Characterization of an analogue of fractured reservoir using LIDAR, GPR and conventional data

Abstract

The Solvay quarry displays karstified and heavily fractured strata of peritidal platform carbonates of late Barremian age, that can serve as an analog to subsurface fractured reservoirs. In addition of being a potential analog, this study also aims to improve the methodology used in building of DOM (Digital Outcrop Model). The originality of the applied methodology is the integration of conventional outcrop analysis, LIDAR (Light Detection and Ranging) and GPR (Ground Penetrating Radar) data. The goal is to produce an accurate and efficient DOM that resolves the three-dimensional sub-seismic heterogeneity of the fracture distribution in the strata. Stratigraphic and fracture analysis with conventional methods was performed on about 2 km of exposed cliff faces that were subsequently scanned with the LIDAR equipment. Transversal and longitudinal 2D GPR lines and 6 GPR cubes were acquired on the quarry floor to correlate the quarry walls. The 2D GPR data were statically corrected using the GPS horizontal coordinates of the transects, high-resolution topography provided from LIDAR data, and a replacement velocity of 0.098m/ns. GPR and LIDAR data were loaded into 3D CAD software to interpret each horizon and to reconstruct the structural framework. To characterize the fracture distribution; scanline measures were performed along the quarry walls, 3D migrated GPR data was interpreted by delineating high amplitude zones originating from focused diffractions that define fracture surfaces (Grasmueck et al. 2005) and LIDAR point clouds were processed to reveal the main planes families that form the rough wall surface. Two of GPR cubes show the coexistence of four sub-vertical fracture families trending N-S, E-W, NW-SE and NE-SW. The NE-SW fracture family is not detected in the outcrop using the scanline method because the fracture is parallel to the direction of the quarry wall, however the LIDAR algorithm found two families planes oriented near this fracture family. This planes are related to the morphological features of NE-SW joints like twist hackles. The 3D fractures constructed with GPR data allow to filter and understand the planes computed with LIDAR data and to determine the sampling bias due to scanline orientation. Subsequently, the LIDAR data and the scanline measures allow to obtain a continuous distribution of the families fractures along the quarry allowing to characterize dip and azimuth variations.