continue - Factors common to all EOR methods

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Factors Common To All EOR Methods


The Arrangement of injection and production well location:

—The relative location of injection & production wells depends on the geology of reservoir, its type & the volume of HC bearing rock required to be swept in a time limited by economics.

—It is advantageous, where possible, to make use of any favorable influence of gravity e.g. in inclined reservoirs, reservoirs with gas-cap or with an underlying aquifer.

 Types Of Injection well location:

A) Central & Peripheral flooding, in which the injectors are grouped together. This type of injection occurs in the following cases:

1) Reservoir with gas cap in which gas injection is taking place. If the reservoir is a fairly regular anticlinal structure, the injection wells are normally grouped together in a cluster around top of the anticline.

2) Anticlinal reservoir with an underlying aquifer in which water injection is taking place. In this case the injectors will form a ring around the reservoir.

3) Monoclinal reservoir  with gas-cap or aquifer  undergoing gas or water injection. The injectors are grouped in one or more lines located towards the base of the reservoir in the case of water injection, towards the top in the case of gas injection.

B) Pattern flooding, in which injectors are distributed amongst the production wells. It is principally employed in reservoirs having a small dip and a large surface area. In order to ensure a uniform sweep, the injection wells are distributed amongst the production wells. This is done either by converting existing production wells into injectors or by drilling infill injection wells. The most common patterns are the following:

       1) Direct Line Drive  2) Staggered Line Drive                   3) Five Spot                4) Seven Spot

      5) Nine Spot

—Direct Line Drive: The lines of injection & production wells are directly opposed. The system is characterized by two parameters:

    a = spacing between wells of same type

    d = spacing between lines of injection & production wells

—Staggered Line Drive: The wells are in lines as before, the injectors & producers being no longer directly opposed but laterally displaced.

—Five Spot: In this pattern each injection well is located at the centre of a square defined by four production wells.

 

—Seven Spot: The injection wells are located at the corners of a hexagon with a production well at the centre.

—Nine Spot: The pattern is similar to that of five spot, but with an extra injection well drilled at the middle of each side of the square.

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Subject:      Enhanced Oil Recovery

Topic:      Factors Common To All EOR Methods

OUTLINES

 

 

—Introduction.

—Factors on which efficiency of an EOR method depends.

—Reservoir characteristics.

—Fluid Characteristics.

—Types of injection well location.

 

 

INTRODUCTION

 

—Enhanced oil recovery is the recovery of residual oil that is done by injecting various materials into the reservoir, which lacks internal energy, sufficient enough to produce naturally at economical rates.

—The efficiency of an EOR method is a measure of its ability to provide greater Hydrocarbon recovery than by natural depletion, at an economically attractive rate

Efficiency Of An EOR Method Depends On:

 

 

—The reservoir characteristics.

—The nature of displacing and displaced fluids.

—The arrangement of injection and production wells.

Following are some of the most important    characteristics of reservoir:

—Average Depth.

—

—Structure, in particular the dip of the bed.

—

—Degree of homogeneity.

—Petrophysical Properties (porosity, permeability, wettability, capillary pressure etc).

Average Depth

—Reservoir depth has an important influence on both the technical and economical aspects of an EOR project.

—Technically, a shallow reservoir puts a restraint on the injection pressure that can be used, since this must be less than the fracture pressure.

—Economically, the cost of an EOR project is directly related to depth.

 

Dip

 

 

—Hydrocarbon recovery from a porous medium is greater when gravity plays a part than when it does not.

—NOTE: Gravitational forces are only truly effective in reservoirs having high permeability or in which the dip is unusually high.

 

 Homogeneity

—In order to have high HC recovery, there should be no impediment (restriction) to fluid flow within reservoir.

—Possible impediments may be of tectonic                 (e.g. isolating faults) or stratigraphic nature.

—In faulted and fissured reservoirs, and those with high permeability streaks, channelling allows the displacing fluid to bypass some of the oil in place and leads to low recovery.

 

Petro physical Properties

—Porosity: Higher the porosity and higher the residual oil saturation after natural recovery phase, more attractive  an EOR project becomes.

—Permeability: High permeability is encouraging for an EOR project. However, higher the permeability greater is the chance that the natural recovery will be so high that any EOR project would be uneconomic.

 

The influence of fluid charateristics:

—The principal fluid property to be taken into account when designing an EOR project is  the viscosity.

—If the fluids are highly viscous the displacement velocities will be low, since the applied pressure gradients are limited.

—Oil production will be at such a low rate that it will not be economically attractive.

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