The in situ combustion process for the recovery of crude petroleum from underground reservoirs is highly complex. Even on an elemental scale its analysis requires physical simulation of realistic reservoir conditions in order to expose its characteristic, but system-specific, physical and chemical reaction mechanism relationships. In the continuing effort to develop experimental systems for the elemental physical simulation of the combustion process, a new combustion tube system was designed, constructed and successfully tested. The system incorporates a novel combination of: an unconsolidated or consolidated core material use capability; the ability to employ high net external pressures while using a chin wall combustion tube: and the use of a modular design with respect to system components. An experimental program undertaken with the newly developed apparatus included isothermal cracking and low temperature oxidation tests and a series of six normal air in situ combustion tests in the 4 to 8 MPa pressure range using different crude oils and core materials. The study was mechanistic in nature, with the goal being to reveal the effects of specific experimental condition changes on the performance of combustion propagation. In addition to generating data from observed stable combustion processes, (i.e. air and fuel requirements) the experimental program revealed that a lower porosity consolidated Berea sandstone core element required a greater injected air flux to allow process self-sustenance compared to an otherwise equivalent higher porosity unconsolidated Berea material pack.
The forward in situ combustion process is a method for allowing or enhancing the recovery of crude petroleum from subsurface reservoirs. The general process involves the propagation of a heat generating combustion front through a reservoir which can, ideally, displace oil ahead of it very efficiently. Air or oxygen enriched air is injected into the reservoir as an oxidant, with water sometimes also injected to increase the process thermal efficiency. Ignition may be accomplished by various means including the employment of downhole burners, chemical agents or even by spontaneous reaction. The combustion front theoretically propagates by consuming carbon rich fuel formed from the original crude oil by physical and chemical reaction mechanisms determined by the nature of the moving front process itself. Among the process interrelated mechanisms are non-isothermal multiphase flow (of oil, water, gas) and overlapping reaction regimes of high temperature oxidation, thermal cracking, and low temperature oxidation of complex crude oil constituents.
The study of in situ combustion has been undertaken using both theoretical and physical modelling. Numerical simulation is necessary for field scale simulation and has been applied to laboratory experiments(e.g. Belgrave1, Lin et al.2, and Onyekonwu et al.3). All types of valid theoretical modelling must be based on a well defined process which, in the case of in situ combustion, must be revealed by experiments due to its highly system-specific performance. As it stands, the complex nature of the process dictates that the behaviour of mechanisms and related parameters are not, for a given elemental system, predictable with reasonable certainty.
