Brief procedure to determine the amount of oil and gas in a certain trap. 

   1. Determine the range of drainage area. Drainage area is from where oil and gas flow to the trap.
   2. Find out the loss of oil and gas during migration. This process is generally more complex 
      for gas because gas can move more freely and can be absorbed by oil and water.
   3. Compare the volume of the trap with the volumes of oil and gas and determine the remaining
      amound of oil and gas in the trap.

   The article "Concepts for Estimating Hydrocarbon Accumulation and Dispersion" describes this process
in more detail. It was included in "AAPG Memoir" published by AAPG in 1984. This is brief
and easy to understand. You can find this book in Lindgren Library(the code is TN870.5.P477) 
and I, also, have a copy of it.

   For the real calculation, some geological information on the region is needed. We can get
some factors from that information and estimate the amount of petroleum resource in a specific trap.
However, This procedure is actually a simplification of real process, and the point is that 
it deals the process of formation and migration of oil and gas as if it were an event that 
happened in a moment. So, actually the geological factors in the calculation should be able
to reflect the difference made by the time taken for formation and migration. It takes the
assumption that it is possible to make this simplication, and we should 
think about its validity.

   However, my purpose is not the general theory, but about some specific region in Alaska. 
So, I should investigate the geological structure of the region first.