高温高压下CO_2泡沫压裂液摩阻计算研究

Study on Friction Calculation for CO_2-Foam Fracturing Fluids under High Temperature and High Pressure

进行了CO2泡沫压裂液的室内配制、流变性测定以及摩阻计算方法研究。通过室内试验,观测了CO2泡沫压裂液的形成、动态变化和泡沫结构,测定了CO2泡沫压裂液在高温高压（35-110℃、20-50 MPa）条件下的视粘度变化。结果表明,CO2泡沫压裂液属于屈服假塑性非牛顿流体,其流变参数（n、K）随温度、压力、泡沫质量、配方等变化,为多元复合函数。为了便于求解,假设配方、温度、压力等主要影响泡沫质量,而流变参数（n、K）仅是泡沫质量的一元函数。在井筒中,泡沫压裂液物性随温度和压力（均为井深的函数）而变化,反过来泡沫压裂液的物性又影响井筒内流体温度和压力分布,是一个耦合的非线性问题。提出了一种计算摩阻压降的简化方法,将整个井筒分为若干计算段,每一段内将复杂的耦合关系简化为3个计算过程：1）由温度、压力和排量计算泡沫质量;2）由泡沫质量计算流变参数;3）由流变参数计算摩阻。计算结果与井筒内CO2泡沫压裂液摩阻压降实测结果符合较好,误差在合理范围内,可以在工程中应用。

Lab preparation,rheology measurement,and friction loss of CO2-foam fracturing fluids have been investigated.Development,transient variation,and components of CO2-foam fracturing fluids were examined in lab,along with the measurement of the apparent viscosity variations under high temperature and high pressure（35～110 ℃,20～50 MPa）.Lab tests show that the rheological properties,which is a composite multivariate function,vary with temperature,pressure,foam mass,and its formulation.For simplicity,assuming the formulation,temperature,and pressure mainly impacting the foam mass,the rheology parameters（n,K） are only a function of foam mass.Properties of CO2-foam fracturing fluids,which are a function of well depth,vary with temperature and pressure.The properties of CO2-foam fracturing fluids impact the pressure and temperature;therefore it is a coupled nonlinear problem.A simplified method was proposed to calculate circulating pressure loss by dividing the wellbore into several calculation parts.In each of the calculation part,the complicated couple relation was simplified to 3 procedures： 1） calculating the foam mass using the pressure,temperature and flow rate,2） calculating rheological parameters using foam mass,3） calculating pressure loss using the rheological parameters.The calculation results were consistent with the measured fluid friction.The error are in the reasonable range and this method can be used in the field application.