A preliminary feasibility analysis of in situ combustion in a deep fractured-cave carbonate heavy oil reservoir

As an effective thermal-enhanced oil recovery technique, in-situ combustion (ISC) can achieve large oil displacement efficiency and upgrade the heavy oil technically, but there are still various barriers for ISC application in naturally fractured carbonate heavy reservoirs. In addition, the potential risk of wellbore plugging and formation collapse, caused by the possibility of carbonate rock decomposition at high temperatures, furtherly hinders the application of ISC technique and focuses more attention on feasibility evaluation. Hence, this paper attempted to estimate the preliminary feasible application of ISC in Tahe oilfield, characterized with fractured-cave carbonate heavy reservoir. From macro and micro aspects, results indicated that owing to large microscopic surface area and high oxygen contact ability between the deposited coke and oxygen, the oxidized ultra-heavy oil, under adiabatic condition, in simulative fractured-cave carbonate oil reservoir was successfully ignited and maintained the combustion process with the combustion front temperature. Besides, a large amount of heat generation from the combustion front can activate the ultra-heavy oil with better mobility ability. Additionally, in this process, the decomposition process of Tahe carbonate rock was not triggered ( similar to 631.6 degrees C) where the decomposition risk of running in-situ combustion process in Tahe carbonate reservoir can be neglected. Preliminarily, it implied that ISC is a feasible technique to upgrade the ultra-heavy oil for Tahe oilfield.