The Application of Drill Cuttings to Evaluate the Fracability in Unconventional Shale Gas Resources

Abstract

Selecting a good fracturing candidate that can maximize the complex fracture network in advance is beneficial for enhancing the fracturing effectiveness and the economic development of shale gas reservoirs. Brittleness is generally used to evaluate the capability of complex fracture networks by using critical mechanical parameters, but these parameters must be acquired from well logs and time-consuming triaxial core-scale mechanical tests. However, considering the physical and chemical instability of shales, standard-sized core plugs are difficult to obtain in some zones of interest. Thus, the analysis of drill cuttings by the combination of SEM/EDS (scanning electron microscopy-energy dispersive spectrometer) analyses and grid nanoindentation was used to replace conventional standard measurements on high-quality sized cores. A significant advantage of this technique is that drill cuttings can be collected from most wells. Furthermore, in contrast to traditional tests, the petrophysical and mechanical properties of shales can be characterized simultaneously. Thus, a comprehensive brittleness model can be established based on the mineral brittleness and mechanical brittleness. Experimental results demonstrate that the integration of grid nanoindentation and the deconvolution technique can provide reliable estimations of the homogenized Young's modulus and Poisson's ratio, while EDS mapping can provide accurate mineral compositions of the indentation area. The method is successfully applied to evaluate the brittleness of a shale gas well in a shale gas field in China, which demonstrates that this method is a fast and cost-efficient way to evaluate the brittleness of shale gas formations with a small volume of rock samples.