The Pipeline Transport Institute has developed the solution formulations for the underwater crossings construction by directional shield drilling method using a tunneling complex in clay soils. This development received a patent for invention.
Two solution formulations have been developed, which is used as a washing fluid for a tunneling shield. The first formulation includes an encapsulating polymer, sodium formate or acetate, and water. The second variety, in which the formulation is supplemented with vegetable oil, is most effective when drilling soils consisting of hard loams and clays.
The Pipeline Transport Institute has successfully conducted tests to find the optimal solution formulation with the required rheological properties, both of which have confirmed their effectiveness and environmental safety.
The effect of using this development in trunk pipelines underwater crossings construction is to provide the possibility of strengthening wells in zone of clay soils, increasing the ability to take out drilling waste, and increasing the speed of the tunneling complex passage.
In the long term, the development of The Pipeline Transport Institute is planned to be used in trunk pipelines underwater crossings construction using directional shield drilling method at the facilities of Transneft subsidiaries in order to increase the reliability and safety of construction.
The directional shield drilling method is an innovative technology of trenchless pipeline laying, which is a symbiosis of directional drilling and microtunneling methods: well drilling is carried out using a remotely controlled microtunneling complex connected to a pipeline, while pushing a welded siphon into a drilled well.
This technology has a limited distribution in the territory of the Russian Federation and have not been used in underwater crossings construction at Transneft facilities. Its main advantage is the one-stage work and the possibility of applying the technology in difficult soil conditions.
Traditionally, in pipeline underwater crossings construction in clay soils, water or water-based washing fluids are used as a hydraulic weight - a solution under a certain pressure is conducted from shield nozzles into a well.
When passing through clay soils, the speed of a tunneling complex is reduced by 2-3 times (the usual average speed is 10 cm/min). This is due to the fact that water intensively interacts with clay soil and increases its moisture, which provokes clogging of shield holes, and leads to a decrease in the ability to take out drilling waste along the hydraulic transport line.
To avoid these problems, various clay inhibitors or stabilisers are used, lubricating additives for a tool and well walls to facilitate penetration, polymers that thicken the drilling fluid to maintain its required viscosity. The drilling fluid itself performs the functions of soil strengthening, hydrostatic balance maintaining, well cleaning from drilled solids, soil erosion, lubricating and cooling, etc.