Estimation of Average Permeability of Shale From Swelling Data
Authors: Osisanya S.O. 
Published: March 2010

The concern over contamination of underground sources of drinking water continues to increase as the volume of hazardous materials injected into the subsurface increases. Containment and demonstration of minimal migration outside the injection zone are two major requirements by the Environmental Protection Agency (EPA). Permeability of shale is one of the major factors that determines containment. Analysis of a series of atmospheric swelling data of a shale contacted by various aqueous fluids showed that 8hale permeability can be estimated from a model equation that was developed from the total flow potential (or pressure) concept and laboratory-derived shale swelling strain data. The method is simpler than the classical measurement techniques used in petrophysical studies. The calculated permeability values correspond to the range of values measured under steady-state flow conditions using sophisticated equipment The proposed technique was developed based on experiments conducted under atmospheric conditions, but can be extended to experiments conducted under down-hole conditions. The paper presents the experimental procedure, the developed model equation and a numerical example to illustrate the steps involved in determining the permeability of shale from swelling data.

Introduction

Shale is the generally accepted class name for all fine-grained argillaceous sediments, including mud, clay and mudstone. Shale also has been the "taken forgranted" matrix between lithologies of greater scientific or economic interest (sandstones and carbonates) in spite of the fact that shale forms more than 60% of the world sediments(1). Shales have been studied extensively in the petroleum drilling industry for more than five decades with respect to wellbore instability (2,4). Wellbore instability yearly expenditure for the petroleum drilling industry.

Recently interest in the study of shales has been tremendous for the following reasons:shales are an important primary source of oil and gas andshales are useful as landfills.

These interests are related to the fact that shales form barriers to fluid flow and therefore provide traps for groundwater, hydrocarbons and for the solutions that precipitate stratiform mineral deposits. One important shale parameter from this discussion is permeability. A knowledge of shale permeability is essential in evaluating the containment properties of shales associated with deep-well hazardous waste injection zones. In addition, shale permeability data are prerequisite to the determination of pore pressure of shale necessary for predicting wellbore stability in stable formations. Furthermore, shale permeabilty is an important parameter in determining the recovery economics of oil and gas from shale.

Permeability measurements are commonly made on hydrocarbon bearing formations such as sandstones and carbonates. However, permeability information is required in the evaluation of containment properties of shales associated with deep-well hazardous waste injection zones(9). Many of the hazardous materials disposed of by deep-well injection are organic compounds. These compounds are known to react with clay minerals in such a way that shale permeability might increase. Obviously, increased permeability of the shale raises the question of the shales ability to contain organic wastes. Therefore, permeability is an important parameter indicating the degree of containment of injected hazardous waste.