2019 AAPG Annual Convention and Exhibition:

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Identifying and Drilling through Intra-salt Hazards—A Case Study from Stampede Field, Deep-Water Gulf of Mexico

Abstract

Intra-salt features, such as salt sutures, sediment inclusions, and base salt complexity, often pose drilling hazards which could significantly raise drilling days and cost. If possible, these features must be identified and avoided. Occasionally, sub-salt reservoir target locations and drilling constraints force drilling through these features. Therefore, identification and evaluation of these features are critical, in addition to mitigation plans, to deal with an adverse outcome.

Stampede is a sub-salt middle Miocene age oil discovery currently in development and production phase. Located in the Green Canyon protraction area of deep-water Gulf of Mexico, it is the deepest TVD subsea production in the GOM (>30,000’ TVDSS) and lies in a 4-way structural closure segmented by faults. The reservoirs are accessed by drilling through almost 15,000’ thick salt, which is composed of multiple salt bodies. This salt, which once was at the bottom of an ancient GOM basin, moved due to high sediment input and density disequilibrium. As the basin grounded out, multiple phases of salt build-up formed the canopy as evidenced by several sutures. Some of the sediments dragged by salt became inclusions within and near the base of salt. Stampede wells had to be drilled through some sutures and sediment inclusions to reach the reservoir target locations.

In this paper we will discuss an inter-disciplinary effort towards identifying the intra-salt hazards, designing the wells and making a mitigation plan to avoid any undesirable drilling issues. Results from drilled wells will be presented. 3D seismic data of various types, salt tectonics concepts, data from nearby wells, pore pressure considerations and, above all, collaboration between subsurface and drilling proved to be major factors behind a successful drilling campaign through a complex salt body over the Stampede field.

ACKNOWLEDGMENTS

The authors would like to thank Stampede co-owners (Union Oil of California, Nexen, and Equinor), and Hess management for their permission to submit the abstract.