Estimation of Permeability for Tight Sandstone Reservoir Using Conventional Well Logs Based on Mud-Filtrate Invasion Model

Abstract

Permeability is an important but barely accessible parameter for fluid flow. In tight sandstone reservoir, it is more difficult to estimate permeability accurately because of the complexity of pore structure. Log interpretation is one of the most common and effective approaches to estimate permeability, especially nuclear magnetic resonance (NMR) log, which is considered the industry-leading technique for permeability determination in tight sandstone. However, this relatively new well log is missing in many oil-fields, which force us to explore new methods to estimate the permeability base on conventional well logs. This paper introduces a convenient and effective method to assess permeability using mud-filtrate invasion model which is established on the mechanic of mud-filtrate invasion. Only resistivity logs with different investigation radius are used in estimation. The difference of resistivity among different resistivity logs are considered to be the reflection of the saturation difference of mud-filtrate in undisturbed zone, invaded zone and flushed zone. On the one hand, the volume of mud filtrate is calculated using resistivity logs based on Archie's equation. On the other hand, the volume of mud filtrate is obtained based on Darcy's law. Then the volume of mud filtrate is used as a bridge to combine these two functions, where permeability will be the only unknown parameter in the equation and can be evaluated smoothly. This permeability estimation method was used in Sulige gas field. Results show that the estimated permeability matches well with the laboratory measurements.