Cyclic Steam Stimulation has already been proved as an important thermal recovery technology in the development of heavy oil reservoirs, which accounts for more than 60% percent of the annual heavy oil production in China. While with the increase of stimulation cycles, the cyclic production performance becomes poor because of the reservoir heterogeneity, high insitu oil viscosity and formation rhythms, which result in steam channeling along high permeability zones, limited heated radius and steam overriding.

Many previous researches[1-5] have proved that nitrogen foam assisted steam injection can increase the sweep efficiency, supply formation energy and control steam mobility, and thus increase oil recovery of cyclic steam injection. However, research on the screening of optimum foam for a particular reservoir is important to enhance the field production performance. This paper is to present a detailed process of the planning, implementation, and evaluation of a field trial of N2-foam assisted cyclic steam stimulation at the Fuyv heavy oil reservoir in Daqing oilfield.

At present, Fuyv heavy oil reservoir has experienced 6-7 cycles of CSS in average. Because of the high oil viscosity (viso. @ reservoir: 3200mPa.s), thick oil formation (avg.: 40m) and high heterogeneity (permeability range: 61.5 to 3650 mD), the injected steam advances suddenly along high permeability positions, resulting in serious channeling and low oil recovery factor. Therefore, in view of the geologic characteristics and fluid properties, 4 sets of N2-foam system are screened by static tests of foam adaptability to temperature, salinity, and different oil samples, and then operating parameters including foam concentration, injection rate and injection pattern are optimized by numerical simulation based on the detailed geologic modeling and history match for the target area. According to the operation strategy of N2-foam assisted cyclic steam stimulation acquired by evaluation experiments and numerical simulation, the N2-foam assisted cyclic steam stimulation are conducted in two wells successively and the pilot injection has foreseeable results in enhancing oil recovery factor.

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