A Comprehensive Geomechanical Risk Assessment for Drilling and Completion of a Deep Horizontal Well in Highly Stressed Subsalt Carbonate Formation – A Case Study from Kuwait

Chinmaya Pattnaik
Kuwait Oil Company

Horizontal well placement into deep sub-salt tight naturally fractured carbonate reservoirs in North Kuwait involves high risk due to high magnitude of pore pressures, stresses and anomalous stress orientation patterns on field scale. While vertical wells are drilled on a routine basis in these HPHT reservoirs, drilling of horizontal wells is constrained due to associated drilling hazards and the geomechanical challenges.

First horizontal well, targeting Tight Fractured Limestone of Oxfordian –Callovian age, immediately below the Gotnia Salt+Anhydrite section, is planned with possible barefoot/pre-perforated un-cemented liner completion. Detailed geomechanical study revealed that in-situ stress field de-coupling occurs between the formations overlying and underlying the Gotnia interval. Understanding the high-resolution geomechanical properties of this Gotnia section requires a lot of data, which is nearly impossible due to practical operational constraints.

This study covers well planning aspects from geomechanical perspective, in this complex sub-salt stress setting through reconciliation of independent geomechanical observations at the same time overcoming issues related to data limitation. Sub-surface data from offset vertical wells was used in conjunction with customized geomechanical rock tests to constrain the stress setting as accurately as possible. These field and lab data provided inputs for stress simulation and enabled understanding of local mechanisms that are causing failure in the reservoir. Based on field characteristics and geomechanical modeling, the horizontal well plan was optimized with suggestions on customized drilling practices. This study also provided guidelines for envelope of stable drawdown conditions without jeopardizing the well stability during production.

AAPG Search and Discovery Article #90178©2013 AAPG Geosciences Technology Workshop, Baltimore, Maryland, July 16-17, 2013