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FILTRATION AND RHEOLOGICAL PROPERTIES OF NATURAL RUBBER
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LATEX ADDED DRILLING FLUID
Thanarit Riyapan* and Akkhapun Wannakomol
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Running head: Properties of Natural Rubber Latex Added Drilling Fluid
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Abstract
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Drilling fluids play very important role in rotary drilling activities. It is
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necessary to control its properties to optimize and to enhance efficiency of drilling
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operation. The objective of study is to measure filtration and rheological properties of
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water-based mud using natural rubber latex (NRL) additive which is derived from the
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Hevea brasiliensis tree. This ecologically-friendly biopolymer water-based mud was
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tested by API RP 13B standard procedure for testing water-based drilling fluids. The
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effects of NRL concentration and temperature on filtration properties were
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investigated. The test results can be summarized as follows; (1) The presence of NRL
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containing mud had better static filtration properties compared to base bentonite mud,
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(2) The influence of elevated temperature showed negative effects on filtration
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properties by increasing fluid loss rate, (3) The rheological parameter of NRL
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containing mud increased with increasing of NRL concentration and temperature
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except plastic viscosity which slightly decrease with increasing temperature, and (4)
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The NRL could be used as drilling fluid additive for borehole having bottom hole
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temperature up to 80oC without thermal degradation.
*
School of Geotechnology, Institute of Engineering, Suranaree University of Technology, 111
University Avenue, Muang District, Nakhon Ratchasima 30000, Thailand.
Email: thanaritr@gmail.com
*
Corresponding Author
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Keywords: Natural rubber latex, Hevea brasiliensis, Drilling mud, Lost circulation
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additive, static filtration
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Introduction
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In rotary drilling, there are a variety of functions and characteristics that are expected
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of drilling fluids. The drilling fluid is used in the process to (1) clean the rock
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fragments from beneath the bit and carry them to separate at the surface, (2) exert
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sufficient hydrostatic pressure against subsurface formations to prevent inflow fluids
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into the well, (3) keep the newly drilled borehole open until steel casing can be
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cemented in the hole, and (4) cool and lubricate the rotating drillstring and bit
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(Bourgoyne et al., 1986). In addition to serving these functions, the drilling fluid
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should not (1) have detrimental properties to use of planned formation evaluation
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techniques, (2) cause any adverse effects upon the formation penetrated, or (3) cause
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any corrosion of the drilling equipment and subsurface tubulars.
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The bentonite used in drilling fluid is monmorillonite clay (Chilingarian and
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Vorabutr, 1983). It is added to fresh water to (1) increase the hole cleaning properties,
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(2) reduce water seepage or filtration into permeable formation, (3) form a thin filter
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cake of low permeability, (4) promote holes stability in poorly cemented formation,
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and (5) avoid or overcome loss of circulation. The added bentonite is sometimes
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unable to provide satisfactory those properties that required for optimum performance
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in an oil well drilling. Hence, the polymers are added to achieve desired result.
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Polymers are practically part of every water base-system in use today and they can be
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classified their usage (Devereux, 1998). The major uses of polymers in drilling mud
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are flocculants, deflocculants (or thinners), viscosifiers, filtration control additives,
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and shale stabilization. It has been discovered that polymer latex added to the water-
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base drilling fluid can reduce the fluid loss rate that invade to the borehole wall. The
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polymer latex is capable of providing a deformable latex film for sealing the
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formation (Stowe et al., 2004). Since filtration problems are usually related to
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flocculation of active clay particles, the deflocculant also aids filtration control. The
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common of polymers used for filtration control are starch, sodium carboxymethyl
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cellulose, sodium polyacrylate and xanthan gum. They reduce water loss by
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increasing the effective water viscosity (Bourgoyne et al., 1986). There are various
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kinds of polymer that have been studied in aboard but it is less study in Thailand.
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Natural rubber latex is a good selection for study because Thailand is a large rubber
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producer. Therefore, it is easy to provide a lot of this local inexpensive material. For
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mentioned purposes, natural rubber latex (NRL) was selected to study. The NRL is a
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biodegradable polymer. It can be designed for better environment friendly additive in
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drilling mud system that used to minimize the drilling fluid invasion into the
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permeable formation. Natural rubber latex used in this study is derived from the
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Hevea brasiliensis tree which is common tree in Thailand. The NRL is a white,
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creamy and free flowing liquid. The rubber component from is an entirely more than
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98 percent of cis-1,4-polyisoprene. It exists as an amorphous and rubbery material.
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Natural rubber latex (NRL) typically contains 34 percent (by weight) of rubber, 2-3
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percent proteins, 1.5-3.5 percent resins, 1.0-2.0 percent sugar, 0.5-1 percent ashes,
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0.1-0.5 percent sterol glycosides, and 55 to 60 percent of water. It has a pH 6.5-7.0
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and a density of 0.98 grams per cubic-centimeter. Rubber particles size varies from
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0.15 to 3 micrometer (Sridee, 2006).
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Material
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The Sodium montmonrillonite (bentonite) clay was obtained from Mi-Swaco
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Company, Indonesia. The barite was obtained from Ajax Finechem Pty Ltd, Australia,
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and 60 percent rubber latex concentrate was produced by Thaihua rubber public
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company, Sakonnakorn, Thailand.
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Mud Preparation
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A base bentonite-water suspension was prepared using 30 grams of bentonite per 500
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milliliter of water and 60 grams of barite were added to control its density. The mud
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components were mixed for 15 minutes using Hamilton Beach high-speed mixture.
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During mixing, the NRL was added slowly to agitated base fluid to avoid a lump
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occurring within mud system. The testing mud samples were weighted of 1.2 grams
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per cubic-centimeter containing 6 percent bentonite weight by volume as a base
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composition. A various NRL concentrations were added to perform as fluid loss
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additive. These systems were prepared to compare the fluid loss control potential
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properties of the mud. The formulations of the mud are shown in Table 1.
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Testing
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The static API filtration tests were run for all mud samples under 100 psi differential
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pressure of nitrogen by using API fluid loss apparatus (Fann Filter Press Series 821).
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The mud samples were filtered through 3.5 inches hardened filter paper. Rheological
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parameters were measured by Fann 35SA viscometer. Thermal treatments were run
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under temperature at 30, 45, 60 and 80oC, respectively. The temperature of mud
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samples were controlled by water bath. The mud samples were tested in triplicate and
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average values were determined. The testing procedures were followed the API 13B
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standard procedure for oil field testing water-based drilling fluids (API Recommended
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Practice, 1985) after a period of components blending. The apparent viscosity, plastic
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viscosity and yield point were calculated from 300 and 600 rpm readings using
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following formulas:
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Apparent viscosity
 a  600 / 2
(cP)
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Plastic viscosity
 p  600  300
(cP)
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Yield point
 p  600   p
(lb/100 ft2)
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Where,
600 = viscometer dial reading at 600 rpm
300 = viscometer dial reading at 300 rpm
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The Gel strengths were measured by rotational speed at 3 rpm. The drilling mud was
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allowed to stand undisturbed for 10 seconds and 10 minutes which are referred to
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initial gel strengths and 10 minutes gel strength.
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lb/100ft2.
Gel strengths are reported in
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Results and discussion
Filtration properties of NRL containing mud
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The filtration properties of base bentonite mud measured at 30oC and others elevated
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temperatures are shown in Figure 1. The filtration properties of NRL containing mud
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measured at 30oC also demonstrated in Figure 2. Both of graphs show time-dependant
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filtration behavior of base bentonite mud and indicate that the fluid loss exponentially
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increases as the time increase. Results also show a progressive decrease in filtration
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rate of mud with increasing time of filtration. The decreasing in filtration was resulted
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from continuous mudcake deposition and compaction until the layer of a constant
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thickness and stable mudcake had been formed completely. From Figure 1,
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comparison of curves indicates a significant increase in the static filtration of
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bentonite mud as the temperature increase. This is due to adverse temperature effects
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on filtration that result in fluid phase viscosity decreasing and a colloidal fraction tend
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to flocculate. This could be the cause of mudcake permeability increasing.
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Figure 2 shows the effect of NRL concentration on filtration properties at 30 oC. The
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static filtration curves indicate that at 1 percent NRL concentration shows no
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improvement in filtration prevention behavior of bentonite mud. Comparison of 3
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and 5 percent NRL concentration with base bentonite mud it is clearly showed
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reduction of fluid loss rate. The 3 and 5 percent NRL bentonite mud indicate about 5
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and 10 percent improvement of 30 minutes filtration prevention properties
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respectively. This is due to the effective bentonite mud swelling and NRL particles
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distributing. The more NRL concentration indicates more NRL particles dispersed in
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bentonite mud which facilitated quick and tight mudcake layer on the filter paper.
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Analyses of filtration behavior of the mud after thermal treatment at 45, 60 and 80oC
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are demonstrated in Figure 3. The figure represents 30 minutes static fluid loss values
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of 5 percent NRL containing mud and indicates that the presence of 5 percent NRL in
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bentonite mud can reduce fluid loss about 10 to 15 percent. Moreover, there is no sign
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of thermal degradation of NRL in bentonite mud. Therefore, it can be concluded that
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the NRL additive could be performed under this temperature range. Thus the most of
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mud possess a good thermal stability at tested temperatures. The thermal stability of
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the NRL mud indicated that the NRL additive could be used in subterranean well
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having downhole temperature up to 80oC. For example, in Gulf of Thailand,
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geothermal gradients generally vary from 2.95 to 7.00oC per 100 meter in area of
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hydrocarbon exploration (Lekuthai et al., 1995). Hence the NRL containing mud
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could be used in the drilling well having depth in range between 700 and 1600 meter
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depended on ambient temperature of well formation.
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Table 2 shows the thickness of mudcake deposited by NRL containing mud. The table
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shows a thicker mudcake as the NRL concentration and temperature increase. The
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qualities of mudcakes deposited by the NRL containing mud were also investigated.
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The toughness and slickness of NRL containing mud is more than base bentonite mud
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that indicates the presence of mudcake stability and lubricity. Moreover, filtration test
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results indicated that the presence of NRL containing mud had a favorable mudcake
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quality under the tested temperature range. A good quality mudcake is an effective
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means of preventing inflow, minimized formation damage by screening out fines
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migration to invaded formation and easily removed when reservoir fluid is produced
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(Amanullar and Yu, 2005).
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Rheological properties of NRL containing mud
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The rheological properties of base bentonite mud and NRL containing mud samples
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are summarized in Table 3. For all tested temperature, the results indicated that the
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present of NRL containing mud increase the apparent viscosity, yield point, gel
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strength and plastic viscosity. This is due to the greater colloidal fraction of bentonite
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and NRL in mud sample, thus increasing surface area of particles and friction between
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colloidal particles that result of increasing flow resistance.
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Considering effect of thermal treatment temperature, it clearly sees that for all of NRL
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compositions, the apparent viscosity, yield point and gel strength increase with
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increasing temperature except the plastic viscosity which slightly decreases with
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increasing temperature. The consequence of temperature increase interaction energy
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of mud system (Luckham and Rossi 1999). This induces more inter-particle attractive
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force between solid particles and so the clay particles come into contact with another
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and agglomerate.
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Conclusions and Recommendations
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The presence of NRL containing mud indicated a better fluid loss control properties
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and increases rheological properties of bentonite mud. Therefore, the Combinations of
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NRL with bentonite clay could reduce lost circulation and produced favorable
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rheological properties. These properties are required for optimum performance of
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drilling well having borehole temperature up to 80oC. The NRL is not expensive and
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it is ecologically-friendly biopolymer which is easily affordable in Thailand thus it
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quite suit for using in drilling fluid system.
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For further study, the different bentonite mud concentration should be conducted in
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experiment to represent other condition of fluid composition. It should be directed to
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study the thermal behavior of NRL containing bentonite mud under high pressure and
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temperature which represents a real borehole circulation condition by using dynamic
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filtration test. The formations damage are concerned and should be measured due to
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erodibility of mudcake NRL deposited are presence.
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Nomenclature
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a
=
Apparent viscosity
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p
=
Plastic viscosity
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p
=
Yield point
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rpm
=
Rotational speed
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Gelin
=
Initial gel strength
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Gel10
=
10 minutes gel strength
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Acknowledgement
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The authors gratefully acknowledge School of Geotechnology, Institute of
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Engineering, Suranaree University of Technology for providing financial support and
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facilities.
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References
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Amanullar, Md. and Yu, L. (2005). Environment friendly fluid loss additives to
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protect the marine environment from the detrimental effect of mud additives.
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J. Pet. Sci. Eng. 48: 199-208.
202
203
Recommended Practice. (1985). API Recommended Practice for Field Testing
Drilling Fluids. (11th ed). Washington: API, Vol. 13 B, pp. 9-10.
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Bourgoyne Jr, A.T., Millheim, K.K., Chenevert, M.E., and Young Jr, F.S. (1986).
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Drilling Fluids. In: Applied Drilling Engineering. SPE Vol. 2. p. 41-84.
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Chilingarian, G.V. and Vorabutr, P. (1983). Drilling and Drilling Fluids. 2nd ed.,
207
208
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Amsterdam: Elsevier. 767p.
Devereux, S., (1998). Drilling Fluids program In: Practical Well Planning and
Drilling Manual. Oklahoma: PennWell. p. 205-253.
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210
211
212
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Lekuthai, T., Charusirisawad, R. and Vacher, M. (1995). Heat flow map of the Gulf of
Thailand. CCOP Technical bulletin. 25: 63-78.
Luckham, P.V. and Rossi, S. (1999). The colloidal and rheological properties of
bentonite suspensions. J. Colloid Interface Sci. 82: 43-92.
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Sridee, J. (2006). Rheological properties of natural rubber latex. Thesis: Master of
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Engineering (Polymer Engineering). Suranaree University of Technology,
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Nakhon Ratchasima, Thailand.
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Stowe, C.J., Bland, R.G., Clapper, D.K., Xiang, T., and Benaissa S. (2004). Water-
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based drilling fluids using latex additives. inventers: Baker Hughes assignee,
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Mar 9. U.S. patent no. 6,703,351 B2.
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30
80oC
60oC
45oC
30oC
filtrate loss (ml)
25
20
15
10
5
0
0
5
10
15
20
Time (min)
Figure 1. Static filtration versus time of bentonite mud.
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30
12
20
Bentonite mud
filtrate loss (ml)
Bentonite +1% NRL
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Bentonite +3% NRL
Bentonite +5% NRL
10
5
0
0
5
10
15
20
25
30
Time (min)
Figure 2. Static filtration of NRL containing mud versus time at 30oC.
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30
API Fluid Loss (ml)
25
20
15
10
Betonite+ 5% NRL Mud
5
Bentonite Mud
0
20
40
60
Temperature (oC)
Figure 3. 30 minutes API fluid loss of mud system.
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100
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Table 1. Composition of mud
Mud components Bentonite
mud
Water (ml)
500
Bentonite (gram)
30
Barite (gram)
60
NRL (ml)
-
Bentonite+
1%NRL mud
500
30
60
5
Bentonite+
3%NRL mud
500
30
60
15
Bentonite+
5%NRL mud
500
30
60
25
15
Table 2. Mudcake thickness deposited by mud system
Tested Temperature
30oC
45oC
60oC
80oC
Mud composition
Bentonite
Bentonite+ 1%NRL
Bentonite+ 3%NRL
Bentonite+ 5%NRL
Bentonite
Bentonite+ 5%NRL
Bentonite
Bentonite+ 5%NRL
Bentonite
Bentonite+ 5%NRL
mudcake thickness (mm)
2.40
2.58
2.82
2.89
3.12
4.07
3.43
4.23
3.45
4.92
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Table 3. Rheological parameters of mud samples
Tested
Temperature
Bentonite
mud
composition
a
p
p
(cP)
(cP)
(lbf/100 ft2)
30oC
1%NRL
3%NRL
5%NRL
1%NRL
3%NRL
5%NRL
1%NRL
3%NRL
5%NRL
1%NRL
3%NRL
5%NRL
10.8
11.7
12.5
13.8
12.5
14.5
15.5
16.2
15.2
16.6
18
18.5
18.3
19.5
20.5
23.2
4.7
5
5
5.3
5
5.3
5.3
5.3
4.7
5.2
5.3
5.3
4.2
5
5
5
12.3
13.3
15.0
17.0
15.0
17.3
20.3
21.7
21.0
22.2
23.3
25.7
28.3
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31
36.3
45oC
60oC
80oC
Gelin
(lbf/100 ft2)
Gel10
(lbf/100 ft2)
11.3
11.3
13.2
14.7
14.8
16.3
18
19.0
20.7
21
22.7
23.3
24.7
26
31.5
31.7
13.7
13.7
15.7
15.7
18.7
19.3
21.2
19.3
20.2
21.3
22.2
22.3
24.2
24.5
27.7
31.3