well bore. Existing
apparatus u~ed to measure the density of the drilling
- mud sample i~ called a mud balance and consists of a
container having a known volume on one end and a scale
and weight on the other end. The apparatus ti.e. mud
container, scale and weight) is then placed on a knife
edge fulcrum. ~he container is then filled to its
capacity with the sample of interest. The weight i8
moved along the scale until balanced. Indicia on the
~cale at the location of the weight indicate the
den~ity of the mud sample. That is, the observed
welght of the sample may be used to derive a measure of
density by dividing the weight by the known volume of
the container. The same scale can be calibrated in any
set of units desired.
However, this and other conventional denRity
monitoring procedures exhibit certain limitations. For
instance, the monitoring of the drilling mud density is
performed on an intermittent basis, and must be
manually performed. This manual operation takes
approximately 10-15 minutcs. When conditions are
encountered that cause rap~d change~ in ~he mud
density, the density may drastically change in a matter
of minutes or seconds. Frequently, it is not
economical or practical to weigh samples of the
drilllng mud on an ongoing basls, since a skilled
technician or engineer is required to perform the test.
Les~ frequent samples introduce a time lag into the
monitoring process that is undesirable. Further,
manual weighing of a drilling mud sample on a mud
balance is relatively inaccurate and requires visual
interpretation, thereby introducing the possibillty of
human error. Finally, weighing of the drilling mud
~29Z886
sample must be performed on 9 ~ te and cannot
conveniently be conducted remotely. None of the
existing methods or apparatus for monitoring dr$11ing
mud den~ity adequately solve the problems outlined
above.
Summary of the Invention
This invention provldes a method and apparatus
to measure the den~ity of a liquid on a continuou~
basis, such as drilling mud returning from circulation
in a well bore. The physical principal utilized is
that a force ~F) is proportional to pressure (P) and
area ~A), where F equals the orce in pounds and P
equal~ pressure in PSI and A equals area in square
inches. A continuous sample of the drilling mud is
flowed through a conta$ner having a fixed predetermined
volume. The container and the sample o the liquid is
~upported on at least one bed of pressurized fluid.
The pressure of the fluid is varied by fluctuatlons in
the weight of the container and liquid sample, 80 a~ to
equalize the forces acting across the seal of the
valve. A pressure transmitter is connected to the
chamber and generates a continuous electrical ~ignal
indicative of the instantaneous pressure in the bed of
pressurized fluid required to support the container and
liguid sample. The electrical signal from the pressure
transmitter is converted to a measure of the density of
the drilling mud by electronically dividing it by a
constant signal representative of the volume of the
container cavity. Preferably, the valve is a spherical
vaive and acts to automatically maintain the container
in an upright position, and is designed to have
negligible pressure drop across the seal of the valve.
Therefore, it is a principal feature and
advantage of this inventlon to provide an improved
method and apparatus for continuou~l~ monitoring the
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density of a liquid.
It i8 another feature and advantage of this
invention to provide an improved method and apparatus
for instantaneou~ly and automatically monitoring the
density o~ a liquid.
It i 8 another eature and advantage of thi 8
invention to provide an improved method and appara us
for monitoring the den~ity of a llquid in which the
density of the liquid made may be remotely monitored.
Brief DescriPtion of the Drawin~s
So that the manner in which the above recited
features and advantages of the inventlon, as well as
others which will become apparent to tho~e skilled in
the art, are obtained and can be understood in detail,
a more particular description of the invention briefly
summar~zed above may be had by reference to the
embodiments thereof whlch are illustrated in the
accompanying drawings, which drawings form a part of
the ~peciflcation and in which like numerals depict
like parts in the several views. It is noted, however,
that the appended drawings lllustrate only a preferred
embodiment of the invention and are therefore not to be
consldered limitlng of its scope, for the invention may
admit to other equally effective embodiments.
Figure 1 is a schematla representation of a
density measuring device according to thls invention.
Figure 2 i8 a front view, partially in cross
section, of a density measuring device according to
this invention.
Figure 3 is a side v~ew, partially in cross
section, of the density measuring device of Figure 2.
Figure 4 is a cross sectional view along view
4-4 of the density measuring device of Figure 3.
F$gure 5 is a magnified view of the ball valve
of Figure 3.
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Detalled De~cri~tion of the Invention
Referring now to Figure 1, the reference
numeral 10 generally ~ndicates the apparatus of thi~
invention, including generally rectangular housing or
enclosure 12. The housing is po~itioned over mud p~t
14 containing a quantity of drllling mud 16. Drilling
mud intake pipe 1~ i3 connected at one end tnot shown)
to the circulatlon ~ystem tnot shown) for the drilling
mud and is adapted to continuslly convey to the hou~ing
a sample before the drilling mud is returned to the mud
pit. Drilllng mud outlet 20 extends downwardly from
the bottom of the housing and i8 positioned to return
the sample stream of drilling mud to the mud pit after
exiting from the housing. Pressurized fluid conduit 22
is connected at one end ~not shown) to a source of
pressurized fluid tnot shown). Although air may be
utilized as the fluid, any suitable fluid may be
utilized within conduit 22 if desired. The other end
of the fluid conduit extends into the interior of the
housing, as will be explained hereinafter. Wire or
cable 24 extends outwardly of the housing and is
remotely connected to meter 26 for providing a display
indicative of the density of the drilling mud ~ample.
Turning now to Figures 2-4, the hou~ing is
shown in greater detail mounted on rigid external
framework 28 tnot a part of the apparatus) which
consists of interconnected beams and trusses and is
provided to support the hous~ng over the mud pit tnot
shown). Housing 12 includes top, bottom, front and
bac~ walls and defines left and right sides, 12a and
12b, respectively, a~ seen in Figure 2. Container 30
iq provided within the housing to receive a continuous
sample of the drilling mud. The container consists of
a cylindrical body with an open upper end communicating
with cavity 31 therewithin having a fixed and
predetermined volume. Drilling mud is continuously
~2928~36
introduced into tbe cavity of the container through
drill~ng mud intake pipe 18, which does not contact
container 30 at any place. Preferably, orifice 32 of
the drilling mud inta~e pipe i8 located at a point
below the upper rim of the container and the incoming
drilling mud is pres~urized sufficiently to maintain
the entire volume of the cavity completely filled with
the dr$11ing mud at all tlmes. If necessary! a pump
(not shown) may be interposed into the drilling mud
intake pipe upstream of the housing.
The drilling mud i8 most conveniently induced
to overflow the upper end of the container and 8pill
downwardly therefrom. Referring now again to Figure 1,
it will be seen that the drilllng mud spilling from the
container will fall through drilling mud outlet 20 and
be returned to the mud pit on a continuous basis. As
previously explained, drilling mud usually contains
various additives. If the drilling mpd is allowed to
run down the sides of the container, these additive~
will have a tendency to be deposited on the container
and to accumulate thereon, adding to the weight of the
container and thereby introducing errors into the
density measurement of the drilling mud. To prevent
this accumulation, splash guard 34 is mounted on the
upper rim of the container and flares outwardly and
downwardly therefrom. The splash guard acts to direct
the drilling mud spilling over from the container away
therefrom and into the drilling mud outlet. The
container and splash guard are mounted on support 36
which extends upwardly within the apparatus housing.
The container support is connected to valve 38, as will
be explained in greater detail hereinafter.
Even with the splash guard, it may be
deQirable to periodically clean or inspect the
container or other portions of the apparatus. To
accomplish this in the illustrated embodiment, the
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entire lower portion of the hous~ng i~ con~tructed as a
unitary structure h~nged at 37 ~shown in Figure 3)
along the bac~ side thereof and secured by latch 39 on
the front side, which may be a magnetic latch.
Further, support 36 includes a lower portion secured to
the container and splash guard and hlnged at 41 along
its front side and secured by latch 43, which may be a
magnetic latch. When cleaning or in~pection of the
container i~ desired, the lower portion of the housing
is released and rotated in a counter clockwise
direction ~as seen in Figure 3), exposing the
container. The lower portion of the support is
released and rotated in a clockwise direction, bringing
the container outside of the housing and providing
ready access. Reversal of the above procedure places
the container in position to resume monitoring
operation~.
Pressurized fluid conduit 22 enter~ the
housing through its back wall and extends to preqsure
regulator 40 mounted on the interior of the housing.
The pressure regulator reduces the pressure of the
fluid in the apparatus downstream of the pressure
regulator to a level convenient for the purposes
hereinafter described. Although not shown, the
pressure regulator may include a pressure guage to aid
in ad~uQting the output of the pre3sure regulator to
desired levels. Conduit 22 extends from the outlet of
the pressure regulator to pressure transmitter 42
mounted on internal framework 44 mounted on the
housing. The pressure transmitter is sensltive to the
pressure of the flu$d in the conduit downstream of the
pressure regulator and generate~ a contlnuou~
electrical signal indicat~ve of the pre~sure. The
electrical signal from the pressure transmitter is
conveyed externally of the housing by wire 24 to meter
26, where the calibrated pressure reading of the
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pre~8Ure tranBmitter i8 electronically converted to a
signal, di~played by the meter, which i5 a mea~urement
o~ the liquid denslty, as will be explained
hereinafter. Pre~sure reservoir 46 is mounted on an
upper portion of the container support over the valve.
Conduit 48 extend~ from the pres~ure tran~mitter to the
pressure reservoir to convey the pres~urized fluid to
the pre~ure reservoir.
F~gure ~ ~how~ in detall the constructlon of
valve 38. Bracket S0 i8 mounted on internal framework
44 of the housing. Valve member 52 i8 mounted on the
bracket, such a8 by ~olt 54 or any other conventional
means. In the preferred embodiment of the invention,
the valve member is spherical, as shown in Figure 5.
Upper valve portlon 56 1B mounted on the under slde of
pressure reservoir 46. The upper valve portion
includes conduit 58 communicating with the pressure
reservoir and terminatlng in conical valve seat 60.
The valve seat includes 0-ring seal 62 mounted ln annu-
lar groove 64 of the valve seat. The valve member ispartlally located wlthin the valve sQat ad~acent the
seal and i8 loosely restralned therewlthln by retaining
plate 66 mounted on the upper valve portlon by bolts 68
snd secured by spacers 70 carrled about each of the
bolts 68. The retalning plate lncludes concentric
openlng 72 of le~ser dlameter than the dlameter of the
valve member. The spacers 70 enable limited vertical
movement of the upper valve portlon, bolts, spacers,
and retalning plate wlth respect to the valve member in
directlons 74 ~downward) and 76 ~upward). The upper
valve portion is inherently urged downwardly in direc-
tion 74 into seallng engagement wlth th~ valve member by
the comblned weight of the contalner~ container support,
pressure reservoir, pressure transmitter, and the weight
of the drilling mud sample carried by the container.
It is one of the advantages of the spherical valve
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member that it inherently acts w~th the conical valve
~eat to center the support and the container and
maintain the container in an upright and level pos~tion
over the drilling mud outlet. The contalner is thus
maintained in an upright and level posltion and the
ample of drilllng mud prevented from overflowing the
container at a greater rate than the drilling mud i8
in~ected into the cavity.
In operation, a continuous ~tream of the
drilling mud iB in~ected into the cavity through the
orif$ce of the drilling mud input plpe at a regulated
flow rate, completely filling thè cavity at all times.
The contents of the container at any qiven tlme
constitut2s a representative and timely sample of the
drilllng mud emerging from the well bore. The rate of
flow through the input pipe is ad~usted, 80 that the
pace of sampling may be any selected pace. For
instance, should the chamber of the container have a
capacity of 1 gallon and the desired pace of the
sampling be one minute intervals, then the flow rate
into the container would be ad~usted to a rate of 1
gallon per minute. The drilling mud is in~ected withln
the cavity o~ the container at 3ufficient pressure 80
that the sample stream continuously flows upward
through the cavity and overflows the container onto the
splash guard, through the drilling mud outlet and into
the mud pit. At the same time, pressurized fluid is
introduced into pressure reservoir 46 through conduits
22 and 48, pressure regulator 40 and presure
transmltter 42. The pressurized ~luid is lntroduced
into the upper valve portion of the spherical valve
through conduit 58 and acts against the surface of the
valve member above the 0-ring seal to liEt the
container and the contalner ~upport upwards ln
direction 76, llm~ted by contact between the lower part
of the valve member and the retaining piate. If the
lZ9Z~86
combined weight of the container, support, and the
sample of drilling mud contained in the cavity i.8 less
than or equal to the force of the pressurized fluid
acting on the valve, then the valve will remain closed.
However, if the force of the pres~urized fluid on the
valve member exceeds the welght of the conta~ner,
support, and the sample of drilling mud contained in
the cavity, then the valve will be opened and the flu~d
will be vented from the reservolr through the valve.
This venting will continue until the pressure in the
pres~ure reservoir i8 reduced to a point that the force
exerted on the valve $8 sufficient to maintain the
valve slightly open with a relat~vely small constant
rate of fluid being vented, thereby creating a stable
pressure ln the pressure reservoir. Thus, the pressure
of the fluid in the pressure reservoir will rapidly
assume the equilibrium level determined by the combined
weight of the container, support, and the sample of
drilling mud contained in the cavity. Of course, the
pre~surized fluid as controlled by the pressure
regulator, must be supplied to the pressure reservoir
at a level high enough to open the valve for all
anticipated drilling mud denslties.
Since the weight of the aontainer, pressure
reservoir, pressure transmlttQr and the ~upport is
flxed and predetermined, any fluctuation in the force
urging the valve towards A closed position, as measured
by the lnstantaneou~ equlllbrlum pressure wlthin the
pressure reservoir, must be due to changes in the
weight of the drilling mud sample in the cavity of the
container. Because the volume of the cavity is also
fixed and predetermined, the welght of the sample
varies as the density of the drilling mud varies. The
electrical signal of the pressure transmltter is
indicative of the weight of the drilling mud sample.
Since the volume of the cavity i~ known, the slgnal
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from the pressure transmitter may be electronically
divided by a fixed electrlcal signal representative of
ths cavity volume, in a manner known in the art, to
achieve a measurement of the drilllng mud density,
which is displayed on the meter, which may be remotely
located with respect to the remainder of the apparatus.
Alternatively, the density measurement may be recorded
for future use~ in lieu of or in addition to display on
the meter.
~hus, the apparatus and method of the pre~ent
invention enables the density of the drilling mud
returning from the well bore to be monitored on a
continuous basis and is instantly responsive to
fluctuations ln that den~ity, indicative of downhole
conditions. Further, monitoring operations may be
conducted automatically and controlled remotely, and
provides a more accurate ~nd consi~tent measurement
than conventional systems.
Although the invention has been disclosed
above, with regard to particular and preferred
embodiments, these are advanced for illustrative
purpoQes only, and are not intended to limit the scope
of this invention. For instance, although the
invention has been de~cribed as having u single bed of
pressurized 1uid above the container and from which
the container i~ su~pended, the invention may employ
more than one bed of pressurized 1uid or the bed or
beds may be located below or to the side of the
container. Further, although the spherical valve i8
utilized as having self centering features in order to
maintain the container in an upright and level
position, other types of valves may be used and
separate means employed to maintain the container in an
upright and level position. Finally, the invention is
not l$mited to monltoring of drilling mud density, but
may be applied to various other liquids. These varia-
tlons remain within the invention as claimed ~elow.
