Horizontal well fracturing for the shallow metamorphic rock reservoir in Jilantai

The buried hill metamorphic rock reservoir of the Jilantai oilfield features shallow burial (400−650 m), high heterogeneity, and the development of high-angle natural fractures and the bottom water system. The fracturing reservoir stimulation suffers from high difficulties in cracking strata, proneness to connection with the bottom water, and blindness for sweet spots. The analysis of the characteristics of the metamorphic rock reservoir combined with the gained fracturing experience showed that the optimal height of water avoidance for water production control is 100−120 m. The bridge plug-perforating integrated technology with the 25 ℃ low-temperature soluble bridge plug was applied to facilitate high-pump-rate large-scale multi-stage fracturing. The perforating azimuth was optimized to avoid perforating the upper 120° range and lower sand production risks. The water-soluble temporary plugging agent was adopted for inter-layer/intra-layer temporary plugging, which led to a pressure rise of 5−8 MPa. The geological-engineering dual sweet spots were identified via long-distance sonic imaging, and the reservoir stimulation model featuring fewer stages and more clusters was formed. The presented fracturing technology was applied to 13 wells of the buried hill metamorphic rock reservoir in the Jihua-1 block, including 74 fracturing stages and 361 perforation clusters. Compared with the testing wells in early 2020, these wells presented the average fracturing stage reduction by 2 stages/well and the growth of initial post-fracturing daily oil production by 48%. By the end of June 2022, the cumulative liquid production exceeded 26600 tons and the cumulative oil production surpassed 24500 tons, which represents high-efficiency reservoir stimulation and recovery of the shallow metamorphic rock reservoir.