Study of microscopic imbibition and formation plugging mechanism of the compact oil reservoir based on SEM and NMR analysis

Unconventional reservoirs, such as compact reservoirs, have been extensively developed. The Changqing Oilfield is currently the largest compact reservoir oilfield in China. An effective method for developing compact reservoirs using hydraulic fracturing for reservoir modification is required. Some wells exhibited small production increases after fracturing, and some showed reductions in production. The impact mechanism of the fracturing fluid on the reservoir remains unclear. We used nuclear magnetic resonance (NMR) analysis and scanning electron microscopy (SEM) to investigate the utilization of a nano-micropore fluid and the surface morphology of the matrix during imbibition after fracturing. The results indicated polymer adhesion on the rock wall after the imbibition. The capillary force and the soaking pressure were the dominant driving forces during the imbibition. The capillary force was dominant in the small pores, and the soaking pressure had a larger influence on the fluid utilization of the large pores. The medium pores exhibited more significant solid phase damage, and the fluid utilization degree was relatively low. This study clarifies the impact mechanism of the fracturing fluid on the reservoir and the imbibition mechanism of slickwater. The results provide theoretical support and a scientific basis for optimizing fracturing, flowback methods, and post-fracturing stimulation in compact reservoirs.