Effects of external temperature and dead volume on laboratory measurements of pore pressure and injected volume in a rock fracture

The accurate evaluation of pore pressure and injected volume is crucial for the laboratory characterization of hydromechanical responses of rock fractures. This study reports a series of laboratory experiments to systematically demonstrate the effects of external temperature and dead volume on laboratory measurements of pore pressure and injected volume in a rock fracture. We characterize the hydraulic aperture of the fracture as a function of effective normal stress using the exponential aperture model.This model is then employed to predict the pore pressure change and injected volume in the fracture without the influences of external temperature and dead volume. The external temperature changes in the cyclic loading test due to the Joule-Thompson effect for fluids. The effect of external temperature on pore pressure change in the fracture can be well explained by thermal pressurization of fluids. Our results also show that the external dead volume can significantly lower the pore pressure change in the fracture during the cyclic loading test under undrained conditions. The injected volume can also be substantially enlarged due to the external dead volume in a typical pore pressure system. Internal measurement of the pore pressure in the fracture using a fiber optic sensor cannot exclude the influences of external temperature and dead volume, primarily because of the good hydraulic communication between the fracture and pore pressure system. This study suggests that the effects of external temperature and dead volume on pore pressure response and injected volume should be evaluated for accurate laboratory characterization and inter-laboratory comparison.

Research on the distribution characteristics of explosive shock waves at different altitudes

There are great differences in the distribution characteristics of shock waves produced by ammunition explosions at different altitudes.At present,there are many studies on plain explosion shock waves,but there are few studies on the distribution characteristics of plateau explosion shock waves,and there is still a lack of complete analysis and evaluation methods.This paper compares and analyzes shock wave overpressure data at different altitudes,obtains the attenuation effect of different altitudes on the shock wave propagation process and proposes a calculation formula for shock wave overpressure considering the effect of altitude.The data analysis results show that at the same TNT equivalent and the same distance from the measuring point,the shock wave overpressure at high altitude is lower than that at low altitude.With the increase in the explosion center distance of the measuring point,the peak attenuation rate of the shock wave overpressure at high altitudes is smaller than that at low altitudes,and the peak attenuation rate of the shock wave overpressure at high altitudes gradually intensifies with increasing proportional distance.The average error between the shock wave overpressure and measured shock wave overpressure in a high-altitude environment obtained by using the above calculation formula is 11.1389%.Therefore,this method can effectively predict explosion shock wave overpressure in plateau environments and provides an effective calculation method for practical engineering tests.

A new measurement method for radial permeability and porosity of shale

To more conveniently and accurately obtain the radial permeability of shale,a new measurement method was proposed for the pressure attenuation of radial permeability and porosity in shale.Through experiments,this method could be used to get the pressure attenuation curve in annular space between the core and inner wall of PVT vessel under the helium along shale radial flow.Accordingly,a mathematical model was established to obtain the semi-analytical solution between pressure and time in the radial model.Meanwhile,through fitting the experimental results,the concentration conductivity and porosity of shale were obtained,and their relationship was used to derive the radial permeability of shale.This method was adopted to measure the permeability and porosity of two cores under three sets of different initial pressures in the annular space.The permeability test results were compared with those obtained by the conventional Dicker method and Smits pressure-attenuation method,and the porosity test results were also compared with those obtained by the conventional porosimeter,thus the feasibility and superiority of this method were confirmed.In contrast to the conventional pressureattenuation methods,this new model had advantages of simpler instruments and more convenient operation,and was also easy to measure the radial permeability and porosity of shale.