关键词: 高密度水基钻井液, 高温高压, 流变性, 线性拟合, 数学模型

Abstract:

High-density drilling fluid is a thick colloid-suspension dispersed system with high solid phase content, high dispersion of solid phase and low content of free water. Under the conditions of high temperature and high pressure (HTHP), the rheology of high-density drilling fluid is hardly controlled. The rheologies of two types of high-density water-based drilling fluids including the fresh water-based drilling fluid and salt water-based drilling fluid were tested at high temperatures of 50℃, 80℃, 120℃, 150℃, 180℃, 200℃ and 220℃ respectively, and at high pressure of 5MPa using Fann50SL Reometer. The test results showed that the temperature was the key factor for controlling the rheology of high-density drilling fluid. The apparent viscosity and plastic viscosity of the fresh water-based drilling fluid decreased with temperature increasing. For the salt water-based drilling fluid, the apparent viscosity decreased with temperature increasing, and the plastic viscosity decreased to the lowest value at 150℃ and then increased with temperature rising. Four rheology models including the Bingham Model, Power Law Model, Casson Model and H-B Model were used to simulate the rheological parameters of two drilling fluids. The results showed that the H-B Model was the best to depict the high-density drilling fluid at high temperature and high pressure, and the Power Law Model was the worst. A new mathematical model for describing the relations of apparent viscosity of the fresh water-based drilling fluid with temperature and pressure was proposed. The tested data proved the validity of this model in practice.

Key words: high-density water-based drilling fluid, high temperature and high pressure, rheology, linear fitting, mathematical model