Mathematical Correlations of Olefin and Methane Mixtures to be Applied to Synthetic Drilling Fluid During Well Control Operations

Abstract Lost circulation is one of the major concerns when drilling a well because it affects downhole well integrity, leads to monetary losses and is detrimental to the reservoir. In drilling operations, it generally occurs when the drilling fluid density exceed the formation fracture pressure. Another concern during drilling is the gas-formation influx to the wellbore, which occurs when the hydrostatic pressure becomes lower than the formation pore pressure. Therefore, the knowledge of drilling fluid density is a key factor to the operational safety and efficiency. In view of it, a number of experiments were performed at isothermal conditions in a PVT (pressure/volume/ temperature) system with full sample visibility to study the influence of pressure, temperature and mixture composition on fluid thermodynamic properties. Based on experimental data, mathematical correlations for density, solubility ratio and formation volume factor (FVF) for methane and linear olefin mixtures have been developed and presented in this article. In addition, an empiric correlation was presented for pure linear olefin density and was compared with results published in literature. These analytical correlations are fundamental to well control simulations. They make possible the estimation of the pit gain (increase of drilling fluid volume on the surface after a kick has been taken) and are used in computational methodology of kick simulators as constitutive equations to improve the reliability of their predictions and consequently increasing the operational safety and efficiency. The equations for the density, solubility ratio and oil-FVF shown in this paper are in excellent agreement with the experimental data showing a maximum absolute deviation of 3.2%. However, as the experimental data ranged from 25°C (77°F) to 80°C (176°F) and pressures up to 103 MPa (14940 psi), extrapolation of the equation may lead to larger errors. The paper also presents a well control case study showing the practical application of these correlations.