Effect of nanoclay on the electrical resistivity and rheological properties of smart and sensing bentonite drilling muds

• Electrical resistivity has been identified as the sensing property for the smart drilling mud.
• Rheological properties of the drilling mud have been correlated to the electrical resistivity.
• Effect of nanoclay on the bentonite drilling mud behavior has been quantified.

In this study, the effect temperature on the electrical resistivity and rheological properties of a water based bentonite drilling mud modified with nanoclay was investigated. Based on the experimental and analytical study the electrical resistivity was identified as the sensing property of the smart drilling mud so that the changes in the properties can be monitored in real-time during construction. The bentonite contents in the drilling muds were varied from 2% to 8% by the weight of water and temperature was varied from 25 °C to 85 °C. The nanoclay (particle size in range of 12 nm to 20 nm) content was varied between 0 and 0.6% by the weight of the drilling mud to modify the rheological properties and enhance the sensing electrical resistivity of the drilling mud. The nanoclay and bentonite clay were characterized using the X-ray diffraction analysis (XRD) and thermal gravimetric analysis (TGA). Based on the X-ray diffraction (XRD) analyses the major constituents in the nanoclay were montmorillonite (MMT) (hydrated sodium calcium aluminum magnesium silicate hydroxide, (Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2·nH2O)), quartz (SiO2), magnesium aluminum silicate ((MgAl) SiO3) and calcium–aluminum silicate hydrate (CaAl2 (SiO4)2(OH)4). The TGA analyses on the bentonite and nanoclay showed weight loss in the temperature range of 600 °C to 800 °C, which supported the presence of montmorillonite. The weight loss up to 120 °C represented the loss of moisture (free water) in both bentonite and nanoclay which was 6.4% and 12.8%, respectively. The total weight loss at 800 °C for the bentonite decreased from 12.9% to 7.15%, about 45% reduction, when the bentonite clay was mixed with 0.6% of nanoclay. The results also showed that 0.6% nanoclay decreased the electrical resistivity of the drilling mud from 15% to 36% based on the bentonite content in the drilling mud. The electrical resistivity of the drilling mud with and without nanoclay decreased with the increase in the temperature. The nanoclay modification increased the yield point (YP) and plastic viscosity (PV) by 30% to 61% and 12% to 37% respectively based on the bentonite content and temperature of the drilling mud. Addition of nanoclay also increased the apparent viscosity and gel strength of the drilling muds. The rheological properties of the drilling muds have been correlated to the electrical resistivity of the drilling mud using nonlinear power and hyperbolic relationships. The model predictions agreed well with the experimental results. Hence the performance of the bentonite drilling muds with and without nanoclay can be characterized based on the electrical resistivity which can be monitored real-time in the field.