River crossing of natural gas pipe lines a study of Bangladesh experience

Abstract

Natural gas is often transported over significant distances- across rivers, hills, and other natural obstacles. River crossing is arguably the most challenging part of a land based pipeline project. Procedures and technologies for pipeline construction and river crossing have matured over the years. However, each new project offers a set of challenges and opportunities unique to that project. In Bangladesh, pipelines were installed across a number of rivers since the beginning of commercial usage of natural gas. The Government of Bangladesh has plans to extend the natural gas network. Therefore, more river crossings will be forthcoming. It is important to examine the river crossings in Bangladesh and identify the challenges and solutions related to those projects. However, it is possible to analyze the problems and to table the common items to bring them under a systematic procedure. For Horizontal Directional Drilling (HDD), pipe site and rig site selection and development is the initial stage of a river crossing project. An unplanned or faulty selection and development of a HDD site may cause severe problems which may even jeopardize the entire pipeline project. The natural gas transmission pipeline infrastructures in Bangladesh represent a complex mechanical system. This system has been developed over the last few years and is controlled at a very low level of sophistication. State owned organization Gas Transmission Company Limited (GTCL) under Petrobangla is now responsible for maintenance, operation and expansion of the gas transmission grid across the country. GTCL is constructing the pipeline crossing the river by HDD method with the help of international agencies who are specialized in HDD sector. Despite having the drilling experience, it is difficult to get a generalized idea on the HDD issue due to lack of compilation of the individual experience. In this section GTCL has implemented a 60km X 30″ Bakhrabad-Siddhirganj gas transmission pipeline project having six river (Shitallakhya-556.32m, Old Brahmaputra-665.41m, Kajla- 657.84m, Meghna-1593.18m, Asharier-856.80m & Meghna-Gumoti-1941.87m) crossings by HDD method. Each river crossing has the unique challenges and remedial measures of six representative river crossing sites have been analyzed. It is revealed that selection of right-of-way, selection of crossing location, sub-soil investigation and selection of work procedure pose the biggest and most common problem for the preconstruction activity before HDD. In general, drilling profile design, mobilization of rig unit and its accessories, selection of guidance system, selection of equipment/accessories, selection of bentonite mixing ratio and viscosity, pipe string preparation, scarcity of manpower etc. should be taken into account to plan the successful HDD project. This study also includes the nature of the problems and their reasons, degree of severity which cause time and cost overrun of the project.