ISO TR 14685 pdf download – Hydrometric determinations- Geophysicallogging of boreholes for hydrogeologicalpurposes -Considerations and guidelines for making measurements.
Correlation of logs is carried out by curve matching logs of similar types using the same depth scale (Figure 3). With a number of recent techniques, which include the computer digitization of logs and the direct recording of logs in the field for replay on different scales in the office, it is possible to correlate or display the logs fran, a wide range ci sites in a uniform manner for ease of correlation. In particular the logge’ig of disused boreholes in an area of investigation can also prove productive.
Correlation may also be accomplished using computers. This is particularly useftd where the log responses are less clearly defined and more than two logs per borehole are being assimilated simultaneously.
4.2.4 EvaluatIon of physIcal properties
The third purpose of formation logging Is for physical property measurements and this permits quantitative interpretation of geophysical logs.
In certain cases other parameters such as permeability can be estimated where they can be related to, for example, porosity or clay content by an independent means
Geophysical logs can be interpreted to determine the foaowing properties: formation resistivity; formation fluid resistivity (often measured as fluid electrical conductivity): formation resistivity factor; clay content; bulk density; primary porosity; secondary or fissure porosity; zones of water movement; zones of contamination; aquifer bouridanes: borehole geometry; casing position and type; casing condition, bonding and borehole condition,
4.3 Fluid logging
4.3.1 General
The mast important geophysical logs run, for investigating the borehole fluid column, are borehole flowmeter logs (both mechanical and thermal), fluid conductivity logs and fluid temperature logs. Fluid logs are run for three main reasons:
a) to determine flow in the borehole;
b) to identify regional groundwater movement;
c) to assess groundwater quality.
4.32 Flow in the borehole
The existence of an open borehole may connect zones of differing in situ hydraulic head and water quality. Recognlzw’ig and understanding the effects of natural flow mixing by use of fluid logs Is often important to the general hydrogeofogical interpretation of the site. During the drilling and siisequently with time, flow mixing will occur within the water column (see Figure 4).
When pumping or artesian movement induces flow conditions, fluid logging can accurately determine the depths from which the yleid of the borehole Is being denved In fissured aquifers. fkid logs will Indicate those fissures that are contributing yield. Accuracy wifl increase if supported by temperature logs.
Where a borehole penetrates more than one aquifer the contribution fran, each can be identified. Using flowmeters. quantitative measurements of the flow being derived form each zone or horizon of interest are often carried out
In appfopnate situations, fluid logs can be taken in recharge boreholes or through a packet assembly to identify active fissures, flow rate and direction, and water quality changes with time. This requires careful consideration of borehole access arrangements.
Evidence of cascading and seepage can be obtained from closed-cvcuit television (CCTV) logs.
5.5 Equipment
All equipment should be regularly serviced in accordance with the manufac*ure?s recommendations It Is good practice to mamtain logging sondes and rocks and the general working environment ii a dean, dust-tree condition and to carry out routine pie-logging checks on each function. Attention should at all tiT’es be paid to the condition of the equipment as slow deterioration can often go unnoticed; In particular the safety of all electrical connections and the con-ed condition and operation of the cable head. Appropriate rrieasures should be taken to ensure that any equipment used in a water supply borehole is washed and sterilized immediately before use.
5.6 Borehole details
To prepare equipment adequately, basic details of the borehole will be required before arriving at the site. Certain systems w1h data recording facilities may also require the Input of header Information or supplementary comment. It is useful in any case to have as much data on the borehole as possible in order to aid on-site interpretation. A list of relevant data to be considered is as follows:
a) location and national grid reference:
b) national water well number or other identifier;
C) total depth of the borehole;
d) standing water level andior pump.ng water level;
e) date constructed;
f) drilling fluid, whether water, mud, air or foam;
g) lining or casing detaIls including diameter, depth, plain or slotted, material (plastics, steel, fibreglass. etc.), grouting details, construction of borehole top and datum levels:
h) uncased hole diameters and reductions:
i) borehole fluid:
j) zones of collapse or possible constriction;
k) presence of pump (dip tubes, flanged rising main, electrical cables, etc.):
I) likelthood of junk i borehole.
ISO TR 14685 pdf download – Hydrometric determinations- Geophysicallogging of boreholes for hydrogeologicalpurposes -Considerations and guidelines for making measurements
