Large Versus Small Reservoirs

Haeberle, Frederick R.
Consulting Geologist, Delaware, OH

Why do some reservoirs contain more hydrocarbon reserves than others? Is it strictly a mater of acreage or do any of the reservoir properties have an effect? A review of reservoir properties and percent of reserves may show if any of the commonly measured reservoir properties assist in the accumulation of large reserves.

Data was reviewed for 225 reservoirs in one basin. Measurements for depth, oil-column thickness, porosity, permeability, pressure, temperature, API gravity, gas-oil ratio, and water saturation compared with the percent of reserves showed all reached maximum values in the lower half of the reservoir property measurements and then decreased mainly in the higher half of the values. Although some interesting results appeared it is difficult to arrive at any conclusion that these properties might be important in the accumulation of reserves.

The influence of depth is shown as it increases so do the oil-column thickness, gravity pressure, temperature and gas-oil ratios but the number of reservoirs, percent of reserves, the average porosity, permeability, water saturation all decrease. The results of this review apply to one basin and should not automatically be expected in other basins. This type of study can be used to determine what, if any, effect the reservoir and fluid properties have on the amount of reserves present in any basin.

AAPG Search and Discovery Article #90031©2004 AAPG Eastern Section Meeting, Columbus, Ohio, October 3-5, 2004