Study on Annular Mud Consolidation Property after Pipeline Installation by Horizontal Directional Drilling

Abstract

Horizontal directional drilling (HDD) is being widely used as a technique to install large-diameter pipelines. Using this method, there exists annular space after the pipeline is installed in the borehole. The annular space is filled with drilling mud, whose cross-sectional area can reach up to approximately one square meter. When pipeline installations by HDD involve a watercourse area, annular mud may result in several post-construction issues such as: settlement or even collapse of the surface above the HDD bore path; penetration destroy in gravelly sand; or soil deformation of the nearby embankment. Based on the similarity principle, a series of experiments was carried out to reveal the consolidation and deformation law of annular mud. First, an iron experiment box located in the laboratory was filled with sand containing clay; this was designed to simulate the formation. Secondly, a horizontal borehole with annular mud was drilled by a HDD rig and sensors were placed in it to record the stress-strain variation of annular mud during the consolidation process. Meanwhile, samples of annular mud were taken from the box periodically, and drilling fluid tests, soil strength tests and SEM image analyses were performed to obtain the property parameters of the samples. Subsequently, the annular mud was excavated for visual observation and strength measurement after seven months. The laws of seepage and consolidation of annular mud in sand obtaining clay can be obtained through this study and it can supply experimental proof for evaluating the influence on crossing area caused by annular mud using HDD.