Under-Balance Method for Trenchless Pipeline Directional Drilling

Trenchless pipeline directional drilling has been widely used in the pipeline crossing recent years. But the problem about serious drilling fluid losing often appears in drilling process because of large stratum of porosity. The characteristic of under-balance drilling is that the pressure of fluid in wells is less than stratum pressure, which can effective control the leakage of drilling fluid in wells and prevent stratum from polluted by leakage of the drilling fluid. Furthermore, the technology of under-balance drilling has advantages such as high drilling speed, less differential pressure sticking. The method of under-balance with the trenchless pipeline directional drilling has been researched in this paper. The selection of under-balance drilling method has been discussed, including Air drilling, Foam drilling, Atomization drilling and Aerate drilling. Advantages and applicability of under-balance method in pipeline directional drilling construction are illustrated. The problem of drilling fluid selection, negative pressure designing, density of drilling fluid calculating and drilling methods in construction has been introduced and analyzed, and some solutions have been obtained. Under-balance drilling method provides a new method and a reference for construction of pipeline directional drilling.