Reservoir Engineering Theory: Proven, Probable and Possible.

This is written theory. No calculations are included. The material has been written in my own words and for the purpose of improving my knowledge of exam based topics in the Master of Science in Petroleum Engineering semester one course – Reservoir Engineering 1 at Heriot Watt University.

Reserves Definition: It is important to get this definition correct close to word-by-word. Reserves are those quantities of materials that are anticipated to be economically commercially recoverable from known accumulates from a specific date forward.

Reserves can be broken up into three classifications:

  • Proven
  • Probable
  • Possible

Proven Reserves Definition: Proven reserves are quantities of petroleum which by analysis of geological and engineering data, can be estimated with reasonable certainty to be commercially recoverable, from a given date forward, from known reservoirs and under current economic conditions, operating methods and government regulations. There’s a lot here so let’s write that out in a list. A proven reserve has a 90% probability that it is at least as large as indicated. Proven Reserves can also be broken into developed and undeveloped categories.

  1. Quantities of petroleum analysed by engineering and geological data
  2. Estimated to be commercially recoverable
  3. From a given date forward
  4. From known reservoirs
  5. Under current economic conditions
  6. With current operating methods
  7. And current government regulations

Probable Reserves Definition: Probable reserves are unproven reserves which by analysis of engineering and geological data have a greater probability of being recovered than not. When probabilistic methods are used we can say at least a 50% probability that these quantities can be recovered.

Possible Reserves Definition: Possible reserves are unproved reserves which by analysis of engineering and geological data are less likely than probably reserves to be recovered. Using probabilistic methods we can reference a probability of at least 10% that these reserves can be recovered.

Notice the subtle wording between proven reserves definition and the other two. Proven reserves has a 90% probability that at least that quantity of material will be recovered. Whereas probable and possible have at least 50% and 10% probability their listed quantities will be recovered.

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