Slim-Hole Induction Tool (SIND):Field Evaluation @ Batu Dam, Gombak

May 11th 2010

Contents

• Introduction

• Location & Background

• Field Operation

• Data Collected

• Log Analysis

• Conclusion

•

Introduction

To check on the tool’s performance against a known fluid conductivity in large water bodies and to establish the percentage of tool’s accuracy under

controlled conditions (min. borehole influence) against ELOG tool.

Also, to compare both log response in various environments; alluvial, hard rock and open water

bodies

Location

•

Background

Induction log is a very useful tool to study subsurface stratigraphy and formation conductivities in water

well.

It uses EMF (~40KHz) to induce formation’s magnetic field which induced formation’s current flow which is

proportional to formation’s conductivity.

It works best in low resistivity (<100ohmm) formation or non-conductive medium (air).

•

Background

Interpretively, low conductivity value (i.e 50mS/cm) indicate very fresh water while high conductivity

value (i.e 1000mS/cm) indicates salty water.

Resistivity is a reciprocal of conductivity. Hence, the former can be computed from that of the latter.

•

Background

The tool has been 1st order-calibrated in RG’s factory in the UK.

A 2nd order calibration can be done using the available calibration loop with a known max.

conductivity value.

A ‘zero’ calibration can be done by holding the probe up in the air though practically it’s none existent

(only in the vacuum).

Field Operation

60m walk-way to the intake tower

6.0m drop

Station

Set-up

Depth encoder

WinchRope to secure the wheel

Tool’s Cable12V DC for winch

12V DC for micrologger

Equipment

Conductivity Meter model WTW Multi 350i

Sign as in slide #9

Equipment

centralizer

Calibration loop from RG

Induction (SIND) tool Flow-meter tool

Definition

• Conductivity(Siemens) = 1/ resistivity (ohm.m)

• Standard units of conductivity = microS/cm

• microS/cm = 10^4/ohm.m

Data Collected

• Fluid conductivity (microS/cm) by Conductivity meter

• Conductivity in (mS/m); Gamma in CPS plus (derived bulk resistivity) by SIND tool

• SNR, LNR(Ohmm); SP (mV); SPR (Ohm); Gamma (CPS) by ELOG tool

• No available conductivity data in DID’s archive for comparison and data integrity checking

Tabulated Data

Cond. meter possibly needs lab calibration

ELOG’s data needscomparing with external data for integrity check

Resistivity dataOff recommended range for SIND tool

Log Analysis

• Example 1 – shows tool’s min. operating range for resistivity is “zero” Ohmm

• Example 2 – shows tool’s max. operating range for resistivity ~100 Ohmm

• Example 3 – Shows log response in alluvial

• Example 4 – Shows log response in hard rock

Example 1 - Batu Dam

Showing “zero” conductivity readings before tool reaches water surface

Slide 18: SIND data_run01 Slide 19: SIND data_run03

Depth: 1.0m-6.0m (air column)

Air column – “zero” conductivity

Possible humidity effect

Water surface

(Tool’s min. range reached)

Air column – “zero” conductivity

Possible humidity effect

Water surface

(Tool’s min. range reached)

EXAMPLE 2 - Batu Dam

ELOG’s short resistivity vs. SIND’s derived resistivity in open water

bodies

Slide 21: SIND Data Slide 22: ELOG Data

Depth: 18m-23m

86Ohm.m ~11.9mS/m (119µS/cm)

(Value couldn’t hit beyond 100Ohmm due to to tool’s max. range reached unlike ELOG)

257Ohm.m Conductivity=10^4/Ohmm = 10000/257 = 38.9 ~ 39µS/cm

See slide#15 under ELOG

EXAMPLE 3- KLT017 (alluvium)

ELOG’s short resistivity vs. SIND’s derived resistivity in Alluvium

Slide 24: SIND Data

Slide 25: ELOG Data Depth: 61m-67m

SIND’s;15.46Ohmm

ELOG’s;23.55Ohmm

EXAMPLE 4 - SK198 (hard-rock)

ELOG’s short resistivity vs. SIND’s derived resistivity in hard rock.

Slide 27: SIND Data

Slide 28: ELOG Data Depth: 76m-82m

2.11 Ohmm

12.93 Ohmm

Conclusion

1. A consistent shift in resistivity values are observed from that of SIND & ELOG tools in

alluvial and hardrock environment.

2. Recommended resistivity operating range for SIND’s tool is between 0 – 100 Ohmm. Readings are unreliable beyond the recommended range

as shown in Batu Dam evaluation exercise.

Acknowledgements

1. DID, Northern Zone Div., Federal Territory – Tuan Hj Zul Mohamad, Mohd Ezla, Izrul Faris,

Bachtiar Effendi & Mohd Shariff

2. DID, Water Resources Management and Hydrology dept., Ampang – Yuhaslin, Khairul

Fadzilah