Integrated Reservoir Characterization of a Posidonia Shale Outcrop Analogue: From Serendipity to Understanding

Shale gas reservoir stimulation procedures (e.g. hydraulic fracturing) require upfront prediction and planning that should be supported by a comprehensive reservoir characterization. Therefore, understanding shale depositional processes and associated vertical and lateral sedimentological variability is key in predicting the character and position of sweet spots and to estimate their geomechanical properties. The Toarcian Posidonia Shale Formation is considered to be the main shale gas prospect in the Netherlands. However the scale at which reservoir heterogeneities occur is unknown and not easily estimated from the limited subsurface datasets. Therefore, a multidisciplinary reservoir study was performed on an outcrop analogue in the Cleveland Basin (UK), including sedimentological, biofacies, petrophysical and geomechanical analysis. The results help developing predictive models of sweet spot detection and allow to generate pseudo logs that can be compared with surface data. In spite of the apparent mudstone uniformity at outcrop and hand samples it is clear that the Toarcian succession presents complex patterns of heterogeneity at mm to outcrop scales. Climatic control on run off and the input of riverine material and coinciding changes in production of organic material appear the main controls on the distribution of sweet spots and zones of high fraccability.