The Applicability of Different Fluid Media to Measure Effective Stress Coefficient for Rock Permeability

Ying Wang,Min Li,Guozhi Li,Jing Zhang

doi:10.1155/2015/391851

Ying Wang, Min Li + Show 2 more

Open Access

https://doi.org/10.1155/2015/391851

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Abstract

Effective stress coefficient for permeability (ESCK) is the key parameter to evaluate the properties of reservoir stress sensitivity. So far, little studies have clarified which ESCK is correct for a certain reservoir while rock ESCK is measured differently by different fluid media. Thus, three different fluids were taken to measure a fine sandstone sample’s ESCK, respectively. As a result, the ESCK was measured to be the smallest by injecting nitrogen, the largest by injecting water, and between the two by brine. Besides, those microcharacteristics such as rock component, clay mineral content, and pore structure were further analyzed based on some microscopic experiments. Rock elastic modulus was reduced when water-sensitive clay minerals were encountered with aqua fluid media so as to enlarge the rock ESCK value. Moreover, some clay minerals reacting with water can spall and possibly block pore throats. Compared with water, brine can soften the water sensitivity; however, gas has no water sensitivity effects. Therefore, to choose which fluid medium to measure reservoir ESCK is mainly depending on its own exploitation conditions. For gas reservoirs using gas to measure ESCK is more reliable than water or brine, while using brine is more appropriate for oil reservoirs.

Highlights

The characteristics of reservoir stress sensibility for rock permeability mainly behave as follows: with the on-going exploitation of oil and gas, the pore pressure of reservoir is decreasing, while the effective stress is increasing
The relationships among permeability, confining pressure, and pore pressure for the sample when unloading and loading the pore pressure under nitrogen, distilled water, and brine are shown in Figures 7, 8, and 9, respectively
All of rock permeabilities were measured under the same external experimental conditions, including temperature and loading/unloading confining pressure/pore pressure processes

Summary

Introduction

The characteristics of reservoir stress sensibility for rock permeability mainly behave as follows: with the on-going exploitation of oil and gas, the pore pressure of reservoir is decreasing, while the effective stress is increasing. Some studies, conducted by Coyner [7], Kwon et al [8], Nur et al [4], Al-Wardy and Zimmerman [9], Boitnott et al [10], and others, in accordance with using brine as the fluid medium show that the ESCK value of Berea sandstone is larger than 1, those for shale containing. Reservoir ESCK value is affected by multifactors such as fluid media, rock components, clay content and its distribution, mineral composition, and pore structure. The ESCK value measured by distilled water is close to 1 for granite while it is larger than 1 for sandstone and is increasing with clay mineral content increasing up to 7.1. A series of ESCK measurement experiments by using three different fluid media (e.g., 99.99% nitrogen, distilled water, and brine with 50000 ppm potassium chloride, KCl) to flow through a fine sandstone sample were conducted in this study. The behaviors of fluid media with rock ESCK were discussed in this study

Experimental Setup and Method

Experimental Theory and Method

Experimental Setup and Procedures

Results and Analyses

10 Sample HH50-06

Conclusions