Geometric properties and scaling laws of the fracture network of the Ypresian carbonate reservoir in central Tunisia: Examples of Jebels Ousselat and Jebil

Abstract

The fracturing network has a significant impact on fluid circulation and productivity in fractured buried reservoirs. In this work, we present the results of the analysis of outcrop fracture networks in the Ypresian nummulitic limestone hydrocarbons reservoir, located in Central Tunisia. The study is based on outcrops in two anticlinal structures of different extensions and geometries: Jebels Ousselat and Jebil, in the North-South Chain of Central Tunisia. The fracture network was characterized by the analysis of lineament attributes, derived by photo-interpretation of the fracturing data at the regional scale. Herein, we demonstrate that the distribution of fracture lengths (L), treated as distinct sets or taking in consideration the whole directions, fits a power law. Likewise, the spacing (E) between fractures of length (L), for each distinct set, adjusts to a law of the same type. Statistical distributions of lineament length and spacing follow power laws, highlighting the fractal nature of the fracture network. Further, the coefficient of variation of lineament spacings and the characteristic exponent of the power-law of lineament length indicate that the fracturing process is intense in the region and the fracture network reaches a mature stage of development. Fractal analysis of the fractures network of the Ypresian Reservoir in Jebels Ousselat and Jebil displays a self-similar nature of these parameters over a scale range extending from 0.7 cm to 22.4 cm. The obtained geometric parameters (scaling laws) indicate that the network has reached an advanced stage of development (distribution of fracture lengths in power-law) and is fractal (self-similar).