S.A. Barclay1, R.S. Haszeldine1, P. W. M. Corbett2, D. K. Potter2, C. Graham1
(1) The University of Edinburgh, Edinburgh, United Kingdom
(2) Heriot-Watt University, Edinburgh, United Kingdom
ABSTRACT: Scaling-up Diagenetic Analyses From The Micro-scale To Macro-scale: A Shallow Marine Genetic Unit, North Sea
How can expensive and time-consuming micro-analyses from a few samples in a single well be reliably scaled-up to represent larger sandbodies? To address this problem a comprehensive suite of micro-scale analyses were performed on core through a single depositional unit in shallow marine Upper Jurassic sandstones from the UK North Sea.
Two coarsening-up cemented units each 10m thick were examined, and compared with the same uncemented units 800m shallower, 3km distant. Reservoir quality and authigenic cement distribution were determined by sampling at, 30cm intervals with conventional core-plug poroperm, thin section modal analysis, SEM-CL petrography, magnetic susceptibility and Rietveld quantitative XRD data. Selected samples were then analysed using SIMS to determine the variation in authigenic quartz d18O values with reservoir quality.
Relative reservoir quality is controlled by primary grainsize and sorting. Authigenic quartz and illite decrease absolute quality with increased burial. The data show that (a) volume of illite is linked to 1/grain size, 1/Kh, magnetic susceptibility, volume of pyrite and sample depth and (b) volume of quartz is linked to grain size, 1/Kh, 1/volume of illite and 1/sample depth. Authigenic quartz d18O data show similar variations. Single samples are needed to characterise uniform zones, whereas multiple samples are needed in heterogenous zones. This type of approach allows targeting of representative samples to reduce diagenetic analyses as opposed to uniformly-spaced or random sampling. Fewer, but representative, data enable statistically robust scale-up.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado