Influence of In-Situ Stresses on Wellbore Trajectory and Stability

Abstract

Wellbore stability is of critical importance in the success of drilling
operations. One of the main goals of any drilling operation is to drill
the well as cost-effective as possible. During drilling, there are two
major instability problems namely, borehole collapse and fracture.
The consequences of these drilling problems are severe, they can lead
to serious non-productive time and loss of huge amounts of money.
Wellbore instability has become an increasing concern for horizontal
and extended reach wells, open hole lateral section, and in some
cases, open hole build-up section through shale cap rocks. More
recent drilling innovation such as underbalanced drilling techniques,
high pressure jet drilling, re-entry horizontal wells and multiple
laterals from a single vertical or horizontal well often gives rise to
challenging wellbore stability questions. In this paper, a
geomechanical software “Optiwell” was utilized to perform stability
analyses and calculations for different inclinations and azimuths.
Results obtained showed that wellbore stability is a function of
several factors such as inclination and azimuth, in-situ stresses, mud
weight, rock strength parameters, etc. Some of these factors are
controllable, while some are not. It was established that stability
problems can be significantly reduced by appropriately varying these
parameters. Knowledge of the in-situ stress state in a field is a
prerequisite for varying these parameters, and hence, a very essential
component for well design.