Fluides de forages : gestion, traitement et recyclage pour les travaux sans tranchée

International audienceTrenchless Technology, mainly Horizontal Directional Drilling (HDD) & Micro tunnelling using drilling fluids, has been expanding for several years. These new construction methods have undoubtedly gained wide acceptance, particularly in highly congested urban areas and in environmental engineering like soil remediation of industrial sites. In the framework of the National Project “Microtunnels” a work group of FSTT (French Society for Trenchless Technology) has proposed “a drilling fluids research program” to manage the drilling fluids used during soil’s excavation. It’s worth looking at for various criteria: technical performances, economic and environmental considerations to reduce dumping and wastage during the underground works. HDD requires the use of large volumes of drilling fluids that provide the following functions: hydraulic cutting with a jet, providing energy to the drill motor, lubricating and cooling the cutting head to reduce torque and drag, transporting drill cuttings to the surface, stabilising the hole against collapse, guarding against loss of drilling fluid into surrounding formations. The drilling mud is pumped downhole, circulates back to the surface and is collected in return the pit, then passed through machinery that separates the cuttings from the slurry. Drilling muds are bentonite based. They are very sensitive to either physical chemical contamination. During drilling operation, their physico-chemical properties are constantly modified because of the excavated soil/water interaction inducing different flow and filtration properties, which have implications for the drilling performance. Significant amounts of drilling mud are normally disposed of at the end of a project. Logistics for disposal is extremely site specific.This drilling mud can be disposed of by:- Use at another drilling location.- Spread onto raw land for water retention improvement.- Evacuation to dump site after treatment with cement, lime, water retention polymer…- Treated to separate the solid phase (bentonite and cuttings) and the liquid fraction (water).This paper describes:1. Consequences of waste treatment and disposal at the working end; management criteria, key parameters and limit value.2. Different cases obtained from standard bentonite fluids to more complex bentonite/polymers systems.Le forage horizontal dirigé est une technique assez récente, qui permet de passer sous des obstacles (voies d’eau, voies ferrées, bâtiments…), de linéariser les réseaux et de limiter la gêne due aux travaux en tranchées ouvertes. La réussite d’un forage dépend notamment du fluide de forage utilisé, qui est souvent composé de bentonite et de polymères. Or la nature de ce fluide peut varier fortement d’un site à l’autre en fonction des terrains traversés. En fin de chantier, la boue devient un déchet, qu’il faut éliminer et traiter éventuellement. Les entreprises sont juridiquement responsables, comme productrices et détentrices, des boues de forage considérées comme un déchet. L’objet de ce travail est de présenter une analyse permettant de définir des critères à considérer pour l’admissibilité en décharge, et des résultats de tests pratiqués en laboratoire sur plusieurs types de fluides