Modifications of methods for the fracture analysis from borehole data in application to shale formations

Systematic joints play an important role in effective fluid conductivity and in the mechanical response of shale reservoirs to hydraulic fracturing. Specific features of joints, such as their strata-bound aspect, and their attitude, commonly normal to bedding, make it necessary to modify standard methods of their analysis from borehole data. Our study, based on borehole core and microresistivity image logs, is adjusted to typical exploration procedure, with vertical boreholes penetrating subhorizontal beds. This simple configuration makes it possible to measure the true height of most joints. We have used joint height as the weighting parameter for the construction of orientation diagrams and for computation of fracture intensity profiles. We also propose here a method for evaluation of fracture orientation error on directly oriented core, show how to distinguish joints present in the scanner record but absent from the core, and how to apply this kind of data filtering to core/log correlation. We also propose to extend the analysis of mineralized joints by using the type and degree of vein cracking in order to better characterize their susceptibility to hydraulic stimulation. Application of the modified methods revealed a stratification of joint distribution which, in some cases, may not be observed due to the scarcity of joint data from boreholes.