Mathematical Model and Experimental Study on Drill-In Fluid Loss Control and Formation Damage Prevention in Fractured Tight Reservoir

摘要

Drill-in fluid loss is the most important cause of formation damage during drill-in process in fractured tight reservoirs. Lost circulation material (LCM) addition into drill-in fluid is the most popular technique for loss control. However, traditional LCM selection is mainly performed by trial-and-error method, due to lack of mathematical models. The present work aims at filling this gap, by developing a new mathematical model to characterize the performance of drill-in fluid loss control using LCM during drill-in process of fractured tight reservoirs. Plugging zone strength and fracture propagation pressure are the two main factors affecting drill-in fluid loss control. The developed mathematical model consists of two sub-models, i.e., the plugging zone strength model and the fracture propagation pressure model. Explicit formulae are obtained for LCM selection based on the proposed model, in order to control drill-in fluid loss and prevent formation damage. Laboratory tests on loss control effect by different types and concentrations of LCMs are performed. Plugging pressure and total loss volume are measured and compared with modeling results. Effects of LCM mechanical and geometric properties on loss control performance are analyzed, for optimal fracture plugging and propagation control. Different combinations of acid-soluble rigid particles, fibers and elastic particles are tested in order to generate a synergy effect for drill-in fluid loss control. The derived model is validated by laboratory data.