A New Resistivity-Based Model for Improved Hydrocarbon Saturation Assessment in Clay-Rich Formations Using Quantitative Geometry of the Clay Network

摘要

The importance of clay-network conductivity in resistivity-based saturation assessment has been well recognized over the years. The existing shaly sand models are oversimplified by assuming that the clays are present in the rock predominantly as laminated, dispersed, or structural. This assumption, however, is not reliable in many clay-rich formations because, in nature, clay minerals can have complex spatial distributions. Furthermore, the conventional shaly sand resistivity models, such as Waxman-Smits, dual-water, and Simandoux, do not take into account spatial distribution and connectivity of the clay network. Spatial distribution of the clay network can significantly affect resistivity of clay-rich formations and oversimplifying this distribution can lead to huge uncertainties in estimates of water saturation. In this paper, we introduce a new resistivity-based model that quantitatively takes into account the actual clay-network geometry and distribution and type of clay minerals. Reliable incorporation of spatial distribution of the clay network (i.e., not limited to extreme cases of dispersed, layered, and structural) improves reserves evaluation in clay-rich formations with complex clay network structure.