Abstract
Rock fracability characterization is a key issue for unconventional reservoirs stimulation. This property not only controls hydraulic fracture initiating and propagating pressure, but also affects the stimulated reservoir volume (SRV) which determines well productivity. Several parameters such as brittleness, plasticity and toughness among others are frequently referred in the literature to describe rock fracability. This paper discusses the validity of some of these parameters and emphasizes the fracture mechanics approach to characterize rock fracability based on the critical stress intensity factor (KIC).
An experimental study was conducted using synthetic and real Vaca Muerta (VM) shale samples. KIC was determined using two types of specimens, the notched Brazilian disc and the semicircular three point load tests. The influence of applied load rate, material composition and medium was analyzed. The implications of these parameters in the hydraulic fracture process are discussed. The experimental results were compared with KIC values calculated using information obtained from Vaca Muerta fracture jobs.
1. INTRODUCTION
Effective hydraulic fracturing is a key issue for successful shale play development and exploitation. This challenge demands characterization of appropriate rock mechanical properties. The concept of rock "fracability", referred as a material property that determines the capability for fracturing the rock during a stimulation operation, has become one of the main drivers to select sweet spots in a given unconventional formation. This property not only controls hydraulic fracture initiating and propagating pressure, but also affects the stimulated reservoir volume (SRV) which determines well productivity.[1]
Several parameters such as brittleness, plasticity and toughness, among others, are frequently referred in the literature to describe rock fracability. The different brittle indexes (B*) proposed by several authors, which are calculated using other rock mechanical properties as the Young´s modulus (E), Poisson´s ratio (?) among others, are good examples of this.
