Reservoir Description of the Subsurface Eagle Ford Formation, Maverick Basin Area, South Texas, USA (SPE 154528)

The Eagle Ford Formation (EF) is a marl deposited during a highstand on a broad shelf along the paleo-Texas coast. It is thickest in the Maverick Basin, a small sag related to crustal thinning. Datasets were collected including core, cuttings, chemostrat, biostrat, and well logs. From the core and cuttings, core CT scans, thin sections, SEM images, FIB-SEM volumes, and XRD/XRF tables were acquired. The purpose of the data was to understand EF depositional processes and rock textures, and to create a predictive model for reservoir properties. The regional EF study began with correlation of 400+ logs. The correlation involved a sequence stratigraphic framework (SSF) based on log character and refined with ash correlations, biostrat and chemostrat. Texture seen in core, core CT scans, and the SEM/FIB-SEM work was compared to the SSF. These data gave insights into patterns of fluctuating oxygen and energy levels which were then included into the depositional model (DM). The DM shows regional patterns of composite parasequences in which properties such as TOC, porosity, carbonate content and rock texture are predictable. SEM/FIB-SEM images show that pores in the EF are mainly intergranular or within organic matter (OM), and that the structure of OM pores is related to maturity level. Using the SSF, reservoir properties can be predicted along the EF trend: cycles of EF with good reservoir properties can be mapped with respect to hydrocarbon fluid zones to yield risk maps. By understanding how and where different parts of a parasequence stack you can better predict sweet spots for well productivity, both geographically and stratigraphically. Each unconventional play is unique; what works for reservoir characterization and risk mapping in one is not always applicable to another. It is important, then, to document which strategies work in each play.