The Barnett and Eagle Ford shale formations are two of the most actively drilled shale plays in the U.S. The petrophysical properties of these organic-rich shales are essential to assess their potential to be developed economically. In this paper, we present a systematic laboratory methodology we have used to characterize and compare the petrophysical properties of Barnett and Eagle Ford shale formations.
Preserved core samples from these two formations were used for the characterization. Petrophysical properties measured include the native water activity of the shales, the swelling induced by different fluids in directions perpendicular and parallel to bedding, Brinell hardness, and P-wave and S-wave velocities. Brinell hardness and wave velocities were compared before and after shales came into contact with water-based fluids to study the effects of shale-fluid interactions on these properties. A unique 2-D swelling indicator in our lab allowed us to measure swelling in two directions simultaneously. A pressure transient technique was used to determine the permeability of water-based fluids flowing through the shale samples.
Our results showed a good correlation between changes in weight, swelling, Brinell hardness, and sonic velocity measurements. Anisotropic swelling was observed in directions parallel and perpendicular to the bedding planes. Sonic velocities were converted to dynamic elastic moduli. Our results also demonstrated the uniqueness of individual shale plays in terms of petrophysical properties.
Hydrocarbon production from low permeability formations has existed in the U.S. for more than 100 years. However, it was not until a decade ago that shale gas development and production experienced a sudden expansion, thanks to the use of horizontal drilling and hydraulic fracturing. These technologies enable natural gas to be produced from shale reservoirs economically.
Among all the shale formations, the Barnett and Eagle Ford shales are two of the most actively drilled plays in U.S. Hydrocarbon production from the Barnett shale started in the 1980s while that from the Eagle Ford was more recent (Mullen et al., 2010). The Barnett shale's daily gas production of 1.3 billion cubic feet (bcf) in 2007 was the highest in Texas. The growth rate has been more than 10% annually (Bowker, 2007). On the other hand, the Eagle Ford shale has been developed at a tremendous pace since early drilling and completions activities began in 2008. Over 1,000 wells were drilled between 2008 and 2011 (Centurion, 2011). Despite their different periods of development history, both the Barnett and Eagle Ford shales have served as testing grounds for some of the most innovative methods for drilling and completing wells.