Brittleness evaluation method of shale based on confining pressure correction

The influence of confining pressure on the brittleness of shale is very significant, usually with the increase in confining pressure; the shale shows a tendency to change from brittle to plastic. Therefore, the confining pressure correction is an important part of the brittleness evaluation, but it is often neglected in the conventional shale brittleness evaluation methods. This paper proposes a two-step confining pressure correction method to integrate the brittleness evaluation methods of mineral components, elastic parameters, and mechanical parameters and to comprehensively construct a shale brittleness evaluation index based on confining pressure correction. Step 1 zero confining pressure correction: the elastic brittleness index at zero confining pressure is calibrated using the mineral brittleness index to remove the effect of envelope pressure on brittleness and thus represent the intrinsic brittleness characteristics of the rock. Step 2 confining pressure trend correction: the mechanical parameters are used to correct the rock for the trend of confining pressure in order to reasonably characterize the weakening effect of the confining pressure on the brittleness of the rock, and reasonably characterize the transition from brittle to plastic as the confining pressure increases. By applying it to the brittleness evaluation of actual logging data, the evaluation results can truly and objectively characterize the brittleness of rock under in situ confining pressure.