Experimental Study on the Sliding Friction for Coiled Tubing and High-Pressure Hose in a Cuttings Bed During Microhole-Horizontal-Well Drilling

Abstract

Summary Microhole–horizontal–well–drilling technology is a high–efficiency and low–cost technology that has developed rapidly in recent years. However, during microhole–horizontal–well drilling, cuttings deposit easily at the bottom of the wellbore because of gravity and nonrotation of the pipe. The pipe sliding on the cuttings bed will cause extremely serious friction between the pipe and cuttings bed, which is an important limiting factor on the extended length of the microhole horizontal wellbore. Therefore, it is necessary to study the influencing factors and establish a model for evaluating the friction between the pipe and cuttings bed. In this study, laboratory experiments on the sliding friction between pipe and cuttings bed were conducted. By analyzing the comprehensive sliding–friction coefficient (CSFC) between the pipe and cuttings bed, the effects of dimensionless buried depth (0.2 to 1.0) and average cuttings size (0.249 to 2.667 mm) on the CSFC between the pipe and cuttings bed were obtained. CSFC is a function of dimensionless buried depth and relative roughness in the developed model. The results suggest that the sliding–friction resistance between the pipe and cuttings bed increases as the buried depth of pipe increases or the average cuttings size decreases. We propose a model for estimating the CSFC using experimental data and the least–squares method. The predictions show good agreement with the experimental data within suitable ranges of models. This work is expected to provide the basis for predicting the friction resistance between the pipe and cuttings bed.