Study on Reasonable Amount of Flushing Fluid and Flushing Time

Oil-based drilling fluid has many advantages, such as stable performance, strong anti-pollution ability, and strong inhibition, and it has been widely used in the world. However, at present, there is no unified evaluation standard for the effect of flushing fluid under this condition, and most of them are based on the flushing effect evaluation of water-based drilling fluid. However, there are few studies on wetting reversal phenomenon, reasonable dosage, and flushing time between oil-based drilling fluid and flushing fluid on the two-phase interface. Therefore, it is necessary to establish a comprehensive evaluation method for the effect of flushing fluid under oil-based drilling fluid, and explore the relationship between the amount of flushing fluid and flushing efficiency, so as to determine the reasonable range of flushing fluid consumption. In this paper, using the existing experimental instruments, a type A oil-based flushing fluid commonly used in oil fields was selected for the experiment, and on the basis of the high-temperature and high-pressure filtration meter, a flushing fluid evaluation device was developed. Based on the principle of equal shear rate, the flushing displacement and flushing time were determined, and then the flushing effect was evaluated. In order to comprehensively consider the influencing factors of the well wall flushing effect, five experimental factors, including different core, flushing displacement, flushing time, flushing fluid type, and surfactant concentration, were selected to formulate the flushing experiment scheme. The contrast method was used to test the cementation strength of core and cement slurry under different conditions, and the microscopic morphology of the interface was observed and analyzed to explore the reasons for the change of cementation strength between core and cement slurry due to the existence of oil-based drilling fluid. The conclusion obtained has very important practical significance to guide the field practice.