Enhanced Oil-Recovery Techniques-State-Of-The-Art Review
Authors: Gangoli Narendra , Thodos George 
Published: March 2010

Abstract
A comprehensive review of the different oil-recovery schemes is presented. These sehemes are concerned with secondary and tertiary stages of crude oil recovery and deal with the basic techniques involving the use of solvent gas drive, alkaline, polymer, surfactant and foam drives. In addition, thermal methods suck as forward and reverse combustion schemes are discussed in addition to the soluble oil micellar method of recovery. The pros and cons and mechanisms of these schemes are presented.

Introduction
THE CURRENT ENERGY CRISIS has been precipitated by the limited availability of oil reserves and the accelerating demand of products such as natural gas, liquefied petroleum gases, gasoline and heavier constituents that find outlets as diesel fuel, lubricating oils, waxes and others. The ever increasing demand for petrochemicals makes the availability of crude oil more critical to the maintenance of the balance between demand and supply. The problems brought into sharp focus by this crisis have been so acute that they have caused a major shift in the general 'outlook and a careful evaluation of the energy picture as a whole, A rational, approach has suggested a multi-pronged strategy for seeking a satisfactory solution involving:improvement of current methods used for oil recovery and the adaptation of novel and effective methods;prospecting for new reserves and, in particular, off-Shore reserves;development of alternate sources of energy, such as coal, solar, geothermal and nuclear.
The major efforts currently being initiated for enhanced oil recovery stem from the fact that onlyabout one-third of the oil available has been produced, leaving the remaining two-thirds still left behind in the rock formation. Recovery processes which in the past were considered to be uneconomical are now being reactivated in an effort to obtain improved recovery of crude oil. This review attempts to bring forth the various aspects associated with the available recovery schemes deployed for the commercial production of crude oil.
Petroleum crude generally can be found, in rock formations located at depths to 20,000 feet below the surface of the earth, This crude may be a thin fluid or a heavy viscous fluid containing asphaltenes, waxes and sulphur compounds, and is usually trapped in porous media ranging in porosity from 5 to 35 per cent. These rocks have a highly variable composition and comprise sands, sandstones; limestones, dolomites and clay minerals. The wide range of variation in the composition of the crude oil and rock formations presents a major challenge to the petroleum engineer. A typical oil well may contain brine, oil and gas mixtures in the interstices of the formation at enormous pressures. The brine may be confined in the oil-bearing strata or be separated from the oil zone. Due to gravity effects, the brine lies beneath the oil and gas-bearing strata. The crude oil is trapped within the rock matrix by natural forces resulting from viscosity, surface tension and capillarity. These forces are, for the most part, responsible for the retention of the oil within the pores of the producing formation.