Fracture Patterns and Controlling Factors of Cretaceous Tight Sandstones - Outcrop Analogues and LIDAR Applications

Fracture is of primary importance to the natural gas production capacity from many tight sandstone reservoirs in the Kuqa foreland area, Tarim basin, NW China, but the orientation, size and plane porosity of the fractures in the subsurface is difficult to measure directly. In this paper, utilizing a multi-level covering, we obtain the three-dimensional point cloud data from a Terrestrial light detection and ranging (LIDAR) survey launched at a typical outcrop and the positions of natural fractures are extracted strictly in the data volume section. It is founded that three groups of shear fractures are mainly developed in two periods with large inclination, short trace length and small spacing of normal distribution. Its patterns has provided a literal distribution of penetrating fracture zone and interlayer fracture zone with a single and a double set of advantage orientation respectively. The fracture plane porosity in the cross section has been calculated quantitatively with a range of 0.026∼0.081% and an average of 0.05% and the fracture development scale is controlled by lithology, layer thickness, paleostress and rock composition with a good exponential relationship. Our work could provide a workflow linking outcrop fracture observations to subsurface fracture modeling and enhances understanding reservoirs heterogeneity.