This is a three-part tutorial of a workflow for evaluating unconventional resources including organic mudstones and tight siltstones. Part 1 reviews the unique challenges and we provide an overview of the proposed workflow. Part 2 describes in more detail the many components of the workflow and how they come together to determine the storage capacity of the reservoir. Finally, Part 3 links the petrophysical results to the production potential in terms of fractional flow and water cut.
One of the most important functions that the petrophysicist provides is the estimation of accurate storage properties. In the oil and gas industry, storage defines the opportunity, and flow pays the bills. Estimation of storage is more than just estimation of porosity and water saturation. It begins with accurate assessment of rock composition which begets accurate porosity and subsequently water saturation. However, storage estimation need not end there. With an understanding of fluid type and properties, and with the application of appropriate equations of state that describe the variation of formation volume factor, bubblepoint or dewpoint pressure, oil viscosity and density as a function of temperature, pressure, GOR, API gravity and gas gravity, very accurate assessments of oil in place (OIP), gas in place (GIP), and water in place (WIP) are possible in profile. These profiles are then integrated into cumulative storage volumes by bench.