The document is a report on enhanced oil recovery through caustic flooding submitted by Dhiman Kakati. It discusses the mechanisms of caustic flooding including reduction of oil-water interfacial tension through formation of in-situ surfactants. Experiments were conducted to measure the interfacial tension between Assam crude oil and an aqueous solution of 1% sodium bicarbonate using a spinning drop tensiometer. The results showed that interfacial tension remained constant for a fixed rotational speed but increased with increasing drop diameter. The report concludes that Assam crude oil would be responsive to caustic flooding based on the experimental observations and outlines some key factors for effective implementation of caustic flooding in oil reservoirs.

1. A Report on
ENHANCED OIL RECOVERY BY THE METHOD OF CAUSTIC FLOODING
Submitted By
Dhiman Kakati
( 18 July 2016 )
Assisted by : Mr Rahul Saha
Under the guidance of
Dr Pankaj Tiwari
Department Of Chemical Engineering
Indian Institute Of Technology, Guwahati
Guwahati-781039

2. INTRODUCTION:
In a reservoir oil field, oil recovery mechanisms are split into three categories namely
primary, secondary and tertiary recovery. Primary recovery is the initial production stage
during which the oil is produced from the wellbore to the surface by natural pressure
difference between the rock formation and producing wellbore. Secondary recovery, however
proceeds when the oil present in the reservoir cannot be produced to the surface by natural
pressure difference. It is processed by injecting external fluids such as water or gas into the
reservoir to increase reservoir pressure and displace the oil towards the wellbore formation.
Two-thirds of the original oil in place (OOIP), are still located in the complex region which
cannot be produced by primary and secondary methods, and has to rely on tertiary or
enhanced oil recovery (EOR) methods [1]
Enhanced Oil Recovery (EOR) technique recovers the oil which is trapped in the pores of the
reservoir that cannot be recovered by secondary water flooding. EOR can be performed in
various physical and chemical forms such as thermal oil recovery, gas injection, microbial
injection and chemical flooding[1]. We have confined our interest to chemical flooding in
particular, and in this report we will take a detailed look at one of the most widely used
chemical flooding methods in the extraction of reservoir crude- Caustic Flooding
Caustic Flooding is a process in which the organic acids present in reservoir crude oils (also
called Napthenic Acids) react with the alkali present in the floodwater (which is injected into
the reservoir) to form in-situ surfactants at the oil-water interface, which drastically lower the
interfacial tension (IFT) between the crude oil and the floodwater (by a factor of several
hundred), and under the proper conditions of salinity, pH, and temperature, they change the
wettability of the porous medium to preferentially oil-wet. When the proper alkaline water
and acidic oil flow simultaneously in a porous medium, a viscous oil-external emulsion is
formed. The flow properties of this type of emulsion permit a high, non-uniform pressure
gradient to be generated across the narrow region in the vicinity of the emulsion front. The
pressure gradients are sufficient to overcome the reduced capillary forces and displace the oil

3. from the pore space. The displacement efficiency can be much improved over ordinary
waterflood efficiencies [2]
The extent to which interfacial tension is lowered depends largely on the properties of the
crude and the floodwater injected. Therefore, it is important to establish the relationship
between interfacial tension and the essential chemical properties of the acidic oil and the
floodwater [3].The process of alkali flooding has been found to work best with heavy or more
viscous oils( Interfacial tension at the oil-water interface was found to decrease at a faster rate
for heavy oils.).
Saline water is preferred over freshwater for the flooding process. The use of saline water
causes the sand to be made oil-wet in the presence of the alkaline water. High salinity also
leads to the formation of a water-in-oil type of emulsion, which does not form in the other
processes. As stated earlier, the most common organic acids in crude oil are naphthenic acids.
The acid content of a crude oil tends to be higher when the base composition of the crude is
high in naphthenic compounds. In cases where acid concentration is low, a bank of oil
containing organic acids could be injected into a reservoir and followed by alkaline water [2]
Mechanism Of Caustic Flooding:-
The mechanisms active at the front where alkaline water is displacing acidic crude oil include
(1) a drastic reduction of oil/water interracial tension, (2) wetting of the matrix grains by oil,
(3) formation of water drops inside the oil phase, and (4) drainage of oil from the volume
between alkaline water drops to produce an emulsion containing very little oil. The low
interfacial tension and the oil-wetting of the matrix result from the forming of soap by an

4. acid-base chemical reaction at the oil/water interface.The soap is rendered practically
insoluble in the alkaline water by salt present in the water. Under such conditions, soap
promotes oil-wetting of the matrix. (In fresh water, soap is soluble and promotes
waterwetting [2]. Nutting believed that alkaline solutions released residual oil from adherence
to sand surfaces, essentially a wettability change. He also noted that alkali prevented
formation of semisolid, crude oil-water interracial films, but he discounted the importance of
this property in improving recovery. Atkinson believed that residual oil was held within the
spaces between sand grains by forces of capillarity and adhesion in conjunction with oil
viscosity, and that alkaline solutions overcame these forces to release the oil , seemingly
referring to low wettability change combined with oil- water interracial tension reduction[4]
The deficiency of hydrogen ions, which are consumed by hydroxyl ion in aqueous
phase,supports the creation of the soap (AW
-), which is an anionic surfactant other than
synthetic surfactant. The creation of such AW
- ions will adsorb at the oil-water interface and
reduces IFT. Alkali can react with reservoir rock depending upon the rock mineralogy by
surface exchange and hydrolysis, congruent and incongruent dissolution rock, and formation
of insoluble salt by reaction with hardness ions in the fluid and those exchanged rock surface
[1]. The reversible sodium/hydrogen-base exchange is also a very important mechanism
which indicates the alkali consumption in reservoir rock as indicated in the figure and the
equation is given below.
𝑴̅ 𝑯 + 𝑵𝒂+
+ 𝑶𝑯−
⬄𝑴̅ 𝑵𝒂+ 𝑯 𝟐 𝑶
Where 𝑀̅ denotes a mineral-base exchange site
Figure above illustrates the alkali recovery process( deZabala,1982) [1]

5. LITERATURE REVIEW
There is an ocean of literature available on the process of caustic flooding, enumerating the
favourable conditions and the experimentally determined responsive samples in great detail.
Dranchuk et al , reporting on laboratory caustic floods of a viscous Lloydminster crude oil,
observed that stable oil-in-water emulsions were produced in situ and that there was evidence
for reduced water mobility during displacement. Because no significant reduction in ultimate
residual oil saturation results from this mechanism, it is directed primarily toward viscous oils
or oils in heterogeneous reservoirs where sweep efficiency is poor. Under these
circumstances, an improvement in vertical and areal sweep efficiency through improved
mobility ratio can be much more important economically than recovery of residual oil from
only the small volume of the reservoir normally swept [4]
Samanta et al (2011) also investigated the interaction between alkali and crude oil and its
effects on enhanced oil recovery. The presence of carboxylic acid group in the crude oil was
analyzed by FTIR, which forms an in-situ surfactant after interacting with the alkali.
Considering the characteristic interaction between alkali and crude oil, a concentration of 0.5-
1 wt% NaOH of alkali slug was injected and maintained. Three sets of flooding were
performed in sand-pack systems to determine the effectiveness of alkali on enhanced oil
recovery. Increment in oil recovery was observed with the increase in alkali slug
concentration and an additional oil recovery of more than 15 % OOIP over the recovered by
conventional water flooding (∼50%) was recovered, which is due to reduction of IFT,
solubilization of interfacial film, emulsification of oil and water and wettability reversal[1]
Wagner and Leach(1959) presented laboratory tests showing improved oil recovery through
injection of water solutions that reverse rock wettability from oil-wet to water-wet. They
demonstrated this could be accomplished by added chemicals that changed injection- water
pH. These chemicals included acids, bases, and some salts. They reasoned, as others before
them, that the injected chemical always would be preceded by displaced connate water so that

6. treated water would encounter only residual oil left behind the untreated, connate water-flood
front. Since residual oil in a waterwet porous medium is discontinuous and immobile, as
compared with the continuous residual oil phase in an oil-wet porous medium, Wagner and
Leach concluded that water-wet rocks could not respond to a wettability reversal mechanism.
Therefore, they limited application to oil-wet reservoirs where wettability could be reversed
from oil-wet to water-wet. This represents the second of the four different mechanisms for
caustic flooding, that of wettability reversal (oil-wet to water-wet) [4]
Haihua Pei et al (2013) conducted a series of experiments in micro-model and Sandpack
flood test to observe the potential of alkali flooding in enhancing the recovery of Binnan
heavy oil. Micro-model test shows the penetration of alkali solution into the crude oil
forming water drops inside the oil phase thus resulting in water-in-oil (W/O) emulsion which
reduces the mobility of water due to the blockage of permeability zone caused by preceding
water flooding and diverts it to the unsweep region thus increasing the overall sweep
efficiency.For sandpack flooding the parameters varied was alkali concentration, alkali slug
size and injection rate which is in the range of 0.1-1 wt% NaOH, 0.25-2.5 PV and 0.1-1
ml/min respectively. The sandpack flooding conducted indicates the tertiary oil recovery
which is about 20% of the initial oil in place (IOIP) using 1.0% NaOH and the recovery
increases further with increase in alkali concentration. Water droplets number and its size in
W/O emulsions increases with increase in alkali concentration resulting in higher recovery;
however an optimum slug size and injection rate was observed which gives the highest
recovery. The optimum condition was 1 wt% NaOH, 0.25 ml/min injection rate and 0.5 PV
slug size. They also investigated the injection pattern and found that continuous alkali
injection gives better oil recovery rather than cyclic injection pattern [1].
Jennings et al proposed yet a fourth mechanism by which caustic injection can improve oil
recovery. Their laboratory experiments showed that if interfacial tension were low enough,
residual oil in a preferentially water-wet core could be emulsified in situ, could move
downstream with the flowing caustic, and could be entrapped again by pore throats too small
for the oil emulsion droplets to penetrate. This mechanism of emulsification and entrapment
results in a reduced water mobility that improves both vertical and areal sweep efficiency.
This is especially important in waterflooding viscous oils where waterflood sweep efficiency
is notoriously poor[4]

7. MATERIALS AND METHODS
Crude Oil sample(Type1) has been used in the experiment, which has been purchased from
Oil India Limited(OIL).Alkali that has been included in the experiment is Anhydrous Sodium
Carbonate(99.9% purity), purchased from Merck Specialties Private Limited, India
The interfacial tension between chemical and oil phase can be performed by using a spinning
drop method with Spinning Drop Tensiometer – SITE100 (Make: Kruss, Model: Site100),
and the results obtained through the following equation:
σ = r3
ω2
(ρH – ρL)/4, L /D ≥ 4
Where σ is the interfacial tension (mN/m), ρHis the density of the heavy water phase (g/cm3),
ρLis the density of the oil phase (g/cm3), ω is the rotational velocity (rpm), D is the measured
dropwidth (mm), L is the length of the oil drop (mm) and n is the refractive index of the
water phase. The Measuring range is up to 10-6 mN/m with rotation speed up to 15,000 rpm
(optionally up to 20,000) and Temperature range of 0 to 100°C [1]. We have maintained a
fixed rotational speed of 2000 rpm while performing this experiment(at room temperature)
Figure: Schematic Diagram Of a Spinning Drop Tensiometer

8. EXPERIMENTAL OBSERVATIONS
The following readings are the result of an experiment performed to determine the interfacial
tension between the interface of Assam Crude Oil(Type 1) and a 1% (by weight) aqueos
solution of Sodium Bicarbonate(in addition a graph has been plotted between IFT and
time).The readings have been taken for a fixed rotational velocity of 2000 RPM at room
temperature.
Time(in
minutes)
Drop
Diameter(D)
IFT(mN/m) Rotational
Speed(RPM)
0 0.56 0.0263 2000
2 0.53 0.0217 2000
4 0.54 0.0237 2000
6 0.54 0.0234 2000
8 0.54 0.0230 2000
10 0.53 0.0224 2000
12 0.53 0.0227 2000
14 0.53 0.0237 2000
16 0.53 0.0234 2000
18 0.54 0.0234 2000
20 0.54 0.0234 2000
22 0.55 0.0248 2000

9. Figure: Plot between Time(X-axis) and IFT(Y-axis)
We can observe from the above plot that the IFT assumes a near constant value( with
extremely minor fluctuations) for a fixed rotational speed.Also we can observe a slight
increase in the IFT value for a corresponding increase in drop diameter D.

10. RESULTS AND DISCUSSIONS
From the graph plotted in the previous section we can see that interfacial tension remains
constant for a fixed RPM supplied at a constant temperature. It is also evident from the
observations that the value of IFT increases as the drop diamteter D increases inside the
spinning drop tensiometer.

11. CONCLUSION
 The following test was performed on Type 1 Assam Crude Oil, whose API gravity is
higher than 15 and whose viscosity falls in the range of 15-35 centipoise.Hence we
can conclude that Assam Crude Oil (Type 1) will respond satisfactorily to the method
of Caustic Flooding( from the observations in the Spinning Drop Tensiometer
experiment)
 Using saline water in place of fresh water for the flooding process helps in altering the
wettability, which is an important factor in extracting maximum oil from the
reservoirs.
 Caustic Flooding is an effective process in extracting maximum oil from the
reservoirs, as the surfactant used for the purpose of IFT reduction is minimised.

12. REFERENCES
[1] Rahul Saha, “Optimum Formulation Of Chemical Slug For Enhamced Oil Recovery of
Assam Crude Oil”, State Of The Art Seminar,Department Of Chemical Engineering,IIT-
Guwahati
[2] C.E Cooke Jr, R.E Williams, P.A Kolodzie, “Oil Recovery By Alkaline Waterflooding”,
SPE-AIME, Exxon Production Research Co.
[3] T.S Ramakrishnan, D.T Wasan, “A Model for Interfacial Activity of Acidic Crude
Oil/Caustic Systems for Alkaline Flooding”, SPE Journal
[4] C.E Johnson,Jr., “Status Of Caustic and Emulsion Methods”,SPE-AIME,Chevron Oil
Field Research Company