Note: Descriptions are shown in the official language in which they were submitted.
11~3~3
~E~HOD O~ SEPARATION O~ SOLID PHASE IN DRIL~ING MUD
~ he present invention relates to borehole-drilling techni-
ques, and more particularly it relates to the methods of sepa-
rating the solid phase in a drilling mud.
The disclosed method can be employed to utmost effect-
iveness at drilling oil, fuel gas and survey wells.
However, the disclosed method can be also efficiently
employed in the chemical, pharmaceutical, metallurgical, mine-
ral concentration and other industry, wherever the solid phase
has to be separated or removed from a suspension.
It is commonly known that drilling mud is a heterogeneous
liquid system wherein colloid-size particles of the solid pha-
se are always present. The presence of these particles i8,
~rom the well-drilling quality point of view, an essential pre-
requisite of adequate rheological properties of the drilling
mud. The latter is expected to retain these gualities, essen-
tial a they are for optimization of the well-drilling condi-
tions. However, stable retaining of the essential properties
of the drilling mud throughout a drilling operation has been
presenting a complicated problem.
The majority o~ drilling operations are carried out in
clayey roc~. The claye~ rock being drilled is partly finelg
disintegrated, and the rock cuttings in the form of colloid
particles get into the drilling mud.
Insufficiently effective purification of the drilling mud
from rock cuttings upon several cycles of mud-pumping in the
1153~3
cour~e of a well-drilling operation has been found to 3ignifi-
cantly slter the composition of the solid phase of the drilling
mud, which necessitates using various methods of enhancing the
drilling mud quality. Therefore, the quality purification of
the drilling mud from roc~ cuttings i~ of paramount importance
for the well-drilling operation.
Poor gualit~ of the purification of the drilling mud has
been a ma~or cause of various emergencies and complications in-
volving losses of the drilling mud, sticking of drill-pipes and
casings, caving-in of rock from the borehole walls.
The technical and economic ratings of a drilling operat-
ion are greatly influenced by the quality of the drilling mud
used, as well as by the degree of its purification from rock
cuttings.
~ uality purification of the drilling mud helps getting
a w~ll down faster, owing to the reduced content of the solid
phase in the liquid one, and enhances the working environment
of the bits and down-hole tools. Apart from stepping up the
mechanical rate of drilling, guality purification of the drill-
ing mud helps reducing the consumption of the materials spent
on maintaining the required properties of the drilling mud,
prolonging the life of the mud, avoiding emergencies and com-
plications of the drilling operation.
In short, quality puirification of the drilling mud from
roc~ cuttings is an essential process of the well-drilli~g ope-
ration, significantly influencing the operation's technical and
economic ratings.
1~5~63
All the hitherto known tachniques of puri~ing drilling
muds enable to remove frDm tbe circulating mud a certain pro-
portiDn of solid particles with a certain degree Df efficiencD
and quality.
Thus, the minimum size of particles that can be separat-
ed from a drilling mud on vibrates sieves is defined by the
mesh size of the sieve. With the finer mesh used to enhance
the quality of the punfication, the pass-through capability
of the sieve becDmes seriously affected, and the 1DSS of the
drilling mud with the sludge is stepped up.
When purified in hydrocyclones, the drilling mud is di-
luted with water, and particles of a relatively high density
are predDminantly removed therefrom. The finer or less dense
particles which becvme resident in the drilling mud as rock
cutti~gs become dispersed therein would not be removed in hyd-
rocyclones and numerous other purification devices currently
in use.
~ hers is known a method of regeneration of a stable clayeg
suspension of a drilling mud, according to which the drilling
mud coming from the well and containing rock cuttings is pre-
diluted with water and has greater particles removed therefrom.
~he thus diluted and precleaned drilling mud cDntains fin7un-
charged particles of cut rDck and negatively charged cDll~id-
-size particle~of clay. Then the negatively charged particles
of clay are separated from the mud by being depDsited on a ro-
tating anode and subsequently removed with a æcraper tDol, the
settling negatively charged particles of clay entraining there-
~1~3~63
~ith some of the uncharged particles which are li~ewise de-
posited on the rotating anode.
~ he abovedescribed method is used to purify but a portion
of the total flow of the drilling mud, while the far greater
remaining portion of the mud is recirculated into the well in
an uncleaned state. Furthermore, the stagewise purification,
first, from the coarser particles, and, then, from the ~iner
one is complicated and, hence, costl~.
It is an object of the present invention to create a
method of separating the solid phase in a drilling mud, which
should provide for purifying the entire volume of the drilling
mud coming from a well in a relatively simple operation.
It is another object of the present invention to reduce
the cost of purification of the drilling mud.
It is a further object of the present invention to provide
for higher drill~ng rates, owing to the improved quality of the
purification of the drilling mud.
With these an other objects in view, there is hereby
disclosed a method of separation of a solid phase in a drill-
ing mud~ which in accordance with the present invention, com-
prises forming an adhesion layer from the drilling mud on a
curvilinear closed surface partly projecting into the drill-
ing mud and being rotated, and separating a portion of said lay-
er onto another rotating curvilinear closed surface positioned
to contact a portion of the adhesion layer, the linear speeds
o~ the adhesion layer and of the other rotating closed curvilinear
1153963
surface in the area of their contact being selected to be sub-
stantially egual.
It is expedient to have separated onto the other curvili~-
ear closed surface the portion of the adhesion layer, rich in
the coarser particles of the solid phase.
The above technique can be used for separating the adhe-
sion layer formed on the external side of a rotating c~rvilinear
closed surface. ~his enables to conduct the process of separat-
ing the solid phase in a drilling mud by regulating the ~alue
of the linear speed of the outer surface of the adhesion layer,
and thus regulating the separation from the adhesion layer of
solid particles having the density in excess of the density of
the drilling mud from which the adhesion layer is formed.
It is also possible to separate onto the other curvilinear
closed surface the portion of the adhesion layer, cleaned from
the coarser-particles of the solid phase.
This technique can be used for separating the adhesion
layer formed on the internal side of a rotating curvilinear
closed surface.
This enables to conduct the process of separating the solid
phase in the drilling mud by regulating the value of the linear
speed of the inner surface of the adhesion layer and that of the
other curvilinear closed surface in the sense of stepping up
this value~ and thus regulating the separation from the adhesion
layer of the particles of the solid phase of the drilling mud.
~ 3~63
It is not lesæ expedient to vary the value of the surface
tension of the adhesion layer, while separating the solid phase
of the drilling mud.
The variation of the surface tension of the adhesion layer
facilitates separation of solid particles therefrom.
It is further ex~edient to vary the surface tension of the
adhesion layer by acting thereupon with a direct-current elec-
tric field.
By passing an electric current through the area of separa-
tion of the particles of the solid phase from the adhesion layer,
the value of the surface tension is reduced, owing to an in-
creased concentration of electrically charged particles in the
surface layer. The reduced value of the surface tension of the
adhesion layer of the drilling mud further enhances the condi-
tions of separation of the solid phase of the drilling mud.
It is not less expedient to vary the value of the surface
tension of the adhesion layer by altering the direction of the
electric current in accordance with the mineralogic composi-
tion of the solid phase of the drilling mud.
Th~ above technique enables to intensify the selective
character of the removal of the solid phase. The feeding of a
positive potential to the other curvilinear closed surface re-
sults in more efficient removal from the adhesion layer of the
drilling mud of negatively charged particles of clay, a~ com-
pared with the removal in the absence of the electric field.
On the other hand, the feeding of a negative potential to the
liS3~63
-- 7 --
other curvilinear closed surface intensifies the removal from
the adhesion layer of the drilling mud of neutral get heavy
particles, e.g. barite ones, and of positively charged mineral
particles.
It ma~ be expedient to vary the value of the surface ten-
sion of the adhesion layer by varying the intensity of the
electric field in accordance with the particle size distribu-
tion in the solid phase of the drilling mud.
This technique broadens still further the range of con-
trol of the removal of the solid phase from a drilling mud.
Thus, by performing the withdrawal of the solid phase of
the drilling mud by the other rotating curvilinear closed sur-
face from the formed adhesion layer, while making a controll_
able electric current flow through the withdrawal area, and
varying the polarit~ of the electric current, there is ensured
efficient control of the process of separating the solid phase
of the drilling mud within a broad range, according to the mi-
neralogic composition of thiæ phase. The separation of the so-
lid phase i~ carried out in a simple and economic operation
offering a high throughput.
Given below is a description of an embodiment of the pre-
sent invention, with reference being made to the accompanying
drawings, wherein:
~ ig. 1 illustrates schematically individual portions of
the adhesion layer of the drilling mud, formed on the external
side of a rotating cylindrical surface;
11~3~63
-- 8 --
~ ig. 2 illustrates schematically individual portions of the
adhesion layer of the drilling mud, formed on the internal side
of a rotating cylindrical surface.
Referring now to the drawings, the method of separating
the solid phase in a drilling mud includes forming from the
drilling mud l (FIG. l) an adhesion layer 2 on a rotating cur-
vilinear closed surface 3.
In the embodiment being described this cylindrical surfa-
ce is that of a drum 4 associated with a drive (not shown) for
rotating the drum 4. The drum 4 is mounted so that a portion of
its surface 3 projects into the drilling mud l. In the course
of the rotation, a portion of the adhesion layer 2 (by the
depth thereof) is separated onto another curvilinear closed
surface 5 which in the presently described embodiment is that
of an auxiliary drum 6 operatively connected with a dri~e (not
shown) for rotating this drum 6. ~he angular speeds of the ro-
tating drums 4 and 6 are selected for their linear speeds in
the area of contact of the adhesion layer 2 and of the other
curvilinear clo~ed surface 5 to be substantially equal.
~ he equality of the linear speeds provides for gradual
stratification of the adhesion layer 2 into two portions with
different contents of the solid phase particles.
; The thickness of the formed adhesion layer 2 of the drill-
ing mud l depends on the ~iscosity of the drilling mud l and
on the speed of the rotation of the drum 4. The adhesion layer
2 contains solid particles of rock cuttings, the weighting ma-
1~3~3
terial and the clayey solid phase. With the drum 4 rotating,
the action of the cent~fugal forces results in redistribution
of the solid particles in accordance with their densit~ and
volume, with the coarser and heavier particles migrating toward
the outer surface of the adhesion lager 2, and the finer par-
ticles, particucarlg, the colloid-size ones, remaining closer
to the lnner surface of this adhesion layer 2.
The speed of rotating the auxiliary drum 6 is set at a
value providing for synchronous rotation of the surface 5 of
the auxiliary drum 6 and of the outer surface of the adhesion
layer 2.
The drums 4 and 6 are mounted for the gap between their
respective peripheries to be not less than the thic~ness of
the adhesion layer 2.
A solid phase particle within the adhesion layer 2 has act-
ing thereon, on the one hand, centrifugal forces
~ mV (l)
R
where "m" i8 the mass of the aprticle,
"R" is the radius of the circle of its rotation,
"V" is the linear speed of its rotation;
and, on the other hand, it has acting thereon its weight or
gravity force, viscous friction forces and the forces "~1" f
the surface tension of the adhesion layer 2:
Fl = 2 ~r ~ ~ (2)
_ 10 --
~here "r" is the radius of the particle of the solid phase
of the drilling mud;
"~" is the surface tension coefficient of the drilling
mud 1.
The evaluation of the relative significance of the forces
taking part in the distribution of the solid particles in the
surface layer can be made by using the ~roude cryterion or
similarity nu~ber characterizing the ratio of the centrifugal
forces to the forces of gravity:
Fr =c~ ~ , (3~
where "~ " is the angular speed of the rotation of the
drum 4,
and "R" i8 the radius of the circle of rota-
tion of the particle, while
"g" is the gravity acceleration.
It is knownthat the minimum and maximum values of the
~roude similaritg number for real-life structures are within a
range from 20 to 2000.
It can be derived from the-abovesaid that in the calcula-
tion of the forces acting upon the solid particles in the ad-
hesion layer 2 their weight may be neglected for practical re-
asons, as long as the centrifugal forces are 20 to 2000 times
greater. Since the friction force between the surface of the
solid phase particles and the liquid entraining them for rota-
li~39~3
-- 11 --
tion is directed tangentially to the surface of the drum 4and perpendicularly to its radius, the peculiarities of the
radial motion of the particles, i.e. the ma~or laws governing
the process of the separation of the phases and fractions (the
purification process) may be considered without providing for
the viscous friction forces.
Th~s, by presuming the equality of the forces "~" and
"Fl", it is possible to arrive at the condition of eguilibrium
of the particles in the adhesion lsyer 2 formed on the cylin-
drical surface 3 of the rotating drum 4:
6 ( ~1 ~2) ~ R = 2 ~ r~ = ~d~ t4)
or else, it can be e~pressed in relation to the diameter
of the particle (which latter is conditionally taken to be
spherical):
d V 6~ (5)
2) ~R
where "~1" and "~2" are, respectively, the densities of
the solid phase and of the liguid;
"d" is the diameter of the particle (d=2r);
'1R" is the radius of the circle of rotation of the par-
ticles;
" ~" is the surface ten~ion coefficient of the liguid
of the adhesion layer.
:1~53~3
It can be seen from expressions (4) and (5) that the
motion of a particle of the diameter "d" in the adhesion
lager 2 depends on the density of the drilling mud l1 the
radius "R" of the circle of rotation of this particle, the
speed of its rotation and the value of the surface tension
of the adhesion layer 2. The radius of the circle of rotatio~
of the particle is defined by the diameter of the drum 4. Ho-
wever, you cannot increase substantially the diameter of the
drum 4 without encountering corresponding complexity of its
manufacturing and mounting. Therefore, the major parameters
of the process of separation of the solid phase of the drill-
ing mud l on the rotating cylindrical surface 3 are the speed
of the rotation of the drum 4 and the value of the surface
tension of the adhesion layer 2.
As a result of the contact between the surface 5 of the
auxiliar~ drum 6 and the adhesion layer 2, a portion of the
last-mentioned layer becomes separated and taken by this sur-
face.
Depending on the relative positions of the drums 4 and
6, the separated portion of the adhesion layer 2 contains dif-
ferent concentrations of the solid phase.
When the adhesion layer 2 is formed on the external surfa-
ce of the drum 4 (~ig. l), the auxiliary drum 6 takes up the
portion of the adhesion layer 4, enriched in the coarser heavy
particles of the solid phase of the drilling mud l. This por-
tion 7 of the adhesion layer 2 is directed by the scraper 8
into a trough 9.
il53~3
- 13 -
Whe~ the adhesion layer 10 (Fig. 2) is formed on the inter-
nal surface 11 of a drum 12, the other closed curvilinear sur-
face 13, i.e. that of the auxiliary drum 13a takes up the por-
tion 14 of the adhesion layer 10, cleaned from the coarser and
heavier particles of the solid phase of the drilling mud 1. In
other words, the taken-up portion 14 of the adhesion layer 10
ha~ been purified from the coarser particles of the solid pha-
se of the drilling mud 1. A scraper 15 removes the portion 14
off the surface of the auxiliary drum 13a and direct~ it into
a trough 16.
Particles of the solid phase projected from the portion
14 of the adhesion layer 10 by the centrifugal forces are in-
tercepted by a guard 17, and flow down this guard 17 into the
trough 16.
To enhance the efficiency of the separation of the solid
phase of the drilling mud, the value of the surface tension of
the adhesion layer is varied bg acting thereupon with a direct-
current electric field. The electric current flows ~ia the cir-
cuit: current source 18 (~IGS. 1 and 2) - drum 4 (12) - adhe-
sion layer 2 (10) - augiliary drum 6 (13a). With a positive
potential fed to the auxiliary drum 6 (13a), the separation of
negatively charged colloid particles is intensi~ied, whereas
with the polarity reversed, more neutral and positively charged
particles are separated on the auxiliary drum 6 (13a).
Depending on the particle size, or fraction content of
the solid phase o~ the drilling mud, the value of the surface
1~3~3
- 14 -
tension of the adhesion layer i8 controlled by varying the in-
tensity of the electric field.
To remove the weighting material, the drilling mud 1
containing ~olid roc~ cuttings is disintegrated prior to the
separation to the size of the weighting material particles.
This speeds up the separation of the particles of the weight-
ing material which are of a density at least twice as great
as that of rock cuttings.
The portion of the adhesion layer 2 (10), remaining on
the drum 4 (12) after the separation of its portion 7 (14~ by
the aux~liary drum 6 (13a), is scraped off by a scraper 19
(~IG. 1) and directed into a receptacle 20. By controlling
the speed of rotation of the drum 4 (12) and the value of the
surface tension of the adhesion layer 2 (10) by varying the
value and the polarity (or direction) of the electric current,
it is possible to regulate the separation of the solid phase
in the drilling mud within a broad range, to remove the excessi-
ve solid phase a~d to retain the fine particles of clay which
make up the major colloid-size component of the drilling mud.
The herein disclosed method is performed, as follows.
Following feeding the drilling mud 1 into a vessel 21
(FIG. 1), the drive (not shown) o~ the drum 4 is energized. As
a result of the contact between the surface 3 of the drum 4 and
the drilli~g mud 1, there is formed on the surface 3 the adhe-
sion layer 2. The angular speed of the drum 4 i9 set to cor-
respond to the ~iscosity of the drilling mud 1 and the required
llt~3~fi3
- 15 -
d~3gree of its purification. The gap between the respective pe-
ripheries of the drums 4 and 6 is adjusted to correspond to
the thickness (or depth) of the adhesion layer 2. The speed
of rotation of the auxiliary drum 6 is set to a value providing
for equality of the linear speeds of the surface of the rotat-
ing auxiliary drum and of the outer surface of the adhesion
layer 2. ~he required polarity of the electric current fed to
the drums 4 and 6 from the direct-current source 18 is set to
correspond to the mineralogic composition of the sludge in the
drilling mud 1.
By gradually varying the value of the electric current,
the required degree of the purification of the drilling mud 1
i8 attained.
Thus, the herein disclosed method of centrifugal separ-
ation of the solid phase of the drilling mud 1 in electric
fields of alternati~e polarity on rotating curvilinear closed
surfaces 3, 5 e~ables to control within a broad range the
amount of the solid phase and the size of the particles being
separated, up to complete clarification of the liouid, which
cannot be attained by using any of the hitherto known methods.
As an example of the implementation of the herein dis-
closed method, it is possible to supply the data obtained in
the study aimed at determining the optimum parameters of the
duty of purifying the drilling mud 1 from sludge taken off the
surface of the adhe9ion layer ~ formed on the surface 3 of the
drum 4.
1~3~63
- 16 _
Drums of various diameters from 100 to 500 mm were
tested as the main drum 4, and were rotated at 10 r.p.m. to
10,000 r.p.m. The tested auxiliary drums 5 has similar param-
eters.
It was found that with the main drum 4 rotated at a speed
from 10 r.p.m. to 150-200 r.p.m., thethickness of the adhesion
layer 2 formed from the drilling mud 1 of a viscosity from 10
to 100 centipoise was 1.5 to 3 mm. The small thickness of the
adhesion layer 2 was in these cases caused by the liquid flow-
ing and drippin down from the surface of the drum 4 rotated
at a low speed. This thickness of the adhesion layer 2 would
not provide for reguired productivity of the drum 4.
Within the range of the speeds of rotation from 200 to
500 r.p.m. the thickness of the adhesion layer 2 on the sur-
face 3 of the drum 4, with the drilling mud 1 viscosity from
10 to 100 centipoise, varied between 3 and 8 mm, and the solid
particles of diameters between 0.8 and 4 mm where separated
from the sur~ace of the adhesion layer 2. All the particles of
the diameters short of the abovementioned ones remained within
the adhesion layer.
The study has shown that the angular speed of the surface
of the adhesion layer 2, contacting the ambient air, is signif-
icantly lower (10 to 30 times) than the angular speed of the
surface 3 of the drum 4. On account of this phenomenon, with
the drum 4 rotated at speeds from 1000 and 2000 r.p.m., which
are the optimum ones from the theoretical calculation made on
1153~63
- 17 -
the assumption that the adhesion layer 2 rigidl~ rotate~ with
the drum 4, the particles of the solid phase of the minimum
size of 0.07 mm cannot be separated to the required degree of
purification.
If, however, the surface lager of the liguid is driven at
the speed equalling the speed of rotation of the drum 4 by the
action o~ the auxiliary drum 6, the theoretical calculation of
the purification degree is completely sustained. When voltage .
of alternative polarity was fed to the drums 4 and 6 from the
direct-c~rrent source 8, the fineness and degree of the purifi-
cation were enhanced, owing to the reduced surface tension of
the adhesion layer, with the minimum size of the solid phase
particles removed from the adhesion layer being 20 microns.
It was found that a potential corresponding to the charge of
the sludge particles, or rock cuttings had to be fed to the
drum 4 while purifying drilling muds. Thus, if the sludge is
represented by negatively charged particles of clay, a nega-
tive potential is preferably fed to the drum 4, whereas with
the sludge being represented by positively charged calcite
particles, it is a positive potential that pre~erably has to
be fed to the drum 4.
The studies also proved that to attain quality purificat-
ion of drilling muds of viscosities from lO to lO0 cent.ipoise
(to the minimum size of the removed particles egualling 20 mic-
rons), it was necessary to rotate the drum 4 at speeds from
, : :
1~$3963
- 18 -
1000 to 2000 ~.p.m. and to feed to the drum 4 the voltage
of 10 to 20 V.
Thus, to purify the relatively clear drilling mud (30 to
40~0 solid phase) with the maximum size of the ~olid particles
up to 200 - 300 microns, the diameter of the main drum was
selected to be 420 to 500 mm, and the speed of its rotation
was set at 1800 to 2000 r.p.m. The diameter of the auxiliary
drum 6 was preferably 140 to 160 mm, and the speed of its ro-
tation was set at 5000 to 6000 r.p.m. Under such conditions
solid particles as small as I2 to 16 microns were separated
from the adhesion layer.
It was further found that when the drilling mud with a
high content of sludge and the size of the solid particles
in excess of 1 mm had to be purified, the diameter of the main
drum ~as preferably 100 to 120 mm, and the speed of its rota-
tion was 1000 to 1200 r.p.m. The auxiliary drum diameter was
preferab b from 30 to 40 mm, and the speed of its rotation was
3000 to 3600 r.p.m, Solid particles of a size from 40 to 50
microns were separated from the adhesion layer 2.
The economic effectiveness of the ~rein disclosed method
of separating the solid phase in a drilling mud is made up of
the reduced purification costs, owing to getting rid of a multis-
tage purification system, of the prolonged life of the drilling
mud and of faster drilling, due to the enhanced purification
guality of the drilling mud.
