High-Temperature Thermal Techniques for Stimulating Oil Recovery

Abstract

Abstract Artificial ignition methods that were developed primarilyto ignite in-situ combustion projects are now used to initiatehigh-temperature thermal stimulation treatments onproduction and injection wells. Where well productivity islimited due to the viscous nature of the crude oil at reservoirconditions, the application of high-temperature treatmentsusually increases oil production rates. A secondarybut often highly beneficial effects is attributed to the removalof certain immobile hydrocarbon materials thatsometimes plug the wellbore, greatly restricting the oilproduction rate. Consolidated formations are oftenshattered by the high-temperature process, or else theirpermanent increase in oil production rates. Similarly, water-injection rates can be increased substantially and thehigh-temperature process is particularly applicable wherelow-permeability formations are to be water flooded. Electricalheaters or down-hole gas burners are used to elevatewellbore temperatures. The equipment and procedures forinitiating the high-temperature thermal treatments are discussed. Introduction The use of thermal energy to correct or improve wellperformance is becoming more important as wider usageof thermal processes results in the discovery of newapplications to related problems. The first widespread use ofthermal methods was in low-temperature production wellstimulations using bottom-hole heaters. While economicallysuccessful where properly applied, this technique waslimited, in that there was no appreciable temperature effecton the reservoir or its fluids at a distance greater thanabout 1 ft from the wellbore. Field application of the in situ combustion processresulted in the development of high-temperature ignitionequipment and techniques. Most ignition methods usegas-fired or electrical down-hole heaters to ignite the oilformation. With these new high-temperature ignition toolsavailable, it soon became evident that many beneficialresults could be obtained by treating a wellbore withtemperatures in the 900 to 1,200F range. Data obtained fromigniting a producing well and moving the burning front ashort distance into the formation indicated oil productionstimulations in excess of that which could be predictedfrom viscosity reduction alone. Investigation led to theconclusion that the high-temperature treatment resulted inphysical changes in the mineral matrix that increased thepermeability or flow capacity of the reservoir rock. Fieldexperimentation to evaluate this phenomenon with injectionwells in waterflood operations furnished proof of thischange in rock properties. This also led to the conclusionthat waterflood recoveries could be accelerated andpossibly improved by proper application of this process towaterflood injection wells. Mechanism of Thermal Stimulation The mechanism of in situ combustion has beendiscussed in detail in the literature. The temperaturedistribution associated with the in situ combustion process, however, is important in thermal stimulation work, andmodifications of the temperature distribution in the vicinity ofthe wellbore are discussed below. JPT P. 1007ˆ