Slug Test in a Large Dip Angle Fracture Zone: Model and Field Experiment

Ying Liu,Chia-Shyun Chen

doi:10.3319/tao.2015.04.09.01(hy)

Abstract

A single-porosity model is developed to deal with a fracture zone slug test in a large dip angle by assuming the fracture zone causes a downward regional flow. For the oscillatory response, a larger dip angle causes larger amplitude while introduces little impact on period. The effective water length, an important parameter necessary for analyzing the oscillatory response, is proven to be independent of the dip angle and can be evaluated using the available horizontal formation methods. The dip angle effect is more pronounced for a larger storage coefficient. An empirical relationship is developed to evaluate the limiting dip angle, below which the dip angle effect is negligible. Field data analysis of a slug test in a 47° dip angle fracture zone indicates that neglecting the dip angle can result in a 27% transmissivity over estimation and a 53% storage coefficient under estimation.

Highlights

The slug test is a relatively simple field method for estimating pertinent hydrogeologic parameters
Field investigations conducted in a Cenozoic folded sandstone formation revealed that the dip angle of a fracture zone is as large as 47°
For a large dip angle, a uniform regional flow prevails through the sloping fracture zone and its presence will cause the flow field due to the slug test to be asymmetrical with respect to the test well

Summary

INTRODUTION

The slug test is a relatively simple field method for estimating pertinent hydrogeologic parameters. For a large dip angle, a uniform regional flow prevails through the sloping fracture zone and its presence will cause the flow field due to the slug test to be asymmetrical with respect to the test well. This asymmetric flow is similar to that of a regional flow superimposed onto a radial flow; e.g., see McWhorter and Sunada 4 - 12) for the steady-state condition As shown by these figures, the asymmertic flow is characteristic of a “groundwater divide” that consists of all the points of a zero hydraulic gradient because of the balance of the radial flow caused by the pumping well and the uniform regional flow. The test response solution and analysis in nearby observation wells will be presented elsewhere

Model Development

Model Solution

THEORETICAL ANALYSIS

DATA ANALYSIS

Findings

CONCLUSIONS