Experimental Investigation on Microscopic Oil-Sweeping Behaviour of Novel Injection-Soaking-Production via Fractures (ISPF) in a Tight Sandstone Oil Reservoir

Abstract In this study, a pragmatic and integrated technique has been developed to experimentally quantify microscopic oil-sweeping behaviour of novel injection-soaking-production via fractures (ISPF) for a multistage fractured horizontal well (MFHW) in a tight sandstone oil reservoir. More specifically, the pore-throat structure together with contact angle were firstly measured by using core samples collected from a tight sandstone oil reservoir. Subsequently, ISPF experiments integrated with the nuclear magnetic resonance (NMR) measurement were carried out to monitor the oil-water distribution and saturation variation within the pores and throats at different stages. By quantitatively characterizing the critical movable throat radius, oil recovery factor, residual oil distribution and saturation variation within pores and throats of different scales, microscopic oil-sweeping behaviour together with its characteristics of pores and throats of different scales at various stages were investigated and analyzed. Compared to traditional displacement methods, the ISPF process can sweep more oil from smaller pores and throats, resulting in a reduction in critical movable throat radius and an increase in oil recovery factor by 8.25%. The oil recovery factor contributed by large pores and throats accounts for 61.41% dominated by displacement, among which 14.72% is contributed via imbibition by small pores and throats. In the first and second cycles, the main characteristics is found to be the rapid oil production from large pores and throats under displacement, while a small proportion of oil produces from small pores and throats due to imbibition. In the third cycle, water breakthrough occurs, and the oil recovery factor of a single cycle contributed by large pores and throats dominated by displacement decreases significantly from 23.83% to 10.45%, but the microscopic oil-sweeping characteristics are still dominated by the production of oil from large pores and throats under displacement. In the fifth and sixth cycles, the main characteristics is the slow production of oil from small pores and throats via imbibition. The findings presented herein serve as a solid foundation for evaluating and optimizing the ISPF processes for an MFHW in a tight sandstone oil reservoir.