Analysis on the risk of static push-the-bit steering rib plunging into well wall

The static push-the-bit rotary steering drilling system provides steering force by making use of the steering rib to support the well wall, and the well wall may suffer yield and plastic deformation under the thrust force of the rib, which can lead to the decrease of WOB transfer efficiency and build-up rate, so as to have adverse impact on the construction of directional drilling. In this paper, the plunging process of steering rib into the well wall during the rotatory steering drilling was simulated by using the finite element software. Then, the factors influencing the deformation of well wall and the deformation laws were analyzed. Finally, several technological measures to reduce the plunging of steering rib into soft formations were proposed. The results show that it is angular contact between existing single-plunger articulated steering rib and well wall and the contact area is small, so the distribution of contact stress is nonuniform with the maximum stress lying at the upper end of steering rib. What’s more, the elastic modulus and plastic parameters (internal cohesion and internal friction angle) of wall rocks have greater influence on the deformation of well wall. Furthermore, when drilling soft formations, the steering rib can plunge into the well wall and the plunging depth increases linearly approximately as the movement goes on. It is beneficial to reduce the risk of steering rib plunging into the well wall by improving the structure of steering rib, reducing the thrust force of steering rib appropriately and carrying out formation adaptability evaluation.