Temperature-Dependent Rheological Response of Organophilic Clay for High-Temperature Drilling Operations

Abstract

During drilling geological formations, several challenges arise from in-situ formation of pressure and temperature. The rheological properties of the mud must be carefully and regularly monitored to ensure that drilled cuttings continue to move to the surface efficiently by improving low-end rheology, averting barite sag. In this paper, oil-based muds (OBMs) with the same composition were prepared, while two industrial organophilic clay products were blended into each mud sample, designated as samples A and B. The properties of both mud samples were evaluated at room temperature, while the rheological response of the two OBM samples was monitored over a temperature range of 80 to 160°F. The results showed that temperature had no significant influence on mud weight, marsh funnel viscosity, alkalinity, or chloride. However, plastic viscosity constantly decreased from 70 cP at 80°F to 30 cP at 160°F, while yield point (YP) gradually increased from 20 lb/100 ft² at 80°F to 23 lb/100 ft² at 160°F. Both samples A and B decreased in the flow behaviour index (n) from 0.83 at 80 °F to 0.66 and 0.70, respectively, at 160 °F. On the other hand, the consistency index (K) for samples A and B steadily increased from 0.5 at 80 °F to about 0.96 and 0.95, respectively, at 160°F, as both mud samples were subjected to increasing temperatures under shearing conditions. While both clay samples proved excellent for cuttings movement, it is important to carefully manage their concentration to prevent the yield point from exceeding the desired limit, as a further increase in YP may hinder the landing of casing pipes at the bottom of the hole due to the fluid's buoyancy. Both clay samples exhibited similar low-end R80° geological performance, which is necessary to prevent drilled cuttings from settling in the cuttings at 160°F to avert stuck-pipe problems.