Chapter 1 - Reservoir fluid geodynamics

Abstract

To understand the present-day fluid and geologic properties of reservoirs, it is best to understand how these properties evolved over geologic time. For reservoir structure, the protocol for evaluation always incorporates the geologic history of the reservoir comprised of depositional setting and postdeposition alteration or structural geodynamics. In contrast, a similar protocol had almost never been used for the fluids contained in the reservoir until now. Trap filling involves concepts of petroleum systems, a mature discipline. However, there had been little modeling or understanding of the myriad processes of postdeposition alterations of the reservoir fluids during and after trap filling to present day. Indeed, there was no name for this discipline; we have named it, reservoir fluid geodynamics (RFG). This former deficiency is now resolved with RFG thereby greatly improving the ability to elucidate fluid complexities in reservoirs such as viscosity variations, heavy oil and tar mat formations, and gas–oil ratio gradients of varying magnitudes. In addition, because fluids respond to their container, RFG can also address structural complexities such as reservoir connectivity and its inverse, compartmentalization, fault block migration, reservoir baffling, and low-productivity index. A comprehensive approach combining structural and RFG provides robust analyses that can be used as a benchmark for data acquired across all disciplines. RFG has been enabled by key engineering advances in downhole fluid analysis and by key scientific advances in asphaltene thermodynamics of reservoir fluids. Specifically, asphaltene gradients are modeled with the Flory–Huggins–Zuo Equation of State with its reliance on the Yen–Mullins model of asphaltenes. When significant scientific and engineering advances are strongly coupled, revolutionary applications often follow; this is shown to apply here, in the oil industry.