CHAPTER when a new oil reservoir is drilled, the

CHAPTER ONE

INTRODUCTION

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1.1 BACKGROUND AND
RESEARCH FOCUS

First and foremost, What
is Enhanced Oil Recovery? In simple terms ,Enhanced oil recovery (A.K.A EOR)
refers to those or any recovery methods carried out on the reservoir after the
implementation of the primary and secondary forms of recovery for the sole
purpose of extracting a larger percentage of the residual oil left in the
reservoir from the former processes carried out as stated earlier.

Due
to the energy crises, rate of increase in the demand for energy worldwide and
along with that the shortage of oil resources and limitations in its
production; enhanced oil recovery is getting a sky rocketing recognition in its
very feasible application for extracting  residual oil from the reservoir after the
primary and secondary recovery methods have failed.

 For instance, this is also undergone by
Indonesia. Before 2004 1, Indonesia is a net oil exporting country but after
that it becomes a net oil importing country. In fact, when a new oil reservoir
is drilled, the oil amount obtained from it is about 20-40% of the potential,
and hence there is still 60-80% oil left in the reservoir. Application of EOR
technology gives an additional chance to get out more oil from the reservoir,
possibly about another 5-30%. Generally, EOR technology is urgently required
especially due to several reasons, i.e. declining oil production since 1995,
non-productive primary and secondary recovery, high crude oil price, increasing
energy demand, approximately 1.5% per year 2, and significant oil remaining
after secondary recovery (~60% of original oil in place,
OOIP).
(A.Z. Abidin et al ,2012). Judging from the above,it can be seen that a lot of
shortcomings gave birth to very productive enhanced oil recovery method.

Looking across most oil
fields in existence today, Hydrocarbons are by natural means extracted from the
subsurface reservoirs by the implementation of the reservoir’s natural energy.
Schemes for oil retrieval are sub-divided into three (3) stages which are of
sequential order namely: primary, supplementary/secondary and tertiary/enhanced
oil recovery phase. It is to be noted that these recovery techniques are in
sequential order.

 where we have the primary recovery method
entailing the use of the natural energy / drive of the reservoir to facilitate
oil production after which this energy depletes over a period of time. The
primary recovery phase which is the original stage involves the utilization of
the natural energy of the reservoir to extract or produce the oil from the
reservoir. Types of natural energy that lead to oil production include: Reservoir
fluid expansion, (Martin, 1996) Gas cap drive, and Solution gas drive as a drop
in reservoir pressure occurs, Aquifer drive and Gravity drainage. The Fig. 1
depicts two natural drive cases (solution gas and water drive)

Figure 1: Primary recovery
(drive) mechanism (solution gas drive and water drive mechanism) Source:
Martin, 1996.

At this point of pressure
depletion in the reservoir is where the secondary recovery methods come into
play. Secondary/Supplementary recovery phase is triggered when the natural
durability of the reservoir is no more being sufficient and the meant oil
recovery as significantly fallen (Martin, 1996).At these times, it is valid to
aid these natural energies with an external form of energy source. The original
secondary recovery methods are the basic immiscible gas injections, water
flooding and pressure maintenance. Usually the water flooding mechanism is
interchangeably used as supplementary recovery. The primary goal of the
injection of either water or gas is to re-pressurize the reservoir to pick up
at an improved pressure and keep maintaining it an increased pressure. Thus,
the term pressure maintenance is often used to demonstrate/depict a secondary
retrieval procedure.

It is a common to
implement gas produced from the reservoir as the injected gas for the purpose
of pressure maintenance. As a result of this, the sales of gas is affected
before completion of  the secondary  technique and the gas jetted down into
reservoir for recovery

Water flooding to a good
extent aids in oil recovery by pushing through the reservoir as a unit force of
flowing fluid, displacing the oil in front of it. The effectiveness of the this
recovery involving water flooding is majorly dependent on the flood sweep
efficiency and mobility ratio of the viscosities of both the displacing
fluid(water) and the displaced fluid(oil). Reduced sweep efficiencies might
occur due to considerable heterogeneities such as faults, fractures or streaks
of high permeability. Rocks of uniform or homogenous nature tend to make
available the most reliable scenarios for high sweep efficiencies. In scenarios
where the injected gas or water happen to be of lesser viscosity than that of
the fluid it is meant to displace (oil), channels would be made by the injected
through the reservoir resulting in a phenomena referred to as viscous fingering
where it occurs due enormous bypassing of residual oil meant to be displaced,
thereby lowering efficiency of the flood. A good instance would be that of a
scenario of heavy crude oil production where the oil is of sufficient viscosity
and may not be feasible to flow under the influence of the reservoir’s natural
energy at rates considered to be economical, thus primary recovery is
considered inadequate in scenarios like this. Moreover, the recovery technique
involving secondary methods of gas injection would not be feasible due to the
injected gas’ high mobile characteristics and low viscosities; each one of
these will result in a large amount bypassed oil ultimately leading to viscous
fingering, decreased recovery and high gas-oil ratio.

However, water injection
may be appropriate since it of considerable low mobility and much more viscous
than oil, shows more oil recovery profile than that of gas injection but due to
heavy nature of oil still leaves behind significant amount of residual
oil.(John mazi felix, 2017).

 

1.2 THE FAST RISING
METHOD OF ENHANCED OIL RECOVERY

Stating this again for
emphasis, EOR technology is urgently required especially due to several
reasons, i.e. declining oil production since 1995, non-productive primary and
secondary recovery, high crude oil price, increasing energy demand,
approximately 1.5% per year 2, and significant oil remaining after secondary
recovery (~60% of original oil in place, OOIP). (A.Z. Abidin
et al ,2012)

Therefore, due to the
shortcomings of these former recovery processes, gave the rise of the tertiary
recovery phase, well known as the enhanced oil recovery method. The use of
tertiary operations was developed in the event of secondary procedures becoming
inadequate. However, the same tertiary operations were also considered for
reservoir applications that secondary techniques were not used as a result of
low recovery probable. Thereby, implementing the tertiary process as a
secondary procedure instead of the normal water flooding. This work can be
boosted by factors such the tertiary process characteristics, availability of
injectants and also cost factor. There might also be a relative bypassing of
the water flooding phase if it could diminish the entire efficiency of the
tertiary procedures as regards to recovery.

The injected fluids
applied in the secondary recovery phase help improve the natural drive of the
reservoir to produce residual oil. The efficiency of the recovery process is entirely
hinged on the means of pressure maintenance. However, the fluids injected in
tertiary recovery operations contact with the reservoir rock and fluid system
which might result to expansion of oil, wettability changes, reduced
interfacial tension, reduced oil viscosity or favorable reservoir phase
behavior. In some circumstances, the tertiary recovery operations might be
employed as a secondary recovery procedure; thereby making the term “Tertiary
recovery” of less value in Enhanced oil recovery books and design become more
accepted. (Green & Willhite, 1998).

 

Enhanced oil recovery
(EOR) procedures can be categorized into four (4) categories namely:

1.     
Miscible flooding process

2.     
Thermal flooding process

3.     
Chemical flooding process

4.     
Microbial flooding process

There are few
criteria/specifications required for selection of which form of EOR process is
to be implemented on a specific reservoir to get the desired recovery. Reason
being that not all Enhanced oil recovery procedures can be assumed applicable
to every reservoir due to unevenness in the reservoir as a lot of parameters
are associated with a certain oil reservoir such as fluid type, temperature,
pressure, rock matrix nature, viscosity and connate water. Thus, an initial
evaluation action would quickly eliminate some techniques from consideration in
a specific reservoir application. This screening program involves the
evaluation of firstly complete geological review, crude oil, reservoir
properties and economics. (John mazi felix,2017).

All these EOR procedures
can be further classified into three (3) as: Thermal, Gas and Chemical methods
as depicted in the diagram below demonstrating the individual methods, the EOR
system and various obstacles.

Figure 2: The categories of
obtainable EOR technologies
(Source: Kong & Ohadi, 2010)

 

EOR strategies are simply
the ones that use the injections of gases, liquid chemicals and or the
utilization of thermal energy. Hydrocarbon gases, CO2, nitrogen and flue gases
are among the list of few gases found in EOR processes. The usage of gas is
recognized as EOR process when the recovery capacity depends on various other
method apart from immiscible frontal displacement seen as a high interfacial
pressure. Several liquid chemicals normally used includes polymers (that really
helps to increase viscosity and reduce injected liquids mobility) as shown in
figure 2, surfactants (which assists with reducing interfacial tension
between  oil and water or oil and gas
interfaces), alkaline (really helps to also reduce interfacial tension and
alter reservoir wettability) and hydrocarbon solvents.

For reservoirs of heavy
crude characteristics (i.e low API gravity), it will be a failed effort to put
into consideration water and gas flooding as a result of the unfavorable low
viscosities when compared with that of heavy crude. Although a polymer
augmented water flooding process may be looked at because of the viscosity
increasing aftereffect of polymers. It therefore means a large amount of
polymers have to be put in to help extract more oil which perhaps is a costly
expenditure although still with regards to the volume of oil recovered.

In most heavy oil
reservoirs, the rest of the oil saturation is obviously high due to the actual
fact that the oil is either too viscous for gas drive to produce before the
reservoir pressure declines or too weak for just about any other normal
recovery procedures to produce. Thermal procedures are a closer option to
increasing oil recoveries in reservoirs of low API. Thermal procedures can be
sub-divided into steam-flooding, in-situ combustion and hot water flood.

The hot water flood has
been implemented infrequently and also with its restricted success rate. The
steam injection procedure is sub-classified steam drive and steam stimulation.
The steam stimulation process entails the treating the reservoir with steam of
high quality and let soak leaving the well shut in and placing it back on
production again after a few days. The period of production is usually
dependent on the rate of oil production and as the case may be when this
pattern of soaking by shutting in and reopening for production is repeated
several times ,the rate of oil production declines after each pattern cycle.
The means of recovery includes:

–         
Reduction of oil viscosity to decrease
flow level of resistance near the wellbore.

–         
Improving solution gas drive methods by
reducing solubility of gas in the oil as temperature is on the rise.

–         
Providing operating pressure to push oil
towards the producing wells.( Martin,1996).

Steam stimulation is
mainly found in reservoirs of heavy oil attributes to boost and develop
injectivity across the wellbore. Steam drive mechanism can be likened to that
of conventional water flood where steam is injected through various injector
wells and oil produced from that of the producer wells. The recovery mechanism
involved includes; thermally driven expansion of oil, decreased in the
viscosity of oil, change in surface tensions 
as there is a rise in reservoir temperature conditons and steam induced
distillation of lighter parts of the crude.

In-situ combustion entail creating an ignition down the hole
and then a steam blast of air or enriched oxygen is injected into the well
where the combustion ignition takes place and then is circulated across the
reservoir. Here, the heavy components serve as fuel for the combustion process
to function properly; hence the abundance of heavy components in the reservoir
is necessary. . Figure 3 shows in-situ combustion process.

Unfortunately,
thermal recovery entails several major disadvantages, for instance; heat being
lost to the environment (i.e both surface and subsurface), practically
impossible to carry out laboratpry experiments on thermal injection at
reservoir temperature conditions, another problem being that the density and
viscosity of steam tends to be lower than that of oil and water, therefore
difficulty in mobility control  alongside
other challenges such as pollution, poor sweep efficiencies and operational
problems to mention a few. Considering these major drawbacks as stated above ,
some methods of Enhanced Oil Recovery need to be looked on and improved.

Figure 3: Process of In-situ Combustion.

 

Improved ways of water
flooding such as surfactant, alkaline, polymer or a blend of the alkaline,
surfactant and polymer flooding (ASP) has been developed to effectively sweep
and ultimately recover more residual oil. The ASP flooding works through by
modifying the wettability of the rock formation and also decrease in
interfacial tension. Polymer flooding can be labeled under chemical flooding
and sub-classified under water flooding as observed in Figure 4. Polymers are
implemented in water flooding to help upturn the viscosity of the injected
substance and decrease the mobility ratio. Because the polymer process is a
well-proven technology by early on onshore applications, especially in China,
it offers high prospect of medium oil (22.3-31.1°API)
and even for bulkier oil recovery.

 

  

Figure
4: diagram showing polymer induced water flooding.

 

1.3 POLYMERS

We hear, talk and handle
plastics in our day-to-day domestic lives. These plastics come about as a
result of the term “polymers”. Polymers can be termed as molecules of macro
scale that are made of units reoccurring in a particular pattern  connected/linked by a bond found to be
covalent. These units are termed “monomers”. Also not to forget, the word
polymer originates from a Greek word “poly” meaning “many” and “meros” meaning
“parts”.

Polymers can be
categorized into three forms mainly;

·        
Biopolymers/Natural polymers

·        
Polymers of semi-synthetic nature and

·        
Synthetic polymers

Water
flood mobility ratio can be controlled by dilute solutions of certain polymers,
which provide a displacing fluid with considerably reduced mobility (Chilekwe Ikeagwu and
Adetila     Samuel,2015).

(
Ezeddin, 2000) reported that a number of other chemicals such as emulsion,
biopolymers, foam and carbon dioxide activated silica gel, have the ability to
increase the viscosity of water. Polymers particularly have the ability to
lower mobility by reducing the relative permeability to water as well as
increasing its viscosity (an index of mobility ratio improvement) .

 

Addition
of polymer increases the viscosity of the aqueous phase, which reduces the
mobility of the phase, thus lowering. 
The presence of polymer does not reduce residual oil saturation except
few polymers (Wang et al, 2000). However, it increases the sweep efficiency
greatly. If the water flooding mobility ratio is high, the reservoir
heterogeneity is serious, or combination of these two happens, polymer flooding
will be useful (Lake, 1989).  (Yang et
al, 2006) observed that an incremental recovery over waterflooding  of more than 20% original oil in place(OOIP)
was  obtained by injection of high
molecular weight, high concentration polymer solution in Daqing field. 

 

It
has been established that an appreciable percentage of the original oil in
place can never be recovered by the natural energy of the reservoir. (Craig,
1971) noted that at the completion of a water flood significant amount of oil
still remains. Polymer augmented water flooding however stands the chance of
improving recovery by mobilizing additional oil from reservoir pore spaces.

 

1.3
BIOPOLYMERS

Biopolymers
being the chemical reagents being applied in this research, they are polymers
obtained from plants and animals( living organisms), simply of biological
nature and can therefore be termed biomolecules of polymeric nature. Polymers
of this nature can further be sub-categorized under the following;

·        
Polysaccharides- These are referred to as
polymeric structures of carbohydrate nature found to bonded linearly.

·        
Polynucleotides- These are referred to as
long chain polymers that constitute of several units of nucleotide monomers.
(i.e DNA and RNA).

·        
Polypeptides- These are simply referred to
as short chained polymers of amino acid units.

·        
Other examples of polymers of this nature
include the likes of natural rubber,proteins just to mention a few.

Also
to note , a striking difference between the biopolymers and the synthetic
polymers is found to be in their structural configurations;  as that of biopolymers are found to be well
defined per say and have units well arranged sequentially like that of the
proteins known to be referred to as the “primary structures”. This trait has
been observed to determine the biological functions and to an extent depend on
these primary structures as stated above. While that of the synthetic polymers
are found to be more of simple and random structures.

 

1.4
STATEMENT OF PROBLEM

First
of all, with the trend of change in oil price levels ; for instance having
sales price for oil being quite higher than the cost price, this scenario in
turn creates a higher profit margin which can then be directed towards the
application of Enhanced oil recovery to extract even more residual oil, also
when the case goes vice-versa and a lesser profit margin is observed ,this also
in turn reduces the feasibility of directing the profit margin attained towards
Enhanced oil recovery. Thus in general terms, the “oil price” is a factor to be
considered and looked out for.

Secondly,
the issue of high temperature ,salinity concentrations  and even bacteria presence are factors to be
considered as polymers have been observed to not function properly or rather
reduce inn performance due to these conditions due to their degradability
unless an optimum range of these conditions are attained by altering, enhancing
or even finding better alternatives that meet the desired  properties of these polymers to function in
unfavorable conditions.

Lastly,
polymers have definitely been getting better and fast rising recognition in the
oil industry as regards to enhanced oil recovery but these polymers even in
small quantities are found to be quite expensive and not readily available per
say which I think is why the method is more of polymer augmented water flooding
to aid the process and sweeping efficiency due to small quantity of polymer
available. 

 

 

1.5
RESEARCH AIM AND OBJECTIVES

The
main aim of this research work is primarily the designing of a biopolymer product
for implementation in Enhanced oil recovery.

The
objectives considered in this research include;

·        
To analyse the effectiveness of the
biopolymer obtained from banana peels as a recovery agent and its impact/effect
on the sweep efficiency as regards Enhanced 
oil recovery.

·        
To formulate a biopolymer which can be
termed “non-harmful,non-toxic and environmentally friendly” and also provide an
avenue for biological substances to be represented as alternatives for polymer
design/formulation.