Unconfined compressive strength of Lower Paleozoic shales from the Baltic Basin (northern Poland)

• Autorzy: Wojtowicz Michał , Jarosiński Marek , Pachytel Radomir Władysław

Identyfikatory

DOI

10.7306/gq.1603

• Języki publikacji: EN

Abstrakty

EN

Unconfined compressive strength (UCS) is one of the crucial parameters for geomechanical modelling of unconventional reservoirs useful for the design of hydraulic stimulation of hydrocarbon production. In spite of a large amount of UCS data collected from the Lower Silurian and Ordovician shale successions of the Baltic Basin (northern Poland), no comprehensive study on this subject has been published so far. Here, we compile the results of 247 single-stage confined compressive strength tests (CCST) provided by our industrial partner from four exploration boreholes. Based on the integration of these results with geophysical logging data, including dipole sonic logs, we derive empirical equations describing the relationship between UCS and Young’s modulus or sonic wave slowness. Considering the strong anisotropy of elastic properties in shales we have introduced different empirical equations for UCS_v (vertical) and UCS_h (horizontal), respectively perpendicular and parallel to bedding. The formula for UCS_h is determined with less accuracy than for UCS_v due to scarce laboratory tests with bed-parallel loading. Based on the empirical formula proposed, we have estimated the VTI-type of anisotropy to be in the range of 12-27%, depending on the lithostratigraphic formation. The results of our UCS estimations are compared with the results of multi-stage CCST from the adjacent borehole. Both confined tests yielded similar results for UCS_v, with slightly higher values obtained from the multi-stage tests. In turn, a comparison of our solution with the results of true uniaxial compressive strength tests (UCST) for vertical samples from one of the studied boreholes revealed a significant discrepancy. The mean UCS results for shale formations from UCST are several times lower than those evaluated from the single-stage CCST. The usefulness of the results obtained for borehole breakout analysis is discussed.

Słowa kluczowe

EN

unconfined compressive strength; triaxial strenght tests; empirical equations; shale complexes; Baltic Basin

• Wydawca: Państwowy Instytut Geologiczny - Państwowy Instytut Badawczy
• Czasopismo: Geological Quarterly
• Rocznik: 2021
• Tom: Vol. 65, No. 2
• Strony: art. no. 33
• Opis fizyczny: Bibliogr. 31 poz., rys., tab., wykr.

Twórcy

autor

Wojtowicz Michał

• Wellfield Geoscience, Grzegórzecka 67C/102, 31-559 Kraków, Poland

autor

Jarosiński Marek

• Polish Geological Institute – National Research Institute, Rakowiecka 4, 00-975 Warszawa, Poland

autor

Pachytel Radomir Władysław

• Polish Geological Institute – National Research Institute, Rakowiecka 4, 00-975 Warszawa, Poland

Bibliografia

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Uwagi

Opracowanie rekordu ze środków MNiSW, umowa Nr 461252 w ramach programu "Społeczna odpowiedzialność nauki" - moduł: Popularyzacja nauki i promocja sportu (2021).