Characterization and origin of fracture patterns in the Woodford Shale in southeastern Oklahoma for application to exploration and development /

Abstract

The Woodford Shale is an important unconventional gas shale in Oklahoma. Production is by artifical fracturing of naturally fractured or unfractured rock. Therefore, understanding natural fracture networks in the Woodford may help in developing fracture stimulation procedure.

This thesis characterizes fractures within an exposed section of the Woodford Shale by integrating outcrop and subsurface data. The main objective of this research is to document and understand the natural fracture patterns within the Woodford Shale by integrating and calibrating fractures and strata in exposed quarry walls using laser imaging detection and ranging (LIDAR) data, 2D seismic lines, and the logs and core acquired in a well drilled behind a quarry wall.

Fracture measurements in the outcrop and LIDAR data revealed two extensional fractures set. Group 1 is a systematic fracture set with parallel orientations, regular spacing and mineral filling , having a median strike direction of N85°E. Group 2 is a nonsystematic fracture set, younger than Group 1, having a median strike direction of N45 °E. There is a greater abundance of fractures in the Upper Woodford Shale because of it s higher content of quartz. There is no lithology or bedding change laterally within the quarry walls , where the average fracture spacing is about 1.2m ( 4ft).

The 2D seismic lines imaged the Upper-Middle Woodford contact and the Woodford-Hunton unconformity surface. The faults interpreted on the seismic follow the same trend as the regional faults observed in the quarry.

The present stress field in the area of study has an ENE-WSW direction that generated fractures in Group 2, different from the paleostress that generated fractures in Group I. In the area of study , there was no relevant relief on the Woodford-Hunton unconformity surface that could have affected the fracture distribution in a greater way than local tectonics.

This information will be used as a baseline for improved understanding of fractures in the Woodford Shale to facilitate gas production by knowing fracture orientation and in situ stress.