Print this pageEagle Ford Condensed Section and Its Oil and Gas Storage and Flow Potential
Slatt, Roger M.*1; O'Brien, 
Neal
R.2;
Miceli Romero, Andrea A.1; Rodriguez, Heidyli 1
(1)
University of Oklahoma, Norman, OK.
(2) State University of New York at
Potsdam, Potsdam, NY.
The Cretaceous Eagle Ford Shale in southwest Texas is actively being pursued for oil and gas. Results are presented of a scanning electron microscopy (SEM) study coupled with energy dispersive analysis (EDX) in evaluating the storage and flow potential for oil (and gas) in this shale.
The Eagle Ford Shale is calcareous (64% average CaCO3), thus its properties and production performance cannot be directly compared to other common, more siliceous resource shales. However, it is like many other shales in containing an organic-rich condensed section (CS) immediately above a combined sequence boundary (SB) and transgressive surface of erosion (TSE); in this case the upper surface of the Buda Limestone. An excellent exposure of this CS occurs at “Comstock West” a roadcut located along Highway 90 about 30 miles NW from Del Rio, Texas. Here, the shale weathers gray; but is black and has a strong hydrocarbon odor on a fresh surface. TOC averages 5.3%, and it contains Type II kerogen, making it an excellent marine oil and gas source rock. However, at this location the rocks are thermally immature with Tmax values of 423-429°C and average Ro of 0.53%.
Scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX) has indicated ‘total area porosity’ can reach 10%, and ‘individual pore area’ can range up to 0.2μm2. SEM/EDX analyses have also revealed the presence of at least three important pore types associated with: a) floccules, b) coccospheres, and c) foraminifera. Floccules are particularly well developed and provide pores up to 1μm in diameter. Both the internal chambers of coccospheres and their spines are hollow, open, and up to 1μm in diameter and several um’s long. Nanopores also exist between the randomly oriented coccolith plates in the matrix. Hollow, internal chambers of foraminifera can be 10’s of μm in diameter. Hydrous pyrolysis treatment followed by SEM/EDX has produced oil within some of the pores, thus providing clues as to residual oil generation and primary migration. Results indicate that the calcareous condensed section within the Eagle Ford has ample storage and flow potential for oil (and gas) relative to some of their more siliceous counterparts.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California