Petrophysical Characterisation of Posidonia Shale (Lias Epsilon)
Research output: Research › Master's Thesis
In contrast to conventional rock samples, the investigated shale samples undergo significant changes (development of micro-fissure, desintegration) during coring, storage and/or experiments unless special procedures are applied. To develop these countermeasures and determine the essential laboratory parameters that control the behaviour of this rock type is the aim of my thesis. The study object was Posidonia shale (Lias, Epsilon) from southern Germany to which 16 different experimental methods were applied. In total, 121 Posidonia shale cores were investigated. My research shows that the linking of standard methods with advanced tools (e.g. micro - Computer Tomography, Field Emission Scanning Electron Microscopy) is necessary to obtain sufficient understanding of the nanostructure. These methods are only applicable when utilizing modification adaptations to deal with the complex behavior of shale gas samples (such as ultra-low permeability, stratification, mineral assemblage, and friability of the samples). Porosity was determined by 6 different methods, compared and detailed analyzed and discussed. Within the scope of this work, a method to prevent the frequent disintegration by utilizing an adapted heat shrink tube technique with an adequate desiccation and saturation method was developed. I proved that this procedure is necessary to avoid secondary porosity. In case of hardly accessible pore systems, I discovered that porosity determination for aqueous medium merely leads to appropriate results by application of pressure saturation technique. A test series was initiated for this particular purpose and I found that the standard gravimetric methods - without countermeasurements - yield a porosity loss in a range of 10-25% compared to Helium porosimetry. Cores drilled parallel to the layering yield gas permeabilities of 10E-17 to 10E-19 m2, while plugs drilled perpendicular have values between 10E-14 and 10E-16 m2. An essential result of investigation is that samples reveal high porosity of approx. 8-10 %. In a 3D analysis by applying SEM images, a low connectivity was documented and explained the low permeability found by hydraulic experiments. Apart from the flow properties, the maturity, residual water, organic matter, clay minerals, etc. were determined. In some samples up to 12% illite and approx. 5% immature kerogen were detected which may lead to potentially hydraulic blocking in pores.