Flow Mechanism of Fracturing Fluid in Shale Oil Reservoir and Its Influence on Production

In order to clarify the flow mechanism of fracturing fluid and, the influencing laws on production and better guide the efficient fracturing and production of horizontal wells in shale oil reservoirs, the dynamic characteristics of production in three types of typical wells (groups) were analyzed and summarized taking X shale oil reservoir in China as an example. By performing a spontaneous imbibition experiment of fracturing fluid in shale cores with different lithology, the imbibition and propagation law of fracturing fluid was clarified. Combined with numerical simulation of the dual medium of fractures and matrix at the core scale, factors such as the development degree of natural microfractures and inter-well fracturing interference were considered, and the retention and flowback mechanism of the fracturing fluid was revealed, as well as its impact on production. The results demonstrate that the natural microfractures are the primary occurrence space for fracturing fluid in shale oil reservoirs, which also serve as the primary fluid flow path into the matrix. During the flowback process in horizontal wells, the natural microfractures gradually close due to the increased effective stress, causing the fracturing fluid to be locked and retained within them. On one hand, it preserves the formation energy; while on the other hand, it allows the fracturing fluid to continue imbibing into the matrix and displacing the oil. The development extent of natural microfracture is a key factor influencing horizontal well productivity. Wells with more extensive natural microfractures exhibit greater fracturing fluid imbibition, deeper propagation into the matrix, lower stable water cut and fracturing fluid flowback rate during production, and ultimately better productivity. When mature shale oil wells are interfered with by infill drilling, the fracturing fluid, under the pressure difference, enters and occupies the larger pores with lower resistance, blocking the small pores that allow spontaneous imbibition and oil displacement, forming a liquid resistance effect. This disrupts the spontaneous imbibition process, resulting in a reduction in the amount of oil imbibed into the matrix. Meanwhile, the crude oil in the pores of the mature well matrix and the fracturing fluid in the high-conductivity fractures between new and old wells form a flow competition, resulting in a decrease in the utilization degree of crude oil in the pores of the mature well matrix, a sharp decline in oil production, and a significant increase in water cut. The research results can provide theoretical guidance for the efficient development of continental shale oil in China.