Integrating Depositional Facies and Sequence Stratigraphy in Characterizing Unconventional Reservoirs in the Cretaceous (Cenomanian-Turonian) Eagle Ford Shale, South Texas

摘要

The middle-to-Upper Cretaceous Eagle Ford Shale of South Texas is a mixed siliciclastic/carbonate unconventional resource play characterized by considerable lateral and vertical reservoir heterogeneity. Detailed analysis of 4 cores from the producing area was performed to evaluate the stratigraphic control on reservoir heterogeneity. Core analysis shows that the Eagle Ford interval consists of a hierarchy of three relatively symmetrical and regionally consistent 3rd order sequences with 2-5 associated 4th order high-frequency sequences (HFS's), all within an overall 2nd order transgressive trend.,Correlating core analysis to wireline logs indicates that the 3rd and 4th order sequences can be confidently identified in the Eagle Ford. Higher frequency (5th order?) cycles (HFC's), however, lack regional continuity and cannot be correlated between wells, likely due to a combination of allocyclic and autocyclic controls. Reservoir quality poroperm correlates to position within the stratigraphic framework, where highest reservoir potential correlates to transgressive systems tract's at all scales of cyclicity. Stacking patterns of 4th order HFS's and 5th order HFC's dictate the vertical variability of reservoir units in the Eagle Ford. These HFS's/HFC's consist predominantly of transgressive systems tract to early highstand systems tract calcareous mudstones (highest reservoir potential) and well lithified, late highstand systems tract to early lowstand systems tract foraminiferal packstone/grain stones that vertically compartmentalize reservoir units. Results of this investigation demonstrate how techniques of identifying and linking depositional facies to reservoir quality in an early coring program, and correlating these observations to wireline log signatures may assist in the characterization of Eagle Ford reservoirs in wells without core data.