Fracture toughness of organic rich shale via nanoindentation: A comparison of energy-based methods
Kouqi Liu, Sirous Hosseinzadeh, Majid Safaei-Farouji, Bo Liu, Hem B. Morta, Mehdi Ostadhassan
Abstract
Fracture toughness is an important mechanical parameter for proper modeling of reservoir stimulation which is necessary for production from tight formations. To measure fracture toughness, several models have been proposed based on nanoindentation data, however, the comparison of these models in organic rich shale is still limited in the literature. To obtain a better understanding of the suitability of these models, we applied two distinct energy based methods, one which takes advantage of the whole force-displacement curve (K IC _whole) and the other one that considers the fracturing-induced pop-in events (K IC _pop). To estimate and compare the fracture toughness from either of these methods, nanoindentation data is acquired from a sample that was collected from the Wolfcamp Formation, USA . The results showed that for the soft mechanical phase (clay minerals), the K IC _whole varied from 0.020 to 0.313 MPa m 0.5 while the K IC _pop from 0.02 to 0.330 MPa m 0.5 . In the hard mechanical phase (carbonate and quartz), the K IC _whole was found between 0.380 and 0.84 MPa M 0.5 , and the K IC _pop was estimated from 0.38 to 0.780 MPa m 0.5 . These values for the intermediate phase was, 0.220–0.588 MPa m 0.5 and 0.215–0.500 MPa m 0.5 , respectively for each method. Statistical analysis of the results based on the t-tests verified that the fracture toughness of different mechanical phases that is derived from these two different models is quite comparable. Overall, considering the simplicity of the calculations and the limitations in the approach that is based on pop-in events, our recommendation would be to use the whole force-displacement curve to obtain the fracture toughness of geomaterials.