A Comprehensive
Classification of Seals Based on Worldwide Subsurface Analogs
Guzmán, José I.1, Rod Sloan2,
Shengyu Wu1, Shaoqing Sun2 (1) C&C Reservoirs, Inc,
Houston, TX (2) C&C Reservoirs, Ltd, Maidenhead, Berks, United Kingdom
We have erected a comprehensive
classification of seals based on the number, type, location, and combination of
sealing surfaces of nearly 1000 reservoirs from around the world. Previous
classifications focused on sealing and leaking mechanisms, on capillary
properties, or on geometric configuration, but they have not been empirically
tested or calibrated with the height of hydrocarbon columns. Our classification
involves three end-members and their combination into nine families: Simple Top
seals, Updip Lateral Fault seals, and Lateral Stratigraphic seals. Over
one-half of the world's largest reservoirs are sealed by combination seals, and
nearly half of the ultimately recoverable reserves in the reservoirs studied
are contained in traps with simple top seals.
Our seals classification is the
foundation for a systematic checklist of parameters that must be accounted for
when evaluating the seal chance of success. For prospects involving only a
simple top seal, key parameters include the lithology, thickness, depositional
system, and orientation of the seal with respect to the trap, as well as the
presence/absence of faults in the cap-rock. When updip fault seals are
required, parameters such as the ratio of fault throw to reservoir thickness,
maximum burial temperature, and structural dip, should be considered in
addition to those listed for simple top seals. If the prospect involves lateral
stratigraphic seals, the nature of the updip change in facies and the
structural dip are the most important parameters. Commonplace conjectures in
risking seals can be minimized by pre-drill methods that provide clues to these
parameters.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California