1/18/2013

1st Chapter Meeting and Guest Lecture of the Spring 2013 Semester - To start, we had our first chapter meeting of the spring, where we went over upcoming events and membership over lunch. Following the meeting, Dr. Richard Bishop provided a great talk (abstract below) to start the 2013 Spring Lecture Series. Dr. Bishop received his Ph.D. from UH, and is mother, Dr. Margaret Bishop, was the first female tenured professor at the Department of Earth and Atmospheric Sciences. He currently works for RSK [UK] Limited and is the 2012-2013 AAPG Foundation Trustees Chairman. Dr. Bishop also gave a talk, "World Oil Supply in Transition", at the EAS Department Seminar, so we appreaciate his time with us!
 

IMPLICATIONS OF SOURCE OVER CHARGE
Percent Trap Fill and Its Implications 
 

Abstract: Numerous publications over the past 30 years have shown examples of fault leak / seal in a wide variety of geologic settings. Importantly, traps filled to a leak point are full traps even though we rarely describe them as such.
 
The widespread occurrence of full traps implies that the source rock productivity has exceeded trap capacity which, in turn has implications such as the following:
 
Oil vs. gas (trap content when both gas and oil are available to the trap):

  • Gas will displace oil so the occurrence of both free gas and oil in a single reservoir requires gas leakage
  • Gas will displace oil, so a trap that seals gas will contain only gas even if oil is available to it
  • Saturated oil occurs because the trap leaks free gas.

Trap volume:

  • Field size is limited by a leak or spill point, not source rock yield.
  • Contacts show trap limits are either leak or spill points.
  • Faulted reservoirs may have bed seal if the faults die in the overlying seal. Such reservoirs may be full to the spill point.
  • Instead of using a continuous distribution to describe trap area, some are more appropriately described as discrete values or a combination of discrete plus continuous distributions (e.g. a combination of discrete plus lognormal). Examples will be shown.

Trap risking: o Spill from downdip traps may reduce risk of charge in updip traps

  • Trap risking can be based on number and type of potential leak points as well as seal quality. Given similar stratigraphy, traps with more potential leak points have greater risk than those with fewer leak points
  • Regional top seals with few faults (e.g. failed rifts or margin sags) can reduce risk perception due to recognizing bed seal rather than fault seal. These traps are more likely to be filled to spill and thus larger field sizes than vertically leaking hydrocarbon systems. The caution, however is that many widespread, thick top seals may also leak vertically.