In-situ combustion (ISC) has been investigated worldwide as a potential EOR process both for heavy oil and conventional oil, and there are some successful field applications such as industrial test in Suplacu and many tests in deep reservoir with low permeability. Most of heavy oil reservoirs recovered by In-situ combustion are known for favor reservoir properties such as limited layers (single layer is best) and appropriate heavy oil viscosity (usually hundreds to thousands of mPa•s). Obviously, it is challenging to recover multilayered heavy oil reservoirs by in-situ combustion method in consideration of heterogeneity between layers. For instance, Du 66 reservoir is a typical multilayered heavy oil reservoir in Liaohe Oilfield, it was not effectively recovered by cyclic steam stimulation (CSS in short) before 2005, and both oil production and OSR were unsatisfactory. There are no alternative but to test in-situ combustion for the purpose of improve oil recovery for such multilayered heavy oil reservoir. As a result, there are up to 91 well groups operated in inverted nine-spot pattern fireflood combined with CCS for production wells in past 10 years.
In this work, feasibility analysis and engineering design of in-situ combustion for multilayered D66 reservoir are primarily investigated based on reservoir engineering study and numerical simulation. Furthermore, recovery performance such as air injection profile and gas production and channeling are discussed based on field measurement and performance. Particularly, principles and treatment of gas channeling and casing collapse are discussed. Additionally, both experience and lessons are presented based on statistical results and typical cases.
The results show that considerable increase in oil production and improvement in ratio of oil production to steam injection (OSR in short) are observed at lower ratio of air injection to oil production (AOR in short). However, gas channeling occurs in some production wells in form of rapid increase in AOR, and it has significant effect on production performance. At the same time, casing collapse are found in many air injection wells, according remedial well treatment had to be carried out considering risk of high temperature, backfire and even explosion, and casing collapse has a much greater impact on injection performance and oil recovery. Therefore, investigation on gas channeling and profile control treatment of air injection wells were extensively carried out to eliminate gas channeling and casing collapse.
In summary, the principles and engineering design of in-combustion in multilayered heavy oil reservoir are much more complex than single layer reservoir. Gas channeling and casing collapse are two extremely difficult problems in such combustion process, which could be eliminated or weakened based on rational engineering design and effective technologies.