Title:  Archie’s Law and Evolution of Water Saturation Using Petrophysical Techniques

Summary: Accurate water saturation estimation is critical for determining reserves, guiding development strategies, and evaluating project economics. Since its introduction in 1942, Archie’s Law has been the cornerstone of petrophysical interpretation, yet its assumptions and limitations—particularly in shaly, unconventional, or mineralized formations—can lead to significant errors. This presentation explores the evolution of water saturation determination, beginning with the fundamentals of resistivity theory and Archie’s equation, through its major derivatives such as Waxman-Smits, Dual Water, Simandoux, and other methods. Using real-world examples from conventional and unconventional reservoirs, we examine the uncertainties associated with key variables, highlighting porosity as the largest driver of error. Through field case studies, once can see how different models and measurements affect calculated OOIP/OGIP and recovery factors.