Chemistry and Technology of Fuels and Oils, Vol. 46, No.6, 2011
PRODUCTION OF SUPERLIGHT SARALINE DRILL-IN FLUID
Badrul Mohamed Yan Muhammad and Abdul Aziz
Abdul Raman
Fragmental rock accumulates around the perforation channel and the permeability of this zone decreases
during drilling. Underbalanced drilling cleans the perforation channel and increases oil production. A
superlight Saraline drill-in fluid produces a pressure differential. Glass bubbles (GB) were used to
reduce the density of this fluid. The required viscosity and stability of the fluid were maintained by
adding homogenizing and stabilizing agents. Laboratory tests showed that the density of the fluid with a
Saraline:GB mass ratio of 60:40 and a homogenizing and stabilizing agent content of 3 and 9 wt. % can
be 500 kg/m 3, i.e., much lower than the density of pure Saraline, 722.2 kg/m3 .
Key words: underbalanced drilling, drill-in fluid, Saraline, glass bubbles.
In many countries, oil wells are drilled with negative differential pressure in the well–bed system [1, 2].
This method of perforation was developed in the 1960s. With this method, the pressure in the wellbore is lower
than in the bed, which increases the productivity of the formation [3]. In the 1970s-beginning of the 1980s, it was
found that the ability of the perforation channel to pass fluid increases with an increase in the pressure differential
Table 1
Saraline:GB
(wt.)
Density, kg/m3
Viscosity,
mPa⋅sec
633.3
604.4
576.7
557.8
19.2
24.5
29
61
90:10
85:15
80:20
75:25
70:30
67.5:32.5
Stability – volume (ml) of Saraline remaining in fluid
after settling for
5 min
30 min
1h
24 h
6
25
4
16
2.5
10
0.5
7
Gel-like structure
Same
28
22.5
15
9
29
24
16
10.5
____________________________________________________________________________________________________
University of Malaya, Malaysia. Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 6,
pp. 27 – 29, 2010.
0009-3092/11/4606–0401 © 2011 Springer Science+Business Media, Inc.
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and it was concluded that the increase in the productivity of a well is due to cleaning of the perforation
channel [4].
It is suggested in [5] that flow of the fluid decreases damage to the perforation zone and washes crushed
rock out of perforation channels.
To attain a pressure differential between wellbore and formation, a stable superlight fluid with safe chemical
properties is required. Such a fluid is obtained from Shell Saraline 185 V high-quality synthetic oil containing
Scotchlite TM HGS 4000 glass bubbles to reduce its density. This solution is designed for use in drilling to great
depths.
Saraline is made from natural gas, so that it does not contain aromatic hydrocarbons, amines, and sulfur
compounds. Saraline-based fluids and other similar products have been used in Malaysia, Thailand, Vietnam,
Myanmar, Indonesia, New Zealand, Bangladesh, India, Australia, China, the Philippines, and in Caspian Sea
fields since 1997 [6]. These fluids are usually stable, homogeneous, and incompressible, can be used to measure
bottom parameters during drilling, and can be used in a wide range of temperatures and pressures and in conditions
of aggressive medium in the well. The low density of the fluids ensures drilling with no pressure differential or
with a negative pressure differential [7].
A light drill-in fluid made of Sarapar oil and glass bubbles with addition of the corresponding stabilizing
and homogenizing agents was obtained in [8]. Field tests of this fluid showed that it increases well productivity
in comparison to ordinary drill-in fluid.
However, the possibilities of obtaining Saraline superlight drill-in fluid have not received enough attention.
We obtained such a fluid with acceptable viscosity and high stability. Glass bubbles to keep it homogeneous – a
homogenizing agent, and a stabilizing agent to increase the stability were incorporated in the fluid to attain the
lowest possible density.
Experiments were conducted in two stages to obtain a superlight stable fluid of acceptable viscosity.
Saraline was first mixed with the glass bubbles in the ratio of 90:10, 85:15, 80:20, 75:25, 70:30, and 67.5:32.5 to
Glass
bubbles
Saraline
Fig. 1. Separation of fluids after settling for 24 h with different Saraline:GB ratio:
A) 90:10; B) 85:15; C) 80:20; D) 75:25; E) 70:30.
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Table 2
Content, wt. %
Density, kg/m3
Viscosity,
MPa ⋅sec
Stability, days
–
571.1
57.2
<1
3
–
583.3
50
<1
75:25
5
–
593.3
46.1
<1
75:25
3
9
604.4
53.6
<1
70:30
3
9
543.3
92.8
3
65:35
3
9
528.9
110.5
7
520.0
246.1
10
Saraline:GB (wt.)
homogenizing
agent
stabilizing agent
75:25
1
75:25
60:40
3
9
57.5:42.5
3
9
Gel-like structure
55:45
3
9
Same
determine the maximum glass bubble content at which the solution would be stable without addition of
homogenizing and stabilizing agents. Then a homogenizing agent was added to the most stable solution with a
Saraline:GB ratio of 75:25 (Table 1) in the amount of 1, 3, and 5 wt. % with 9 wt. % or with no stabilizer, and
homogenizing and stabilizing agents were added in the amount of 3 and 9 wt. %, respectively, to fluids with a
Saraline:GB ratio of 70:30, 65:35, 60:40, 57.5:42.5, and 55:45. The frequency of stirring the components
was 15,000 rpm and the stirring time was 1 h. We used 250 g of fluid consisting of Saraline and glass bubbles for
the experiments. After stirring, the stability of 50 ml of the fluids was determined. The density was measured
with a 25-ml pycnometer and the viscosity was measured on a HAAKE VT 550 viscometer (Gebruder Haake
GmbH, Karlsruhe, Germany). In determining the characteristics of the fluids with no additives, the stability of
the fluid was determined with the volume of Saraline left in the fluid after settling. The more Saraline separated
from the solution, the lower its stability.
As Table 1 shows, the density of the suspension decreases with an increase in the content of glass bubbles,
whose density is lower than for Saraline. The lowest density, 557.8 kg/m 3, is obtained with a Saraline:GB ratio
of 75:25. The viscosity increases with an increase in the glass bubble content in the fluid. The glass bubbles are
made of soda-lime and borosilicate glass so that they are insoluble in water and oil [6]. At a 30 wt. % and higher
content, the fluid is transformed into a gel-like mixture. The characteristics of the mixtures were not determined,
since they are unsuitable for use. A homogenizing agent was added to keep the suspension homogeneous. The
external appearance of the fluids after settling for 24 h is shown in Fig. 1.
The results of determining the characteristics of fluids with different Saraline:GB ratios containing
homogenizing and stabilizing agents are reported in Table 2. Addition of a homogenizing agent in the amount
of 1-5 wt. % to fluid with a Saraline:GB ratio of 75:25 reduces the viscosity of the mixture. This is because
montmorillonite is the basic (of the order of 90%) component of the homogenizing agent, and in reacting with the
glass bubbles, causes agglomeration of the mixture. The density of the mixture containing this agent increased,
which decreased the pressure differential between formation and wellbore. However, the stability of the mixture
is very low (less than 1 day). A stabilizing agent must be added to obtain a stable fluid.
When a stabilizing agent was added to fluid containing 3% homogenizing agent with a Saraline:GB ratio
of 75:25, the density of the mixture increase increased from 583.3 to 604.4 kg/m 3 and the viscosity increased
from 50 to 53.6 mPa⋅⋅sec. The increase in the density of the fluid is due to the higher density of the emulsifier.
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Addition of an emulsifier makes it possible to prepare a fluid with a higher glass bubble content. The maximum
glass bubble content is 40 wt. %. The stability of the mixture increased with an increase in the glass bubble
content. However, increasing the glass bubble content in the fluid to 42.5 wt. % caused formation of a gel-like
structure.
We can draw the following conclusions from the results of the study:
• a low-density drill-in fluid can be prepared from Saraline and glass bubbles;
• addition of a stabilizing agent allows increasing (up to 40 wt. %) the acceptable glass bubble content in
the fluid;
• addition of homogenizing and stabilizing agents is necessary to increase the stability of the fluid.
We would like to thank the Malaysian Ministry for Science, Technologies, and Innovation (Project
No. 13-02-03-3067), Shell MDS Malaysia Sdn Bhd, 3M Malaysia Sdn. Bhd, and Scomi Group Bhd for their
support in conducting the research.
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(April 30-May 3, 2007), OTC 18514.
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Malaysia Sdn. Bhd (April 2002), pp. 1-5.
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