Discussion on the rising segment of the mercury extrusion curve in the high pressure mercury intrusion experiment on shales

In order to explain the rising segment of the mercury intrusion curve in the high pressure (60,000 psi) mercury intrusion tests on shales, this study implemented a series of analyses on 7 Lower Silurian Longmaxi Formation shale samples from 4 wells in the Sichuan Basin, China, including helium-based porosity, TOC abundance and X-ray diffraction. Two pressure balance time values, namely 30 s and 60 s, were used in the high pressure mercury intrusion tests. According to the results, the compressibility of shales, instead of the pressure balance time, was identified as the main contributor to the rising segment in the mercury extrusion curve. Further, it was proposed based on the helium-based porosity and mercury intrusion porosity that the pore space could be compressed to about half of the original in the high pressure condition. The pseudo compression ratio was found to be mainly affected by the bulk density, which was further influenced by the contents of quartz and feldspar. Results of this study were expected to provide a better insight into the influence of rock compression and deformation during the mercury intrusion, and subsequently the calibration of the mercury intrusion method.