Horizontal Well Volumetric Fracturing Technology Integrating Fracturing, Energy Enhancement, and Imbibition for Shale Oil in Qingcheng Oilfield

Shale oil reservoirs in Qingcheng Oilfield have distinct characteristics of low pressure and low brittleness index, which significantly hinder the establishment of an efficient displacement seepage system after volumetric fracturing. In light of this, a volumetric fracturing technology was developed integrating fracturing, energy enhancement, and imbibition. A new method for refined and detailed classification of shale oil reservoirs was formulated. Then, stimulation strategies for different reservoir types were optimized with field big data obtained from tests on long-term fluid production profiles. Finally, the key parameters of the volumetric fracturing technology integrating fracturing, energy enhancement, and imbibition were optimized through the numerical simulation of oil reservoirs. The research results showed that type Ⅰ and type Ⅱ reservoirs, making up 83.6% of the stimulated sections and 95.5% of the total production, were the main contributions to productivity. In contrast, the productivity contribution of type Ⅲ reservoirs accounted for only 4.5% of the total production. Therefore, stimulation treatment priority should be given to type Ⅰ and type Ⅱ reservoirs while only some selective sections of type Ⅲ reservoirs should be stimulated. The optimal intervals of fluid injection intensity for type I and type II reservoirs are 20–25 m³/m and 15–20 m³/m respectively, with synchronous energy enhancement. The volumetric fracturing technology was applied to more than 200 horizontal shale oil wells in Qingcheng Oilfield. The initial single-well production was increased from 9.6 t/d to 18.0 t/d, the single-well annual cumulative oil production was enhanced from 2 380 t to 5256 t, and the single-well estimated ultimate recovery (EUR) was improved from 1.8×10⁴ t to 2.6×10⁴ t. This technology has provided a technical reference for the efficient development of similar unconventional shale oil reservoirs.