Tight Gas Reservoirs (TGR) is attracting the attention of Oil & Gas industry from all quarters. Optimum exploitation depends upon the petrophysical evaluation and geological understanding. An insight into geological complexities of TGR is imperative to have a better evaluation of such reservoirs. This study details the tight gas sands (TGS) only as most of the TGR activities around the world are focused mainly on the clastics. It aims at explaining the different geological events that give rise to the tightness in the sandstone reservoirs and also presents a methodology to properly evaluate the geological complexities introduced. The TGS carry the imprint of both the primary depositional factors and secondary post-depositional ones. Grain size, sorting and distribution of detrital clay within a sequence stratigraphic framework govern the reservoir properties as depositional factors. Diagenesis is the key factor to control the tightness of the reservoirs after the deposition depending upon the compaction and cementation. Fractures are the post-depositional factors; the tectonic fractures along with the drilling induced ones provide an understanding of the stress regime and a clue towards planning the stimulation program. Conventional and sidewall cores with conventional open hole logs provide a larger understanding in terms of depositional environment and lithology variations. Detailed petrography with the help of XRD and SEM aids to understand the cementation pattern. Elemental capture spectroscopy and Spectral gamma logging can help correlating the cementation/ clay distribution within wells. Borehole images are quite helpful in capturing the textural variations which govern the differential diagenesis and also the drilling and natural fractures orientation and their association with rock facies. The study attempts to establish the need of proper geological evaluation which provides the building blocks for petrophysical and reservoir engineering evaluation to optimize the exploitation strategy.

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