Modeling of Diagenetic Controls on Reservoir Characteristics

Abstract

Abstract Diagenesis plays a big role in controlling the reservoir storage and flow properties. Modeling the effects of dominant diagenetic processes on petrophysical properties is of importance in reservoir characterization in order to convert a static geologic model into a dynamic reservoir flow model. This paper presents a study on modeling of microstructure and porosity/permeability evolution controlled by three end-member diagenetic processes, namely mechanical compaction, cementation and chemical compaction. Initial pore scale microstructure is modeled by assuming unit cell of uniform spheres with loose simple cubic packing (SC). Mechanical compaction leads change in packing styles from simple cubic packing (SC) to denser face-centered cubic (FCC) packing, while keeping grain size and shape fixed. Cementation is modeled as a process of grain-growth by precipitation while keeping the initial grain center-center distance fixed. Chemical compaction or pressure solution allows grains to dissolve at grain-grain contacts and reduces bulk volume of the unit cells. In a chemically closed system, pressure solution leads grain growth via precipitation of material derived from grain contacts. In a chemically open system, dissolved material by pressure solution is taken away from the system. Porosity is treated as the degree of diagenesis and is independent to grain size. Permeability is modeled using Kozeny-Carman equation for each end-member diagenetic microstructure and normalized to initial grain size. The relationships between porosity and universal permeability for different diagenetic processes are compared. Two diagenetic paths can be distinguished from the modeling results. Mechanical compaction is a more efficient mechanism for permeability reduction than cementation and chemical compaction. Other petrophysical parameters such as pore throat radius, specific surface area and tortuosity are also given.