This paper presents the barite sagging phenomenon of four OBM systems having the same density, but different rheology properties. The investigations of barite sagging is based on dynamic sagging and viscoelasticity testing. The viscoelastic properties related to gel formation of the drilling fluids were investigated under amplitude and frequency sweeps.
The study also tries to correlate the results obtained from dynamic sag with the dynamic viscoelastic properties of the drilling fluid and standard API rheology parameters.
The results show that as the oil water ratio increases the drilling fluid rheology parameters such as lower shear yield stress (LSYS), yield stress (YS) and plastic viscosity (PV) parameters also increases. In addition, the viscoelastic loss and storage modulus decrease. From the viscoelasticity study, except for 90:10 OWR, it is observed that as the oil water ratio increase, the yield stress and the flow point also increases. The 90:10 OBM shows no viscoelasticity behavior.
Comparing the extreme 60:40 and 90:10 OBMs (i.e. as OWR increase), the experimental result shows that the sagging index increases by 9%. The dynamic sagging factor decreases as the ratio of storage modulus to loss modulus increases (i.e. as OWR decrease).
Except for high viscosity and hydraulics, the overall analysis of drilling fluids shows that the 60:40 OWR is the better in terms of sagging, filtrate loss and hole cleaning performance.