Experimental Investigation of Water Saturation Effects on Barnett Shale's Geomechanical Behaviors

Abstract

Abstract Shale gas is one of the most rapidly expanding trends in onshore domestic oil and gas exploration and production today. Improving the performance of shale gas wells typically requires the improvements of fracturing technologies. One of the most important factors that affect hydraulic fracture propagation is the geomechanical property of rocks (Young's modulus, E and Poisson's ratio, ν and so on). In reservoir conditions, most reservoir rocks contain a certain amount of connate water, which indicates geomechanical properties measured by using dry samples suffer substantial flaws. This paper is to experimentally investigate the impact of water saturation effects on Barnett shale's geomechanical properties (Young's modulus, E and Poisson's ratio, ν and uniaxial compressive strength (UCS)). Nineteen Barnett shale cores (satisfied with ASTM standard) were first partially saturated with KCL water to various water saturation degree. A Material Testing System (MTS-810) was then employed to test the elastic properties and UCS of those partially saturated Barnett shale's samples under uniaxial conditions. Experimental results show 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. In another word, the water saturation does little impact on Poisson's ratio. Correlations predicting elastic properties and UCS under reservoir water saturation conditions from dry core samples are proposed based on experimental findings in this paper. The improvement of accuracy of predicting geomechanical properties of Barnett shale can better understand hydraulic fracture propagations, improve wellbore stability and optimize hydraulic fracture design in Barnett shale reservoirs.