Enhanced Oil Recovery (EOR)

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What will happen if world’s oil and gas reserves ends? Either world can survive without fuel or not because there were not enough technologies which could extract all of the oil buried underground. These were the questions which were asked 50 years ago, but with the advancement of Petroleum Industry new techniques are introduced and used around the world frequently. Enhanced oil recovery is one of the most and pioneering field of petroleum industry. It is defined as “Use of different techniques and methods to increase oil and gas production”. We all know that the hydrocarbons produced from primary recovery are only 10 – 20 % of a total reservoir, which is due to natural energy of the reservoir, while this percentage increases up to 40 % when secondary recovery is used, which includes water flooding and gas flooding in reservoir. There is a third term which is called tertiary recovery. According to the Department of Energy U.S.A, the amount of oil produced worldwide is only one third of the total oil available. With the decline in oil discoveries during the last decades it is believed that EOR technologies will play a key role to meet the energy demand in coming years. So by using tertiary recovery we will be able to produce more oil as the demand increase while we have a shortage in the supply. To get last drop of hydrocarbon from a reservoir, tertiary recovery is used. There are many techniques that are used in tertiary recovery and are collectively labelled as “Enhanced Oil Recovery”. Using Enhanced Oil Recovery the production can be increased up to 60%. Enhanced oil recovery is most demanding technique now a days because it is used to recover the Residual oil which cannot be recovered by primary as well as secondary recovery. Enhanced Oil Recovery includes:
1. Thermal Injection
2. Chemical Injection
3. Gas Injection

One thing should be kept in mind that water injection is not included in Enhanced Oil Recovery, it is used in secondary recovery. These three techniques are discussed as below:
1.Thermal Injection
In this technique, steam is injected in well to lower the viscosity. This steam increases the movement of hydrocarbons towards the reservoir. Steam flooding or fire flooding may be used. In steam flooding the steam condenses to hot water, in the steam zone the oil evaporates and in the hot water zone the oil expands. As a result, the oil expands the viscosity drops and the permeability increases. In fire flooding the gases with the oxygen is pumped down and it generate fire. This fire eventually decreases viscosity of oil and hence production is carried out.
2. Chemical Injection
The chemical injection refers to those processes in which different chemicals are added to the fluids in order to stimulate the mobility between both the displacing and displaced fluid. These are water based EOR methods. Chemical flooding processes can be divided into three main categories:
a. Polymer flooding
b. Surfactant flooding

The most common polymer used are:

  • Partially Hydrolyzed Polyacrylamide (HPAM) or ionic
  • Sodium polyacrylate (SPA)
  • Polystyrene sulfonate
  • Carboxy methyl cellulose
  • Xanthan Gum (corn sugar gum)
  • Guar Gum or detergent -like surfactants are used to help lower the surface tension that often prevents oil
    droplets from moving through a reservoir. The surfactants used are:
  • Carboxylates such as Potassium oleate, Sodium laurate, Potassium stearate, Potassium
    caprolate
  • Alkali metal Alkylbenzene sulfonates such as Sodium nonylbenzene sulfonate and Potassium dodecylbenzene sulfonate
  • Salts of resin acids such as Abietic acid and Dihydroabietic acid.

3. Gas Injection
The concept of injecting gases into reservoirs to improve oil recovery is an old theory. The simple working mechanism is that gases are injected in the productive zone which decrease the viscosity of oil and increase the flow. The gases used are:

  • Carbon Dioxide (CO2)
  • Nitrogen (N2)
  • Air Water Alternating Gas (WAG) injection is an EOR process that was developed to mitigate the technical and economic disadvantages of gas injection. It is the most widely applied and most successful traditional EOR process.
    It involves the injection of slugs of water alternately with gas although sometimes the two fluids are injected simultaneously.

Which EOR is Best:

When we talk about that which EOR is technique is the best one, then CO2 injection gets the number one keeping in view of previous production record of all methods used in EOR. Carbon dioxide injection accounts for nearly 60 percent of EOR production in the United States. Thermal injection accounts for 40 percent of EOR production in the United States. Chemical injection accounts for about one percent of EOR production in the United States. When we talk about the cost effectiveness of techniques mentioned above, then CO2 injection is the best method because CO2 is:

  • Naturally occurring gas
  • Can be used as a bi-product from some industry

On the other hand, if we use Thermal Injection then we have to install a separate plant for the steam injection while using Chemical Flooding we have to prepare or buy costly chemical which ultimately increase the cost of recovery which is not an appreciable process. So leeping in view of all these aspects, we have a conclusion that CO2 injection is the best EOR Technique.

References:
http://energy.gov/fe/science-innovation/oil-gas-research/enhanced-oil-recovery
http://www.rigzone.com/training/insight.asp?insight_id=313&c_id=4
http://www.ijastnet.com/journals/Vol_1_No_5_September_2011/18.pdf

About author

Ahmed Bilal

I'm a Third year student of Petroleum & Gas Engineering at University of Engineering & Technology, Lahore Pakistan. I am high-spirited, devoted and an exuberant person. I am an idealist in dreaming and a realist in acting, who aspires to work in a pragmatic and cooperative environment. Equally inspired to volunteer my talent for the cause I believe in.

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