Stability of In-Situ-Combustion Process to Stoppage of Air Injection

Abstract

Summary Unlike steam injection for heavy-oil recovery, the in-situ-combustion (ISC)process requires an extra step--namely, the initiation of the process, theso-called ignition operation. During ignition, an ISC front is generated nearthe air-injection well and, thereafter, this front is propagated towardproduction wells. Air-injection interruptions can be unintentional orintentional, including scheduled interruptions for 1 day per month for cleaningoil from air lines exiting the compressors. Regarding air-injectioninterruptions, one question arises: Can the process be resumed withoutinitiating a new ignition operation? This paper attempts to provide answers tothis question. The paper reviews information on 10 cases of air-injectionstoppage in the field, involving well-instrumented dry ISC projects, conductedeither in patterns or in a line-drive system. Most of the cases are from theSuplacu de Barcau (Romania) project, which is the world's largest ISCcommercial project. The duration of air-injection interruptions ranged from afew hours to 42 days. Performance before and after interruptions is analyzed interms of changes in air injectivity, effluent-gas composition, and oilproduction. To support various field observations, essential results fromsimulation of the dry ISC process are also included; temperature distributionsduring air-injection stoppage were determined analytically for a linear systemand numerically for a radial system. In both cases, a specific characteristicof the temperature redistribution was noted: the move/shift of the peaktemperature inside the former burned-out zone. Some additional conclusionsregarding the stability of the process as a function of elapsed time since theinitiation of the process were also formulated. Stability of the process wasinvestigated for air-injection interruptions lasting up to 40 days.