Chapter 3 - Tight gas sandstones rock typing

Abstract

The heterogeneous and heterolithic nature of tight sandstone reservoirs has significant control over their reservoir properties. Unraveling the reservoir heterogeneity in these reservoirs requires to differentiation of different rock types in terms of depositional/diagenetic features, petrophysical properties, and dynamic reservoir parameters. On the other hand, due to the hierarchy of heterogeneity scales, each rock typing technique, according to the data used, takes into account some aspects of reservoir heterogeneity. For example, sedimentary rock types derived from core description and thin section observations consider macroscopic (lithofacies) and microscopic (petrofacies) characteristics of reservoir rocks, which the results can be used for the description and interpretation of petrophysical rock types. Petrophysical rock types, including electrofacied and hydraulic rock types, are related to petrophysical properties derived from a log and core analysis. Hydraulic rock types due to their connection to pore system properties and dynamic reservoir parameters can effectively be used for reservoir rock typing of tight gas sandstone reservoirs. A complicated pore system of tight sandstones that mostly consists of isolated pores and micropores interrupts the usual relationship between porosity and permeability. This causes limitations in commonly used rock typing methods for tight reservoirs. Also, in the rock typing process for tight sandstones, some considerations such as non-Darcy flow due to the dominant presence of nano- to micro-pores and also disconnected pores, in-situ reservoir conditions such as pressure and water saturation should be considered. There are various types of tight sandstones based on mineralogy, depositional texture, and burial history. Therefore, care must be taken in using conventional rock typing methods for tight gas sandstones.