Laboratory Studies and Implementation of In-Situ Combustion Initiation Technology for Air Injection Process in the Oil Reservoirs
Authors: Klinchev Valery Andreevich , Zatsepin Vladislav Vyacheslavovich , Ushakova Alexandra Sergeevna , Telyshev Sergey Vladimirovich 
Published: September 2014

Application of air injection as an enhanced oil recovery method involves high risks, both economic and technological. One of the main risks of this technology is the lack of oil self-ignition during air injection and difficulties in creating a combustion front in the reservoir.

In a number of fields the reservoir thermal and pressure conditions and the oil properties cause spontaneous ignition (mainly light oil fields with a high reservoir temperature), while in other fields special ignition programs are required.

In the present paper three possible ways of air injection process development are shown: the method of "pushing" oil with air without combustion front appearance, in-situ combustion (ISC), and thermogas treatment, or, using the American terminology, high pressure air injection (HPAI). The field’s properties that determine which way in-situ combustion process will develop are identified. One way to determine in which of these three ways the process will develop is to study the oxidation characteristics using the pressurised differential scanning calorimetry (PDSC). For the improved study of the combustion process DSC experiments of oil samples oxidation reactivity, oil-saturated core and other actively reactive substances are performed. High precision of modern thermo-analytical PDSC equipment enables investigating the initial stages of oxidation reactions of hydrocarbons and describing the initial stages of the reaction in terms of the Arrhenius theory as well as the theory of chain reactions. This approach allows us to identify the most reactive oil components (oil paraffins), and describe the process of their oxidation in terms of the chain mechanism of birth and death of free radicals. It is shown how oil can change its reaction activity at the reservoir rock samples; the activity among others, is caused by the adsorption of asphaltenes and oxidised components on the core surface during the heating process. In addition, the unsteady type of oil (tarry light oil) has been studied, oxidation of which is accompanied by transition of resins to secondary asphaltenes, which, as it has been first shown, in the presence of core significantly increases the amount of fuel.

In the case when the pressure and temperature conditions of the reservoir and oil reactivity prevent spontaneous ignition, some cases for combustion initiation have been considered. It is shown that due to PDSC experimental results a comparison of hydrocarbon and other fluids in order to find a reagent with the lowest self-ignition temperature can be achieved. It is shown that vegetable oil additions to oil can significantly reduce the temperature of the heat output, and can serve as oil ignition initiators for air injection.

Technical aspects of combustion ignition are also discussed in the paper. The technology integrate heating agent and reactive hydrocarbon liquid injection, which reduces the lack of ignition risks in the oilfields with low temperature.