FRACTURE ARCHITECTURE OF THE HIGH PLAINS AQUIFER, NORTHEASTERN TEXAS PANHANDLE: IMPLICATIONS FOR GEOLOGIC STORAGE OF CARBON DIOXIDE

Aquifer protection is a central imperative of underground injection control in the United States, and so understanding aquifer architecture is an important part of environmental protection in areas favorable for subsurface storage of carbon dioxide.

The High Plains Aquifer of the northeastern Texas Panhandle includes loess-like sandstone of the Ogallala Formation and Quaternary strata that include sand, clay, chert, and caliche. Target formations for CO₂storage and enhanced oil recovery are in Pennsylvanian sandstone deeper than 2,000 m in this area. Field study reveals that the Miocene-Quaternary formations contain numerous joints that provide insight into aquifer architecture and subsurface flow pathways.

Length, orientation, spacing, and cross-cutting relationships of more than 1,700 joints were measured in the field and in high-resolution satellite imagery. The fracture networks consist of well-developed systematic joints and cross-joints. Systematic joints are strongly aligned and have length that commonly exceeds 60 m. Cross-joints tend to terminate at systematic joints, and so joint length is typically equal to systematic joint spacing (~2 m).In vertical section, the joints are typically curvilinear and strata-bound, cutting indurated sandstone and chert and terminating within friable sandstone. Analysis of joints indicate that the strike of the systematic joints varies among beds and regionally. Fracture azimuths are strongly clustered in western siliceous caprock area, showing the vector mean azimuths as 67° and 146°. Whereas the azimuths in eastern Ogallala are less clustered with vector mean azimuths of 52° and 126°. Spacing analysis indicates that the joint spacing in the study area follows a lognormal spacing rule. These fractures may be the product of modern stress regimes in Texas Panhandle and may have a significant effect on flow in the High Plains aquifer system.