Experimental Measurement of Vertical and Horizontal Permeability of Storage Domain Rocks from the Krechba Field, Algeria and Controls on Their Permeability

Armitage, Peter J.¹; Worden, Richard H.¹; Faulkner, Daniel R.¹; Aplin, Andrew C.²; Butcher, Alan R.³; Iliffe, James ⁴
(1)Department of Earth and Ocean Sciences, University of Liverpool, Liverpool, United Kingdom. (2) School of Civil Engineering and Geosciences, Newcastle University, Newcastle, United Kingdom. (3) Intellection Pty Ltd, Milton, QLD, Australia. (4) BP Exploration, BP, London, United Kingdom.

Rock properties play a crucial role in determining the fluid flow properties of a structure and so are important during exploration, appraisal and field development. For unconventional reservoirs, it is of critical importance to understand the controls on fluid flow, requiring increased knowledge of their petrophysical and petrological characteristics. Permeability was measured experimentally using custom-made apparatus across a range of effective pressures for samples (including tight reservoir, caprock, and fluid flow barriers) of a natural tight gas storage domain, and current CO2 storage reservoir, from the Krechba Field, Algeria. Permeability was measured perpendicular to bedding (vertical permeability, kv) and parallel to bedding (horizontal permeability, kh). Mercury injection porisimetry data, textural and mineralogical data from traditional light microscopy, backscatter secondary electron microscopy (BSEM), cathodoluminescence (CL) techniques and the new QEMSCAN® technique were used to elucidate controls on permeability. Permeability was as low as 10-23 m² and thus lies at the very lower end of values reported for fine-grained siliciclastic caprocks. Permeability is effectively controlled by porosity, mean pore throat radius and percentage clay fraction. Permeability generally decreases with decreasing porosity and pore throat radius and increasing clay mineral content. Scatter in the trends was caused by the heterogeneous distribution of clay minerals within samples leading to extreme kh/kv ratios (50,000). Primary depositional features led to contrasting layers of relatively low and high permeability within individual samples. Vertical permeability is controlled by the lowest permeability layer. Horizontal permeability is controlled by the highest permeability layer. Samples with the same porosity, mean pore throat size and clay mineral content can have kh/kv differing by >4 orders of magnitude. If clay minerals are localised into clay-rich beds sandwiched between quartz-rich beds there is an extreme kh/kv ratio but if clay minerals are disseminated throughout the rock, kh/kv approaches unity.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.