Paper: BOREHOLE STABILITY IN HORIZONATAL WELLS- CASE HISTORIES FROM THE PERMIAN BASIN

In the Permian Basin, failure of the borehole wall while drilling vertically (wellbore instability) is seldom a problem. In horizontal wells, however, this is not the case. The imbalance between vertical and horizontal earth stresses, and the fluid pressure in the rock, can lead to problems if insufficient mud weight is used. This can lead to tight-hole and stuck-pipe problems that can escalate into losing the wellbore (and, sometimes, the BHA), requiring a sidetrack.

In this presentation the causes of wellbore instability are reviewed and the methodology for predicting a safe mud weight is described. In contrast to vertical wells, mud weight requirements in horizontal wells are more exacting. An approach to update required mud weight while drilling and geosteering will be described. Case history examples of applying this approach to wells drilled in the Permian Basin will be presented which integrate borehole stability with hole cleaning and geosteering requirements.