Formation damage induced by working fluids sequentially interacting with tight sandstone oil reservoirs

Abstract

Drilling fluid loss is a frequent downhole incident in the process of deep well drilling and completion. Drilling fluid will damage the formation permeability and affect well production, but some wells with high volume drilling fluids loss can have high production. To investigate the mechanism of drilling fluid loss damage in tight sandstone oil reservoirs, this study selects some core plugs and the working fluids from X field in Ordos Basin, China, conducts the evaluation experiments of drilling fluid damage and working fluid sequential contact damage, and analyzes the well history and well production performance data. Results show that the permeability recovery rate decreases continuously, after different fluid displacement. The permeability recovery rate of rock sample after drilling fluid displacement is 46.21–67.14%, and the permeability recovery rate after different working fluid displacement is 22.92–61.45%. Then well history and production fluctuations are analyzed. It shows the incompatibility of working fluid will cause superimposed damage to hydraulic fractures. The main damage mechanism caused by drilling fluid loss is incompatibility damage and particle invasion. Loss of drilling fluid will improve damage risk of the subsequent stimulation operations, though it doesn't show damage features in initial stage. Formation damage degree is related to the storage space type of reservoir. The results serve as a guide for the drilling fluid design of oil in tight sandstone formation.