Recovery Methods

Recovery methods are the methods through which an accumulation of hydrocarbons is produced depending on the behavior of the specific reservoir. They concern both the production mechanisms of oil and gas provided by the energy that is naturally contained in the accumulation, and the energy forms that are artificially introduced in the field through injection wells. Artificial lift methods (gas lift, BCSS, etc.) are not recovery methods, and neither is well stimulation (ex: hydraulic fracturing and acidizing), because these methods are more dependent on the behavior of production wells than that of the reservoir.

The two mechanisms depend solely on natural energy and are used to extract the fluids from the reservoir.

  • Reservoir depressurization leads to the expansion of fluids present in the reservoir and the contraction of the pores. The effect is similar to the deflation of a party balloon, in which air leaving the balloon causes a pressure reduction, leading to both the expansion of the confined air and the retraction of the balloon’s pellicle, contributing to the additional expulsion of air and to refueling the depressurization process until the expulsive energies run out. The gas in the Manati field is produced through depressurization.
  • In the displacement of one fluid by another, as with accumulations of hydrocarbons connected to an aquifer, fluid production stimulates the invasion of water in the hydrocarbon zone, expelling it. The two aforementioned mechanisms are responsible for the production of the Atlanta field. Another example of fluid displacement through natural energy occurs in oil reservoirs with gas caps, in which gas expansion through the depressurization effect is far bigger than that of the oil, helping to expel it towards the producing wells.

The primary recovery method refers to the quantity of hydrocarbons recovered exclusively through natural energy contained in the reservoir (primary energy). However, it is usually associated with low recovery factors, which can be as low as 5% for heavy oils and 10% for light oils, depending on the conditions and properties of the fluids and the characteristics of the reservoir.

In order to increase the recovery factor and/or anticipate fluid production, the secondary and tertiary methods artificially inject energy into the reservoir, supplementing the lost energy and improving the efficiency of oil displacement. Artificial recovery methods are applied in oil fields. Gas fields, in general, are developed exclusively through primary recovery.

Secondary recovery methods re-pressurize the field and displace the oil throughout the reservoir through the artificial introduction of fluids. Water is the most commonly used fluid, but gas can also be used. These methods have the potential to duplicate the recovery factor of the Field.  

Tertiary recovery methods enable a larger oil production than the previous methods, because, in addition to the mechanisms of re-pressurization and displacement of the oil throughout the reservoir, they seek to alter the properties of the fluids and the interaction between them and the rock, reducing the resistance of the oil flow in the porous medium. These methods can be chemical, thermic, miscible or microbiologic, and are always activated through fluid injection throughout a well. Examples include: polymer, surfactant, foam, vapor, hot water, carbon dioxide, nitrogen, and microorganism injections. The tertiary recovery methods that are used the most and that have field scale and commercial viability are: vapor and carbon dioxide injection. The offshore applications of tertiary methods, however, are very restricted.

Recovery methods can be superimposed, as in the use of water injection from the start of a field’s productive life. The application of a tertiary method that is non-concurrent with the secondary method can occur, for example, in extra-heavy oil fields, which are only viable through vapor injection. Secondary recovery methods are also known as “conventional secondary recovery methods”, while tertiary methods are known as “special secondary recovery methods”, “special recovery methods” or “advanced recovery methods” (“Enhanced Oil Recovery”, EOR). 

Last updated on 2015-04-29T18:32:28

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