Fractured Zone Detection Using Petrophysical Logs by Rescaled Windowed R/S Analyses and Discrete Fracture Network (DFN) of Yanchang Formation in Mahuangshan-Hongliugou Area, Ordos Basin, China

Abstract

Structural fractures generally develop in the upper crust strata and are usually distributed in a convergent pattern, forming structural fracture zones with a specific strike. Fracture zones control the reservoir seepage system and seriously affect the migration and accumulation of oil and gas in tight sandstone reservoirs. Therefore, characterizing the characteristics of the fracture zones for tight oil exploration and development effectively is essential. In this paper, the variable scale fractal method is introduced to calculate the petrophysical log, and a new curve $H$ is built. An intensity log is to characterize the intensity of structural fracture development. The $H$ curve is in a good linear relationship with the intensity curve after the comparison of the $H$ curve and intensity curve in 32 wells. A quantitative relationship between $H$ and the intensity curve is established. Based on the parameters obtained from the core and image logs, the discrete fracture network model was established using $H$ curves from more than 300 wells, and the structural fracture zone was analyzed. The model shows that the fracture zones formed by structural fractures are in S-N and NW-SE directions in the study area. The orientation of the structural fracture zone is consistent with that of the fractured fault zone and fault, and the development of the fractured zone is consistent with the regional tectonic evolution characteristics. The characteristics of the fracture zone explain the distribution law of oil accumulation and groundwater salinity in the study area.