Normal Stress Rheology of Drilling Fluids and Potential in Lost Circulation Control

Abstract

Abstract Investigating lost circulation in DEA 13 JIP has shown that it is difficult to arrest losses while drilling with non-aqueous drilling fluids (NAF) as compared to aqueous drilling fluids (AF). In an earlier work (Kulkarni 2012), a novel method was discussed to characterize the plugging (of LCM particles and Fibers) performance of non-aqueous and aqueous drilling fluids using viscoelastic parameters under shear stress (First Normal Stress Difference=N1). This paper discusses the modification of drilling fluids (particularly non-aqueous fluids) to combat lost circulation. N1 measured at low and moderate shear stresses for different aqueous and non-aqueous drilling fluids shows that the magnitude of N1 for AF was significantly higher than that for NAF; although, the FANN® 35 viscometer shear rheology of both was similar. Another important finding was that adding certain polar-organic compounds to the NAF improves its N1 magnitude remarkably, which in turn was found to improve the drilling fluid's performance in lost circulation applications. For representative AF and NAFs, with the same FANN 35 viscometer rheology properties and lost circulation materials, fracture plugging efficiency was probed on a Permeability Plugging Apparatus (PPA) using a tapered slot. The plugging performance of the LCM in the AF was significantly better than in the NAF for the same combination of LCM. This difference in plugging performance was attributed to the noticeable difference in N1 observed for these two drilling fluids. The relation between N1 and plugging efficiency became evident when the addition of polar-organic compounds to the NAF increased its N1 and improved its plugging efficiency. These findings could be used to tailor the NAF for LCM treatment during the mud design phase and help alleviate trial-and-error in the LCM design.