Borehole Geophysics
Borehole geophysics are part of the multi-disciplinary approach adopted by
Ardara International Limited. These methods are often used in conjunction with
surface geophysics and hydrogeological services. Our logging personnel are
highly skilled geophysicists with experience of logging both deep (1500m) and
shallow (10m) boreholes in many different environments. Drilling a borehole is
an expensive investment, therefore, it is a good idea to acquire as much data
as possible from the borehole. Geophysics is a relatively cheap method of
achieving this. The following types of downhole survey are available:
Fluid Properties
From the correct use of temperature / conductivity and flowmeter tools, water
quality and zones of water inflow and / or outflow can be determined. These
data are important for the correct design of a water well. Fluid logging can also
be used by the environmental industry to monitor contaminant plumes.
Formation Properties
Measurements of sonic transit time, clay content, formation density, resistivity
and porosity are also important in the design of a water well. These properties are also be used for lithological determination, petrophysical calculations,
stratigraphical analyses and correlation between boreholes. Formation
properties are also of use in the civil engineering industry when evaluating
rock strength.
Downhole / Crosshole Seismic
Use of a tri-axial downhole geophone with a seismic source at surface or in a
nearby hole yields primary and shear wave velocities at regular intervals. The
ratio of these velocities is used to calculate Poisson's Ratio and when
combined with rock density (from lab analyses or logging), shear modulus,
Young's modulus and bulk modulus can also be calculated. Downhole seismic
is also used to correlate surface seismic data with borehole data.
Seismic Tomography
Similar to crosshole seismic, this technique uses a multi-geophone array in 1
hole with a source in a nearby hole. Large amounts of travel time data are
acquired and processed to produce an image or tomogram of the velocities
between the holes. Poisson's Ratio etc are also determined.
Borehole CCTV
A specially adapted video camera is lowered into the borehole and the image
recorded at surface. This is especially useful during fishing operations to
determine the position of the fish, to evaluate cased holes and can also be
used in open hole for the assessment of fractures.
Cased Hole Evaluation
In many cases no information exists on older boreholes. Screened section and
cement condition can be assessed using cement bond logs, caliper and
borehole CCTV. Surveys can also be done to determine how well gravel pack
is emplaced.
Borehole Imaging
Optical or sonic televiewers are used to produce an image of the borehole
wall. Examination of the images reveals detailed information about fractures
and beds such as orientation, dip and whether fractures are open or not.
Borehole Deviation
The exact track of a borehole can be recorded using tools with magnetometers
and gyroscopes.
Recent clients include:
Ministry of Municipal Affairs and Agriculture (Qatar), Petroleum Development
Oman, Kilkenny County Council (Ireland), Ministry of Housing, Electricity and
Water (Oman), Ministry of Agriculture and Fisheries (Dubai).
