Experimental study of the impact of filter cakes on the evaluation of LCMs for improved lost circulation preventive treatments

Abstract

Methods to prevent the losses of drilling fluids involve approaches to prevent the initiation of fractures and to inhibit the growth of any pre-existing or drilling-induced microfractures. The inclusion of lost circulation materials (LCMs) in drilling fluids is a common method for managing these microfractures. Recent studies have indicated the critical role of filter cakes in continually strengthening the wellbore; however, most of the current LCM design and evaluation methods neglect the effects of filter cakes. In this study, experimental investigations were conducted to understand the effects of LCMs on the creation of filter cakes and the facilitation of fracture sealing. The processes of filter cake rupture and fracture sealing were investigated by changing and monitoring the differential pressure across the filter cakes. The performance of the filter cakes and LCMs in preventing and reducing fluid losses was evaluated based on the maximum sealing pressure, sealing structure stability, and total fluid loss upon the formation of an effective fracture seal. The effects of the filter-cake thickness, shear yield stress, as well as the type, concentration, and particle size distribution of LCM on the filter cake rupture and fracture-sealing processes were investigated.The test results show that filter cakes accelerate the sealing of microfractures, thus facilitating preventive treatments for lost circulation. The properties and effectiveness of filter cakes for these processes are affected by the particle size distribution of the LCMs in the drilling fluids. Therefore, it is recommended to evaluate the performance of LCMs considering the effects of the filter cakes. The results of this study can be used as a reference to develop more realistic evaluations and improved design of LCMs in lost circulation preventive treatments.