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US-12618702-B2 - Methods for assessing groundwater flow zones

US12618702B2US 12618702 B2US12618702 B2US 12618702B2US-12618702-B2

Abstract

There is disclosed a method of assessing a flow of fluid in a borehole. The method comprises dispersing or mixing a tracer in the fluid of a borehole; and measuring a tracer concentration over a plurality of timepoints at a predetermined location in the borehole, wherein a decrease in the tracer concentration over time at said predetermined location indicates the borehole is in fluid communication with a flow of groundwater at or around said predetermined location.

Inventors

  • Michael VERREAULT

Assignees

  • HYDRO-RESSOURCES INC.

Dates

Publication Date
20260505
Application Date
20221031

Claims (12)

  1. 1 . A method for characterizing natural hydraulic exchange zones within a water-containing borehole, comprising: (a) introducing into the borehole water a tracer element that dissolves or disperses to release a tracer material along substantially the entire water column of the borehole; (b) allowing the borehole to remain under ambient hydraulic conditions, without applying any internal hydraulic stress to the borehole water or surrounding formation; (c) performing a first measurement of tracer concentration by moving a probe vertically along the borehole at a substantially constant speed to generate a depth-resolved concentration dataset; (d) repeating step (c) at two or more subsequent times after the initial tracer release, without further mixing of the borehole water or additional tracer addition, to obtain successive depth-resolved concentration datasets; (e) comparing the successive datasets to determine local variations in tracer concentration over time; and (f) identifying natural hydraulic inflow and outflow zones along the borehole based on the local variations.
  2. 2 . The method of claim 1 , further comprising measuring at least one of hydraulic conductivity, flow rate, Darcy's flux, true flow velocity and vertical flow.
  3. 3 . The method of claim 1 , wherein a predetermined quantity of tracer is dispersed.
  4. 4 . The method of claim 1 , further comprising measuring a baseline tracer concentration in the fluid of borehole prior to introducing the tracer.
  5. 5 . The method of claim 1 , wherein the tracer is or comprises a dye, a fluorescent dye, a salt, deionized water, an isotope, a stable or radioactive isotope or a liquid with at least one of a predetermined turbidity and temperature.
  6. 6 . The method of claim 1 , wherein the tracer is a fluorescent tracer chosen from rhodamines family, Xanthenes family, Stylbenes family, Aromatic hydrocarbons family, malachite green, methyl blue, chlorophyl, and mixtures thereof.
  7. 7 . The method of claim 1 , wherein the probe is a fluorometer.
  8. 8 . The method of claim 1 , wherein the borehole is a pumping well or artesian borehole.
  9. 9 . The method of claim 1 , further comprises operating a pumping well located in proximity to the borehole and repeating step (a), wherein a decrease in the tracer concentration when the pumping well is operated compared to when the pumping well is off indicates the borehole is in fluid communication with a flow of groundwater that is in fluid flow communication with the pumping well.
  10. 10 . The method of claim 1 , wherein the probe is an optical fluorometer.
  11. 11 . The method of claim 10 , further comprising performing step (c) at least four times.
  12. 12 . The method of claim 1 , further comprising performing step (c) at least three times.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS The present application claims priority from U.S. application No. 63/275,258, filed on Nov. 3, 2021. This document is hereby incorporated by reference in its entirety. FIELD OF THE DISCLOSURE The present disclosure relates generally to the field of hydrogeology and more particularly to methods for assessing groundwater flow zones. BACKGROUND OF THE DISCLOSURE In operating mines, infiltration of water causes stability problems, adds delays in ore recovery and increases the cost of operations. For these reasons, hydrogeological studies are carried out to develop an efficient mine dewatering system and to control water infiltration. Standard hydrogeological studies require fieldwork and analysis using numerical models. Modeling allows the optimization of mine dewatering, and also to better understand several phenomena. After gathering initial information, fieldwork is the starting point for any hydrogeological study. If the quality and precision of the information collected are not sufficient, the analysis carried out could lead to an erroneous interpretation. Field work usually includes diamond drilling for core recovery, slug test, packer test, flow measurements, and in some special situations, the use of an acoustic camera and spinner flowmeter. These approaches allow to estimate the hydraulic conductivity and assess the heterogeneity of the medium. However, none of these methods allows to clearly identify fractures, faults or other structures that provide sustainable water flow. In fact, an area of high hydraulic conductivity does not necessarily translate to a significant aquifer area capable of providing water on a sustainable basis. High hydraulic conductivity may occur when a fractured zone is local (i.e., trapped water) and not related to another fracture with preferential flow. Using traditional interpretation methods, trapped water could be interpreted as a high flow area. FIG. 1 illustrates two fracture zones crossed by a vertical borehole. The upper fractured zone appears to be very permeable, based on the description of the core (eg. via Rock Quality Designation) although the lower fault could just as well contain water. Traditional tests (packer, flowmeter, etc.) would give high values of hydraulic conductivity for both zones, yet only the lower fracture would carry a perpetual flow because the extent of the fault is large and connected to another regional fault system. Due to the limited area of influence of the packer tests and/or the flow tests (5-10 m), it is likely that the upper fracture zone will lead to a high conductivity value assessment. Accordingly, there is a need for overcoming at least one shortcoming of methods of assessing aquifer areas carrying a preferential flow of water. SUMMARY OF THE DISCLOSURE An aspect of the present disclosure relates to a method of assessing a flow of fluid in a borehole. The method comprises dispersing or mixing a tracer in the fluid in the borehole; and measuring a tracer concentration over a plurality of timepoints at a predetermined location in the borehole, wherein a decrease in the tracer concentration over time at said predetermined location indicates the borehole is in fluid communication with a flow of groundwater at or around said predetermined location. Another aspect disclosed herein relates to a kit for use in assessing a flow of fluid in a borehole, comprising: a tracer;a measuring probe;a device connected to the measuring probe for recording measurements detected by the measuring probe; anda cable dimensioned to move the tracer and/or the measuring probe along the length of the borehole. These and other features and advantages of the present application will become apparent from the following detailed description taken together with the accompanying drawings. However, it should be understood that the detailed description and the specific examples, while indicating preferred embodiments of the application, are given by way of illustration only, since various changes and modifications within the spirit and scope of the application will become apparent to those skilled in the art from this detailed description. BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the various embodiments described herein, and to show more clearly how these various embodiments may be carried into effect, reference will be made, by way of example, to the accompanying drawings which show at least one example embodiment, and which are now described. The drawings are not intended to limit the scope of the teachings described herein. FIG. 1 is a prior art cross-sectional side view of a two fracture zones with variable ambient flow crossed by a vertical borehole; FIG. 2 is a graph showing a Breakthrough curve at a specific location after mixing; FIG. 3 is a graph showing natural logarithm (LN) of concentration vs time; FIG. 4 is a graph showing tracer dilution profile (TDP) results in a borehole; and FIG. 5 is a sc