Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Hydrocarbon Bitumen in Deepwater Gulf of Mexico – An Integrated Petroleum Systems and Geomechanics Perspective
(1) Global E&P Technology, Hess Corporation, Houston, TX.
(2) Americas Developments, Hess Corporation, Houston, TX.
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. These bitumen occurrences pose significant challenges to deepwater Gulf of Mexico drilling operations. A number of field development projects, including Mad Dog and Pony in Green Canyon, Big Foot and Spa Prospect in Walker Ridge, experienced substantial increase in drilling costs associated with such bitumen encounters. The current consensus is to avoid bitumen formations as much as possible.
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 and at an early stage of thermal maturity, prior to peak oil generation.
A series of geomechanics studies were conducted to investigate the effect of temperature, pressure, and drilling fluids on bitumen mechanical behaviors. These lab tests revealed that bitumen mechanical and flow properties are primarily controlled by temperature and conditions of confining stress. A material model for in-situ bitumen was derived and applied in detailed 3D numerical simulations. At reservoir scale, the numerical models analyzed the stress and deformation inside and around the bitumen formations with different lateral extensions and thickness, and evaluated the stability of various bitumen shapes at in-situ conditions.
Subsequent integration of regional temperature data and 3D basin modeling highlighted the influence of subsalt thermal structure on bitumen behavior in the greater Pony area. Bitumen is visible in both sand and shale recovered in cores, and occurs at multiple depth levels in the form of dikes, sills, and disseminated “blebs”. 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.