Effect of CEC, Salinity, Sand Content, and Particle Size Distribution on Mud Rock Properties

Mudrocks are fine grained, extremely low porosity and permeability sedimentary rocks that contain significant amounts of clay minerals. These rocks are difficult to characterize their physical properties or test their mechanical behavior. Clay’s cation exchange capacity (CEC) make these rocks water sensitive due to double layer expansion or collapse. Conductometric titration and methylene blue colorimetry were used to measure CEC and compared to cobalt hexamine technique values provided by a vendor. In this work, we studied petrophysical and geomechanical properties of resedimented mudrock core samples. Three major properties were varied; they are clay’s percentage, cation Exchange capacity and brine salinity. The use of the reconsolidation technique allows us to create mud rocks in the laboratory while controlling mineralogy, sorting, brine salinity, and axial stress, this is similar to sand pack experiments performed by (Hathon & Myers, 2011) which showed that mineralogy, grain size, sorting, stress history and incipient overgrowth cements all affect the porosity as a function of depletion stress. Triaxial testing is commonly used to determine the failure envelope for mudrocks. The most common application of this technique requires multiple identical samples. In heterogeneous formation identical samples are often difficult to obtain. The twinning problem is overcome by performing ‘multistage’ tri-axial tests. These tests were performed on reconsolidated mud rocks to determine their strength properties (Salman, Myers, & Sharf Aldin, 2015). Strength data are compared based on the sample’s variations such as CEC, brine salinity, and clay content.