Experimental study on the interaction mechanism between fracturing fluid and continental shale oil reservoir

Abstract

ABSTRACT Onshore shale oil is difficult to develop due to its special pore structure and low permeability characteristics. Artificial fracturing causes a large amount of fracturing fluid to intrude into the reservoir, resulting in a complex reservoir seepage pattern. Therefore, this paper aims to explore the changes in the reservoir at the macro and micro levels due to the interaction between fracturing fluids and shale oil reservoirs. For this, four rock samples from shale oil reservoirs and two fracturing fluids commonly used in the mine were used. Then, core repulsion, scanning electron microscopy, X-ray diffraction and CT scanning experiments were carried out successively. The following results were derived from our analyses. (1) Permeability of the rock samples was reduced by an average of 24.47% after replacement by fracturing fluid, while the experimental groups with larger fluid-grain sizes and well-developed fracture networks suffered more significant solid-phase damage and fluid-phase trapping. (2) Fracturing fluids have different effects on fractures at different scales; large fractures (>7.71 μm) were widened, while small fractures (<3.47 μm) were shrunk or even plugged. (3) Based on the water-sensitive effect, fracturing fluids can disperse and transport clay minerals, resulting in fluid-phase damage and an average decrease of 14.33% in clay content in the reservoir. (4) Analysis of the digital core model shows that fracturing fluid intrusion and retention can cause solid-phase damage to the reservoir matrix, with 38.14% and 60% damage to the pore and throat channels, respectively. This paper uses a combination of physical experiments and numerical analysis to investigate the interaction mechanism between fracturing fluids and shale oil reservoirs from both microscopic and macroscopic perspectives. Overall, the results of this study provide experimental support for future studies on the seepage characteristics of this type of reservoir and the design of fracturing construction schemes.