Underground Infrastructure - February 2023 - 32

CIGMAT Report
Materials and Methods
The UH biosurfactant used in this study was produced from
waste oil with acclimated bacteria in continuously stirred batch
reactor. The critical micelle concentration (CMC) for this
biosurfactant is 0.5 g/L and the surface tension reduces to 30
dynes/cm. The biosurfactant is water-soluble and based on
Fourier Transform Infra Read (FTIR) spectroscopy analyses;
both carboxyl (COO-) and hydroxide (OH-) groups were
identified in the biosurfactant.
Diesel oil, representing the oil-based drilling fluid, with a
density of 5.6 ppg, was used for the cleaning efficiency test. The
resistivity of the oil was greater than 1000 Ωm.
Spacer fluid preparation used water as the base fluid.
Rheology modifiers, such as Guargum up to 1% and UH biosurfactant
up to 0.4%, were added. Also up to 3% KCl was added
with the weighting agent lead nitrate (Pb(NO3
)2
).
KCl was first mixed with water, thoroughly, until it completely
dissolved. Then rheology modifier Guargum was added,
followed by the UH Bio-surfactant, and mixed until a uniform
solution was obtained. This was then mixed with the weighting
agent to obtain the spacer fluid.
Nano Iron was also added to the spacer fluid to enhance the
performance with pressure, temperature and magnetic field.
The fluid was characterized with electrical resistivity and density
measurements at each stage of mixing.
Density testing plays a major role in providing the needed
hydrostatic pressure in the drilled holes. Density of the spacer
fluid with and without Nano Iron was measured immediately
after mixing, using the standard mud balance cup.
HPHT testing of the spacer fluid went up to 500 psi. The
change in the bulk resistivity of the material with the applied
pressures was measured and modelled using the Vipulanandan
model.
Rheological properties determine the pump ability and
cleaning capability of the spacer. Rheology tests for smart spacer
fluid with different contents of Nanoiron (nanoFe2
O3
to 1024 s-1
), at
temperature of 25°C to 75°C and magnetic fields of 0 to 0.6T,
used a viscometer in the speed range of 0.3 to 600 rpm (shear
strain rate of 0.5 s-1
recorded.
) and related shear stresses were
The speed accuracy of this device was 0.001 rpm. The temperature
of the spacer was controlled to an accuracy of ±2°C.
The viscometer was calibrated using several standard solutions.
All the rheological tests were performed after 10 minutes of
mixing the spacer solutions.
The cleaning efficiency test was performed on the spacer
fluid to quantify the spacer's ability to clean the diesel oil, representing
the oil-based drilling fluid, using the following procedure:
*
Viscometer cup and the spindle were cleaned and dried.
The dry weight of the spindle was measured (W1
).
* Viscometer cup was filled with diesel oil and the spindle
was run for 10 minutes at 100 rpm. After 10 minutes,
32 FEBRUARY 2023 | UndergroundInfrastructure.com
the viscometer spindle was weighed again with the
contamination (W2
).
* Spacer fluid was placed in the cup and the spindle was
rotated again for 10 minutes at 100 rpm. The viscometer
spindle was weighted again (W3
). Also, the change in
the electrical property of the cleaning spacer fluid was
measured.
Modeling
The spacer fluid showed non-linear shear thinning behavior
with a yield stress. Based on the test results, the following conditions
have to be satisfied for the model to represent the observed
behavior:
τ = τo
when γ
.
= 0; and γ
.
j ∞ j τ = τ*
(1)
Rheological models used for predicating the shear thinning
behavior of spacer fluids are summarized below.
The Herschel-Bulkley model (Eqn. 2) defines a fluid with
three parameters and can be represented mathematically as
τ = τo1
+ k × (γ
.
where τ, τo1
, γ
.
)n
(2)
, k and n represent the shear stress, yield stress,
shear strain rate, correction parameter and flow behavior index,
respectively. For τ < τo
assumes that below the yield stress (τo
a rigid solid.
the material remains rigid. The model
), the slurry behaves as
The exponent n describes the shear thinning and shear thickening
behavior. Slurries are considered as shear thinning when
n < 1 and shear thickening when n > 1.
when γ
.
j ∞ j τmax
= ∞
(3)
Hence, the Herschel-Bulkley model doesn't satisfy the upper
limit condition for the shear stress limit.
The Vipulanandan Rheological Model relationship is as follows:
τ
- τo2
= γ
.
/ (C + D × γ
.
Also, when γ
.
)
where τ shear stress (Pa); τo2: yield stress (Pa); C (Pa. s)-1
(Pa)-1
: are model parameters and γ
.
: shear strain rate (s-1
j ∞ j τmax = (1/D) + τo2
).
(5)
Hence, this model has a limit on the maximum shear stress;
the slurry will produce at a relatively high rate of shear strains.
Cleaning efficiency of the spacer is calculated as follows
Cleaning efficiency (%) =
where:
W1
W2
W3
W3 −W2
W2 −W1
× 100
(6)
= weight of the viscometer spindle before the test in gms,
= weight of viscometer spindle with the contamination
in gms and
= weight of the viscometer spindle after the test in gms.
The relation between maximum shear stress capacity and
(4)
and D
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