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Using LIDAR Images for Quantitative Analysis of Natural Fractures in Woodford Shale Outcrops Along I-35 in Southern Oklahoma

Abstract

High resolution LIDAR (Light Detection and Ranging) images help provide a quantitative analysis of natural fractures in unconventional reservoirs for outcrop scale reservoir characterization. The LiDAR creates a precise 3D point cloud of outcrops that can be used to quantitatively measure the systematic natural fracture sets present on the surface. During this study, we have conducted a LIDAR imaging survey of the Devonian Woodford Shale exposed at the surface along the Arbuckle Anticline in southern Oklahoma. The Woodford is an unconventional reservoir that produces hydrocarbons in many unconventional gas fields in Oklahoma and Texas. Only systematic natural fractures sets caused by deformational structures are analyzed and non-systematic fractures are ignored because non-systematic fractures are primarily caused by surface erosion. The primary focus of this study is to explore the relationship between fracture spacing, fracture density and bedding thickness. The secondary focus is to determine the effect of mineral composition and TOC (total organic content) have on systematic fracture sets because these two variables provide primary control of the brittleness of shale beds. Two outcrops were chosen near the I-35 interstate. The first one is along the northern overturned limb of the Arbuckle anticline and the second is located on the southern upright limb. At each outcrop, 1m2 mechanical inventory squares were selected and scanned using a VZ-400 LiDAR machine at a resolution of 0.003. Additionally, rock samples were collected at each 1m2 mechanical inventory square and mineral composition and TOC amounts were determined. Our preliminary results suggest that while structural control is very important, fracture spacing and density on the northern overturned limb and upright limb are not only controlled by deformation. Bedding thickness, mineral composition and TOC are also very important variables on fracture spacing and density of the natural fractures in the two Woodford outcrops.