Abstract: Reservoir Characterization of Thinly Laminated Heterolithic Facies Within Shallow-Marine Sand Bodies

Renu Gupta, Howard Johnson, Beate Myking

Shallow marine sandstones typically form high quality reservoirs but they can contain a significant proportion of extremely heterogeneous facies. Particularly significant are heterolithic (mixed interlaminated sand-mud) deposits which are common in estuarine/incised valley-fill reservoirs and other tidally-influenced depositional environments. The complex mm/cm-scale interfingering of sands and clays in these reservoirs is below the resolution of most logging tools, which poses major problems for the petrophysical evaluation, quantitative reservoir modelling and reservoir performance prediction.

This study outlines an integrated geological/petrophysical framework for the reservoir characterization of heterolithic facies from the Jurassic of the North Sea Basin which utilizes well logs, cores, minipermeameter and analog outcrop data. The calibration of wireline logs (GR, LDT/CNL, EPT and dipmeter) with cores helps in establishing the relationship between the architecture of sand-shale laminations and their wireline log response/electrofacies.The routine sampling procedure for porosity/permeability measurement from cores will not accurately determine the average reservoir properties for these heterolithic intervals. The selection of measurement points is of vital importance for determining average reservoir properties. The minipermeameter measurements are especially useful for hese thin bedded reservoirs and serve as a useful guide for reservoir zonation and evaluation of petrophysical properties from wireline logs. The incorporation of analog outcrop data helps further in establishing vertical and lateral communication relationships at field scale.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela