IN SITU COMBUSTION

Combustion in the reservoir is to burn some oil in-situ «in order to generate heat to produce the remaining oil. In principle, there are 2 types of combustion processes in the locality. One type is called conventional combustion or «forward» because the combustion zone moves in the direction of fluid flow while the second type called Combustion in reverse or «contra-flow» combustion zone moves in the opposite direction to fluid flow. The conventional process is the most common.

Conventional combustion
The basic idea is conventional combustion:

a) Injecting air through certain wells in order to create a high relative permeability to air.
b) Light crude oil in the injection wells.
c) To propagate the combustion front through the reservoir by continuous air injection in order to heat and move fluids in front of her.

Oil is produced by a variety of mechanisms including evaporation, condensation, solution gas drive, miscible displacement, emouje steam, thermal cracking, etc.. The temperature in the combustion zone around the injection well is 700 ° F to 1200 ° F. The later area is characterized by evaporation and cracking of oil is still below the condensation zone, then the water bank, the bank’s oil and finally the wilderness to the producing wells.

The conventional combustion process is ideal in the sense that a fraction undesirable oil is consumed as fuel in the form of «coke» and that the heat generated is used as efficiently as possible. The amount of oil consumed is around 15% but varies depending on the type of oil and air injection rate. It is called the fuel content and is expressed in lbs / lb of rock or rock lb/ft3.

Conventional combustion is applicable to crude oil deposits in the range of 10 ° to 40 ° API and the recovery varies between 60% and 90% of oil in the reservoir at the time of starting the process depending on the type of arrangement, oil properties and oil in situ.

Combustion reserso
It differs from conventional in the fact that the combustion front comes from wells products and spreads to the injectors. In this process, vaporized oil, water and combustion products move in a reservoir that has been heated. Then, because the sand is hot, insert fluid saturation is eliminated in this part of the site which means that there is no upper limit on the viscosity of oil.

Combustion in reverse can be used in fields where the conventional process is impossible to implement due to the high viscosity oil which is why it is recommended for heavy crude oil deposits and oil sands. It is applicable in the range of 5 ° API to 15 ° API and the recovery can reach up to 50% -65% of oil in situ at the time of starting the process.

An important feature of the combustion process in reverse is the improvement of oil in place and you can get 25 ° API oil and 15 cp viscosity of a yacmiento containing 8 ° API and viscosity 10 cp.

Compared with conventional combustion, combustion in reverse is less attractive due to lower recoveries, increased fuel consumption, increased heat loss and equipment problems more severe. However, it has a wider range of applicability and is probably one of the very few methods methods for oil sands.

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