Rheological and PVT Behavior of Synthetic Based Drilling Fluids Under Temperature-Pressure Conditions of the Riser in Deepwater Drilling

Abstract

Abstract Invert emulsion drilling fluids (IEDFs) are water-in-oil emulsions in which the water phase is usually calcium chloride brine as the internal phase and the non-aqueous fluid forms the external phase. They are widely used to drill troublesome shale formations thanks to their main advantages of excellent shale inhibition mechanisms, superior lubricity, and high-temperature stability. The challenges of deepwater drilling operations necessitate the use of invert emulsion systems, and due to environmental regulations, synthetic fluids as a base oil are preferred. Hydraulic optimization in deepwater drilling requires the use of temperature- and pressure-dependent rheological properties and density due to the wide range of temperatures and pressures anticipated in these wells. Temperature- and pressure-dependent rheological properties and density are necessary for managing typical drilling problems such as barite sag, excessive equivalent circulating density (ECD), lost circulation, well control and poor hole cleaning. This study experimentally investigated the rheological and PVT behavior of synthetic-based drilling fluids at low temperatures or high pressures that may occur in the riser during drilling and well control. Synthetic-based drilling fluids were formulated at three different synthetic-water ratios (70/30, 80/20, and 90/10) and four different densities (10, 12, 14, and 16 ppg). EDC99 DW and 25% calcium chloride were used as the external and internal phases, respectively. Rheological and PVT measurements were performed over a temperature range of 40 to 70 °F and a pressure range of 14.7 to 12,500 psi using the Grace M7500 Ultra HPHT Rheometer and PVT module. Plastic viscosity (PV), yield point (YP), 10 s/10 min gel strength and density of IEDF samples were evaluated as a function of temperature and pressure. Additionally, rheological properties and static/dynamic density profiles of the fluid were obtained in a sample deep water well using a temperature-pressure dependent hydraulic simulator, and the results were compared with the traditional approach.