Logging methods

Task-oriented sets of logging methods and their fields of application

Control logging in ground-water monitoring and production wells

Task:
Complex assessment of the well's condition before restoration and rehabilitation and check if the measures were executed successfully. Basis for acceptance of construction work / final acceptance of the newly built well

Determined parameters:
final depth down to which can be descended / geometry of the casing, screens and joints / remaining wall thickness, corrosion, deposits / mechanical defects / inclination / hydraulic tightness of the joints / existence of annular seals / homogeneity of the annular space filling / cementation defects / covered multiple casings / influx chart and detection of colmatages / salinity and anthropogenic pollution of the pore water of all sunk through aquifers

: logging example: control measurements for plastic casingMessbeispiel:

: logging example: complex inspection of a hard-rock well

: logging example: inspection of an older production well

logging method / provided information
SAL/TEMP (salinity/temperature)	measurement of temperature and conductivity of the water in a monitoring or production well determination of ground-water level determination of temperature and estimation of mineralization degree of the water in the monitoring or production well determination of zones with inflow or loss of water detection of leaking joints circulation behind the casing
TV (camera inspection)	optical inspection of the inner casing walls assessment of the actual condition of the casing identification of films and deposits detection of damaged parts of the casing evaluation of the condition of the screen slots recognition of corrosion phenomena if corrosion process takes place from inside to outside
CAL-M (micro-caliper)	mechanical scanning of the casing’s inner walls (with a four-arm caliper tool if applicable, spatial sampling rate of 1 cm) determination of the inner diameter localisation of the joints, casing pipes and the screens identification of casing defects, widening, contractions, excentrities and other deformations detection of deposits inside the casing determination of the volume of the ground-water monitoring or production well
IL (induction log)	inductive measurement of the electrical conductivity can be used only in wells with electrical non-conductive casings like plastic, earthenware etc. identification of electric anomalies in the annular space, especially in wells with large drilling diameters lithological classification of the bedrock in wells with small drilling diameter measurement of the electrical resistivity of the bedrock, even above the water level / can be used in particular for the geological classificationof the bedrock determination of water saturation of the bedrock and annular space
GR (gamma-ray-log)	measurement of the natural gamma-radiation emitted by the surrounding bedrock and annular space check of geological profile obtained by other methods indication of fine grain content of filter gravel detection of colmatages on the screens determination of the position of the annular seals, if high intensity gamma-emitting materials were used
SGL (segmented gamma-ray-log)	simultaneous measurement of natural gamma-radiation in three segments of 120 degrees emitted by annular space fillings and bedrock check, if the filling of the annular space is distributed homogeneously in all directions, thus a check for the effectiveness of supplementary sealing of the annular space by pressure grouting of a clay-cement suspension for the application of this method wells need to have a diameter of at least 100 mm
GG.D (gamma-gamma density log)	measurement of reflected/scattered gamma-radiation (emitted from weak source), intensity depends on density of the formation/annular space estimation of the compaction of the annular space filling (no wash outs, bridges, segregation) identification of annular seals classificationof the surrounding bedrock on the aspect of different densities identification of casings with a differing wall thickness
NN (neutron-neutron-log)	measurement of reflected/scattered neutron radiation (emitted from weak source), intensity depends mainly on total content of hydrogen in formation/annular space identification of annular seals with unknown composition estimation of porosity determination of water content of annular space filling determination of water saturation of the bedrock
MAL (magnetic log)	measurement of magnetic properties of annular space/casing etc. detection of metal (lost casings and metal parts, centralisers, outer core barrels) identification of annular seals if sealing material (e.g. clay) was enriched with magnetic particles (non-magnetic casing only) division of the annular space filling on the aspect of different susceptibility
FLOW (flow meter)	speed of an impeller in the pump current division of the influx characteristics in the screen zone identification of changes of the hydrodynamic settings caused by the rehabilitation process search for possible causes if production rates of the well decrease identification of imported water influx
FW-Pack (packed flow meter)	measurement of the debit through the cross-section of a packed flow-meter (speed of the measuring impeller) qualitative estimation of the permeability of the screen slots and of the filter pack material contiguous to the screen
FEL-B (focussed electric log)	measurement of electrical resistivity location of the casing screens check for tightness of the casing (in particular of the joints, couplings) assessment of the inner casing walls (corrosion phenomena, films, crusts - for this purpose the FEL-B can be applied also in metallic casings!)
SAL_{0... 8} ... TEMP_{0... 8} (fluid-logging)	monitoring of water flow in the well after different types of stimulation, and after injection of a NaCl-tracer suitable in particular for the detection of water flows with small debits, with or without external stimulation assessment of the dynamical conditions inside the well detection of leaks in the casing, especially in the case of steel-cased wells determination of the filtration velocity (velocity of the ground-water flow)
EMDS (electromagnetic casing-wall thickness)	measurement of the thickness of steel casings method for the evaluation of the actual condition of steel well casings yields information about the position of larger leakages and rusted-through zones and corrosion deposits or the remaining wall thickness respectively yield information about multiple telescope-like connected casings quatitative results up casing diameters of 500 mm
RGG.D (annular space scanner)	full circle rotating measurement of relative density changes in the annular space detection of a 360°-homogeneous filling of the annular space, thus an exact check for the hydraulic tightness of annular seals or permeability of filter packs suitable for casing diameters of 100 to 150 mm (4” - 6”)
SGG.D (segmented gamma-gamma density log)	measurement of the density of the annular space filling and the bedrock in two segments, spaced out horizontally with an angle of 180° between them check if the annular space was filled homogeneously, thus check for the hydraulic tightness of annular seals and permeability of filter packs
GDT (gas-dynamic annular seal test)	detection of artificially injected gas bubbles under annular seals by well logging means check for the hydraulic tightness of annular seals
BA (borehole deviation)	continuous measurement of azimuth and inclination check if pilot borehole for a well is perpendicular slight or noe inclination of borehole as condition for a correct insertation of casings and placement of filter packs and other annular space fillings increased inclination is often a cause of sand intake into the well important information for well abandonment by overdrilling
directional taking of samples	use of a motor-operated sampler fixed on the logging cable taking of water samples in different depths / samples are hermetically shielded from further alteration by the surrounding fluids
Packer test	use of a single or double packer for the definite check for hydraulic tightness of the casing joints the packer should be used after the focussed electric logging run (screening method)
FMT (photometric measurement of turbidity)	use of a photo sensor to measure the transparency of the water detection of sand intake even if not visible on macroscopic scale of ground-water flow velocity by injecting a tracer (EU-approved food colouring)
FMK (determination of flow direction)	photometric determination of the ground-water flow direction by using only one monitoring well direct determination of flow direction in monitoring wells by injecting a tracer (EU-approved food colouring) usable in ground-water monitoring wells with a diameter larger than 80 mm it is advisable to preliminarily detect zones of high horizontal water flow velocities with a FMT-log maximum application depth is 300 m
MIL (measurement of local environmental parameters)	measurement of the ph-value, content of oxygen, redox potential, temperature and conductivity of the water detection of inflows with differing ground-water qualities monitoring of contamination determination of water quality in-situ monitoring of ground-water monitoring and production wells

All descriptions and abbreviations correspond to the updated DVGW regulations.