Generation of saturation functions for simulation models of carbonate reservoirs

  • Qingfeng Huang

    Student thesis: Master's Thesis

    Abstract

    A rock type is the unit of rock deposited under similar conditions, which went through similar diagenetic processes, producing analogous rock fabric, with distinct set of pore types, and pore throat size distribution, having specific range of porosity and permeability. Rock typing can generally be used as a guide to assign petrophysical characteristics to different zones for detailed reservoir characterization, modeling and simulation, which provide valid frames for reservoir development. It is often assumed that conventional rock types are capable of assigning multiphase flow characteristics, such as capillary pressure and relative permeability to the cells of dynamic simulation models. However, these conventional rock types, or static reservoir rock types (SRRT) fail to capture the actual variability of capillary pressure and relative permeability, due to lack of representation of wettability difference at different elevation above the free water level (FWL) in carbonate reservoirs, especially in the highly heterogeneous reservoirs. This should be resolved through dynamic reservoir rock types (DRRT), in which wettability effect is imposed on the SRRTs to generate saturation functions for simulation models. This research studies Ghedan's comprehensive DRRT model7, and proposes a modified Ghedan's model. First, the defined static rock types are sub-divided into sub-static rock types based on porosity frequency. Second, three curve-fitting programs are coded to generate the related saturation-height functions. These are the modified Ghedan-Okuyiga equation, Cuddy function and Power Law function. Developed from Ghedan-Okuyiga function113, the recommended modified Ghedan-Okuyiga function has been proposed with saturation and implicit porosity as a function of height above FWL in the transition zone. Third, each sub-static rock type is divided into a number of DRRTs by determining the capillary pressure and relative permeability curves in the oil zone from gas-oil contact (GOC) to dry-oil limit (DOL). The DRRTs are extended to the zone from DOL to FWL by including wettability effect which would affect the curvature of the relative permeability curves but not its saturation end points, through changing the Corey exponents in the modified Brooks-Corey model. The modified Ghedan's model is applied in terms of dynamic rock typing plug-ins to build a comprehensive and automatic approach to generate saturation tables that can be loaded into commercial simulators. The plug-ins accept the input data from geological models and SCAL tests, and automatically generates sub-rock types and saturation tables. The dynamic rock typing plug-ins are composed of two parts. One is called 'SubRockTyping', which produces sub-static rock types from SRRTs. The other is termed 'DRTP', short for dynamic rock typing plugin, which generates saturation tables for DRRTs derived from SRRTs. These saturation tables can be loaded into commercial simulators for reservoir initialization, history match and prediction. Keywords: rock typing, static rock typing, dynamic rock typing, wettability, dry oil limit, saturation-height function, saturation function, reservoir characterization.
    Date of AwardDec 2012
    Original languageAmerican English
    SupervisorShawket G. Ghedan (Supervisor)

    Keywords

    • Applied sciences
    • Carbonate reservoirs--simulation models
    • Petroleum engineering
    • Energy
    • 0765:Petroleum engineering
    • 0791:Energy

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