RELATIONSHIP OF FACIES AND RESERVOIR QUALITY IN ROTLIEGENDES DESERT SANDSTONES, SOUTHERN NORTH SEA REGION

Publisher Website
Google Scholar
Abstract
Permian Rotliegendes desert sandstones cored in two wells in the southern North Sea were grouped as wadi, adhesion‐ripple, dune‐base and dune‐top sandstones on the basis of sedimentary structure and grains‐size characteristics. The porosities of these sandstones differ significantly. Those of wadi origin have the lowest values (φav.=5.5%) and the dune‐top sandstones have the highest (φav.=14.6%). The present study is amied at explaining these differences. The sandstones, which have been buried to a depth of approx. 4.000 m. have a complex diagenetic history marked by envirnment‐and depth‐related changes. Apart from authigenic ferric oxide, dolomite, anhydrite, K‐feldspar and quartz, they are characterised by well‐developed pressure solution and well‐crystallised authigenic illite and chlorite. The chlorite has a pore‐bridging growth habit which disturbs the porosity‐permeability relationship.On the basis of thin‐section petrographic point‐count analyses and porosity and permeability measurements, and by means of multivariate analysis, the nature and the small‐scale distribution of sorting in each of the sandstone facies types are ultimatly isolated as the main variables explaining the porosity differences. These sandstones thus display porosity differences which correlate with primary sedimentary structure. This relationship was not destroyed even at deep burial and marked diagenetic change.