How high can fracture porosity become in the ultra-deep subsurface?

Knowledge of how high can fracture porosity become in the ultra-deep burial conditions is important but remains problematic.Fracture aperture and porosity are measured using X-ray computed tomography(CT)at atmospheric pressure and then calculated by image logs.Special attention is paid to how high fracture porosity can become in ultra-deep(>6000 m)settings,and which situations will result in high fracture porosities.In situ stress magnitudes,which can be calculated using well logs,control fracture performances,and dissolution along fracture improve fracture porosity at ultra-deep burial depths.Low horizontal stress difference(Dr<25 MPa),very high fracture density will result in a high fracture porosity.Fracture porosity can keep as high as 2.0%in relatively low in situ stress conditions even at ultra-deep burial depths.In intense in situ stress conditions(Dr>45 MPa),a high degree of dissolution along the fracture dramatically increases fracture porosity.Dissolution will result in the vuggy fracture planes and improve fracture porosity up to 2.0%.The results provide insights into the detection,characterization,and modeling of subsurface fractures.

Thermodynamics for the non-conventional synthesizing of out-of-plane ordered double-transition metal“312”and“413”MAX phases(o-MAX):A high throughput linear programing first-principles calculation

The reaction thermodynamics for synthesizing the“312”and“413”o-MAX phases using the powder met-allurgy are investigated using a linear programing optimization algorithm based on the high-throughput first principles phonon calculations.The validity and reliability of the current methodology are verified by correctly predicting the impurities in four experimentally known o-MAX systems including Cr-Ti-Al-C,Cr-V-Al-C,Mo-Sc-Al-C and Mo-Ti-Al-C.The formability of each investigated o-MAX phase is evaluated by means of formation enthalpy and formation Gibbs free energy in a temperature range from 0 K to 1700 K.It is revealed that the thermodynamic stability of the“413”o-MAX structure is no better than that of the“312”phase.The formability of“413”o-MAX is also reduced at high sintering temperature,compared to that of“312”phase.The optimal synthetic routes are predicted for all thermodynamically stable“312”and“413”o-MAX phases.It is found that most o-MAX phases considered could be prepared as the single phase using the non-conventional synthetic routes from the aspect of reaction thermodynamics.Few of them including Cr_(2)TaAlC_(2),Nb_(2)HfAlC_(2),Nb_(2)TaAlC_(2),Nb_(2)Hf_(2)AlC_(3),Nb_(2)Ta_(2)AlC_(3),Mo_(2)V_(2)AlC_(3)and Mo_(2)Ta_(2)AlC_(3)are predicted to be either destabilized at high temperature or overwhelmed by the most competing side reaction.