Stability of Junctures for Multilateral/Multibranched Wells

Abstract

Abstract In creating complex well architecture a primary exercise is the initiation of a second branch from an existing "parent" or "mother" hole. The latter can be vertical, inclined or horizontal. The branch can be initiated at a range of angles depending on the drilling hardware used. In creating this angled branch from the main branch the stress concentration at the juncture depends greatly on the state of the far field stresses and their relative magnitudes and the mechanical properties of the rock. This work shows the calculation of the resulting state of stress at an open-hole juncture of two wells and along with a failure criterion delineates the stability of the new hole. The analysis is carried out for an angle of kick off of 2.5° and rock mechanical properties and far-field state of stress characteristic of a formation in Lake Maracaibo, Venezuela. Comparison of the estimated state of stress by the model and the rock failure criterion, predicts no mechanical instabilities at the juncture for this case. The analysis presented here demonstrates that it can be a useful tool for planning multilateral/multibranched wells by seeking formations that can withstand the stress imposed at the kick-off point and by orienting the initiation of the second branch in a direction that can ensure stability at the juncture.