Borehole stability of multilateral junctions

The oil industry has increased its emphasis on multilateral technology to improve production. This new technology, however, introduces a number of challenges. Junction failure is critical and has resulted in well failures because borehole stability must be maintained to drill and complete these wells successfully.Analytical models that take the junction geometry into account to assess the stability of lateral wellbore branches are presented. The junction is classified into the three following geometries: circular, oval and two adjacent boreholes. A principal conclusion is that any geometry that deviates from a circle leads to less stability. The stability window at the junction itself is smaller than the borehole above or below. Both fracturing and collapse at the multilateral junction are analyzed. A field case is discussed to demonstrate the application of the models.