Dry and wet combustion tests were conducted using three different crude oilshaving 10.3, 12.4 and 28.4 API gravities. Experiments were carried out in athin-walled vertical tube having 12.4 cm diameter and 124.5 cm length, whichwas packed with crushed limestone milled with oil and water. Adiabatic controlof the combustion tube was achieved during dry and wet combustion tests usingexternal heaters and adiabatic control system. Throughout the experiments, temperature distribution, air and water injection pressures and rates, producedgas compositions and rate, oil and water productions were recorded. In theexperiments average air flux was 23.0 m3(sk)/m3-h andinjected WAR changed between 0.209 m3/Mm3(st) to 0.607m3/Mm3(st).
The average combustion front temperatures were not significantly affected bythe injected water-air ratios for the experiments conducted. The atomic H/Cratio of the fuel decreased as the combustion peak temperatures increased.Under the adiabatic conditions of experiments, stabilized combustion frontvelocity increased due to injected WAR. The air requirement and fuelconsumption showed a decrease with decrease in API º gravities of crude oils.The higher recoveries were obtained in wet combustion tests.
In situ combustion is an enhanced recovery method which has been mostlysuitable for medium to heavy crude oil reservoirs. In this technique a burningfront supported by air injection is created and subsequently propagated througha reservoir. The burning front travels in the same direction as the injectedair (forward combustion) or counter to the direction of air injection (reversecombustion). The high cost of air compression for dry forward combustion is oneof the major factors that influences the economics. Most of the heat generatedis wasted due to heat losses to the overburden and underburden, and also heatis left unused in the burned out region of the reservoir.
Wet forward combustion is a recovery technique which was conceived to improvethe economics of dry forward combustion. Water is injected along with the airin this process to recover some of the heat remaining behind the combustionzone. The air requirement is also lower with water injection because the amountof fuel, deposited on the sand grains is less and because all of this fuel isnot necessarily consumed.
Several dry and wet forward combustion tube tests have been carried out in thelaboratory by a number of investigators(1–10) in order to understandthe echanisms of dry and wet combustion processes and to determine the processvariables which are necessary or successful propagation of the combustionfront. But studies describing the wet and dry forward combustion processes inlimestones and the parameters influencing these processes are very limited.Most of the oil fields in Turkey are limestones that contain heavy oils.
From this point of view, the objective of this study was to investigate theperformance of dry and wet forward combustion in limestone models saturatedwith crude oils from Turkish fields. The following variables were used toanalyze the process, temperature profile along the combustion tube, condensation, vaporization and combustion front: velocities, produced gascomposition, atomic H/C ratio, fuel consumption race, air requirement, oilrecovery and burning front thickness.