Comparison of Reservoir Quality from la Luna, Gacheta and Eagle Ford Shale Formations Using Digital Rock Physics

Ceron, Maria R.¹; Diaz, Elizabeth; and Walls, Joel
¹[email protected]

A large fraction of all whole core samples recovered worldwide today come from shale reservoirs. The primary reason for so much shale coring is that petrophysical models require rigorous core calibration to provide reliable data for reservoir quality, hydrocarbon-in-place, and hydraulic fracturing potential. However, the uncertainty in interpreting shale well log data is sometimes exceeded by the uncertainty observed in traditional methods of analyzing core samples. Most commercial core analysis methods in use today were developed for sandstones and carbonates exceeding 1 mD in permeability. On the other hand, high quality organic-rich shale is usually lower than 0.001 mD. This extreme low permeability creates challenges for existing methods and has contributed to the rise of a new approach to shale reservoir evaluation called Digital Rock Physics (DRP).

DRP merges three key technologies. One is a high-resolution diagnostic imaging method that permits detailed examination of the internal structure of rock samples over a wide range of scales. The second is advanced numerical methods for simulating complex physical phenomenon and the third is high speed, massively parallel computation using powerful graphical processing units (GPU’s).

The DRP process for analyzing rock properties of shale reservoirs at multiple scales, begins with whole core samples, progresses to smaller plug size samples, then ultimately to very high resolution 3D imaging of the pore space. This imaging, combined with unique and proprietary fluid flow algorithms, allows us to compute shale reservoir properties and provide clear 3D renderings of the pore structure.

A comparison between the results of core samples available from four wells in the Eagle Ford formation of southwest Texas, USA, and this study of core samples from La Luna and Gacheta formations from Colombia show that in many important characteristics (porosity, TOC, permeability), the shale samples from Colombia are comparable or better than those from the Eagle Ford shale of Texas.

In summary, multi-scale rock properties analysis brings several advantages to the process of shale reservoir characterization: Accurate porosity determination (connected, isolated, and porosity associated with organic material); permeability in horizontal and vertical directions; ability to determine relative permeability on low perm samples; improved upscaling of results; it works with whole core, core plugs, and cuttings/fragments.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013