Abstract
An integrated geological and geophysical approach is presented for the recognition of unconventional targets in the Miocene formations of the Carpathian Foredeep, southern Poland. The subject of the analysis is an unconventional reservoir built of interlayered packets of sandstone, mudstone and claystone, called a “heterogeneous sequence”. This type of sequence acts as both a reservoir and as source rock for hydrocarbons and it consists of layers of insignificant thickness, below the resolution of seismic data. The interpretation of such a sequence has rarely been based on seismic stratigraphy analysis; however, such an approach is proposed here. The subject of interpretation is high-quality seismic data of high resolution that enable detailed depositional analysis. The reconstruction of the depositional history was possible due to the analysis of flattened chronostratigraphic horizons (Wheeler diagram). The identification of depositional positions in a sedimentary basin was the first step for the indication of potential target areas. These areas were also subject to seismic attribute analysis (sweetness) and spectral decomposition. The seismic attribute results positively verified the previously proposed prospects. The results obtained demonstrate that the interpretation of the Miocene sediments in the Carpathian Foredeep should take into account the depositional history reconstruction and paleogeographical analysis.
Highlights
The terms “heterolithic bedding” or “heterogeneous sequence” are used commonly in the description of sedimentary series that are built of interlayered packets of sandstone, mudstone and claystone
Their existence proves that we provided the correct definition of the sequence boundaries
In the presented study, we decided to divide sequence boundaries into two types, type I and type II [56], even though type II discontinuities were recently considered to be an integral part of the failing stage system tract (FSST; a shift in the shoreline basinward during one sequence with a fall in the relative sea level)
Summary
The terms “heterolithic bedding” or “heterogeneous sequence” are used commonly in the description of sedimentary series that are built of interlayered packets (laminae or lenses) of sandstone, mudstone and claystone. Considering the ratio of sandstone to mudstone, the thickness of the layers and the frequency of their appearance (i.e., the frequency of sandstone layers appearing in mudstone intervals), various types of heterogeneous sequences can be defined. The increasing interest in the heterogeneous sequence in the Carpathian Foredeep is due to the recent discoveries of gas fields [7,8,9]. Gas flows are present for intervals of low porosity and permeability, which, in well log analysis, are associated with low gas saturation. These intervals are challenging for well log interpretation. The low resolution of well log data and the high clay content associated with these sequences strongly influence the results.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
