The present-day pore system of the Ivishak reservoir is the result of depositional and postdepositional processes. The pore system is a dual system characterized by intragranular porosity, enhanced by leaching, and intragranular microporosity. The combined interaction of deposition and diagenesis together with burial history has caused porosity, permeability, net pay, and water saturation to be highly variable areally and vertically.