U.S. patent application number 10/342852 was filed with the patent office on 2004-07-15 for drilling fluid with circulation loss reducing additive package.
Invention is credited to Gabay, Jacques Reinaldo, Kakadjian, Sarkis, Sanchez, Gerardo Alonso.
Application Number | 20040138069 10/342852 |
Document ID | / |
Family ID | 32711822 |
Filed Date | 2004-07-15 |
United States Patent
Application |
20040138069 |
Kind Code |
A1 |
Kakadjian, Sarkis ; et
al. |
July 15, 2004 |
Drilling fluid with circulation loss reducing additive package
Abstract
A drilling fluid includes a base fluid and a circulation loss
reducing additive package having a polysaccharide, a cellulose
derivative and a pH controlling component.
Inventors: |
Kakadjian, Sarkis; (San
Antonio, VE) ; Gabay, Jacques Reinaldo; (San
Bernardino-Caracas, VE) ; Sanchez, Gerardo Alonso;
(Los Teques, VE) |
Correspondence
Address: |
BACHMAN & LAPOINTE, P.C.
900 CHAPEL STREET
SUITE 1201
NEW HAVEN
CT
06510
US
|
Family ID: |
32711822 |
Appl. No.: |
10/342852 |
Filed: |
January 15, 2003 |
Current U.S.
Class: |
507/111 |
Current CPC
Class: |
C09K 8/10 20130101; C09K
8/514 20130101; C09K 2208/18 20130101; C09K 8/08 20130101 |
Class at
Publication: |
507/111 |
International
Class: |
C09K 007/06 |
Claims
What is claimed is:
1. A drilling fluid, comprising: a base fluid; and a circulation
loss reducing additive package comprising a polysaccharide, a
cellulose derivative and a pH controlling component.
2. The fluid of claim 1, wherein said polysaccharide is selected
from the group consisting of non-ionic polysaccharides, low ionic
charge polysaccharides, and combinations thereof.
3. The fluid of claim 1, wherein said polysaccharide is selected
from the group consisting of double helix compounds, triple helix
compounds and combinations thereof.
4. The fluid of claim 1, wherein said polysaccharide is
scleroglucan.
5. The fluid of claim 1, wherein said cellulose derivative is
selected from the group consisting of hydroxypropyl cellulose,
carboxymethyl hydroxyethyl cellulose, hydroxyethyl cellulose,
hydrophobically modified cellulose, and combinations thereof.
6. The fluid of claim 1, wherein said cellulose derivative is
hydroxyethyl cellulose.
7. The fluid of claim 1, wherein said pH controlling additive is
selected from the group consisting of monoethanolamine,
ethanolamine, magnesium oxide, triethanolamine, sodium hydroxide,
sodium carbonate, potassium carbonate and combinations thereof.
8. The fluid of claim 1, wherein said additive package further
comprises a starch component.
9. The fluid of claim 7, wherein said starch component is selected
from the group consisting of carboxymethyl starch, hydroxyethyl
starch, hydroxypropyl starch, starches cross-linked with
etherifying agents, starches cross-linked with esterifying agents
and combinations thereof.
10. The fluid of claim 1, wherein said additive package further
comprises a bridging agent component.
11. The fluid of claim 10, wherein said bridging agent component is
calcium carbonate.
12. The fluid of claim 1, wherein said additive package further
comprises an antioxidant component.
13. The fluid of claim 12, wherein said antioxidant component is
selected from the group consisting sodium bisulfite, sodium sulfite
and combinations thereof.
14. The fluid of claim 12, wherein said antioxidant is sodium
bisulfite.
15. The fluid of claim 1, wherein said additive package further
comprises a biocide component.
16. The fluid of claim 15, wherein said biocide component is
selected from the group consisting of isothiazolones,
glutaraldehyde, quaternary amines and combinations thereof.
17. A circulation loss reducing additive package, comprising a
polysaccharide, a cellulose derivative and a pH controlling
component.
18. The circulation loss reducing additive package of claim 17,
further comprising a starch, a bridging agent, antioxidant and a
biocide.
19. The circulation loss reducing additive package of claim 18,
wherein said pH controlling additive is selected from the group
consisting of monoethanolamine, ethanolamine, magnesium oxide,
triethanolamine, sodium hydroxide, sodium carbonate, potassium
carbonate and combinations thereof.
20. The circulation loss reducing additive package of claim 19,
wherein said starch component is selected from the group consisting
of carboxymethyl starch, hydroxyethyl starch, hydroxypropyl starch,
starches cross-linked with etherifying agents, starches
cross-linked with esterifying agents and combinations thereof,
wherein said bridging agent is calcium carbonate, wherein said
antioxidant component is selected from the group consisting of
sodium bisulfite, sodium sulfite and combinations thereof and
wherein said biocide component is selected from the group
consisting of isothiazolones, glutaraldehyde, quaternary amines and
combinations thereof.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to drilling fluid and, more
particularly, to drilling fluids including a circulation loss
reducing additive package which is particularly useful in high
permeability reservoirs and the like.
[0002] When drilling through highly permeable, unconsolidated or
micro-fractured formations, for example while drilling wells to
hydrocarbon-bearing subterranean formations and the like, fluid is
circulated through the hole to lubricate the drill bit, remove
cuttings from the bottom of the hole, control pressure within the
hole and for other reasons.
[0003] Unfortunately, highly permeable, unconsolidated or
micro-fractured formations allow flow of the drilling fluid to
leave the hole, which is called lost circulation. This fluid loss
into the formations through which the hole is being drilled results
in extra cost due to the need for constantly replacing the fluid,
and further can result in damage to potentially valuable and
hydrocarbon bearing formations.
[0004] It is clear that the need remains, therefore, for drilling
fluids that can be used in highly permeable, unconsolidated or
micro-fractured formations and the like, without substantial
circulation losses.
[0005] It is therefore the primary object of the present invention
to provide such a drilling fluid.
[0006] Other objects and advantages of the present invention will
appear hereinbelow.
SUMMARY OF THE INVENTION
[0007] In accordance with the present invention, the foregoing
objects and advantages have been readily obtained.
[0008] According to the invention, a drilling fluid is provided
which comprises a base fluid and a circulation loss reducing
additive package comprising a polysaccharide, a cellulose
derivative and a pH controlling component.
[0009] In further accordance with the invention, the additive
package preferably also includes starches, bridging agents,
anti-oxidants and biocides, as well as other additives which may be
desirable for particular applications.
[0010] In still further accordance with the present invention, a
circulation loss reducing additive package is provided comprising a
polysaccharide, a cellulose derivative and a pH controlling
component.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] A detailed description of preferred embodiments of the
present invention follows, with reference to the attached drawings,
wherein:
[0012] FIG. 1 schematically illustrates shear rate verses shear
stress for fluids in accordance with the present invention after
aging for sixteen hours at a temperature of 250.degree. F.;
[0013] FIG. 2 graphically illustrates filtrate volume over time for
drilling fluids in accordance with the present invention;
[0014] FIGS. 3 and 4 illustrate plastic viscosity and yield point
for conventional drilling fluids and a drilling fluid in accordance
with the present invention;
[0015] FIG. 5 graphically illustrates filtration loss over time for
a fluid in accordance with the present invention and for
conventional fluids;
[0016] FIG. 6 graphically illustrates shear stress verses shear
rate for a fluid in accordance with the present invention as
compared to conventional fluids;
[0017] FIGS. 7 and 8 illustrate shear stress verses shear rate for
a further fluid in accordance with the present invention, before
and after aging for sixteen hours at a temperature of 200.degree.
F.;
[0018] FIGS. 9 and 10 graphically illustrate apparent viscosity
verses shear rate in accordance with the present invention, before
aging and after aging for sixteen hours at a temperature of
200.degree. F.;
[0019] FIG. 11 graphically illustrates filtrate volume over time
for a further fluid in accordance with the present invention;
and
[0020] FIG. 12 illustrates storage modulus/loss ratio over a range
of frequencies.
DETAILED DESCRIPTION
[0021] The invention relates to a drilling fluid and, more
particularly to a drilling fluid including an additive package for
controlling circulation loss which is well suited for use in
drilling through highly permeable, unconsolidated or
micro-fractured formations and the like.
[0022] In accordance with the invention, a drilling fluid,
preferably a water based drilling fluid, is provided including a
circulation loss reducing additive package which includes a
polysaccharide component which helps to improve rheology and reduce
filtration losses, a cellulose derivative component which also
serves to improve rheology and reduce filtration losses, and a pH
controlling component. The polysaccharide component and cellulose
derivative component combine to provide the fluid with excellent
elastic properties.
[0023] In further accordance with the invention, it is preferred to
also incorporate starches, bridging agents, anti-oxidants, biocides
and other components into the additive package of the present
invention as will be further described below and package containing
all of these components provides particularly effective fluid loss
control.
[0024] In accordance with the present invention, it has been found
that drilling fluids containing the additive package in accordance
with the present invention advantageously demonstrate much lower
circulation losses when used in drilling through highly permeable,
unconsolidated, micro-fractured and similar formations. Such
drilling fluid formulations containing the additive package of the
present invention further demonstrate desirable shear properties,
filtrate loss, plastic viscosity and yield point, and apparent
viscosity.
[0025] The polysaccharide component is preferably a non or low
ionic charge polysaccharide.
[0026] In accordance with the invention, a preferred non-ionic
polysaccharide is a non-ionic polysaccharide having double helix or
triple helix configuration, or combinations thereof, in aqueous
solutions. A particularly preferable non-ionic polysaccharide is
scleroglucan which can be purified (CS11-Degussa) or not (Biovis or
Actigum CS-Degussa), which, in combination with the cellulose
derivative and bridging agent components, provide the fluid with
improved viscoelastic, Theological and sealing properties
[0027] Suitable low ionic charge polysaccharides include xanthan
gum, which can be clarified or not, and further which can be
acetylated or not. Commercial examples of suitable non and low
ionic polysaccharides include Actigum CS, from Degussa, Xanvis,
Diutam and NAX, all from CP Kelco. Of course, other non or low
ionic charge polysaccharides can also be used in accordance with
the broad scope of the present invention.
[0028] In addition, the additive in accordance with the present
invention also preferably includes a cellulose derivative component
which can preferably be provided in the form of hydroxypropyl
cellulose, carboxymethyl hydroxyethyl cellulose, hydroxyethyl
cellulose, hydrophobically modified cellulose and the like,
preferably hydroxyethyl cellulose. This component of the additive
package, combined with the polysaccharide component, advantageously
serves to improve Theological and viscoelastic properties of the
drilling fluid, and also serves to reduce filtration losses or
losses of fluid into a high permeability, unconsolidated or
micro-fractured formation.
[0029] In accordance with the present invention, the additive
further preferably includes a pH controlling component or additive,
and this pH controlling component can advantageously be selected
from the group consisting of monoethanolamine, ethanolamine,
magnesium oxide, triethanolamine, sodium hydroxide, sodium
carbonate, potassium carbonate and combinations thereof. The pH
controlling additive is preferably added so as to pH at desired
levels, preferably up to about 12.
[0030] A further component of the additive package in accordance
with the present invention may preferably be a starch or starch
derivative, which advantageously serves to provide further filtrate
volume control. Examples of suitable starch or starch derivative
components include carboxymethyl starch, hydroxyethyl starch,
hydroxypropyl starch, starches cross-linked with etherifying and/or
esterifying agents and the like, preferably slightly cross-linked
starches such as FL-7 Plus, M-I Drilling Fluids. These starches,
starch derivatives and modified starches are collectively referred
to herein as a starch component.
[0031] A bridging agent is preferable to include to achieve good
filtration control and low fluid loss, and a particularly preferred
bridging agent is calcium carbonate. Sized calcium carbonate, such
as Milcarb from Baker Hughes Inteq, is particularly suitable for
use in the package of the present invention. The size of the
calcium carbonate particle is selected to avoid formation damage
and also to control fluid loss. Although calcium carbonate serves
mainly as a bridging agent, to control fluid loss into the
reservoir, calcium carbonate also serves to increase density of the
fluid as desired so as to provide a final fluid having the desired
density.
[0032] A still further component which may be included in the
additive package of the present invention is an antioxidant
component, and suitable antioxidants include sodium bisulfite,
sodium sulfite and the like, preferably sodium bisulfite. These
components serve to protect the biopolymers used in the additive
package and drilling fluid formulation from oxidation, and thereby
help to maintain the molecular weight of the polymers relatively
constant as desired.
[0033] A biocide component is also preferably incorporated into the
additive package of the present invention. Suitable biocide
components include isothiazolones, glutaraldehyde, quaternary
amines and the like. The biocide component advantageously serves to
avoid undesirable hydrolysis of biopolymers in the formulation by
reducing oxidative and enzymatic degradation of same.
[0034] In accordance with the present invention, the fluid itself
can advantageously be water-based, and thus the base fluid may be
water. Of course, other base fluids can be used as well. However,
water based fluids are preferable in that the cost of the base
fluid is desirably low, and the additives perform as desired in a
water base.
[0035] A drilling fluid containing a circulation reducing additive
package according to the invention preferably includes at least
about 0.05 ppb of polysaccharide component, at least about 0.05 ppb
of cellulose derivative component, at least about 1.0 ppb of pH
controlling component, at least about 0.05 ppb of starch component,
at least about 20 ppb of bridging agent, at least about 1.0 ppb of
antioxidant and at least about 0.05 ppb of biocide, all taken with
respect to weight of the component per barrel of drilling
fluid.
[0036] Table 1 below sets forth preferred ranges and specific
values for amounts of the various components of a drilling fluid
and drilling fluid additive in accordance with the present
invention.
1 TABLE 1 Preferred Preferred range values Guar gum derivative
0.05-5 2.36 (CMHPG) (ppb) Hydroxyethylcellulose 0.05-5 1.15 (HEC)
(ppb) Scleroglucan (ppb) 0.05-4 2.00 Xanthan gum (ppb) 0.05-4 2.00
Starch (ppb) 0.05-5 4.00 Biocide (ppb) 0.05-0.50 0.02 Sodium
bisulfite (ppb) 1.00-2.00 2.00 Monoethanolamine (ppb) 1.00-2.00
1.00 Magnesium oxide (ppb) 0.25-2.00 0.50 Potassium chloride (ppb)
0-7.00 7.00 Calcium carbonate (ppb) from at least 10 about 20 to
amount needed to reach weight 2 Mineral oil (% v/v) (*) 0-15 Clay
swelling 0-3 inhibitor (% v/v) (**) Magnesium oxide may be used
instead of the monoethanolamine as the pH controller agent (*)
Mineral oil is used to improve lubricity during drilling operation
(**) This additive is used only when drilling through reservoirs
containing reactive shale.
[0037] Further examples of specific combinations of additive
components include combinations such as those illustrated in Table
2 below.
2TABLE 2 Additive Form. A Form. B Form. C Form. D Main function
Water (bbl) 0.950 0.950 0.950 0.950 Fluid base Guar gum derivative
(CMHPG) (ppb) 2.36 0 2.36 0 Viscosifier Hydroxyethylcellulose (HEC)
(ppb) 0 2.36 0 1.15 Filtration control agent Scleroglucan (ppb)
2.00 2.00 0 2.00 Main viscosifier Xanthan gum (ppb) 0 0 2.00 0 Main
viscosifier Starch (ppb) 4.00 4.00 4.00 4.00 Filtration control
agent Biocide (ppb) 0.20 0.20 0.20 0.20 Biocide Sodium bisulfite
(ppb) 2.00 2.00 2.00 2.00 Antioxidant Monoethanolamine (ppb) 1.00
1.00 1.00 1.00 Buffer agent Potassium chloride (ppb) 7.00 7.00 7.00
7.00 Inhibitive agent (shales) Calcium carbonate (ppb) 60.0 60.00
60.00 60.00 Bridging agent
[0038] In accordance with the present invention, the drilling fluid
can advantageously be prepared by sequentially mixing in the
various additive components into the base fluid.
[0039] For example, assuming water is the base fluid, a starting
volume of water may advantageously first be mixed with potassium
chloride, then fumaric acid and then the hydroxyethylcellulose.
After these components, then biocide materials can be added,
followed by sodium bisulfides, scleroglucan, starch and finally
calcium carbonate, each with a mixing time of between about 5 and
about 20 minutes before addition of the next component.
[0040] Of course, other methods can be used to prepare the drilling
fluid well within the scope of the present invention.
[0041] It has been found that fluids prepared in accordance with
the present invention have excellent high pressure, high
temperature Theological and viscoelastic properties. For example, a
fluid prepared in accordance with the present invention was aged
for sixteen hours at a temperature of about 250.degree. F., and
then subjected to HPHT Theological property testing, and the
results are shown in FIG. 1. As shown, formulas A, B and C from
Table 2 each provided excellent shear stress over shear rate, as
desired.
[0042] These same fluids, formulas A, B and C from Table 2, were
then also evaluated for filtration properties after aging at
250.degree. F. for a period of sixteen hours, and the results are
shown in FIG. 2. As shown in this figure, although the filtrate
volume loss was most ideal for formula B, and least ideal for
formula C, the values obtained are nevertheless excellent,
particularly as compared to conventional fluids.
EXAMPLE 1
[0043] In order to compare to conventional fluids, a series of
fluids were prepared, with fluids 1-3 being prepared according to
conventional or commercially available formulas, and with formula D
being prepared in accordance with the present invention, the
components of each of these fluids are shown below in Tables
3-6.
3TABLE 3 Service company No. 1 Mixing Additives Concentration time
(min) Water 0.976 bbl -- Fumaric acid 0.30 lb/bbl 5 HEC 2 lb/bbl 10
Biocide 0.20 lb/bbl 5 Sodium bisulfite 2 lb/bbl 5 Starch 4 lb/bbl
15 Calcium carbonate 60 lb/bbl 20
[0044]
4TABLE 4 Service company No. 2 Mixing Additives Concentration time
(min) Water 0.971 bbl -- Xanthan gum 2 lb/bbl 15 Magnesium oxide 2
lb/bbl 5 Biocide 0.20 lb/bbl 5 Sodium bisulfite 2 lb/bbl 5 Starch 4
lb/bbl 15 Calcium carbonate 60 lb/bbl 20
[0045]
5TABLE 5 Service company No. 3 Mixing Additives Concentration time
(min) Water 0.976 bbl -- Polymer 1 5 lb/bbl 15 First activator 1
lb/bbl 15 Second activator 1 lb/bbl 5 Polymer 2 1 lb/bbl 5 Polymer
3 1 lb/bbl 5 Calcium carbonate 60 lb/bbl 20
[0046]
6TABLE 6 Formulation D Mixing Additives Concentration time (min)
water 0.950 bbl -- Potassium chloride 7 lb bbl 5 Fumaric acid 0.05
lb/bbl 5 HEC (hydroxethylcellulose) 1.15 lb/bbl 10 Biocide 0.20
lb/bbl 5 Sodium bisulfite 2 lb/bbl 5 Scleroglucan 2 lb/bbl 10
Starch 4 lb/bbl 15 Calcium carbonate 60 lb/bbl 20
[0047] The plastic viscosity and yieldpoint were then determined,
at 120.degree. F., and after sixteen hours of aging at 250.degree.
F., and the results of this evaluation are shown in FIGS. 3 and 4.
As shown, the fluid in accordance with the present invention
provides excellent properties as desired. This is particularly
advantageous when combined with the filtration loss control
properties of the fluid of the present invention as well.
[0048] The filtration loss was then measured, after aging for
sixteen hours at 250.degree. F., for the conventional formulations
and also the formulations in accordance with the present invention
as described in connection with Tables 3-6 above. These
formulations were evaluated and the results are shown in FIG. 5. As
shown, the fluid of the present invention had the best
characteristics in terms of low volume of filtration loss over
time.
[0049] Fluid loss sealing tests were run with commercial
formulations, that is, commercial fluids 1, 2 and 3, and
formulation D in accordance with the present invention. After
plotting filtrate volume as a function of time for all
formulations, new curves were plotted dividing filtrate volume
between area of filtration and extracting the square root of time,
in order to determine the spurt loss values and Cw
coefficients--intercepts and slopes of the curves, as indicated by
filtration theory. Table 7 shows the data obtained.
7 TABLE 7 Spurt loss Fluids Cw (cm/min.sup.1/2) (mL/cm.sup.2)
Commercial fluid 1 0.324 0.558 Commercial fluid 2 0.155 0.095
Commercial fluid 3 0.109 0.406 Form. D 0.063 0.435
[0050] Table 7 shows that the fluid of the present invention has
excellent properties in connection with Cw coefficients and spurt
loss.
[0051] Next, the conventional fluids and fluid in accordance with
the present invention were evaluated for shear stress verses shear
rate after aging at a temperature of 250.degree. F. for a period of
sixteen hours. The results of this testing are shown in FIG. 6, and
show excellent performance of the fluid in accordance with the
present invention as compared to the commercial formulas, which is
particularly advantageous in light of the filtration control
qualities of the fluid of the present invention.
[0052] A further fluid was prepared in accordance with the present
invention, and this formulation, designated Formulation E, was
prepared as shown in Table 8 below.
8 TABLE 8 Additives Concentrations Hydroxyethylcellulose 3.0
(lb/bbl) Scleroglucan 2.0 (lb/bbl) Starch 2.5 (lb/bbl) Biocide 0.15
(lb/bbl) Magnesium oxide 0.5 (lb/bbl) KCl 2.0 (%) CaCO.sub.3 20.0
(lb/bbl) Mineral oil 10.0 (%) Clay swelling inhibitor 2.0 (%)
[0053] Formulation E was evaluated in a series of tests so as to
determine shear stress verses shear rate for various temperatures
after no aging, and after aging for sixteen hours at a temperature
of 200.degree. F. FIGS. 7 and 8 show the results of this testing,
and show excellent results for the fluid of the present invention,
both prior to and after aging.
[0054] The measurements obtained in order to show FIGS. 7 and 8 are
based upon parameters derived from adjustment to a Bingham model
(between 350 and 1450 l/s). Further, data was obtained from a Haake
HPHT viscometer at a pressure of 300 psi and at different
temperatures and this data is set forth in Table 9 below.
9 TABLE 9 Aged at 200.degree. F., No aging 16 hours Yield Yield
Plastic Point Plastic Point Temperature viscosity (lb/100 viscosity
(lb/100 (.degree. F.) (cP) sq. ft.) (cP) sq. ft.) 150 20.6 48 17.9
51 180 20.9 46 15.2 26 200 18.1 50 13.1 34 220 15.4 55 12.6 31 250
14.4 57 15.7 20
[0055] The properties of formulation E were further evaluated so as
to determine apparent viscosity as a function of shear rate, and
the results of this testing are shown in FIGS. 9 and 10. FIGS. 9
and 10 demonstrate that apparent viscosity is maintained as desired
even after aging at 200.degree. F., and that the apparent viscosity
is not affected by increases in temperature in the range of
150.degree. F.-250.degree. F.
[0056] Permeability return tests were then carried out as
follows.
[0057] A semi-dynamic test was run at a temperature of 150.degree.
F. and filtrate volume using a fluid prepared with formulation E
was measured.
[0058] The core conditions for carrying out this evaluation include
a Berea core type, permeability of 500 mD, formation water
containing approximately 2% wt. KC1, crude oil from a field in
Western Venezuela, and the additive package of Formulation E. FIG.
11 shows the filtrate volume obtained With this formulation, and
the test further shows an initial Mobility of 1.04 mD/cP, a final
mobility of 0.84 mD/cP, and a delta P of 1000 psi, and a formation
damage of 18.87% had occurred.
[0059] Formulation E in accordance with the present invention was
also evaluated to determine storage and loss moduli as a function
of frequency at a deformation located in the linear viscoelastic
range, by using an oscillatory rheometer. Moduli of a high
commercial viscoelastic fluid were also evaluated and compared to
results obtained using Formulation E. Both formulations had been
aged for 16 hours at 120.degree. F. before taking of these
measurements, and FIG. 12 shows the results in terms of the storage
modulus/loss modulus (G'/G"), vs. frequency. FIG. 12 shows that
Formulation E has G'/G" values that are comparable to those of the
high performance commercial viscoelastic fluid, and both fluids
have a high elastic component over a wide range of frequencies,
since the G'/G" ratio is greater than unity. Such fluids are
reported to provide better cuttings suspension and hole cleaning
functions when used as drilling fluids. Thus, Formulation E
provides a drilling fluid having desirable cutting suspension
properties and sealing properties, and elasticity is comparable to
high performance commercial viscoelastic fluids.
[0060] In addition, Formulation E was also subjected to this
testing after having been aged at a temperature 150.degree. F. for
16 hours, and even after such aging Formulation E holds elasticity
over a wide range of frequencies as demonstrated by the ratio G'/G"
which is still greater than unity.
[0061] A displacement test was conducted for a fluid similar to
Formulation E, but not having the CaCO.sub.3 additive. The test was
conducted under severe conditions to maximize formation damage and
to simulate fluid invasion. The core type was Berea, with a 500 mD
permeability, and fluid conditions included 2% KCl, West Venezuela
crude, and Formulation E in the form of an additive package
according to the invention. The test was conducted under these
conditions to maximize potential damage and simulate fluid invasion
of the well.
[0062] This was done at a fluid injection pressure of 1500 psi, a
fluid injection volume of about 5 pore volumes, and a fluid soaking
time of about sixteen hours.
[0063] The results obtained include an initial mobility of 0.78
mD/cP, a final mobility of 0.59 mD/cP, a percent damage of 24.44,
and a final delta P which was higher than an initial delta P.
[0064] The drilling fluid of the present invention was also field
tested during the drilling of a horizontal reservoir in Western
Venezuela. The fluid weight was 8.8 ppg, and estimated production
was 800 bpd. Real production reached 1500 bpd, and no operational
problems were observed during the entire course of the operation.
Thus, field testing confirmed the excellent performance of the
fluid of the present invention.
[0065] It should readily be appreciated that an additive package
has been provided in accordance with the present invention which
provide excellent results in terms of creating drilling fluid that
have desirable properties for use in high permeability
reservoirs.
[0066] It is to be understood that the invention is not limited to
the illustrations described and shown herein, which are deemed to
be merely illustrative of the best modes of carrying out the
invention, and which are susceptible of modification of form, size,
arrangement of parts and details of operation. The invention rather
is intended to encompass all such modifications which are within
its spirit and scope as defined by the claims.
* * * * *