高密度水基钻井液高温高压流变性研究

Rheology of high-density water-based drilling fluid at high temperature and high pressure

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。

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.