15.2 Common Issues in Petrophysical Analysis of Tight Gas Sandstones

We discuss petrophysical analysis of wireline logs, methods for formation evaluation and issues in evaluating tight sandstone formations. The main concerns of log interpretation in tight gas sandstones include porosity interpretation, understanding the effect of clay on the log responses, accurate computation of water saturation, and permeability determination (Kukal et al., 1985). Moreover, validation of wireline-based petrophysics with routine and special core analysis, well tests, and petrography is often needed to develop a reliable interpretation model. Petrophysical analysis can help evaluate the hydrocarbon potential, estimate gas in place and, to some extent, producibility of tight gas sands; completion technique and effort drive the economic viability for each play. Many tight gas sandstone formations are known as “tease” intervalsdthere is a gas show or gas kick but no or little production occurs on a conventional test. Improved technology in drilling and completion has made it possible to produce gas from many tight sandstone reservoirs. An appropriate stimulation program is critical to make wells economic in these types of reservoirs. For optimal development of a field, a reservoir model that integrates all the data can be extremely valuable for planning the drilling, completion, and production design. The integrated data should include geological (including depositional and lithofacies such as discussed in the previous chapter), petrophysical, and engineering data. In this chapter, we first review some common issues in petrophysical analysis of wireline logs in tight gas sandstones. We then discuss the three main reservoir properties based on well logs and core data, including porosity, permeability, and water saturation. The three-dimensional (3D) modeling of these properties is presented to populate the reservoir model based on data from the wells. Issues in dynamic modeling of tight-gas sandstone reservoirs are also discussed. CHAPTER