A new multi-method approach to assess thermal maturity of Lower Paleozoic sedimentary successions: the case history of Polish Baltic Basin

Caricchi C., Corrado S., Di Paolo L., Romano C., Aldega L.,Grigo D., Vona A. (2014)
Poster, 87° Congresso della Società Geologica Italiana, 10-12, settembre, Milano
Rend. Online Soc. Geol. It., Suppl. n. 1 al Vol. 31

ABSTRACT

The problem of the reliable assessment of thermal maturity of sedimentary successions is crucial for the evaluation of hydrocarbons generation/expulsion. Sometimes, the use of traditional indicators of thermal maximum exposure might be misleading or insufficient to define thermal maturity levels, in particular in sedimentary successions that are devoid of vitrinite-huminite group macerals (e.g., Lower Paleozoic in age). To solve this problem we propose a successfully adopted multi-method approach to assess thermal maturity. This strategy consists of: (i) measurement of organoclasts reflectance; (ii) FT-IR and (iii) Raman spectroscopic analysis (iv) pyrolysis on dispersed organic matter and (v) X-Ray diffraction on fine grained sedimentary rocks. This approach guaranteed a robust cross check among thermal indicators as an input to burial and thermal modeling. Studied Lower Paleozoic sections derive from three deep wells, recently
drilled in the Polish Baltic Basin by ENI, with analysed depth intervals ranging between about 2 and 3 km. Firstly, from spectroscopic analyses (both Raman and FT-IR), we have devised selected indexes, sensitive to temperature increase, and correlated them to commonly adopted parameters (eg., vitrinite reflectance, Tmax etc). In the three analysed sections the integration among organoclasts reflectance, FT-IR and Raman indexes and XRD analyses provide a robust and well constrained assessment of thermal maturity that ranges from mid-late mature to over-mature. Furthermore, the late diagenetic zone has been identified by means of XR-Diffraction in agreement with results obtained from organic matter analyses. In conclusion this multi-method approach provided very encouraging results that make it a powerful tool for the assessment of thermal maturity of problematic organic facies. This could drastically reduce uncertainties concerning thermal modeling and positively influence decisions on the development of prospects, especially when aimed at exploring shale gas targets.