Abstract:
Rock characterization in term of brittleness is necessary for successful stimulation of shale gas reservoirs. High
brittleness is required to prevent healing of natural and induced hydraulic fractures and also to decrease the breakdown
pressure for fracture initiation and propagation. Several definitions of brittleness and methods for its estimation has been
reviewed in this study in order to come up with most applicable and promising conclusion. The brittleness in term of
brittleness index (BI) can be quantified from laboratory on core samples, geophysical methods and from well logs. There
are many limitations in lab-based estimation of BI on core samples but still consider benchmark for calibration with other
methods. The estimation of brittleness from mineralogy and dynamic elastic parameters like Young’s modulus, Poison’s
ratio is common in field application. The new model of brittleness index is proposed based on mineral contents and
geomechanical properties, which could be used to classify rock into brittle and ductile layers. The importance of
mechanical behavior in term of brittle and ductile in shale gas fracturing were also reviewed because shale with high
brittleness index (BI) or brittle shale exist natural fractures that are closed before stimulation and can provide fracture
network or avenues through stimulation. The brittle shale also has low breakdown pressure and no fracture healing as
compared to ductile shale. The integration of laboratory and geophysical methods (determination of P and S waves from
well logs) are recommended for accurate estimation of brittleness index (BI) for shale gas reservoirs.
