Estimation of elastic parameters, mineralogy and pore characteristics of Gondwana shale in Eastern India for evaluation of shale gas potential

摘要

Studies on resource potential of unconventional reservoirs are drawing the attention of scientific community since the last couple of decades. Because of low permeability of shale, the production demands hydraulic fracturing in shale layers. Brittleness index gives an idea on the toughness of shale layers and helps in setting the parameters for hydraulic fracturing. Elastic properties such as Young's modulus are important parameters for building geo-mechanical models for rock strata which are essential for several applications related to mechanical rock failure during well drilling, completion and stimulation. The physical and geochemical properties of Gondwana shale samples from Eastern India were analysed for mineralogy, pore types and dynamic elastic properties using powder X-ray diffraction (XRD), scan electron microscopy (SEM) and ultrasonic velocity measurements respectively. The measured P- and S-wave velocities and the estimated elastic parameters of Gondwana shale samples show an increase in magnitude with depth indicating the effect of hardness and compaction. The effect of hardness on velocity and elastic parameter is also supported by the increase in quartz percentage in shale with depth. An empirical relationship between P- and S-wave velocity is proposed for Gondwana shale. The XRD experiments reveal the dominance of clay minerals over non-clay minerals in the samples lower the shear strength of South-Karanpura field, at shallow depth, supported by measured elastic properties. The presence of flaky clay texture/topography and abundant micro (&0.75 mu m) and nano (&0.75 mu m) pores of various shapes in the samples with organic matter in the SEM images suggests that formations are of high shale gas prospecting zones.