COMPARATIVE PERFORMANCE OF CASSAVA STARCH TO
PAC AS FLUID LOSS CONTROL AGENT IN WATER BASED
DRILLING MUD
Cassava starch was extracted from 46.5kg of TMS 98/0505 species of fresh cassava tubers (Type
of cassava) and characterized to establish the rheological properties. The analytical results
showed the following; pH (7), dispersion (poly dispersed), bulk density (617.34kg/m33) and
particle size distribution (fine). It was also compared to the standard Polyanionic Cellulose
(PAC) used in the oil and Gas industry for water based mud (WBM) formulation. The result also
indicated closer similarity between TMS 98/0505 (Could use another type of cassava) and PAC.
It was therefore employed in the formulation of drilling mud. Different ratios (100:0 and 100:0)
of cassava starch and PAC and used to formulate standard drilling mud. The fluid loss properties
of the different drilling mud samples were tested. The filtrate volume (fluid loss) obtained for
various samples using a concentration of 2g/bbl of starch/PAC were 9.2 ml and 4.2ml, while that
obtained at 4g/bbl ,6g/bbl, 8g/bbl of Cassava starch (100:0) were 8.0ml,7.2ml and 6.0 ml. The
result also showed that the amount of cassava starch used is indirectly proportional to the filtrate
volume. Conclusively, cassava starch could be used as a fluid loss additive and improved to yield
a better performance in terms of its water retention capability.
Keywords: cassava starch, Water Based Mud (WBM), Fluid loss and PAC
Abbreviation: PAC – Polyanionic Cellulose
Composition of Drilling Mud Samples
Sample Mass of Bentonite (g) Volume of Water (ml)
Sample 1
50.0
200
Sample 2
50.0
200
Sample 3
50.0
200
Sample 4
50.0
200
Sample 5
50.0
200
Formulation of Drilling Mud (Materials)
Additive
Concentration
Water
500.0ml
Caustic Soda
0.5g
Soda Ash
0.5g
Polyanionic Cellulose (PAC)
2.0g
Xanthum Gum
2.8g
Potassium Chloride
18g
Barite
50.0g
Cassava Starch Concentration (g)
0
2
4
6
8
Function
Base Fluid
Alkalinity Control
Calcium ion Removal
Filtration Control
Viscosifier
Inhibition Control
Weighting Agent
Rheological properties of Cassava Starch
Parameter
TMS 98/0505
pH @ 25oC
7
Bulk Density (kg/m3)
617.3
Particle size Distribution
Fine
Dispersion
Poly dispersed
Appearance
Whitish`
PAC (Reference)
7
641-881
Fine
Poly dispersed
Whitish
PH
The pH accounts for the acidic or basic nature of substances. The level of hydrogen cyanide
(HCN) content in cassava is the basis for its toxicity. The cassava starch sample was in the range
of 7-8 indicating neutral or slightly alkaline on the pH meter. TMS 98/0505 had a pH value of 7.
The HCN content in cassava is inversely proportional to the pH value, i.e the higher the content
of HCN, the lower the pH value and vice versa. The starch sample had the same pH value as the
PAC.
20.0g of cassava starch sample was weighed separately and 200ml of distilled water was mixed
with sample in a Hamilton Beach mixer cup with the aid of an electric stirrer to obtain
homogenous mixture (complete dissolution). The pH of starch solutions were determined by
dipping the indicator probe into the solution. Three repetitions were made for each of the
samples and the mean value recorded.
Fluid Loss Test
The mud sample was poured into the API filter press assembly and using the 50 filter paper, the
reservoir was filled up to the scribed mark. A previously graduated measuring cylinder was kept
in place under the mud reservoir. Then, pressure of 100 Psi was applied to the reservoir at 25oC
for 30 minutes. The filtrate in the cylinder was read and recorded as the fluid loss after
30minutes.
The amount of filtrate collected for each sample at the same period of time is shown in Table 1.
For a drilling mud to be accepted, the fluid loss additive used should be able to give filtrate loss
volume less than 15 ml over a period of 30 minutes (API 13 A, 1993). All the mud samples met
these criteria. From the graph above it is seen that sample 2 which is 2g/bbl PAC had the least
filtrate volume while the volume of filtrate was observed to be in reduction as the concentration
of the cassava starch was increasing. This reduced fluid loss may be due to the similarities in the
polyanionic cellulose and cassava starch molecules. The cassava starch molecules are attracted
towards the polyanionic cellulose molecules and also induce the formation of micelles. The main
attraction forces are hydrophobic and the presence of oppositely charged particles enhances
interaction (Odeh, 2006). It was also observed that as more concentration of cassava starch was
added to the formulation of Sample 1 the volume of the fluid loss was reduced implying that
more concentration of cassava starch was required for a less concentration of PAC.
Table 1; Fluid properties of Produced Mud Samples
Sample
1
2
3
4
5
Volume of Filtrate (ml) 9.2
4.2
8.0
7.2
6.0
20
18
16
14
12
Plastic viscosity Cp
10
Starch mass
8
6
4
2
0
1
2
3
4
Bulk Density
The values of bulk density of starch sample showed slight differences, it was observed that starch
from different varieties had large differences in bulk density depending on the specie source,
(Moorthy 1999). However, starch sample is whitish similar to that of PAC.
Bulk density for starch; The industry standard measurement for producing water based drilling
fluid sample is based on pounds per barrel (lb/bbl). This is the expected density of the drilling
fluid which determines the proportions of the other additives.
Mass of starch = 0.05kg, Volume of occupied = 0.000081m3
Density of starch = 617.3kg /m3
Identifying the density of mud is very important, considering the function of the drilling sludge is
quite strategic and critical such as primary well control against formation pressure and
hydrostatic, hole cleaning, and drill bit lubrication, density in the program mentions to 9.0ppg
Water-Based Mud (WBM), on reference other drilling locations with the same mud phase ranges
from 9.8-10.5 even. The value is pure without the LCM mixture weighed with Fann 140 Regular
Mud Balance, and any additional concentration will be weighed. The effects of LCM can make
the density of mud reduced or increased, and the condition is influenced by the composition of
LCM.
Mud balance
Measurement of plastic viscosity, yield point, and gel strength
We use a Mash funnel viscometer, cup and measured time in seconds. Fill the cup until a
designated level with mud sample is the initial step before initiating the measurement test. Allow
the filtrate to pass through to the cup and then measure the time taken in seconds on the timer for
it to fill the cup. Rotate rotor at 600 RPM continuously until reached a stable dial readings.
Reduce rotor velocity gradually to 300, 200, 100, 6, and 3 RPM followed by the recording of dial
readings at each velocity. Determination of plastic viscosity follows the equation (1)
is plastic viscosity in centipoise (cp) while R600 and R300 are Dial readings at 600
and 300 RPM rotor velocity (in degree unit). Using value, calculate yield point value (YP) in
lb/100 ft2 using equation (2):
Procedure for calculating gel strength (in lb/100ft2) is conditioning the mud sample inside the
mash funnel by constantly rotate the rotor at 600 RPM for 10 seconds, turn off the rotor for 10
seconds and then re-run the rotor at 3 RPM. Record the maximum dial reading during this time
and repeat until 10 minutes rotation time. Repeat gel strength procedure to obtain 10 minutes gel
strength. Repeat all procedure of measurement with different mud composition.
Plastic viscosity
This is a resistance to flow caused by movements between solids in the mud, solids - liquid and
friction between layers of liquid. Plot of plastic viscosity over a sample contain various
composition of starch additive is displayed below. Plastic viscosity increase as the concentration
of cassava starch from 2 g to 10 g. This due to the viscous nature of starch that affects the flow
resistance of the drilling mud. High plastic viscosity has an advantage regarding the cutting
removal issue.
Concentration of starch(g) RPM(600)
RPM(300) seconds
Plastic
seconds
viscosity(cp)
2
10
4
12
6
16
8
18
10
21
25
20
15
Plastic viscosity Cp
Starch mass
10
5
0
1
2
3
4
5
Yield point
Yield point is measuring the electro-chemical force between solids, liquids, liquids and solids in
chemicals in dynamic conditions associated with flow patterns. Calculation result of mud yield
point with various composition of starch plotted in fig. 10. By adding more starch additive to
drilling mud results a higher yield points. Higher yield point is effective because the rheology of
fluid change to non-Newtonian fluid that is better in cutting removal from the wellbore to
surface. The equation of the trend line yield point = 2.714 + 1.257 starch mass, meaning an
increase in starch mass gives a positive influence on starch mass that is equal to 1.257. In the test
obtained a correlation value of 0.994 or a positive value, means two variables increase together.
Concentration
starch (g)
of
cassava RPM(300) Plastic
seconds
viscosity(cp)
2
10
4
12
6
16
8
18
10
21
Yield point
25
20
15
Plastic viscosity Cp
Starch mass
10
5
0
1
Gel strength
2
3
4
5
6
Gel strength is a value that shows the mud ability to hold solids in a reservoir. Gel strength
shows the thickness of mud in a static condition for a certain period. Gel strength value with the
addition of cassava starch additive is shown below. The value of Gel strength increase from 0.40.6 lb./100 ft2 when the starch mass rise from 2 g to10 g. The main reason of this phenomenon is
the nature of cassava starch as polymeric substance. Thicker mud has higher gel strength value,
which is effective at the time of circulation stops. Result from the software indicates a linear
trend line with 98.9% R-sq (adj) value. The obtained equation is gel strength = 0.3371 + 0.2741
starch mass, means an increment in 1 unit starch mass has a positive influence on gel strength
that is equal to 0.2741. In the test obtained a correlation value of 0.996 or a positive value which
means that the two variables increase together.
Concentration of starch(g)
Gel strength (lb/100ft2)
2
0.40
4
0.45
6
0.50
8
0.55
10
0.60
25
20
15
Plastic viscosity Cp
Starch mass
10
5
0
1
2
3
4
5
CONCLUSION
For a drilling mud to pass this crucial test it filtrate loss volume must be less than 15 ml over a
period of 30 minutes (API 13 A, 1993). All the mud samples met the criteria. The result of the
properties of the starch from the cassava specie measured shows that TMS 98/0505 has closer
similarities in terms of pH value and bulk density to PAC. Consequently, starch obtained from
improved cassava varieties and increased concentration in formulation can replace PAC as a
fluid loss control agent in the formulation of the water based drilling fluid.
Existence of cassava starch with higher concentration yields drilling mud with higher with
plastic viscosity, yield point, and gel strength.