Volumetric Reservoirs

[Ahmed Essam Tawfik]

what is meant by the volumetric reservoir and the non volumetric reservoir ?

[DAH7542]

That´s a common term in Reservoir Engineering that is worth discussing.

A reservoir is called "volumetric" when the volume occupied by the hydrocarbons (or Hydrocarbon Pore Volume, HCPV) does not decrease during pressure depletion (Dake - Fundamentals of Reservoir Engineering, p. 25). The following excerpt is modified from Ezekwe - Petroleum Reservoir Engineering Practice (p. 191) and explains this in greater details:

"Volumetric reservoirs are defined as completely isolated, closed systems with approximately constant hydrocarbon pore volumes. Volumetric reservoirs are presumed not to gain significant pressure support or fluid influx from outside sources, such as water influx from aquifers or neighboring shale (non-reservoir) layers. On the other hand, nonvolumetric reservoirs exhibit evidence of pressure support or influx of fluids (mostly water) from outside sources, such as aquifers or neighboring shale intervals".

Volumetric or non-volumetric reservoirs can be either oil or gas reservoirs since this classification is intended to describe the characteristics mentioned above, not the type of hydrocarbons being accumulated. In order to determine if a reservoir is o not volumetric, Material Balance Analysis is commonly used: a plot (seldom called "Campbell Plot" for oil reservoirs or "Cole Plot" for gas reservoirs) of the fluids produced at reservoir conditions (also underground withdrawal or "F") versus the sum of the expansive energy terms of the hydrocarbons, water and rock (known as "Et") should shield a horizontal straight line if the reservoir is trully volumetric. If this is the case, then the reservoir is also believed to produce under "Depletion Drive".

PS: the attached figure was taken from SPE 75354.

[Ahmed Essam Tawfik]

I strongly thanks you for this detailed answer