How XLOTs Can Reduce Uncertainty Related to Regional Stress and Wellbore Stability Assessments

Even today, extended Leak-off tests (XLOT) are rarely performed in the Oil and Gas Industry. Concerns about creating a fracture in the wellbore on purpose usually supersede the positive effects of gathering valuable rock mechanical data. An example is presented where considerable uncertainties related to prevailing stresses have had a negative impact on the wellbore stability study for a highly deviated exploration well sidetrack. The resulting mudweight recommendations to the drilling team were so conservative, the well would not have been drillable anymore. By including an XLOT at the casing shoe above the planned kick-off point, it was possible to update the initial very conservative wellbore stability study with accurate stress data. This not only led to more realistic mudweight recommendations to the drilling team, but in addition, it was possible to determine the actual fracture closure pressure. With that, a true upper limit for Equivalent Circulating Density (ECD) while drilling was established. Unforeseen surprises due to pre-existing fractures or weak zones were avoided and the well was drilled and completed successfully as planned.