Shear Waves Anisotropy and Image Logs Integration for Improved Fracture Characterization

Abstract

ABSTRACT: Natural fractures aperture and porosity have a significant impact on the quality and production of naturally fractured tight reservoirs. The existence of fractures that channel fluids towards the wellbore enhances the productivity of the field. In this context, near wellbore fracture characterization is a key parameter for accurate discrete fracture network (DFN) modelling and therefore evaluation of fractured reservoirs productivity. In this paper, fracture parameters are estimated using coupling of advanced logging tools in the Cambro-Ordovician tight sand reservoir situated in the Central Ahnet basin, Algeria, where natural fracturing is critical and plays a key role in reservoir production. Cores are expensive and their recovery in highly fractured reservoirs is limited. In addition, the non-oriented cores, and the difficulty to expose them to downhole conditions make the use of the image logs analysis more valuable. As a first step, fractures were identified and evaluated using the FMI images and 498 natural fractures were discerned. The integration of Sonic Scanner allowed a reclassification of the fractures to 267 open and 231 closed fractures based on the interpretation of anisotropy dispersion curves obtained from the three wells. An advanced processing workflow was executed on the open fracture traces observed on the FMI logs in order to estimate the kinematic and hydraulic aperture of the fractures. The results obtained were used to characterize fracture porosity. Three sets of open natural fractures were identified based on their orientations and apertures. 1. INTRODUCTION Naturally fractured reservoirs are found all over the world and contain considerable volumes of oil and gas reserves. The study of fluid flow and transport processes in fractured porous media has attracted lots of interest over the last half-century and has been one of the most active areas in examining flow in subsurface reservoirs (Wu, 2016). Highly fractured reservoirs are generally due to the complex tectonic activities and their characterization is a recurring challenge. The interconnected fracture network ensures the flow of fluid at large scale and the fracture system (i.e., aperture, spacing, etc.) needs to be characterized in order to understand and simulate the fluid flow process. Discrete Fracture Network (DFN) models are constructed to help with field development and optimization, and this need an accurate integration of natural fractures in the near-wellbore regions to improve the inter-well fracture prediction by involving and combining various advanced well logging technics such as, high-resolution image logs and sonic scanner (Rezig et al., 2018).