An Experimental Study of Drilling Fluids Dynamic Filtration

Abstract

ABSTRACT An experimental study was carried out by the ARTEP research group on the filtration of drilling fluids under borehole conditions and on its main consequences (differential pressure sticking, rate of penetration, damage to formations). The filtration of drilling fluids has long been recognized as an important parameter for drilling operations, but filtration properties and cake characteristics under borehole conditions are not usually well estimated, as laboratory testing procedures only consider static conditions. Laboratory tests performed with special apparatus on three mud types allowed a better knowledge of the phenomena.Dynamic filtration is dependent upon cake build-up. The results show the relation between shear rate and fluid loss; the time necessary for dynamic filtration stabilization can be long. The main parameters of dynamic filtration seem to react differently to those of static filtration.Differential sticking: a comparative study underlines the importance of fluid nature and filter cake characteristics on the pull-out force required to free a stuck pipe.Rate of penetration: generally accepted rules were confirmed, but in some circumstances the effect on R.O.P. of actual filtration under the bit can also depend on other parameters (mud type, bit selection).Damage to permeable formations: damage to clean (non clayey) sandstone can be limited by controlling cake quality. Special attention must be paid in the case of oil-based muds, whose dynamic filtration and cake properties can be unexpectedly detrimental.