Shale Mechanical Properties Influence Factors Overview and Experimental Investigation on Water Content Effects

摘要

In the last decade, the unconventional resource has changed the global energy and petroleum industry. The technological innovations of hydraulic fracturing and horizontal drilling techniques, which require a good understanding of the rock mechanical properties of shale, have driven the economical production of shale reservoirs. However, the intrinsic rock-mechanical properties of shale rocks are extremely complex; they are affected by many factors, including confining pressure, water content, water salinity, TOC (total organic carbon), clay content, bedding plane orientation, mineralogy, anisotropy and others. Some factors (i.e., water content, TOC and clay content etc.) can significantly decrease the strength of shale rocks, and this weakening mechanism needs to be considered in hydraulic fracture designing and wellbore stability. This paper systematically investigates various key factors that impact the rock-mechanical properties especially the mechanical properties of shale rocks, including confining pressure, water content, TOC (Total organic carbon), clay content, bedding plane orientation, porosity, anisotropy, and temperature effects. We experimentally investigated the impact of water saturation on Barnett shale's rock-mechanical properties (Young's modulus, E and Poisson's ratio, v and uniaxial unconfined compressive strength (UCS)) using a Material Testing System (MTS-810). Experimental results showed that: 1) water saturation has a significant impact on Young's modulus and UCS. Young's modulus decreases 6.1% with an increase of a water saturation (1%) of Barnett shale core corresponding to the value of dry shale's Young's modulus; 2) Young's modulus and UCS decrease linearly with increasing water saturation; And 3) the relationship between water saturation and Poisson's ratio is not obvious.