Ordovician-Silurian shale gas resources potential in Poland : evaluation of Gas Resources Assessment Reports published to date and expected improvements for 2014 forthcoming Assessment

The paper comprises a brief history and results of Assessment Reports of shale gas resources for the Polish Ordovician-Silurian Basin. The Reports have been confronted in the context of used criteria of assessing. The comparison shows that the early, most optimistic assessments (Wood Mackenzie, ARI & EIA) were based on very generalized data and different assessment methods than those used in the PGI and USGS Reports. In turn, the PGI and USGS Reports, based on USGS assessment methodology, were not so diverse taking into account the presented extreme low values of recoverable gas resources and the used methods of shale gas occurrence probability. The terms EUR (Estimated Ultimate Recovery) and AU (Assessment Unit), used in the USGS methodology of shale gas and shale oil resources assessment are characterized. The paper also presents assessment methods of technically and economically recoverable shale gas, and the significance of "sweet spots " as areas with the greatest probability for shale gas productivity. Finally, proposals for the reconstruction of future work on the new assessment (at the turn of 2014) of recoverable shale gas resources for the Polish Ordovician-Silurian Basin are recommended. The future assessment of shale gas resources should be more detailed, not only due to new geological input data (including results of exploration wells), but also thanks to segmentation of the whole Ordovician-Silurian assessment area into five smaller regional assessment units. The paper presents the criteria of area segmentation and the characteristics of proposed assessment units. The key geological, geophysical and geochemical criteria, which should be taken into consideration in the methodology of new shale gas resources assessment, are compiled. Moreover, to better understand the peculiarity of the Polish Ordovician-Silurian shales and reservoir attributes, and to fit these to shale gas recovery technology, the lessons coming from the US shale basins are discussed. In summarizing, the authors, presenting the conclusions and recommendations, refer to future shale gas resources assessment that, in their opinion, would help particularize the results and thus make them more authenticated