Evaluation of Fracability Index for Reservoir Rock - a Laboratory Study

Brittleness Indices (B.I.) defined based on varied input parameters have been historically used as a guideline for evaluation of target zones meant for hydraulic fracturing. However, a number of recent studies have raised valid concerns regarding the efficacy of the utilization of Brittleness Index alone as selection criteria for hydraulic fracturing purposes. The alternative selection criteria proposed by researchers is a measure of the ease of fracability which utilizes a combination of the Brittleness Index along with the fracture toughness. In the present study, experiments were performed on rocks representing multiple lithologies to obtain the various input parameters required to estimate B.I. Parameters obtained from the experiments include the unconfined compressive strength (UCS), Young’s Modulus, Poisson’s ratio and Brazilian tensile strength. The ISRM recommended Cracked Chevron Notched Brazilian Disk (CCNBD) method was used to evaluate the fracture toughness of the samples. Brittleness Indices based on lab measured properties were then calculated to observe variation of Brittleness Index, fracture toughness and fracability index (F.I.) with rock mechanical properties and to provide a data based evaluation of the applicability to hydraulic fracturing design.