Formation of the wellbore at the boundary of engineering-geological elements in the implementation of the HDD method in the construction of an underwater crossing

The article is devoted to the study of the problems of changing the trajectory of the wellbore at the boundary of the change in the physical and mechanical properties of the drilled soils during the construction of the main pipelines by the method of directional drilling. The article discusses the interaction of the rock cutting tool with the extensionof the pilot well with the drillable soils and describes the mechanism of formation of the ledges in the borehole that change theeffective diameter of the constructed wellbore and lead to an increase in traction forces while dragging the pipeline into the well.
Materials and methods
Geometric construction of the interaction between drilling tools and drillable soils.
Results
To avoid the occurrence of ledges in the borehole during the drilling of the wellbore, it is necessary to design the expander design, the location of the centralizers in the assembly of the drill string, equipping the expander with armament, relying on the force elements of the interaction of the drilling tool with the passable soils, and also taking into account the actual angle of interaction between the expander andthe rock boundary with various mechanical properties.When carrying out engineering and geological surveys, it is necessary to pay attention to the placement of geological wells to determine the structural elements of occurrence of rocks along the axis of the projected transition. To date, the rules for engineering and geological surveys do not standardize the requirements for determining the elements of occurrence of lithological boundaries.
Conclusions
The study of the interaction of the drilling tool with the drilled rock at the lithological boundaries will avoid changing the well trajectory for pulling the pipeline and reduce the likelihood of accidents during the construction of pipeline crossings through natural and artificial obstacles.