Logging methods

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

Open exploration wells / pilot boreholes for ground-water monitoring and production wells / geological drilling

Task:
Well logging to support hydrogeological and geological drilling for the exploration of sites for ground-water monitoring and production wells, as well as for the exploration of raw materials. The methods can be modified to execute logging runs in large exploratory wells for ground-water production with diameters bigger than 400 mm.

Determined parameters
geometry of the borehole / continuous and complete documentation of the lithological profile / synthesis with core data if available / evaluation of porosity / calculation of a profile with contents of cohesive, non-plastic and organic rock components as well as porosity / estimation of the coefficient of hydraulic conductivity (if substantial analytic data is available) / quantitive evaluation of the pore water salinity in all aquifers that were sunk through

Determination of lithological classification in steel-cased 'dry boreholes'
In case of continuous steel casing, only the following small caliper logging methods can be used from the ones listed above.

GR-gamma-ray-log
GG.D-gamma-gamma-density-log
NN-neutron-neutron-log

With a growing number of telescope-like connected casing tubes (telescope drilling) the possibilities of interpretation are more and more limited.

Logging in large diameter boreholes
With advanced technologies, logging can be executed nowadays also in wells with large diameters (400mm - 1000mm) with an excellent content of information. For that purposes we use modified tools.

: logging example: exploration logging in large diameter pilot borehole for a ground-water production well

: logging example: exploration logging with complete analysis and evaluation

Standard logging program

logging method / provided information standard logging program:
CAL (caliper)	mechanical scanning of the borehole wall determination of borehole diameter necessary correction factor for calculation of formation density early recognition of possible difficulties to lower logging tools into borehole or well determination of the amounts of filling like gravel, sand, grout or clay (calculation of borehole volume)
EL (ES; short and long spacing, 16" and 64" )	measurement of the electrical resistivity of the surrounding formations lithological classification of the stratigraphic sequenz calculation of true formation resistivities for small borehole diameters,determination of mud infiltration depth
GR (gamma-ray-log)	measurement of natural gamma-radiation of the formation classification of lithological profile determination of fine-grain-content (silt and clay) of the formation
GG.D (gamma-gamma- density-log)	measurement of reflected/scattered gamma-radiation (emitted from weak source), intensity depends on denstity of the formation density-dependent classification of formations (e.g. distinction of silt from glacial till, identification of carbonous and other organic matter) determination of porosity
NN (neutron-neutron-log)	measurement of reflected/scattered neutron radiation (emitted from weak source), intensity depends mainly on total content of hydrogen in formation estimation of porosity determination of water saturation of formations second important method to identify clay, silt and silt-clay containing formations, in particular with occuring gravel beds of increased gamma-radiation
based on the hydrogeological standard set of methods listed above the computer program "LITHOLOG" can be run directly on drilling site if required
LITHOLOG (lithological profile)	computer-based processing of logging traces compilation (as chart or table) of a geological sequence on drilling site, enables direct on site decisions about well completion and annular space filling

possible supplementary methods for special demands:
IL (induction log)	inductive measurement of electrical conductivity of the formation identification of lithologal units / formations determination of electric resistivity - incuding above the water table - useful for large borehole diameters and low-resistivity formations determination of water saturation
FEL (focussed electric log)	measurement of specific electric resistivity lithological classification of geological sequence, especially for identification of sheets (layers of slight thickness) and intercalations (inclusions) search for lost casings or other metal parts
BA (borehole deviation)	continuous measurement of azimuth and inclination check if borehole is perpendicular slight inclination of borehole as condition for a correct insertation of casings and placement of filter packs and other annular space fillings
SP (spontaneous potential)	measurement of potential difference between a measuring and a reference electrode yields under favourable conditions (no influence of electrical conducting parts in the surrounding area – e.g. cables, railroad tracks, pumps) hints for the location of cohesive and non-plastic layers in the bedrock, especially in mesozoic profiles, which have a low pore water salinity
SAL/TEMP (salinity/temperature)	measurement of temperature and conductivity of the drilling mud correction factor for the computation of the electrical resistivity of the bedrock, which is needed for the determination of the total mineralisation ('salification') of the water bearing beds or parts of them immediate indication of strong inflows into the well
MAL (magnetic log)	measurement of magnetic properties of the bedrock lithological classification, in particular indentification of coarse factions like gravel, pepples, boulders detection of metal

All descriptions and abbreviations correspond to the updated DVGW regulations.