椭圆井眼同心环空赫巴流体流动规律研究及压降计算简化模型

因岩石和地应力的非均匀性易形成椭圆井眼,导致现有规则圆形井眼环空流动模型存在较大误差。为明确椭圆井眼同心环空赫巴流体流动规律,建立了解析模型和Fluent仿真模型,分析椭圆井眼对环空流速和压降梯度的影响规律;通过修正水力直径和引入有效黏度的方法建立了椭圆井眼同心环空压降计算简化模型,实现流动压降的准确快速预测,并利用解析模型、仿真模型和实测结果对简化模型有效性进行验证。结果表明:当流量一定时,轴向平均流速和最大流速随椭圆长短轴轴长比值的增大呈线性和指数型增加;无量纲压降梯度随椭圆长短轴轴长比值增大呈线性增加;简化模型与仿真模型、解析模型和实测结果均吻合较好,误差分别为±8%、±5%和±5%。研究成果为椭圆井眼同心环空流动压降准确快速预测提供了理论支撑。

Study on Flow Rules of Herschel-Bulkley Fluid in Concentric Annulus of Elliptical Wellbore and Simplified Model for Pressure Drop Calculation

The wellbore is easy to become elliptical due to the uneven rocks and in-situ stress, leading to great deviation in the existing annulus flow model of regular circular wellbore. In order to identify the flow rules of Herschel-Bulkley fluid in the concentric annulus of the elliptical .wellbore, an analytical model and a Fluent simulation model were established to analyze the influence of the elliptical .wellbore on the annulus flow velocity and pressure drop gradient. A simplified model was established for pressure drop calculation of concentric annulus of elliptical wellbore by correcting the hydraulic diameter and introducing effective viscosity to realize accurate and rapid prediction of flow pressure drop. The effectiveness of the simplified model was verified by the analytical model, simulation model and measured results. The results showed that when the flow rate was constant, the axial average velocity and maximum velocity increased linearly and exponentially with the increase of the ratio of the long and short axis of the ellipse; the dimensionless pressure drop gradient increased linearly with the increase of the ratio of the long and short axis of the ellipse; the simplified model was well fitted with the simulation model, analytical model and measured results, and the deviations were ±8%, ±5% and ±5%, respectively. The study results can be used as a theoretical support for accurate and rapid prediction of flow pressure drop in concentric annulus in elliptical wellbore.