--> ABSTRACT: Influence of Depositional Sand Quality on Porosity and Permeability: Examples from Brent Group Reservoirs in the Northern North Sea, by S. N. Ehrenberg, P. A. Bjorkum, and P. H. Nadeau; #91019 (1996)
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Influence of Depositional Sand Quality on Porosity and Permeability: Examples from Brent Group Reservoirs in the Northern Previous HitNorthNext Hit Previous HitSeaNext Hit

S. N. Ehrenberg, P. A. Bjorkum, and P. H. Nadeau

Multivariate statistical analysis was applied to examine correlations between reservoir quality and petrology in two data sets from the Middle Jurassic Brent Group. One of the data sets is from relatively shallow depth and has been little affected by chemical diagenesis (Statfjord Nord & Ost Fields; 2.3-2.6 km below the Previous HitseaNext Hit floor), while the second data set is from a more deeply buried reservoir having an advanced degree of diagenesis (Huldra Previous HitFieldNext Hit; 3.6-3.9 km). Much of the total variation in porosity and permeability (0.02 mD to >7 D in both sets) can be accounted for by laboratory measurements of parameters mainly related to depositional sand quality, including "shaliness" (represented by bulk-rock alumina content), early carbonate cement, feldspar content, and grain size. De pite major differences in the proportions of different sedimentary facies in the two data sets, they have similar ranges of depositional sand quality and therefore probably had similar reservoir quality early in their burial history. Deeper burial diagenesis at Huldra Previous HitFieldNext Hit has shifted the average porosity and permeability lower and produced a bimodal permeability distribution, apparently reflecting preferential preservation of permeability in the cleaner sandstones.

Based on these examples, a method is outlined for "unmixing" the diagenetic and lithologic components of variation in regional compilations of sandstone porosity-permeability data. The procedure and its consequences are illustrated using a regional compilation of core data from the Brent Group of northern Previous HitNorthNext Hit Previous HitSeaTop.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California