大庆油田古龙页岩岩屑在幂律流体中的沉降阻力系数研究

The Settlement Drag Coefficient of Gulong Shale Cuttings in Power-Law Fluids in Daqing Oilfield

大庆油田古龙页岩油开发大多采用长水平段水平井,但长水平段水平井钻井过程中,岩屑易在井筒内自由沉降而形成岩屑床,导致沉砂卡钻等井下故障,因此需要研究岩屑颗粒的沉降规律,优化钻井液性能及水力参数,确保井眼清洁。为此,利用可视化的试验装置和高速摄像机,系统记录了试验中颗粒在幂律流体中的沉降行为,获得了196组球形颗粒和224组不规则形状岩屑在幂律流体中自由沉降的试验数据。采用一种依赖于沉降颗粒受力平衡的力学模型对试验数据进行统计分析,建立了幂律流体中球形颗粒阻力系数预测模型。在此基础上,引入二维形状描述参数,建立了幂律流体中不规则形状岩屑阻力系数预测模型。该模型预测准确性较高,平均相对误差仅6.93%,能够满足钻井工程中预测岩屑沉降速度的需求。

Horizontal wells with long horizontal sections are mostly adopted in developing the Gulong shale oil in Daqing Oilfield.However,during the drilling process of the horizontal wells with long horizontal sections,the broken cuttings in the borehole annulus easily settle freely in wellbore drilling fluids to form cuttings beds.In order to avoid downhole failures such as sand sinking and sticking caused by cuttings deposition,it is necessary to study the settlement law of cuttings particles and predict the final velocity of cuttings settlement.In this paper,the settlement behavior of particles in power-law fluids was systematically recorded by visual devices and high-speed cameras during experiments.The experimental data from the free settlement of 196 groups of spherical particles and 224 groups of irregularly shaped cuttings in the power-law fluids were obtained.A mechanical model dependent on the force balance of settling particles was adopted,and the experimental data were analyzed in detail.A model for predicting the drag coefficient of spherical particles in the power-law fluids was established.On this basis,a two-dimensional shape description parameter was introduced to establish a model for predicting the drag coefficient of irregularly shaped cuttings in the power-law fluids.The prediction model showed high accuracy,and the average relative error was only 6.93%.Therefore,the model can meet the need of predicting cuttings settling velocity in drilling engineering.