Abstract
Drilling and well completion fluids are complex fluids designed with many components. Oil-based fluids are in addition an oil continuous fluid with emulsified water droplets, typically with an oil water ratio from 60/40 to 90/10. Drilling fluid properties with respect to stability and hydraulic conditions are characterized in detail as well as measured regularly during operations. The thermal properties are not characterized and documented in detail comparable to other fluid properties. Current heat capacity data are calculated from theoretical or measured values of the components. These values can differ significantly from measured values. In addition, measuring heat capacity of these complex fluids is challenging. Correct values for thermal properties are important for safety considerations during drilling, completion and through the production phase. During drilling accuracy of models increase accuracy of detection if gas flows into the drilling fluid. Especially during CCS drilling into existing storage areas early detection of gas influx can avoid significant incidents. During production a well completion fluid is permanently placed in the annulus. The well construction can lead to shut-in incidents in these annuli. Expansion due to thermal cycling is dependent to the thermal properties of the fluid. Uncertainties in thermal properties must be considered when dimensioning the well construction. Improved accuracy can potentially save considerable amount of steel in a well. In this study, heat capacity was measured using: (1) Differential Scanning Calorimetry (DSC) with the sapphire standard, run under the same temperature program using multiple sampling approaches to assess robustness, where blank-corrected signals from the sample and a high-purity sapphire of known Cp(T) calibrate heat-flow sensitivity and convert the sample’s mass-normalized signal to Cp; and (2) a CPA200 reaction calorimeter with a 250 mL double-walled stirred reactor in a thermostat controlled water bath (≤80 °C), recording reactor–Peltier heat flow. Through this work a method of heat capacity measurement of drilling fluids, brines and base oils is derived. The recommended method shows good consistency and repeatability for the fluid samples tested. This method is compared to alternative methods, and the advantages are shown through measurement results and feasibility.