Abstract
In this work, we show a case study of using fire flooding process in thin interbeded heavy oil reservoirs to tackle the problems of low oil production rate, low gas oil ratio, and low oil recovery factor in later stage of cyclic steam stimulation (CSS) operations. The fire flooding process was adopted for the Block D reservoir in Liaohe Oilfield, China.
The depth of Block D heavy oil reservoir is 800-1200m. The reservoir includes 30-40 thin layers in vertical direction, with average thickness of 2.2m per layer. Through laboratory experiments, numerical simulation, and analysis of surveillance data from the initial small scale field pilot, we improve the understanding of fire flooding recovery mechanisms in thin interbeded reservoirs. Then, technical limits such as reservoir thickness, number of layers and permeability contrast are established for successfully conducting fire flooding with high temperature oxidation. Reaction types identification methods based on corresponding field surveillance data are also proposed. Using such guideline, we have deployed fire flooding expansions in Block D reservoir with more well patterns.
It has been proven that fire flooding process with the designed well patterns can improve recovery and sweep, and make the wells more productive with enhanced inflow from multiple directions. The process technical limits successfully guides us in properly expanding the project. Reaction type identification method further helps to perform continuous dynamic surveillance of the high/low temperature oxidation burning state of the combustion front in the field. The initial pilot test includes 7 well patterns, which have been operational since 2005. Up to now, we have deployed a total of 105 fire flooding well patterns in Block D reservoir. Within the fire flooding area, the single-well oil production rate has doubled on average, with the reservoir pressure also doubled. For the multi-layered block D reservoir, the ultimate oil recovery factor for fire flooding can reach up to 55%, an increase of 28% from the expected recovery of CSS.
In conclusion, we have shown in this work that fire flooding process can be applied to deep thin to medium thickness interbeded heavy oil reservoirs. As a follow-up process in later stage of cyclic steam stimulation, it can significantly increase oil recovery and process performance.
