U.S. patent application number 14/953916 was filed with the patent office on 2017-06-01 for method of producing sodium bentonite.
This patent application is currently assigned to KING FAHD UNIVERSITY OF PETROLEUM AND MINERALS. The applicant listed for this patent is KING FAHD UNIVERSITY OF PETROLEUM AND MINERALS. Invention is credited to Ibnelwaleed Ali Hussein, Musaab Ibrahim Magzoub, Mohamed Ahmed Nasr Eldin Mahmoud, Mustafa Saleh Nasser, Abdullah Saad Sultan.
Application Number | 20170152184 14/953916 |
Document ID | / |
Family ID | 58777862 |
Filed Date | 2017-06-01 |
United States Patent
Application |
20170152184 |
Kind Code |
A1 |
Magzoub; Musaab Ibrahim ; et
al. |
June 1, 2017 |
METHOD OF PRODUCING SODIUM BENTONITE
Abstract
Method of converting calcium bentonite to sodium bentonite that
is suitable for use as drilling mud or a cement additive. After the
addition of a calcium bentonite sample to a prepared soda ash
solution at predetermined soda ash/bentonite weight ratios, the
bentonite suspension is continuously heated and stirred for up to
24 h. The heating and stirring are crucial towards enhancing the
sodium activation of the bentonite, as well as other rheological
properties of the bentonite.
Inventors: |
Magzoub; Musaab Ibrahim;
(Dhahran, SA) ; Nasser; Mustafa Saleh; (Dhahran,
SA) ; Hussein; Ibnelwaleed Ali; (Dhahran, SA)
; Mahmoud; Mohamed Ahmed Nasr Eldin; (Dhahran, SA)
; Sultan; Abdullah Saad; (Dhahran, SA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KING FAHD UNIVERSITY OF PETROLEUM AND MINERALS |
Dhahran |
|
SA |
|
|
Assignee: |
KING FAHD UNIVERSITY OF PETROLEUM
AND MINERALS
Dhahran
SA
|
Family ID: |
58777862 |
Appl. No.: |
14/953916 |
Filed: |
November 30, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K 2208/34 20130101;
B28C 1/04 20130101; C04B 33/04 20130101; C04B 2235/349 20130101;
C01B 33/40 20130101; C09K 8/032 20130101 |
International
Class: |
C04B 33/04 20060101
C04B033/04; B28C 1/04 20060101 B28C001/04; C09K 8/03 20060101
C09K008/03 |
Claims
1. A method of converting calcium bentonite to sodium bentonite,
comprising: adding a calcium bentonite sample to a sodium carbonate
aqueous solution to form a bentonite suspension comprising calcium
bentonite, sodium carbonate, and water, wherein the bentonite
suspension has a sodium carbonate/calcium bentonite weight ratio of
1:7 to 1:23 and a calcium bentonite concentration of 5-10 wt %
based on a total weight of water; and continuously heating and
stirring the bentonite suspension at 60-80.degree. C. for 6-24
hours to form sodium bentonite and calcium carbonate.
2. The method of claim 1, wherein the sodium carbonate aqueous
solution has a sodium carbonate concentration of no more than 1% by
weight based on a total weight of water.
3-4. (canceled)
5. The method of claim 1, wherein the sodium bentonite formed has
an apparent viscosity of at least 15 cP.
6. The method of claim 1, wherein the sodium bentonite formed has a
yield point of no more than 30 lb/100 ft.sup.2.
7. The method of claim 1, wherein the sodium bentonite formed has a
Na/Ca molar ratio of at least 2.5.
8. The method of claim 1, wherein the sodium bentonite formed has a
viscometer dial reading of 33-35 lb/100 ft.sup.2 at 300 rpm and
39-40 lb/100 ft.sup.2 at 600 rpm.
9. (canceled)
10. The method of claim 1, wherein an average particle size of the
sodium bentonite is more than 500 times larger than an average
particle size of the calcium bentonite sample.
11. The method of claim 1, wherein the calcium bentonite sample is
a raw bentonite sample that has not been purified.
12. The method of claim 1, wherein the calcium bentonite sample has
been purified by at least one method selected from the group
consisting of dry-sieving, wet-sieving, dispersion in deionized
water with hexametaphosphate, dispersion in deionized water without
hexametaphosphate and sedimentation.
13. The method of claim 1, wherein the sodium carbonate aqueous
solution has a sodium carbonate concentration of 0.28-0.86% by
weight based on a total weight of water.
14. The method of claim 1, wherein the sodium carbonate/calcium
bentonite weight ratio is 1:20 to 1:23.
15. The method of claim 1, wherein the bentonite suspension is
heated at 65-70.degree. C.
16. The method of claim 1, wherein the bentonite suspension is
stirred for 12-24 hours.
17. The method of claim 1, wherein the sodium bentonite formed has
a Na/Ca molar ratio of 2.8-3.0.
18. The method of claim 1, wherein the sodium bentonite formed has
a particle size of 1100-1400 .mu.m.
19. The method of claim 1, wherein the sodium bentonite formed has
a yield point of 12-28 lb/100 ft.sup.2.
Description
BACKGROUND OF THE INVENTION
[0001] Technical Field
[0002] The present invention relates to a method of preparing
sodium bentonite. Specifically, calcium bentonite is converted into
sodium bentonite by a combination of chemical, thermal and
mechanical treatment procedures. The produced sodium bentonite is
suitable for but not limited to oil and gas drilling and cementing
applications.
[0003] Description of the Related Art
[0004] The "background" description provided herein is for the
purpose of generally presenting the context of the disclosure. Work
of the presently named inventors, to the extent it is described in
this background section, as well as aspects of the description
which may not otherwise qualify as prior art at the time of filing,
are neither expressly or impliedly admitted as prior art against
the present invention.
[0005] Bentonite is a natural clay consisting primarily of
montmorillonite that is usually formed from weathering of volcanic
ash in the presence of water. There are different types of
bentonite, each named after the respective dominant element, such
as potassium (K), sodium (Na), calcium (Ca), magnesium (Mg) and
aluminum (Al).
[0006] Na-bentonite expands up to 15 times its volume when wet,
adsorbing as much as several times its dry mass in water. The
excellent colloidal and adsorbent properties of Na-bentonite have
popularized its use, compared to other types of bentonite, in
drilling mud or drilling fluid for oil and gas wells and boreholes
for geotechnical and environmental investigations. Na-bentonite is
used as a viscofier or lubricant and in water control to reduce
filtration loss. Further, the mixing of Na-bentonite in the
drilling fluid helps to cool the cutting tools, to remove the soil
and rock cuttings, to support the borehole and to prevent it from
collapsing through the formation of a mud cake. Most high-grade
natural Na-bentonite in the United States, which is the world's
largest bentonite producer, is produced from the western part of
the country in area between the Black Hills of South Dakota and the
Bighorn Basin of Wyoming. In addition to drilling fluid
applications, Na-bentonite is also useful as a sealant, providing a
self-sealing, low permeability barrier, for example, at the base of
landfills.
[0007] Ca-bentonite, which is found abundantly in the southern part
of the United States such as Mississippi and Alabama, also has good
adsorbent properties but is only capable of swelling 2-3 times of
its unwetted volume.
[0008] Researchers and bentonite producers have attempted to
utilize their local resources of bentonite. For example, different
methods have been used to purify or treat raw bentonite, such as
dry-sieving, wet-sieving, dispersing in hexametaphosphate
solutions, sedimentation and mixing with soda ash. These attempts
have been found to be time-consuming or have low efficacy:
[0009] Al-Homadhi et al. attempt to treat local bentonite with soda
ash and to upgrade the treated bentonite with extenders or
additives such as salt and polymers. The final modified bentonite
did not satisfy API specifications for evaluation of drilling mud
(Al-Homadhi, E. S. "Improving Local Bentonite Performance for
Drilling Fluids Applications", Society of Petroleum Engineers Saudi
Arabia Section Technical Symposium, 7-8 May 2007, Dhahran Saudi
Arabia--incorporated herein by reference in its entirety).
[0010] In Australian Pat. No. AU566345B (incorporated herein by
reference in its entirety), magnesium- and/or calcium-containing
bentonite are agglomerated by soda ash treatment to produce
Na-bentonite for laundry applications. The produced Na-bentonite
has not been evaluated for drilling fluid applications.
[0011] Chinese Pat. No. CN1061946C (incorporated herein by
reference in its entirety) describes a process of producing
Na-bentonite from Ca-bentonite by soda ash treatment followed by
ion exchange reaction. The produced Na-bentonite also has not been
evaluated for drilling fluid applications.
[0012] Yildiz et al. activate local Ca-bentonite with soda ash to
increase the Na/Ca ratio and disperse the activated bentonite in
sodium hexametaphosphate solutions to increase the stability of the
suspension. The rheological properties of the activated bentonite
are tested at different sodium hexametaphosphate and NaCl
concentrations but not according to the API standards for drilling
fluids (Yildiz, N., Sarikaya, Y., alimli, A. "The effect of the
electrolyte concentration and pH on the rheological properties of
the original and the Na.sub.2CO.sub.3-activated Kutahya bentonite"
Applied Clay Science 14(5-6):319-327, 1999--incorporated herein by
reference in its entirety)
[0013] Kaufhold et al. activate Mg/Ca-bentonite with sodium
carbonate (soda ash) in both dry state and in solution with
excessive water with no heating. The authors conclude that despite
the addition of the sodium carbonate in excess (1-5 wt. %), the
activation process whether it is conducted in a dry state or a wet
state may be incomplete and partial (Kaufhold, S., Emmerich, K.,
Dohrmann, R., Steudel, A., Ufer, K. "Comparison of methods for
distinguishing sodium carbonate activated from natural sodium
bentonites" Applied Clay Science 86:23-37, 2013--incorporated
herein by reference in its entirety).
[0014] Karaguzel et al. activate local bentonite with 1.5-3 wt. %
soda ash and 0.5% MgO without heating and a prior purification
step. The combination of soda ash and MgO is found to influence the
viscosities, swelling indices and filtration losses to produce an
activated bentonite that satisfies drilling mud standards
(Karaguzel, C. etinel, T., Boylu, F., inku, K., elik, M. S.
"Activation of Na, Ca)-bentonites with soda and MgO and their
utilization as drilling mud--incorporated herein by reference in
its entirety).
[0015] In view of the foregoing, it is evident that treatment of
raw non-sodium bentonite with soda ash alone can only improve
characteristics such as swelling to a limited extent that would not
suffice for oil and gas drilling applications. Accordingly, it will
be beneficial to provide methods of producing Na-bentonite from
local, raw Ca- and/or Mg-bentonite for drilling mud applications.
Preferably, a minimal number of additive compounds is added to the
raw bentonite to modify the rheological properties so that the
produced Na-bentonite maintains a high purity.
BRIEF SUMMARY OF THE INVENTION
[0016] In one aspect, there is provided a method of converting
calcium bentonite to sodium bentonite. The method comprises adding
a calcium bentonite sample to a sodium carbonate aqueous solution
to form a bentonite suspension and continuously heating and
stirring the bentonite suspension to form sodium bentonite and
calcium carbonate.
[0017] In one embodiment, the sodium carbonate aqueous solution has
a concentration of no more than 1% by weight.
[0018] In one embodiment, the continuous heating and stirring is
carried out at 60-80.degree. C. for 6-24 hours.
[0019] In one embodiment, the bentonite suspension comprises the
sodium carbonate and the calcium bentonite at a sodium
carbonate/calcium bentonite weight ratio of 1:7 to 1:23.
[0020] In one embodiment, the sodium bentonite formed has an
apparent viscosity of at least 15 cP.
[0021] In one embodiment, the sodium bentonite formed has a yield
point of no more than 30 lb/100 ft.sup.2.
[0022] In one embodiment, the sodium bentonite formed has a Na/Ca
molar ratio of at least 2.5.
[0023] In one embodiment, the sodium bentonite formed has a
viscometer dial reading of 33-35 lb/100 ft.sup.2 at 300 rpm and
39-40 lb/100 ft.sup.2 at 600 rpm.
[0024] In one embodiment, the method is effective in increasing the
water control of the calcium bentonite sample by 35-70%.
[0025] In one embodiment, the method is effective in increasing the
average particle size of the Ca-bentonite sample by more than 500
times.
[0026] In one embodiment, the Ca-bentonite sample is a raw
bentonite sample that has not been purified.
[0027] In one embodiment, the Ca-bentonite sample has been purified
by at least one method selected from the group consisting of
dry-sieving, wet-sieving, dispersion in deionized water with
hexametaphosphate, dispersion in deionized water without
hexametaphosphate and sedimentation.
[0028] The foregoing paragraphs have been provided by way of
general introduction, and are not intended to limit the scope of
the following claims. The described embodiments, together with
further advantages, will be best understood by reference to the
following detailed description taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] A more complete appreciation of the disclosure and many of
the attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0030] FIG. 1 is a map image showing the location of Khulays area
in Saudi Arabia where raw bentonite can be derived and converted
into Na-bentonite according to one embodiment.
[0031] FIG. 2 shows the spectra from the X-ray diffraction (XRD)
analyses of a raw bentonite sample and a raw bentonite sample that
has been purified by dry-sieving.
[0032] FIG. 3 shows the particle size distribution in terms of
volume percentage and frequency for standard bentonite and purified
bentonite.
[0033] FIG. 4 shows the weight percentages retained of different
raw bentonite samples, as measured by scanning electron microscopy
(SEM) after being subjected to different purification
procedures.'
[0034] FIG. 5 shows the clay content for sample DS-1 as revealed by
hydrometer analysis.
[0035] FIG. 6 shows the particle size distribution in terms of
volume percentage and frequency for raw, unsieved bentonite samples
RB-1 and RB-2.
[0036] FIG. 7 shows the particle size distribution in terms of
volume percentage and frequency for wet-sieved local or standard
bentonite passed through 400 mesh (<38 .mu.m).
[0037] FIG. 8 shows the zeta potential values for standard,
dry-sieved and wet-sieved bentonite samples.
[0038] FIG. 9 shows the effect of soda ash on plastic viscosity
(PV), yield point (YP) and apparent viscosity (AV) (without heating
and stirring).
[0039] FIG. 10 shows the effect of aging on the rheology of
different treated bentonite samples.
[0040] FIG. 11 shows the impact of aging and stirring on the
viscosity of the soda ash-treated RB-2 sample.
[0041] FIG. 12 compares the low pressure, low temperature API
filtration volumes of 1 g or 3 g of soda ash on standard bentonite,
RB-1 and RB-2 local bentonite samples.
[0042] FIG. 13 shows the particle size distribution in terms of
volume percentage and frequency for different bentonite samples:
standard bentonite, local raw bentonite that has been treated with
soda ash and local raw bentonite that has been treated with soda
ash then heated and stirred for 24 h.
[0043] FIG. 14 illustrates the influence of heating and stirring
time on complex viscosity for 1 g of soda ash mixed with RB-1 local
bentonite sample.
[0044] FIG. 15 illustrates the influence of heating and stirring
time on shear viscosity for 1 g of soda ash mixed with RB-1 local
bentonite sample.
[0045] FIG. 16 illustrates the influence of heating and stirring on
viscosity at a high shear rate (64 s.sup.-1).
[0046] FIG. 17 illustrates the influence of heating and stirring on
viscosity at a low shear rate (1 s.sup.-1).
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0047] Referring now to the drawings, wherein like reference
numerals designate identical or corresponding parts throughout the
several views.
[0048] The present invention pertains to a method of converting or
upgrading calcium (Ca) bentonite to sodium (Na) bentonite.
Advantageously, the produced Na-bentonite is of drilling mud grade,
satisfying the specifications and standards that are set forth in
the American Petroleum Institute (API) Recommended Practice 13B-1
(for Field Testing Water-Based Drilling Fluids), which is
incorporated herein by reference in its entirety.
[0049] In the method, a sodium carbonate (soda ash) solution is
initially prepared by dissolving sodium carbonate powder or
crystals in water (preferably distilled water) to a final sodium
carbonate concentration of no more than 1 wt. % (weight percentage
based on total weight of water), preferably 0.1-1 wt. %, more
preferably 0.2-0.9 wt. %, more preferably 0.3-0.6 wt. %, more
preferably 0.4-0.5 wt. %, most preferably 0.28-0.86 wt. %. The
sodium carbonate used can be anhydrous or occur in hydrated forms
(most commonly as monohydrate, decahydrate or crystalline
heptahydrate). The soda ash solution acts as a source of carbonate
and sodium ions for an ion exchange process with Ca-bentonite where
calcium from Ca-bentonite can be precipitated as calcium
carbonate
[0050] A Ca-bentonite sample is then added to the prepared sodium
carbonate solution to a final bentonite concentration of 5-10 wt. %
(weight percentage based on total weight of water), preferably 5-8
wt. %, more preferably 6-7 wt. %. The amount of sodium carbonate
and the amount of bentonite present in the bentonite suspension
ranges from 1:6 to 1:25 (sodium carbonate/bentonite weight ratio),
preferably 1:7 to 1:23, more preferably 1:10 to 1:23, even more
preferably 1:20 to 1:23.
[0051] The Ca-bentonite sample is a raw, unpurified bentonite
sample that has been dried to remove water. The Ca-bentonite sample
has a moisture content no more than 10%, preferably 0.5-10%, more
preferably 1-8%, even more preferably 1-5%. In some embodiments, a
Ca-bentonite sample that has been purified using routine
purification methods may be used. Such purification techniques
include but are not limited to dry-sieving, wet-sieving, dispersing
in deionized water with or without hexametaphosphate, sedimentation
and combinations thereof. Sieves used in dry- or wet-sieving have
U.S. sieve or mesh sizes ranging from 100 to 400 mesh, such as 100,
115, 150, 170, 200, 250, 270, 325 and 400. In some embodiments, the
Ca-bentonite sample, when existing as a colloidal dispersion, has a
zeta potential charge of -40 to -20 mV across a pH range of 3 to
12.
[0052] After the addition of the bentonite sample to the sodium
carbonate solution, the bentonite suspension is then heated and
stirred. The heating and stirring are critical towards at least the
following phenomena: increase in bentonite platelet or particle
size, the expansion the bentonite platelets for enhanced swelling
and ion exchange, the penetration and invasion of the bentonite
layers by water, movement of sodium ions to the surface of the
bentonite layers allowing enhanced Na.sup.+ activation and
swelling, increase in Na/Ca ratio and changes in rheological
properties (e.g. apparent viscosity, plastic viscosity, yield
point, etc.). The continuous heating and stirring are especially
advantageous in supplementing soda ash activation when the latter
alone does not suffice to produce drilling mud grade bentonite that
meets the API requirements.
[0053] The heating temperature is maintained at below 100.degree.
C., for example, 60-80.degree. C., preferably 60-75.degree. C.,
more preferably 65-70.degree. C. The inventors are cautious about
avoiding the water boiling point so as to minimize evaporation of
the bentonite suspension. At the aforementioned temperature ranges,
the thermal activation effects can be accomplished while water lost
during evaporation can be easily compensated for by deionized water
produced from the ion exchange to maintain the same bentonite
concentration in the suspension.
[0054] The stirring mechanism can be achieved through the use of
agitation devices such as but not limited to a magnetic agitator
having a vessel containing the bentonite suspension and a magnetic
bar rotating about a magnetic field disposed within the vessel. The
stirring rotational speed is kept at 50-300 rpm, preferably 100-250
rpm, more preferably 200-250 rpm. In alternative embodiments, the
bentonite suspension can be put into motion by a shaking
mechanism.
[0055] The continuous heating and stirring needs to be sustained
for at least 3 hours to achieve maximum viscosity increase. The
bentonite suspension is continuously heated and stirred at 3-24
hours, preferably 6-24 hours, more preferably 9-24 hours, even more
preferably 12-24 hours.
[0056] After the combination of soda ash activation, thermal
treatment and mechanical stirring, the produced bentonite has a
Na/Ca molar ratio of at least 2.5, for example 2.5-3.0, preferably
2.7-3.0, more preferably 2.8-3.0. The method is effective in
increasing the Na/Ca ratio of a treated bentonite sample by at
least 50%, preferably 50-65%. The average particle size (diameter)
can be increased by more than 500 times, for example, from
.about.2.5 .mu.m to 1000-1500 .mu.m, preferably 1100-1400 .mu.m,
more preferably 1200-1300 .mu.m, with more than 90% of the
particles being in the average particle size range (1000-1500
.mu.m). Without the continuous heating and stirring, soda ash
activation alone increase the average particle size by only up to 8
times. Particle size distribution and average particle size can be
determined by dry-sieve or wet-sieve analysis or any other
equivalent grain size analysis.
[0057] The method described herein also provides a systematic
increase in the various functional forms of viscosity that are used
to measure rheological properties, including but not limited to
apparent viscosity, plastic viscosity, shear viscosity and complex
viscosity. These viscosity parameters can be measured with a
viscometer or a rheometer, or derived by calculations. As used
herein, "apparent viscosity" or "AV" (.eta..sub.app) refers to the
value of viscosity measured and evaluated at a nominal average
value of the shear rate. Per API requirements, a water-based
drilling mud should have an apparent viscosity of at least 15 cP.
In one embodiment, the bentonite produced by the method herein has
an apparent viscosity of 12-20 cP, preferably 15-20 cP, more
preferably 17-20 cP (increased from about 1 cP).
[0058] As used herein, "plastic viscosity" or "PV" (.eta..sub.pl)
is a parameter of the Bingham plastic model and represents the
viscosity of a drilling mud when extrapolated to infinite shear
rate on the basis of the mathematics of the Bingham model. The
bentonite product provided herein has a plastic viscosity of at
least 5 cP, preferably 5-10 cP, more preferably 6-8 cP, even more
preferably 6-7 cP. The Bingham model is expressed in the following
equation:
.tau.=.tau..sub.0+.eta..sub.pl.gamma. (Equation 1)
where .tau. is the measured shear stress at a shear rate of
.gamma., .tau..sub.0 is the yield stress or yield point, and
.eta..sub.pl is the plastic viscosity.
[0059] As used herein, "yield point" (YP) is a critical shear
stress point at which a material begins to deform plastically. The
soda ash-heated stirring bentonite method can significantly
increase the yield point to up to 30 lb/100 ft.sup.2, for example,
10-30 lb/100 ft.sup.2, preferably 20-30 lb/100 ft.sup.2, more
preferably 25-30 lb/100 ft.sup.2. The maximum yield point per API
specifications is 50 lb/100 ft.sup.2.
[0060] In one embodiment, the bentonite produced by the method has
a viscometer dial reading of about 35 lb/100 ft.sup.2 at 300 rpm
and about 40 lb/100 ft.sup.2 at 600 rpm. Per API requirements,
these readings have to be a minimum of 23 lb/100 ft.sup.2 at 300
rpm and a minimum of 30 lb/100 ft.sup.2 at 600 rpm.
[0061] The effects of continuous heating and stirring during soda
ash activation can also be demonstrated by the increase in water
control or reduction in filtration loss, i.e. filtration or
filtrate volume measured at the end (30 min) of an API filtration
test (low-pressure, low-temperature or high-pressure,
high-temperature). The filtrate volume is further reduced by up to
50% when soda ash activation is accompanied by the continuous
heating and stirring compared to soda ash activation without the
heating and stirring, preferably 10-50%, more preferably 25-50%.
The combined soda ash activation, heating and stirring results in
an overall improvement in water control by up to 70%, preferably
35-70%, more preferably 55-70%.
[0062] The following examples further illustrate protocols
undertaken to first investigate the suitability of bentonite
samples derived from local clay deposits for use in oil and gas
drilling fluid formulations. Examples 1-5 illustrate different
purification methods and different techniques used to evaluate the
efficacy of the purification methods, as well as the chemical
composition and physical properties of raw and purified local
bentonite. Examples 6-8 illustrate the upgrading of the local
bentonite to Na-bentonite by a combination of soda ash, thermal and
mechanical treatment procedures, as well as the API drilling fluid
tests performed on the produced bentonite. These examples are
presented for illustrative purposes only and are not intended as
limiting the scope of the invention which is defined by the
appended claims.
Example 1
Rawbentonite Samples and Reference Samples
[0063] The Khulays area in Saudi Arabia, which is 95 km north of
Jeddah as shown in the map image of FIG. 1, has the largest clay
deposit in the Kingdom. The Khulays area is 800 m long.times.600 m
wide, with a thickness of 200-300 m, and is estimated to contain 3
million tons of raw bentonite clay. The bentonite is 90% semctite
with 10% kaolinite and/or 5-15% quartz (Spencer C. "The Khulays
Bentonite Prospect." Ministry of Petroleum and Mineral Resources,
Open-File Report BRGM-of-06-10, pp. 7-8, 1986--incorporated herein
by reference in its entirety). Saudi Arabia has a huge bentonite
clay deposit resources. This enormous amount of bentonite was
enhanced for applications such as drilling fluid and cementing
additive. The enhancement was necessary because the bentonite in
the Khulays Area in North Jeddah Saudi Arabia is classified as
Ca-bentonite, which is not suitable for drilling fluids or
cementing applications, because it has low swelling capacity and
low rheological properties.
[0064] Raw bentonite samples were collected from two different
locations in the Khulays area and are designated as RB-1 and RB-2
herein.
[0065] Commercial bentonite was collected from a local supplier and
used as a reference and standard for comparison of chemical
composition and physical properties. The properties of raw
bentonite were measured before and after treatment and compared
with the standard. Standard grade bentonite as specified by API
must meet some requirements. The quality-check-tests are performed.
Bentonite suspension in distil water should satisfy API
requirement, that viscometer dial reading at 600 r/min should be
above or equal to 30, and yield point not more than 3 as per API
13I recommended practice (American Petroleum Institute Recommended
Practice 13 B-1 for Field Testing Water-Based Drilling Fluids,
Fourth Edition, pp. 11-13, March 2009--incorporated herein by
reference in its entirety) and OCMA (Oil Company Materials
Association) specifications.
[0066] X-ray diffraction (XRD) analyses were initially carried out
to determine the mineralogical composition for raw bentonite,
treated bentonite and standard bentonite samples. Scanning electron
microscopy (SEM) was used to show the microstructural changes in
clays with high spatial resolution The diffraction pattern of the
XRD spectra is compared to known standard patterns to determine the
contained minerals in the sample. The highest peak at 27.28, as
shown in FIG. 2 corresponds with montmoriillonite while the other
minor peaks are peaks for impurities.
[0067] As shown in FIG. 2, the analysis of XRD confirmed that the
Khulays bentonite is mainly montmorillonite (.about.80%) with small
amounts of kaolinite and quartz. SEM confirmed that in the raw
bentonite Al.sub.2O.sub.3/SiO.sub.2 ratio was 0.38 and Na/Ca ratio
was 2.2. As per API specification for bentonite used in cements,
the favorable bentonite properties should have: zero free water,
lightweight cement system, and good rheological properties and
controlled fluid loss (Grant, W. H. J., Rutledge, J. M., Gardner,
C. A. "Quality of Bentonite and Its Effects on Cement-Slurry
Performance" SPE Production Engineering 5(4):411-414
1990--incorporated herein by reference in its entirety). In
drilling fluids, good montmorillonite clay forms a gel like
structure at low solid content of 4-5% by weight (Rossi, S.,
Luckham, P. F., Zhu, S., Briscoe, B. J.
"High-Pressure/High-Temperature Rheology of
Na.sup.+-MontmorilloniteClay Suspensions" Society of Petroleum
Engineers (50725) pp. 243-257 1999--incorporated herein by
reference in its entirety. The percentage composition of
montmorillonite in clay is preferred to be >80%. But in most
standard bentonite, the percentage is around 55-70% (Guven, N.
Grim, R. "Bentonites: Geology, Mineralogy, Properties and Uses"
Elsevier Developments in Sedimentology Vol. 24, 1978--incorporated
herein by reference in its entirety). XRD for standard bentonite
showed 54% montmorillonite, 12% illite, 7% muscovite and only 2%,
0.9%, 0.8% for gypsum, feldspar and quartz, respectively.
[0068] Low pressure/low temperature API filtration test was also
used to evaluate bentonite quality. The suspension of bentonite in
deionized water should not give more than 15 ml filtration volume
as spurt loss when the sample is prepared by adding 22.5 g of
bentonite to 350 ml of deionized water, mixed for 20 min and aged
for 16 hours.
[0069] Drilling mud grade bentonite is recommended to have uniform
particle size distribution to avoid settlement of the larger size
and phase separation. Generally, in drilling fluid particle size is
important to determine. It is important to know whether there will
be erosion or formation damage if bentonite is trapped in the
formation pores and whether it will control fluid loss and allow
effective bridging in mud cake. Particle size analysis for standard
grade bentonite gave d(0.1)=1.69 .mu.m, d(0.5)=4.692 .mu.m and
d(0.9)=29.055 .mu.m (FIG. 3).
[0070] Montmorillonite particles are less than 2 .mu.m. API and
OCMA specifications recommended that drilling mud grade bentonite
should have particle size less than 75 .mu.m and the residue
retained by a 200 mesh is less than 4% when 50 g of bentonite is
sieved. The commercial reference samples used herein passed 47.1 g
out of 50 g through 200 mesh which is 95%. For the local raw
bentonite after purification and grinding, 100% of the sample
passed through the 200 mesh.
Example 2
Comparison of Raw Bentonite Purification Techniques
[0071] Raw bentonite exists in nature associated with many mineral
impurities, with different composition due to the difference in
location and environment. Elements other than montmorillonite
should be removed (U.S. Pat. No. 3,865,240--incorporated herein by
reference in its entirety). Purification of bentonite is the
process of removing all impurities other than montmorillonite,
including clay and non-clay impurities. Low water loses of slurry
has great advantages in cementing formulation. Cements containing 8
to 12 percent bentonite allow controlling setting properties with
good placement and increased performance. Drilling mud grade and
cementing additives bentonite have certain specifications
attributed to special chemical composition and physical properties.
API and OCMA specification are the guidelines for evaluation of
bentonite performance. Bentonite quality can be determined by the
content of materials other than montmorillonite, besides the
presence or absence of small amounts of extending polymers and the
size and charge of the montmorillonite platelets.
[0072] As known in the art, pure bentonite can be obtained by
dispersing the clay into deionized water, a method described by
Ahmed et al. (Ahmed, A. S., N. Salahudeen, C. S. Ajinomoh, H.
Hamza, A. Ohikere. "Studies on the Mineral and Chemical
Characteristics of Pindiga Bentonitic Clay" Petroleum Technology
Development Journal, 1:1-8, January 2012--incorporated herein by
reference in its entirety). Raw bentonite is put into water and
allowed to swell for 24 hours, then stirred for 30 min before it
settled in a container for a period of time that is recommended by
Stoke's law (10 h). After retention time the supreme solution will
contain particles with sizes less than 2 .mu.m which is collected
and dried at 90.degree. C., grounded and sieved through 200 meshes
(Patel, H. A., Rajesh, R. S., Bajaj H. C., Jasra R. V. "Synthesis
and characterization of organic bentonite using Gujarat and
Rajasthan clays" Current Science (Ser. No. 00/113,891) 92(7), pp.
1004, April 2007--incorporated herein by reference in its
entirety). Also, hydrogen peroxide (H.sub.2O.sub.2) has the ability
to remove any organic and inorganic matter in the clay and can be
used for purification, with only 10% H.sub.2O.sub.2 solution. The
disodium ethylenediaminetetraacetate EDTA (Na.sub.2EDTA) can be
used to purify raw bentonite (U.S. Pat. No. 3,865,240--incorporated
herein by reference in its entirety). Raw bentonite is crushed and
screened and then dispersed in 0.01 M Na.sub.2EDTA in 0.1 M NaCl.
Then, the suspension is stirred for 30 minutes and the solution is
left in a shaker for 30 minutes. The solution is allowed to stand
for 48 h to obtain pure clay particles of size 2 .mu.m which can be
extracted through repeated sedimentation process followed by
siphoning (James, O., Mesubi, M. A., Adekola, F. A., Odebunmi, E.
O. Adekeye J. I. "Beneficiation and Characterization of a Bentonite
from North-Eastern Nigeria" Journal of the North Carolina Academy
of Science, 124(4):154-158, 2008--incorporated herein by reference
in its entirety). High grade bentonite like Khulays deposits
containing over 90% montmorillonite may still require further
treatment such as purification to match API requirements for
drilling fluids and cementing. Ca-bentonite has lower swelling
capacity compared to Na-bentonite. The best quality bentonite can
produce organoclays or nanoclays used in polymers, paints and other
industrial applications (Patel, H. A., Rajesh, R. S., Bajaj H. C.,
Jasra R. V. "Synthesis and characterization of organic bentonite
using Gujarat and Rajasthan clays" Current Science (Ser. No.
00/113,891) 92(7), pp. 1004, April 2007--incorporated herein by
reference in its entirety). For drilling mud sodium exchange
bentonite is preferable and can be obtained by upgrading the
Ca-bentonite by treatment with soda ash. The treatment increases
sodium to calcium ratio and enhances the swelling
characteristics.
[0073] Different purification methods were applied onto the Khulay
area raw bentonite samples RB-1 and RB-2: dry-sieving through 200
mesh (DS-1, DS-2; size <75 .mu.m), wet-sieving with a mesh with
diameter opening greater than 200 mesh (WS-1; size >75 .mu.m)
wet-sieving through 200 mesh (WS-2, WS-3; 63 .mu.m<size <75
.mu.m), 350 mesh (WS-4; 38 .mu.m<size <63 .mu.m) and 400 mesh
(WS-5; size <38 .mu.m), dispersion in deionized water with
sedimentation and hexametaphosphate (SD-1, SD-2) or without
hexametaphosphate (SD-3). The SEM results for the bentonite samples
purified with different techniques are compared to their unpurified
forms and standard bentonite in Table 1 and FIG. 4.
TABLE-US-00001 TABLE 1 SEM results for bentonite samples purified
through different methods. Stan- Element dard RB-1 RB-2 DS-1 DS-2
WS-1 WS-2 WS-3 WS-4 WS-5 SD-1 SD-2 SD-3 O 58.65 50.88 51.19 50.62
51.30 57.27 51.82 51.67 52.37 55.46 54.04 51.19 54.52 Na 1.39 1.77
1.73 1.73 1.69 0.79 0.88 1.79 0.80 1.13 2.35 1.73 0.75 Mg 0.93 1.36
1.46 1.43 1.44 1.41 1.63 1.36 1.50 1.55 1.58 1.46 1.40 Al 6.83 9.49
9.59 9.44 9.56 8.70 10.74 9.46 9.80 9.26 8.87 9.59 9.16 Si 28.90
25.31 25.10 26.24 25.28 22.97 26.17 24.80 27.32 24.57 24.30 25.10
24.08 P 1.25 Cl 1.60 1.22 1.51 1.40 0.43 0.74 1.39 0.45 1.25 0.98
1.22 0.14 K 0.19 0.59 0.54 0.61 0.60 1.68 0.43 0.56 0.55 0.48 0.54
0.58 Ca 0.48 0.89 0.91 0.98 0.95 0.65 0.96 0.87 0.92 0.95 0.80 0.91
0.82 Ti 0.89 0.83 0.93 0.81 1.42 0.88 0.79 0.78 0.70 0.53 0.83 0.79
Fe 2.69 2.83 6.64 6.51 6.97 5.63 5.76 6.13 5.52 4.65 5.59 6.64 5.53
Cu 6.57 0.74 0.82 0.89 1.28 Zn 0.88 0.71 0.88 0.94 S 0.15 Total
100% 100% 100% 100% 100% 101% 100% 100% 100% 100% 100% 100% 100%
Na/Ca 2.896 1.978 1.891 1.756 1.789 1.209 0.913 2.043 0.873 1.182
2.950 1.891 0.915 ratio
[0074] Hence, in this example it is shown that simple purification
methods can be used to produce pure bentonite with good quality out
of the local bentonite from the Khulays. Wet-sieving and dispersion
in deionized water with or without hexametaphosphate gave the
purest bentonite compared to grinding and mechanically dry
sieving.
Example 3
Determination of Clay Content by Hydrometer Analysis
[0075] The clay content of the various purified bentonite samples
from Example 2 was estimated by hydrometer analysis. The particle
size distribution was measured for the small size particles of clay
in addition to clay, sand and silt content as shown in FIG. 5 for
sample DS-1 (raw bentonite sample RB-1 dry-sieved through a 200
mesh). When the sample was mixed with water the particles settled
at different velocities, depending on their shape, size, weight and
viscosity of water. The velocity of soil particles can be expressed
by Stokes' law. Since the silt has a higher grain size than clay
(clay is .about.4 .mu.m while sand has 0.45-2 mm), the silt will
fall to the bottom before the clay does, leaving only silt and clay
particles in suspension. Then silt settles and leaves only clay in
the suspension. Dry sieved sample DS-1 contains 35% clay, while wet
sieved samples are almost 100% clay. The chemical and mineralogy
composition of purified bentonite has almost matched the standard
grade following the removal of the impurities through
wet-sieving.
Example 4
Particle Size Distribution Analysis
[0076] A Frisch-type particle size analyzer (PSA) was used to
obtain the full particle size distribution of raw bentonite derived
from the Khulays (RB-1 and RB-2 samples). The results show raw
bentonite wide range of particle sizes from 0.8 .mu.m up to 2000
.mu.m. The findings from RB-1 and RB-2 are identical as shown in
FIG. 6. After purification, the larger particles are removed. FIG.
7 shows particle size distribution for wet-sieved samples (400
mesh) after sedimentation. The majority of impurities have been
removed and the size distribution matches that of standard
bentonite. Table2 summarizes the comparison between raw local
bentonite and standard bentonite.
TABLE-US-00002 TABLE 2 Comparison of particle size of raw local
bentonite and standard bentonite. Particle size of Particle size of
raw standard bentonite Vol. (%) local bentonite (.mu.m) (.mu.m) 5
0.8 0.7 10 1.1 1 25 1.6 1.6 50 2.8 2.8 75 5 4.7 90 29.8 7 95 57.4
8.9 99 395.3 18.3
Example 5
Evaluation of Bentonite Stability
[0077] The stability of pure bentonite was evaluated using zeta
potential (ZP) which is a measurement of particle charges. FIG. 8
shows the ZP measurements for standard bentonite, dry-sieved
bentonite and wet-sieved bentonite at different pH values.
Example 6
Activation by Soda Ash, Thermal Treatment and Continuous
Stirring
[0078] Raw bentonite in natural form without treatment may not be
qualified as drilling fluid additives even when it is rich in
montmorillonite or if it possesses good sodium quality. Despite the
aforementioned qualities, raw bentonite may not deliver the
required functions such as viscosity and filtration control (Bol,
G. "Bentonite Quality and Quality Evaluation Methods" SPE Drilling
Engineering 1(04):288-296, August 1986--incorporated herein by
reference in its entirety). Bentonite performance and properties
can be enhanced by employing different methods of treatments, such
as inorganic additives. Addition of soda ash is well-known process
to increase bentonite quality (Karaguzel, C. etinel, T., Boylu, F.,
inku, K., elik, M. S. "Activation of Na, Ca)-bentonites with soda
and MgO and their utilization as drilling mud--incorporated herein
by reference in its entirety). Only 2-4% of the soda ash (by weight
per weight of bentonite) can enhance bentonite properties. Sodium
content, usually measured as a Na/Ca ratio, affects disperse
characteristics and other physical properties of bentonite
(Lebedenko, F., Plee, D. "Some Consideration on the Ageing of
Na.sub.2CO.sub.3-activated bentonites" Applied Clay Science
3(1):1-10 Jan. 1988--incorporated herein by reference in its
entirety).
[0079] The two batches of local bentonite from the Khulay area,
RB-1 and RB-2 were treated with soda ash and aged for different
times. A soda ash solution was prepared by adding 1-3 g to 350 ml
of distilled water and mixing for 5 min, resulting in a final soda
ash concentration of 0.28-0.86% (weight/volume based on volume of
water or weight/weight based on weight of water). After that, 22.5
g of bentonite (or 6.4% by weight per weight of water) was added to
the prepared soda ash solution. The amount of soda ash is therefore
4-13% by weight based on the weight of the bentonite. Instead of
aging for several days after the addition of the bentonite to the
soda ash solution, the Na-activation and swelling process was then
enhanced for some samples by heating and continuously stirring the
bentonite-soda ash suspension at 65-70.degree. C. for 24 hours. The
soda ash treatment and aging results are shown in Table 3 as well
as FIGS. 9, 10 and 11. Apparent viscosity and plastic viscosity
increased significantly and a peak was observed when 1 g and 3 g of
soda ash were used in the treatment process, as shown in FIGS. 9
and 11.
TABLE-US-00003 TABLE 3 Impact of soda ash treatment followed by
heating and stirring on rheology. Treated Treated RB-1 RB-1 (3 g
soda (1 g soda ash + 24 h ash + 24 h Standard of heating and of
heating Property bentonite RB-1 RB-2 stirring) and stirring)
Apparent 11.5 1.3 2.2 12 20 viscosity(cP) Plastic 8 1 2 6 6
viscosity (cP) Yield point 7 1.5 0.5 12 28 (lb.sub.f/100 ft.sup.2)
Filtration (ml) 15 75 86.5 38.3 28.4 Yield/plastic 0.87 1.5 0.25 2
4.6 viscosity ratio Na/Ca ratio 2.896 1.97 1.78 2.04 2.950
[0080] The soda ash activation method is usually conducted by
adding 2-4% of soda ash (percentage based on weight of bentonite)
to water. Then, bentonite is added and mixed to allow ion exchange
of sodium and calcium to convert Ca-bentonite to Na-bentonite and
to increase swelling capacity. In the present disclosure, the soda
ash concentration used in the activation step is 4-13%.
Importantly, heating at about 70.degree. C. and continuous stirring
for a specific time is introduced to the bentonite-soda ash
suspension to enhance the Na-activation and the swelling process.
At the end of the hot stirring process, water lost due to
evaporation, which is minimal, is easily compensated for by
deionized water produced from the ion exchange to maintain the same
bentonite concentration in the suspension.
Example 7
API Filtration of Bentonite Samples
[0081] Filtration through API filter press was performed to
determine the water hold capacity of various bentonite suspensions.
FIG. 12 shows that water control increased with sodium activation
and the heated and stirred samples exhibited the best lowest
possible filtration results. Bentonite is used in drilling fluids
with 80% for the upper formation or 5% for oil zones. The 28 ml of
filtration is acceptable for the upper formations drilling in 80%
bentonite mud. This section of the well can tolerate that
filtration, but for the pay zone a maximum of 15 ml should be
maintained to avoid formation damage which is usually controlled by
filtration additives such as starch.
[0082] FIG. 13 shows the combined effect of heating and stirring on
particle size distribution. The distribution of untreated bentonite
has 90% of the particles below 5 With soda ash treatment, 90% of
the particles were below 20 .mu.m. However, major increase in
particle size is achieved when both heating and stirring for 24 h
was implemented where 90% of the particles were around 1000 .mu.m.
This indicated that heating and stirring greatly enhanced swelling
capacity that led to the improvement in rheological properties as
shown in FIG. 12.
Example 8
Heating and Stirring Durations
[0083] To obtain more information on swelling kinetics the combined
heating/stirring process was repeated at different times to obtain
the minimum time required to achieve the desired enhancement in
viscosity.
[0084] The heating/stirring duration was varied from 1-24 h. FIGS.
14 and 15 indicate that a minimum of 3-6 h is needed to achieve the
maximum viscosity. FIGS. 16 and 17 show the viscosity buildup with
heating time at low and high shear rate. FIGS. 16 and 17 indicate
that at both high and low shear rates, after 6 h of heating the
viscosity can reach its peak and no further significant increment
will take place. Lower heating times could be used to achieve
optimum values.
Example 9
Comparison of Soda Ash-Hot Stirring to Hot Rolling Treatment
[0085] In bentonite water suspension preparation, API recommends
using hot rolling for 16 h to allow for dehydration. The hot
rolling conditions are described by API as 150.degree. F.
(65.degree. C.) for 16 h at a pressure of 120 psi in closed
pressurized cell. The hot rolling procedure, when applied onto the
local bentonite, successfully increased the rheological properties
of the bentonite but not enough to satisfy the API
specifications.
[0086] On the other hand, the method of combined heating and
stirring accompanying soda ash activation as outlined in Example 6,
increased the swelling capacity significantly. The average particle
size increased from 2.4 .mu.m for untreated bentonite to 1286.9
.mu.m. The rheological properties and fluid control properties have
enhanced and achieved the target standard API specifications.
Therefore, the obtained pure Ca-bentonite from natural deposit in
Khulays area can be modified to Na-bentonite and sufficiently used
in drilling fluid and cementing additives using the new hot
stirring method.
[0087] Thus, the foregoing discussion discloses and describes
merely exemplary embodiments of the present invention. As will be
understood by those skilled in the art, the present invention may
be embodied in other specific forms without departing from the
spirit or essential characteristics thereof. Accordingly, the
disclosure of the present invention is intended to be illustrative,
but not limiting of the scope of the invention, as well as other
claims. The disclosure, including any readily discernible variants
of the teachings herein, defines, in part, the scope of the
foregoing claim terminology such that no inventive subject matter
is dedicated to the public.
* * * * *