AN INTEGRATION OF ROCK PHYSICS AND SEISMIC REFLECTION COEFFICIENT MODELLING FOR IMPROVED SOURCE ROCK EVALUATION OF PATALA SHALES

Abstract

Increasing global energy consumption has led to the exhaustion of conventional natural resources. To compensate for this deficit, the use of unconventional resources has become inevitable. One such resource is shale gas reserves which provide an effective alternative for conventional reservoir. The objective of this research is to evaluate the shale resource potential within Patala Formation of the Paleocene age in the Meyal area, using integration of seismic and well data. A novel approach is applied to identify the potential zones and shaly plays. Passey ΔlogR, Schmoker’s and Myers and Jenkyn’ methods have been used for TOC estimation using well data. Petrophysical, elemental log have been performed to characterize Patala Formation. A sophisticated workflow of anisotropic rock physics model (RPM) has been built to predict the effective elastic characteristics of organic-rich shale, incorporating minerals, kerogen, fluid and pores. Self-consistent approach (SCA) formulations and inclusion models, i.e., Kuster Toksoz and DEM model are used to construct a model. On the basis of developed RPM, petroelastic analysis has been performed in order to identify the zone favorable for hydraulic fracturing. The prediction of shale density distribution is further carried out using Monte Carlo simulation. The impact of minerals, organic content and pores on anisotropic reflection coefficient (AVO) has also been determined. Furthermore, a probabilistic technique has been used to deduce lithofacies values from inverted seismic properties and well data such as Ip, VpVs using post stack inversion. The results show a good TOC content ranging between 4-5 wt% on average. Potential shale resource zone has been identified for hydraulic fracturing based on TOC values and low Young’s modulus (E), high Poisson ratio (PR) and high brittleness index (B). The result from AVO analysis shows negative reflection of amplitude dims with offset for Patala formation. Moreover, constructed probability maps of lithofacies provide an accurate estimate of reservoir producing and non-producing zones in Patala Formation. The output of spatial distribution of elastic properties are well calibrated with the help of estimates obtained at control points, which improves the confidence level. Instead of 2D seismic lines, a 3D seismic block might be deployed to iterate elastic attributes throughout the cube using geostatistical tie based on shear impedance (SI) values rather than being constrained to a 2D section. This study hopes to provide a methodology for source rock characterization in terms of spatial distribution of elastic attributes for any basin in the world.