Petrophysical Properties of Barnett Shale
Argyrios Karastathis, Chandra Rai, and Carl Sondergeld
Mewbourne School of Petroleum and Geological Engineering, The University of Oklahoma, Norman, OK
In this study, we report results of a petrophysical study on Barnett Shale from Fort Worth Basin, Texas. A total of 1,350 ft of core from two wells was analyzed. The following measurements were made: density, porosity, mineralogy, total organic content (TOC), P- and S-wave velocity, velocity anisotropy, and fracture orientations. A new technique for measuring effective porosity was developed. The porosity values compare well with those measured by a commercial laboratory. The porosity values of upper Barnett are found to be more depth dependent as compared to the lower section. Quantitative mineralogy, using Fourier Transform Infrared spectroscopy, was measured at almost every foot of core. In the first well the upper Barnett exhibits a higher average concentration of carbonates with calcite being the dominant component compared to the lower Barnett where dolomite dominates. In terms of quartz and clays, both sections have approximately the same average concentrations. In the second well the two sections have similar mineralogy. Based on porosity and mineralogy measurements it is evident that the shale formation exhibits substantial heterogeneity. Velocity anisotropy measurements showed that only the upper Barnett exhibits transverse isotropy. P- and S-wave velocities are found to be more sensitive to TOC as compared to porosity. Preferred fracture/microcrack orientations as determined on sixteen core samples by circumferential velocity analysis (CVA) agree well with directions determined from visual examination of cores. Formation Microresistivity Imager (FMI) log data do not agree with the CVA results. This is most likely due to the fact that FMI senses electrical resistivity contrast where as CVA senses elastic properties contrast.
AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas