Abstract
During well cementing and drilling operations, proper control of downhole pressure is critical for controlling the well, i.e. avoiding formation fluids influx or fracturing the formation, and hence ensuring successful well construction operations. At the planning stage, well control is investigated using numerical hydraulics simulations. During actual operations, annular pressure-while-drilling (APWD) is often, but not systematically, available while drilling but not while cementing. Here again well control relies on simulations. Accurate prediction of downhole pressures is therefore a key requirement for well control, whether at the planning stage or in real-time during operations.
Fluid properties are a key input to the hydraulics simulations, in particular fluid viscosity, which is required to estimate friction pressure losses. A difficulty is the dependence of viscosity on pressure and temperature. At a given shear rate, the viscosity of drilling and cementing fluids continuously changes within the flow path, and variations of several tens of percent are common. Hence it is paramount to measure cementing and drilling fluids viscosity over the pressure and temperature domain that will be experienced in the well, but also to fit to the measurements a pressure and temperature dependent rheological model that will allow the hydraulics simulator to obtain viscosity at any shear rate, temperature, and pressure values.
We first provide an overview of the algorithms needed to analyze rheological lab measurements, where care must be taken to account for potential wall slip effects. We then review how to account for pressure and temperature effects, via the use of Arrhenius and Barus laws, and why the modeling needs should inform the test requirements.
