Mudstone Lithofacies Evaluation for Play Fairway Analysis: Characterization of the Paleozoic Shales of Poland

Abstract

A comprehensive sedimentologic analysis of the mudstone-rich Silurian and Ordovician intervals in the Baltic Basin, Podlasie Depression and Lublin Trough of Poland comprises a key stratigraphic component of Play Fairway Analysis. This study provides the basis for regional mapping and prediction of presence, thickness, and richness of three mudstone intervals across the play. The evaluation incorporates cores from legacy wells and recently drilled wells and includes macro core and computed tomography (CT) scan descriptions of conventional cores, thin section petrographic analysis and associated X-ray diffraction and geochemical data, and evaluation of wireline logs. The goals were to analyze the rock data to determine lithofacies assemblages within mudstone-dominated stratigraphic intervals; to capture the vertical and lateral heterogeneity of the assemblages; and, to model TOC-enriched preferred environments. The Poland Play Fairway Analysis focuses on three target intervals: Late Ordovician Upper Caradoc, Silurian lower Llandovery and the Silurian lower Wenlock. Paleogeographic setting, biostratigraphy and sequence stratigraphy are related to variations in rock composition and texture in order to identify lithofacies assemblages and interpret environments of deposition. Lithofacies assemblages are recognized based on multiple data sets at multiple scales of observation from thin section to core to wireline data, and capture the vertical and lateral heterogeneity of the assemblages. Key factors driving lithofacies distributions include water energy (position relative to fair weather wave base and storm wave base), accommodation space and intrabasinal seafloor topography. Depositional models, interpreted from the lithofacies assemblages, are used for fairway risking. Elevated TOC is found mainly in mudstones associated with transgressive systems tracts. Organic richness is highest where the section onlaps submarine highs and is condensed into thin intervals. The Upper Caradoc onlaps pre-existing submarine highs and consists of organic-rich, radiolaria-rich mudstone lithofacies that commonly occur in the Baltic Basin depression. Regionally, the lower Llandovery Formation, potential Baltic and Lublin basin targets, is highly variable in thickness as well as organic-richness. Faulting and folding associated with the Caledonian Orogeny (∼450–420 Ma) affected the thickness, richness and facies distributions in the southern Baltic and Podlasie Basins.

AAPG Datapages/Search and Discovery Article #90189 © 2014 AAPG Annual Convention and Exhibition, Houston, Texas, USA, April 6–9, 2014