Interface properties evolution and imbibition mechanism of gel breaking fluid of clean fracturing fluid

Abstract

Capillary forces are usually considered to be the main driver of imbibition behavior in low-permeability reservoirs. Recent studies show that the presence of mass active substances in the clean fracturcing fluid can reduce the oil–water interfacial tension as well as reduce the hydrophilicity of the pore wall, which would greatly weaken the capillary force driving effect. However, the final oil recovery still increases, suggesting the presence of other effects to promote fluid imbibition. Herein, the evolution law of gel breaking fluid of clean fracturing fluid at oil/water/solid interface is investigated, and the main controlling factors of imbibition behavior are analyzed. Osmotic pressure is proven to be a major imbibition driving force. The change of interface properties due to adsorption of active substances reduces the driving effect of capillary force during the imbibition and intensifies the osmotic pressure of micro-nano pores. For reservoirs rich in mineral content, the contribution of osmotic pressure to imbibition recovery is increasing with time, and even becomes the main driving force in the later stage. In addition, the driving effect of osmotic pressure is positively related to the clay minerals and salinity of reservoir. When the clay mineral content is 18.6%, the contribution of osmotic pressure to ultimate imbibition recovery can reach 33.2%. This study proposes new insights into the imbibition mechanism, providing guidance to the practical applications of long-term stable imbibition and improved oil production.