Visualized Characterization of Reservoir Pore–Throat Blockage Induced by Injection of Various Oily Sludges Using Micro-CT

This paper explores the internal rock plugging rules induced by oily sludge profile control systems in oilfields. Three typical sludges including wastewater tank bottom sludge (WTBS), crude oil tank bottom sludge (CTBS) and floating scum sludge (FSS) are adopted. Combined with micro-CT scanning and digital core technology, this paper systematically investigates the pore–throat structure evolution and damage mechanism before and after sludge injection into rock cores. Key parameters such as plugging rate, average pore radius, throat radius, coordination number, shape factor, pore–throat ratio and pore–throat volume are quantitatively characterized macroscopically and microscopically, which reveal diverse damage modes and plugging mechanisms of the three sludges. The results indicate that pores of 10–50 μm are preferentially blocked by all sludges. CTBS causes the severest core damage with an average plugging rate of 79.67%, and the average coordination number decreases from 4 to 1, governed by the mechanism of adsorption diameter reduction and structural destruction. WTBS leads to uniform jamming of fine particles. Its average parameters change slightly, yet permeability declines due to broken critical throats. It follows the mechanism of uniform filling and weak adsorption with an average plugging rate of 56.75%, showing mild reservoir modification capacity. FSS causes moderate damage. Retained emulsion droplets trigger uniform slight shrinkage of pore throats under partial and overall selective filling mechanism, with an average plugging rate of 63.36% and favorable selective plugging performance. This study clarifies the inherent correlation between macroscopic damage and microscopic behaviors of oily sludge, offering microscopic theoretical references for differentiated management of sludge reinjection and oil displacement with composite sludge profile control agents.