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

摘要：

高密度水基钻井液属于较稠的胶体-悬浮体分散体系，固相含量大，固相颗粒分散程度高，自由水量少，在深井高温高压条件下流变性容易失控。以室内研制的抗高温高密度淡水基和盐水基钻井液为基础，采用Fann50SL高温高压流变仪对钻井液在不同温度下的流变性进行了测试。结果表明，温度是影响高密度水基钻井液流变性的主要因素。随着温度升高，淡水基钻井液的表观黏度和塑性黏度都出现降低趋势；而盐水基钻井液的塑性黏度在150℃达到最低值，然后升高，表观黏度呈降低趋势。利用测试数据，运用宾汉、幂律、卡森和赫巴4种流变模式进行线性拟合发现，无论是淡水基还是盐水基钻井液，赫-巴模式最佳，幂律模式最差。建立了预测淡水基钻井液表观黏度与温度、压力关系的数学模型，实测数据验证表明，该模型可以应用于生产实际。

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