Hydraulic fracturing has become an important stimulation method for unconventional oil/gas reservoirs to achieve industrial capacity. Fracability evaluation has become one of the most important step during the reservoir characterization and fracturing job design, which is beneficial for identifying the best candidate fracturing zone. In this paper, we provide a detailed review of the existing fracability evaluation methods. The evolution of the fracability evaluation method from the single-factor method, i.e. the brittleness method, to the multi-factor methods which incorporate brittleness, fracture toughness, in-situ stress as well as natural fracture parameters has been summarized. For the brittleness methods, different definitions of brittleness have been summarized and compared. For the multi-factor fracability evaluation methods, particular emphasis has been paid on illustrating how the factors were selected and incorporated into different fracability evaluation methods and possible field evidences validating the effectiveness of different fracability evaluation methods. In addition, the emerging 3D fracability evaluation attempts based on 3D seismic data and geomechanical analysis, which may serve as a guidance for finding the so-called engineering sweet spots, have been introduced in details. Finally, possible future work to improve the effectiveness of fracability evaluation is discussed.
With the increasingly prominent contradiction between international energy supply and demand, the exploration, development and consumption of conventional oil and gas resources are becoming rapider. Due to great market demand, the exploration and development of unconventional oil and gas resources has gradually become a hot spot in the current oil and gas resource exploration and development research. China has abundant reserves of unconventional oil and gas resources. According to statistics, 42 major coal-bearing basins in China have coalbed methane reserves with a depth of less than 2000 m in coal beds reaching 36.8×1012 m3; National shale oil reserves reach 7199×108 t; The estimated total amount of shale gas resources has also reached 30.7×1012 m3 [1]. Obviously, unconventional energy resources are of great development potential.
