Chemically assisted ignition technologies for in situ combustion were investigated and developed to achive the following objectives:
to avoid high temperatures in the injection wells; and
to increase the effectiveness of ignition in heterogeneous reservoirs.
Several experiments were performed to examine the relative effects of catalysers and initiators and to find the optimal mixture and concentrations of additives at variable initial temperatures, pressures and air injection rates.
For more homogeneous reservoirs was found the solution in the injection of two slug following each other without heating of the oil bearing layer start temperature of high velocity oxidation in this mixture was 30 ° C. For heterogeneous reservoirs a single slug mixture, combined with low heating rate was investigated. The combined ignition technology was studied in radial model of the near-wellbore region which was packed with two layers of different permeability (with variable permeability ratio).The test stated that a stable burning front could be formed at all permeability ratios.
Several technologies are used at forming of combustion front at in situ combustion processes. The overall methods are the heat injection into near-wellbore region by electrically heated air or hot gases generated by gas-burner, or with increase of layer temperature by steam injection. Other way of ignition IS a totally chemical reaction based on: the spontaneous ignition. All of these methods have several advantages and disadvantages. At the electric ignition the greatest problems are the power-losses In the cable, stresses at the high temperature heating or long-time process If the used temperatures in the well are lower. But this technology is more regulable than the ignition with gas burner where there is no possibility to avoid the work over jobs and pressure problems. The spontaneous ignition is totally unregulable, for the steaming necessary to use special equipment and its use in light oil reservoirs is not recommended.
The main aim of the chemical or chemically assisted ignition technologies is to decrease the temperature and damages of the well and increase the start temperature, as well as the velocity of oxidation reactions and initial heat generation rate in the near-wellbore region.
For examination of the ignition generally there are used micro reactors to determine the kinetical parameters of oil combustion (by use of Arrheneus equation) and measurement of thermo physical properties of the reservoir rock. On the basis of these data it is possible to calculate the ignition time and heat-Injection demand.
If we wish to change the time, temperature or kinetics of ignition, it is necessary to use some paralel methods of Investigation.
These methods are following:
Thermoanalytical methods (OTA, OSC measurement) for the screening tests.
Static and dynamic microreactors and adiabatic tube reactors for the measurement and evaluation of kinetical parameters.
Modelling system which is in conformity with planned technologies to be applied at field application.
Laboratory examinations of chemical or chemically affected ignition are going on in three steps:
