Effect of Decreased Porosity with Depth on Oil and Gas Reserves in South Louisiana Sandstone Reservoirs

G. I. Atwater, E. E. Miller, and G. B. Wiggins, III

The decrease in porosity with depth is the most important single factor controlling the amount of oil and gas in place per unit volume of sandstone reservoir rocks. A study of more than 17,000 conventional cores taken almost entirely from Miocene and younger sediments between approximately 1,500 and 19,500 ft showed that on the average porosity decreases 1.265% of total volume/1,000 ft of burial. Data from abnormally pressured reservoirs also fit the straight-line plot of porosities from all reservoirs.

Since 1965, conventional core data have become available for about 1,800 samples from lower Tertiary sediments between depths of 9,000 and 14,000 ft and more than 2,200 samples from Cretaceous sediments between depths of 15,000 and 22,000 ft. Improved wireline logging techniques have provided additional porosity data, particularly at depths where conventional core data are limited.

Data available since 1965 confirm the conclusion that, in south Louisiana, porosity and recovery of oil and gas per unit volume decrease with depth.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.