Characterization of rough-walled fractures in crystalline rocks
Published:January 01, 2003
S. R. Ogilvie, E. Isakov, C. W. Taylor, P. W. J. Glover, 2003. "Characterization of rough-walled fractures in crystalline rocks", Hydrocarbons in Crystalline Rocks, N. Petford, K. J. W. McCaffrey
Download citation file:
The full characterization of the rough surfaces of fractures and their resulting apertures is an important step in the drive toward an improved understanding of the factors which control fluid flow through rocks. This is crucial in igneous and metamorphic rocks, since fractures in these rocks may form the only significant pathways for fluid migration. Here we describe a three-pronged approach for the full characterization of rough fracture surfaces in a selection of crystalline rocks using a suite of software developed in house. Firstly, profiling is carried out using an optical method, which converts images of epoxy fracture surfaces covered with dyed water into topographies using the Lambert-Beer Law. Many hardware and software (OptiProfTM) developments give this method the upper hand over previous attempts at spectrophotometric analysis. It is not possible to profile every fracture surface, therefore numerical modelling of fluid flow is carried out using synthetic fractures with rough fracture surfaces that are representative of the natural rock fractures. ParaFracTM allows the analysis and parametrization of fracture surfaces and apertures. SynFracTM enables the numerical synthesis of fracture surfaces and apertures with prescribed basic parameters. Both procedures take full account of the complex matching properties of the fracture surfaces as a function of wavelength, as well as anisotropy within the properties defining the fracture surfaces and their resulting aperture. They have been rigorously tested on a large suite of synthetic fractures as well as real rock fractures. These tests have allowed relationships between the standard deviation of surface asperity heights, the fractal dimension and the matching parameters to be related to the resulting aperture of the fractures.
Figures & Tables
Hydrocarbons in Crystalline Rocks
‘Commercial oil deposits in basement rocks are not geological “accidents” but are oil accumulations which obey all the rules of oil sourcing, migration and entrapment; therefore in areas of not too deep basement, oil deposits within basement rocks should be explored with the same professional skill and zeal as ccumulations in the overlying sediments’, Landes et al. (1960), AAPG Bulletin.
Given that most OPEC countries are currently at or within 5% Production capacity, there is a growing need to look for ‘new oil’ and other hydrocarbons in non-traditional sources.
While oil and gas fields in crystalline basement are still discovered mostly by accident, as shown in this book, such reservoirs can be very prolific, especially if the basement rock is highly faulted or fractured. The chapters in this volume cover a diverse range of topics related broadly to the theme of hydrocarbons in crystalline rocks, and challenge explorationists’ definition of basement rock, which needs to be less narrow and more responsive to new geological ideas.