Objective  To address the problems of poor clay anti-swelling performance and low imbibition oil displacement efficiency of the existing fracturing fluid systems applied in the shale oil reservoirs of Jiyang Depression, this study focused on optimizing the fracturing fluid formula to mitigate clay mineral swelling damage and enhance fracturing oil displacement as well as production recovery effects. The ultimate goal was to develop a low-cost functional fracturing fluid system adapted to the shale oil reservoirs in Jiyang Depression.

Method Based on the investigation of reservoir rock physical properties, high-efficiency imbibition agents and anti-swelling additives for fracturing fluids were screened and optimized. These additives were integrated with the oilfield’s existing high-temperature-resistant fracturing fluid base agent, thus formulating a functional fracturing fluid system that simultaneously exhibits high-temperature resistance, clay anti-swelling capability, and imbibition oil displacement performance, tailored for the shale oil reservoirs of Shengli Oilfield. Field application of this developed system was successfully implemented.

Result After shearing at 200 ℃ and a shear rate of 100 s⁻¹ for 120 min, the viscosity of the fracturing fluid system remained at 56 mPa·s. The imbibition displacement efficiency of the broken gel fluid on rock cores was 2.32 times higher than that in pure water. The maximum anti-swelling rate reached 88.6%, and the core damage rate was less than 25%. Field tests of this functional fracturing fluid system were conducted across 37 intervals in Shengli shale oil reservoirs. During the 6-month production period after fracturing, the average daily oil production was 71.4 t, a 16.29% increase over adjacent wells; the average daily gas production was 12 530.9 m³, an 18.64% increase relative to adjacent wells, indicating favorable stimulation effects.

Conclusion The research findings can provide a theoretical basis and technical support for further improving the imb.