<p>Water–oil displacement is a basic rock fracture seepage problem involved in underground water-sealed oil storage (UWSOS) operations, and it is an important engineering problem affecting oil storage construction. In this study, a model experiment was carried out by using a self-developed multiphase seepage visualization device in single and cross fractures. The water–oil two-phase displacement laws of rough single and cross fractures were systematically studied. Furthermore, this study examines how to drive leaked oil back into the cavern in the event of a leak. The results show that in the water–oil displacement of a single fracture, an increase in the initial displacement velocity and aperture increases the water–oil displacement efficiency, while an increase in roughness reduces the water–oil displacement efficiency. In the water–oil displacement of cross fractures, the pressure difference first decreases and then increases with increasing aperture, reaching a minimum at 0.3—0.4&#xa0;mm. The impact of the flow distribution is the opposite. When the flow distribution is 1:1, the pressure difference reaches the maximum. Affected by the water–oil interfacial tension, wettability and fracture surface roughness, oil flooding in a single fracture mainly presents piston-type propulsion, while water flooding presents progressive propulsion. Crude oil is prone to leakage. When crude oil leaks, the oil displacement efficiency of horizontal fractures can reach up to 74%. The displacement efficiency of nonhorizontal fractures can reach 98%, and gravity differentiation between oil and water plays an important role during this time. Therefore, a sufficient groundwater source should be ensured during the construction process.</p>