Influence mechanism and optimization of the plugging capacity of temporary plugging zones with different particle sizes based on pore structure

Abstract

Reducing the temporary plugging zone permeability is the key to the success of temporary plugging and diverting fracturing. The pore structure of the plugging zone determines the permeability of the temporary plugging zone. This paper introduces a new method based on micro-computed tomography (micro-CT) to quantitatively characterize the pore structure of temporary plugging zones with different particle size. The permeability of temporary plugging zone was measured, and seepage simulation was carried out based on pore network model (PNM). The particle compound method and formula were proposed to reduce the permeability of the temporary plugging zone. Finally, a permeability prediction model of temporary plugging zone based on pore structure was established. The results show that the porosity and tortuosity of the temporary plugging zone are independent of particle size under natural accumulation, and the pore radius decreases with the decrease in particle size. After compaction, the pore structure of the temporary plugging zone changes more obviously with smaller particle size. The seepage simulation shows that the number of flow channels in the temporary plugging zone formed by 2–3 mm particles is only 23.5% of the 0.6–1 mm flow channels. However, several obviously dominant channels are found in the 2–3 mm particles, resulting in a higher permeability. The 0.6–1 mm particles are used to fill the pores formed by 2–3 mm particles so that the dominant channel is divided into several small flow channels to significantly decrease the permeability of the 2–3 mm particles. When 2–3 mm and 0.6–1 mm particles are mixed according to the established particle size recombination formula, the pore radius and permeability of the temporary plugging zone decreased by 42.3% and 53.2% compared with 2–3 mm particles. The permeability prediction model can predict the permeability of temporary plugging zone well, and the average error is 9.145%. The sample preparation methods, pore structure testing and permeability prediction model were established in this work, providing a new method for the selection and design of temporary plugging agents.