Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A DRIL~ING MUD COMPRISING A HIGH
SURFACE AREA MAGNETITE CONCENTRATE
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This invention relates to drilling muds
comprising magnetite (Fe3O4) having the ability to absorb
hydrogen sulfide.
Often, during drilling operations in oil or gas
wells, exhalations of hydrogen sulfide occur, which can
cause damage to the personnel involved in the drilling
operation. Concentrations as low a 1 ppm may irritate
mucous membranes, and cause headaches, and nausea. Short
exposure to high concentrations can even lead to death.
Furthermore, hydrogen sulfide is a drawback to the
environment, and corrodes equipment, chiefly linings,
which may be weakened and leak~ When drilling columns are
broken, drilling must be stopped, causing big losses to
the oil company.
In order to eliminate or reduce to reasonable
levels the hydrogen sulfide present in drilling sites,
various materials have been used. The alkalinity of the
drilling mud itself serves in part to control the sulfides.
Copper salts, such as carbonates ~preferably, cupric
carbonate~ are commonly used as well as zinc salts, such
as the basic carbonate of zinc and, more recently, zinc
chelates. These compounds are efficient scavengers of
soluble sulfides such as H2S, HS and S up to certain
concentrations above which the reaction products may
change the rheology of the drilling mud. In such case,
the use of these scavengers is rendered inadequate. The
use of certain synthetic iron oxides with special
characteristics is then indicated, especially hematites
and magnetites of high surface area. The term "magnetite"
means any mixture in which Fe3O4 predominates, and
"hematite" any mixture in which Fe2O3 predominates.
The reaction between Fe3O4 and H~S, in acidic
or neutral medium, forms pyrite, whose insolubility in
hydrogen chloride is greatly advantageous, in case of
acidification of the oil wellO
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In U.S. Patent 4,008,775 there is described an
iron oxide product made essentially of Fe3O4, ~Ihose
particles are sponge-like. This product is highly
effective for absorbing large amounts of hydrogen sulfide.
This synthetic product is obtained by the oxidation of
carbon-bearing iron or iron wastes, under strictly
controlled oxidation conditions, the particles being
further de-agglomerated through a special crushing
technique~ rrhis product is marketed under the trademark
"Ironite Sponge".
U.S. Patent 4,324,298 discloses a compound made
essentially of high surface area Fe2O3, the compound being
prepared through conventional oxidation of ferrous sulfatb
at high temperature, followed by quenching. Nevertheless,
no proof of the efficiency of such a product is known when
used in connection with drilling rigs.
The present in~ention provides drilling muds
containing magnetite with a high content of magnetic iron
oxide, high porosity, and a high capacity for quick
absorption of hydrogen sulfide, in the form of the magnetic
fraction of a product obtained by roasting pyrite to
oxidize the iron sulphides therein to iron oxides, with or
without any subsequellt preliminary separation.
More particularly, the present invention resides
in an aqueous drilling mud comprising a high surface area
magnetite having a particle size of 0.208 to 0.037 mm and
a surface areaof 2.04 to 3.3 m /g as a sulfide sequestering
agent, said magnetite being obtained by the process comprising:
(a) roasting pyrite; and
(b~ magnetically separating a residue obtained
as a result of roasting step (a) to recover a magnetic fraction
rich in magnetite;
and during the process carrying out particle size classification
to retain particles from 0.208 to 0.037 mm, the surface area
of the retained particles being from 2.04 to 3.3 m /g.
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~n the accompanying drawing, Figure 1 is a
flowsheet of a pyrite roasting process suitable for
producing a high surface area magnetite for use in khe
present invention.
By "pyrite" is meant a pyritous material i.e.,
a mineral made basically of iron sulfides of the type FeS2
(pyrite) and FeS (pyrrhotite), besides the arsenopyrites
(FeAsS). Typically, the iron content of pyrites is from
40 to 44%. The carbonaceous pyrites are those made by the
physical treatment of coals and which retain some carbon
not removable by this treatment.
Pyrite roasting aims at producing sulfuric acid
or elemental sulfur. Iron oxides for ironworks are also
produced. With the arsenopyrites,~the main product is
often valuable metals such as gold, which may be included
in them. Pyrite roasting is a high temperature oxidation
of the sulfides, typically at 850C, conducted in the
presence of air and in the absence of li~uid phase, i.e.,
without melting. The gas produced contains 13.5% of
sulfur dioxide and a solid, roasted product~ It is
believed that the following series of reactions is
indicative of the order in which the oxidation reactions
occur:
FeS2 -~ FeS i~ FeO ~ FeO.Fe203 = Fe203
the formula FeO.Fe2O3 being equivalent to Fe3O4.
Depending on the operation conditions, the
behaviour of the substances involved in the roasting can
vary widely. At present, a fluidized bed reactor is the
most economical and competitive equipment in which to
conduct roasting. The partial pressures of the gases,
oxygen and sulfur dioxide, temperature and residence time
are of utmost importance and control of them provides
oxidation to various degrees.
In Figure 1, the pyrite fluidized bed reactor 1
is fed with the pyrites at a rate of about 19 tons/day and
per m~ of feeder. Also, the reactor is blown with air,
at a rate of about 1900 Nm3/h and par m2 of feeder.
Typically, the pyrites size range is: 3~ from 4 to 6 mm,
15% from 2 to 4 mm, 25~ ~rom 1 to 2 mm, 30~ from 0.5 to
1 mm and 27~ below 0.5 mm. Part of the contents of the
reactor evolve as effluent gases 3, which contain
entrained solids and are directed to a heat recovering
boiler ~ Nearly 30% of the roasted product exists as a
reactor residue 2 - i.e., the reactor overflow. Water
enters and vapor leaves the heat recovery boiler. Also,
a~out 40~ of the roasted product is di~charged as boiler
residue 5. Solid particles of smaller size than those of
the boiler residue are entrained by the gaseous flow 6
which exits the boiler and is directed to the cyclone 7.
The top flow of the cyclone contains a small percentage
~z
of solids fines and is directed to an electrostatic
settler 13. The cyclone residue 8 is discharged through
the bottom and makes up about 27% of the roasted product.
From the electrostatic settler 13 exit the gases which
are washed in a gas washer. About 3% of the roasted gases
is discharged into the electrostatic settler.
The solid roasted residue is a mixture of purple
iron oxides (purple ore). The boiler takes up the larger
entrained particles, the cyclones take up chie~ly the
particles of next reduced size, and the settler collects
the fines.
The boiler residue 5 and the cyclone residue 8
are useful in the practice of the present invention.
Preferably, it is the cyclone residue 8 which is subjected,
after cooling in air at about 50C, to magnetic separation,
since, besides being richer in magnetic substance, unlike
the boiler residue it does not require grinding and this
serves better the objects of the present invention, in
which the magnetic concentrate is used in the absorption
of hydrogen sulfide in drilling muds. Also, the surface
area of the magnetic Eraction from the cyclone residue is
nearly always larger than that of the magnetic fraction
from the boiler residue. This preferred form of operation
is shown in Figure 1, where the cyclone residue 8 is led
to a magnetic separator 10 where the separation into a
magnetic fraction 11 (about 57 weight %, in a typical
operation condition) and a non-magnetic fraction 12
(about 43 weight %) occurs.
Part of the cyclone residue can be separated by
particle size to enhance the magnetic substance content
of the concentrate, since the larger size fractions have
a higher content of magnetic material. For example, the
40 weight % of larger size (above 73 microns) contain,
on the average, 68% of magnetic substance, whereas all the
cyclone residue has on the average 57.3~ of magnetic
material.
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The cyclone fraction has particles of a wide range of
particle sizes, including particles ranging from 65 mesh
(0.208 mm) up to 400 mesh (0.037 mm) and even finer. For
the cyclone fracti.on, surface area measurements indicate
that the 65 mesh fraction (0.208 mm) has a surface area of
2.04 m2/g, the 270 mesh fraction has a surface area of
2.97 m /g and the 400 mesh fraction has a surface area of
3.33 m2/g.
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Any adequate magnetic separator (wet or dry) can
be used in the present invention, for example one of low
intensity of the type David tube model E.D.T.
The magnetic separation produces the magnetite
concentrate of high surface area which is used in the
present invention.
In order to evaluate the performance of the
magnetite concentrate used in the present invention, the
following Examples describe tests of reactivity and
consumption, in comparison with commercial products.
EXAMPLE 1 - Reactivity
1~40 g of Na2S.9H2O were dissolved in 47.5 ml
of water and adjusted to pH 8~5. The content A of sulfide
ion was determined in an aliquot of 5 ml. To the remain-
ing solution was added excess of test product (2.5 g),allowing the reaction to proceed for one hour at room
temperature. An aliquot of 5 ml was collected in 4 ml of
Na2CO3 solution of pH of about 12. After addition of
2 g of NaCl and centrifugation, the content B of s2 ion
was determined in the supernatant layer.
For each product the reactivity index A - B was
calculated and the results are listed in Table 1. In
the table, the meaning of each symbol is:
*
- COAT 1131 refers to a commercial salt mixture
containing chromium an-d zinc;
- cyclone means the cyclone residue;
- boiler means the boiler residue;
270 after "cyclone" or "boiler" refers to the
size fraction from 53 to 74 microns (270 to 200 mesh).
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'~ * Trademark
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TABLE I
Product Reactivity Index, ~ _
COAT 1131 ~rademarkl 100
"Ironite Sponge" 100
5 Overall cyclone magnetic 100
Cyclone 270 magnetic 99.5
Overall boiler magnetic 91
Boiler 270 magnetic 82
Overall cyclone non-magnetic 68
Cyclone 270 non-magnetic 90
Overall boiler non~magnetic 63
Boiler 270 non-magnetic 67
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EXAMPLE II - Kinetics
The procedure of Example 1 was repeated with the
exception that instead of taking only one aliquot after one
. hour reaction, four aliquots were taken, after 15 minutes,
30 minutes, 45 minutes and 60 minutes of reaction. The
treatment of each aliquot was identical.
For each aliquot was calculated the non-consumed
fraction B/A/ and the results are listed in Table II. The
meaning of the symbols is the same as for Table 1.
TABLE II
~ % ions s2 non-consumed after
- 25 t (min~
- Product _ t=0 t-15 t=30 _t=45 t=60
COAT 1131 (trademark).lQ0 3 2 1 0
"Ironite Sponge" 100 3312 4 0
Overall cyclone magnetic 100 3413 4 0
30 Cyclone 270 magnetic 100 3414 4 0.5
Overall boiler magnetic 100 7167 50 37
Boiler 270 magnetic 100 72 4 53 33
Overall cyclone.non-magnetic 100 69 53 45 32
Cyclone 270 non-magnetic 100 70~4 23 10
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EXAMPLE III - Sulfide Consumption
1.40 g of Na2S.9H2O were dissolved in water,
diluted to 55 ml and NaHCO3 was added up to pH ~.5. A 5
ml aliquot was taken and its content of sulfide ion was
determined~ To the remaining solution was added test
product in limited amount - ~ = 0.100 g allowing the
reaction to proceed for one hour at room temperature.
A 5 ml aliquot was taken into 4 ml of Na2CO3 solution of
pH of about 12.2 of NaCl were added, the whole was
centrifuged and the content B of s2 ion was determined in
the supernatant.
The consumption of s2 ion per gram of test
product was calculated:
Consumption of s2 = A - B = g s2 /g product,
W x 20.000
wherein A and B are expressed in mg/l and W is in grams.
The results are listed in Table III.
TABLE III
Product Consumption of S2_ ions_(g s2 /g product)
COAT 1131 0.120
"Ironite Sponge" 0.085
overall cyclone magn. 0.090
cyclone 270 magn. 0.105
. . _ _, _ . . _ . . _
Exam~le IV - Consumption of H2S in various media,
at pH = 7.0
A nitrogen gas stream containing hydrogen sulfide
from the acidulation of sulfide solution was bubbled into
100 ml of ~est liquid or mud, the test sample containing
0.1 g of the test product. The merging gas was collected
and its hydrogen sulfid~ was absorbed in 50 ml of a 0.lN
NaOH solution. After one hour the content of sulfide in
the NaOH solution was determined. The consumption of H2S
was calculated:
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X -- Y
H2S consumption = - - = g H2S/g product, where
W
X = initial amount of s2 ions, in the sulfide solution to
be acidulated, mg;
Y = amount of s2 ions, in the NaOH solution, mg;
W = weight of test product to be tested, mg.
For each test product, the procedure was carried
out in three liquids or muds:
A - 1% NaHCO3 solution
B - mua based on sea water, starch treated
C - mud based on KCl.
The results are listed below in Table IV.
TABLE IV
15 Product H2S consumption, g H2S/g product
A B C
. _ _
COAT 1131 0.13
"Ironite Sponge" 0.75 0.42 0.91
*overall cyclone magn. 0.72 0.47 0.65
20**overall cylcone, magnØ63 0.48 0.50
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* 1st experiment
** 2nd experiment
From the Examples it can be inferred that the
product of the present invention is better than the
"Ironite Sponge" in alkaline and neutral media, starch-
treated, for muds based on seawater.
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