--> Abstract: Geochemical Controls on Petrophysical Responses and Properties; #90063 (2007)

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Geochemical Controls on Petrophysical Responses and Properties

 

Davies, Sarah1, Tim Brewer1, Joe Macquaker2, Mike Lovell1 (1) University of Leicester, Leicester, United Kingdom (2) University of Manchester, Manchester, United Kingdom

 

Petrophysical responses, such as nuclear and electrical measurements, are used to help constrain our petrophysical understanding against a geological model. Petrophysical properties such as porosity, saturation and permeability, define the storage and flow potential of fluids. The mineralogy and geochemistry of the rock matrix contribute to both the responses and the properties, but also affect the fluids.

 

Fine grained siliciclastic rocks (particularly shales) that comprise seals and sources differ from coarser siliciclastic reservoir rocks. Their more diverse mineral assemblages and chemical compositions produce complex systems that can be extremely heterogeneous. A fine grained nature combined with a clay-rich composition means the matrix has a large surface to volume ratio with significant total porosities, but small effective porosities, with little free water as it is bound. This reduction in available pore space has significant consequences for predicting saturation and permeability from petrophysical responses in these sedimentary rocks. This effect depends very much on the clay mineralogy and consequently the petrophysical properties of mudstones are dominated by their mineralogy and chemical variations. Clearly to understand the petrophysics of mudstones, and hence source rocks, fluid migration pathways and baffles, it is important to decipher: (a) the petrophysics of the minerals that build such rocks (e.g. clays, pyrite, quartz, zircon, monazite), and (b) how these minerals, particularly clays, affect the pore space (e.g. through cation exchange capacity) and bound water.

 

We examine the nature of the mineralogy and chemistry of mudstones and the control these exert on both the petrophysical responses and properties.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California