Hydrocarbon Bitumen in Deepwater Gulf of Mexico - An Integrated Petroleum Systems and Engineering Perspective

Hydrocarbon bitumen, here defined as a highly viscous hydrocarbon accumulation, has been encountered during the exploration and development of several deepwater discoveries in the Gulf of Mexico (GOM). These bitumen occurrences pose significant challenges to deepwater GOM drilling operations. Several field development projects experienced substantial increase in drilling costs associated with such bitumen encounters. Our study was aimed at a holistic understanding of subsurface bitumen behavior through a broad integration of both geoscience and engineering approaches. Petroleum systems analysis indicated that bitumen encountered in the greater Pony area is low-maturity kerogen derived from a mobilized source rock of Jurassic age. This bitumen was most-likely mobilized in early Miocene, prior to peak oil and gas generation. A series of rock mechanics tests revealed that bitumen mechanical and flow properties are primarily controlled by temperature and conditions of confining stress. The highly viscous nature of subsurface bitumen at source level forces the bitumen migration and emplacement process to utilize sediment interfaces such as fractures, faults, and salt welds, rather than Darcy flow through porous media. These multidisciplinary findings provide important constraints to bitumen emplacement timing, spatial distribution and geometry which, in turn, have direct implications for mitigation strategies in drilling operations.