Enhanced Reservoir Description: Using Core and Log Data to Identify Hydraulic (Flow) Units and Predict Permeability in Uncored Intervals/Wells

Abstract

Abstract Understanding complex variations in pore geometry within different lithofacies is the key to improved reservoir description and exploitation. Core data provide information on various depositional and diagenetic controls on pore geometry. Variations in pore geometrical attributes in turn, define the existence of distinct zones (hydraulic units) with similar fluid-flow characteristics. Classic discrimination of rock types has been based on subjective geological observations and on empirical relationships between the log of permeability versus porosity. However, for any porosity within a given rock type, permeability can vary by several orders of magnitude, which indicates the existence of several flow units. In this paper, a new, practical and theoretically correct methodology is proposed for identification and characterization of hydraulic units within mappable geological units (facies). The technique is based on a modified Kozeny-Carmen equation and the concept of mean hydraulic radius. The equation indicates that for any hydraulic unit, a log-log plot of a "Reservoir Quality Index," (RQI), which is equal to 0.0314k/ϕ, versus a "Normalized Porosity Index" (ϕz) which is equal to ϕ/(1-ϕ) should yield a straight line with a unit slope. The intercept of the unit slope line with ϕz = 1, designated as the "Flow Zone Indicator" (FZI), is a unique parameter for each hydraulic unit. RQI, ϕz and FZI are based on stressed porosity and permeability data measured on core samples. FZI is then correlated to certain combinations of logging tool responses to develop regression models for permeability predictions in cored and uncored intervals or wells. The proposed technique has been successfully tested in clastic rocks from East Texas, South America, West Africa, South East Asia and Far East Asia, as well as carbonate sequences from West Texas and Canada. This paper documents the theoretical development, validates and characterizes the hydraulic units, and presents predicted versus actual permeability data to demonstrate the efficacy of the proposed technique.