Even though the Macondo incident in the Gulf of Mexico did not directly involve shallow drilling hazards, since Macondo, the oil and gas industry has focused increased attention on all possible hazards involved in deep water drilling. The new focus has followed a three-step approach to address various drilling hazards that may be encountered in deep water: Identification, Prevention, and Mitigation.
This presentation focuses on understanding the geologic origin of various hazards in deep water by reviewing the geologic origin, physical characteristics, and behaviors of the three main deep water geo-hazard types.
- Man-made surface hazards including linear geometry and single site geometry hazards.
- Sea-floor geologic hazards including pockmarks, mud volcanoes, unstable sea floor, unstable slopes, and mass sediment movements.
- Sub-surface geologic hazards including shallow water or gas flows, reactivated faults to surface, gas chimneys, disassociating gas hydrates, and anomalous pore pressure effects.
In the past few years exploration below major salt canopies (allochthonous salt) and layered evaporites (autochthonous salt) has discovered significant accumulations of hydrocarbons in the GoM and along the Atlantic basin margin, but has also identified several types of drilling hazards that can significantly increase the risk and cost of exploration in salt basins. This presentation also examines potential drilling hazards often associated with massive salt and layered evaporates including:
- Entering salt (cap rock),
- Drilling within the salt (sutures, inclusions, layered evaporites of variable density and creep rate),
- Exiting the salt (rubble zones, feeders and welds), and
- Drilling immediately below the salt (mobile bitumen and diagenetic alteration).
Examples are presented from the Gulf of Mexico, Brazil, Angola, and other Atlantic margin basins.