| Summary: | To understand the reason why the initial injection pressure is high and the normal injection pressure increases rapidly in the Chang 8 layer, this paper analyzes the mineral composition, clay mineral type and content, pore structure, formation sensitivity, wettability, water chemistry, and injection water quality of the reservoirs as well as core injection experiment. The high initial injection pressure results from tight reservoirs, fine pores and middle-oil wetting; core injecting water experiment reveals that middle degree water sensitivity and the scale of BaSO4 and CaCO3 caused by the blending of formation water and injected water are the main reasons for the formation damage and the rapid pressure increase. The analysis of influences of different injection procedures on the water-injecting pressure shows that he perforation-hydraulic fracturing procedure is the most useful technique to keep pressure constant, and the treating diameter in anti-swallowing and plug removing should reach to 4 meters. Recovery waste water reinjection is advantageous to maintain the water-injection pressure stability. Key words: Xifeng oilfield, injection pressure, water injection volume, water sensitivity damage, formation scale, water injection measures, perforation-hydraulic fracturing process
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