Logging Equipment and Technology

The trisonde is a convenient alternative to the standard RG sidewall density probe whenever borehole diameter is restricted and qualitative density measurements are sufficient. One common application is logging through drill pipe when unstable borehole conditions prevent use of unprotected nuclear probes. The probe is unfocussed and indicates the average density of material surrounding the borehole.

Principles of Measurement

The probe contains a gamma source and two high-sensitivity scintillation gamma detectors.
Gamma radiation from the source is backscattered by the formation (Compton effect) and reaches the two detectors where the relative count-rates provide a measure of formation bulk density.

Features

Long-spacing density (LSD)

High-resolution density (HRD)

Bed Resolution density (SSD)

Temperature

Natural gamma

Minerals

Lithology, Bulk density variations, Correlation with other logs, Bed thickness and boundary location, Borehole inclination and true vertical depth.

Engineering

Optional 110/220VAC power supply (also powers SMART portable winch).
Detection of weathered or fractured zones, Ground compaction studies.

Water

Location of aquifer and aquitard, Detection of cavities and missing cement around casing.

Borehole type

All

This highly compact tool is designed specifically for geotechnical and mining applications. The probe measures high (HR) and medium (MR) resolution transit-time and full-waveform data simultaneously from three receivers. The HR measurement gives good resolution of bed boundaries while the MR provides the average formation velocity even in the presence of moderate caving. Shear-wave velocities from full-wave data may be used to calculate rock elasticity parameters.

Principles of Measurement

The piezoelectric transmitter is stimulated by a high-voltage pulse and radiates a high-frequency sonic wave through the borehole fluid and formation to a receiver. An accurate quartz clock measures the first arrival transit time.

Compensated sonic mode: 
Three receivers are used. The probe measures the velocity of the first compressional arrival at each receiver. The difference in arrival times between each pair of receivers allows determination of the formation velocity independent of the borehole fluid path.
Full waveform sonic mode: 
The probe records the full sonic wave-train at all three receivers simultaneously and also the velocity of the first arrival at each. The data can be displayed as a variable-density log (VDL) or as a waveform (wiggle trace). The waveform data may exported to 3rd-party packages for calculation of compressional, shear and Stoneley velocities.

Short probe can be handled by single operator and easily shipped

Slim diameter for narrow boreholes

Rigid construction for effective centralisation

Down-hole digitisation of waveform data at 1cm interval

Data rate selectable up to 200kbaud for maximum logging speed

Detection gain and threshold under operator control. Detection point and wavelet visible on 'oscilloscope' display during logging

Formation velocity (slowness)

Time of first arrival (delta-t)

Integrated transit time

Full waveform from 3 receivers simultaneously

Shear and Stoneley velocities (requires precessing software)

Geotechnical

Fracture and permeability indication in hard rock

Mining

Rock strength and elasticity
Lithology identification

Water

Correction of seismic velocity
Porosity

Borehole type

Sonic: open-hole, water-filled

Centralisation: 2 essential

The RG verticality probe provides accurate, continuous measurements of borehole inclination and direction. These are output directly as log traces or may be processed further to produce tabular and graphical outputs of borehole position, borehole drift and true vertical depth.

Principles of Measurement

The probe includes a triaxial magnetometer to deduce the probe bearing relative to magnetic North and three accelerometers to measure inclination. The outputs from the transducers are processed by a downhole microprocessor to give final borehole inclination and azimuth data in real time. The operation of the probe is limited in steel casing or in the presence of magnetic minerals which affect the magnetometer. Under such conditions, only borehole inclination (without directional information) can be logged. The gyroscopic verticality probe should be used in preference to the standard verticality probe in these cases.

Features

Borehole inclination

Borehole direction

Borehole drift

True vertical depth

Minerals

Lithology, Bulk density variations, Correlation with other logs, Bed thickness and boundary location, Borehole inclination and true vertical depth.

Engineering

Optional 110/220VAC power supply (also powers SMART portable winch).
Detection of weathered or fractured zones, Ground compaction studies.

Water

Location of aquifer and aquitard, Detection of cavities and missing cement around casing.

Borehole type

All

The HRAT is the latest RG development in acoustic borehole imaging and replaces the previous borehole televiewer probe (BHTV). It provides
high-resolution orientated 'unwrapped' images of the borehole walls.

Applications

Fracture identification and orientation
Stratigraphic studies
Local stress studies (break-out)
Core orientation

Principles of Measurement

The probe uses a fixed acoustic transducer and a rotating acoustic mirror to scan the borehole walls with a a focussed ultrasound beam. The amplitude and travel time of the reflected acoustic signal are recorded simultaneously as separate image logs. Features such as fractures reduce the relected amplitude and often appear as dark sinusoidal traces on the log. The travel-time log is equivalent to a high-precision 360-arm caliper and shows diameter changes within open fractures and 'break-outs'. Directional information is also recorded and used to orient the images in real time.
The HRAT includes many new features such as automatic optimisation of head rotation speed according to borehole diameter, cable speed and desired resolution. A new design of acoustic transducer provides improved image focus and resolution compared to the previous BHTV probe.

RG-DIP, the RG image interpretation package, offers manual and automatic feature recognition options. Feature orientations (dip/strike and azimuth) are automatically calculated. Display options include stereographic projections of zone axes, orintation frequency plots and 'synthetic cores' for comparison with real core data. The last option is invaluable for orientating core samples, particularly in the case of incompete recovery. The HRAT format is also compatible with the popular IMAGER interpretation package from Geomechanics International (GMI), available through RG.

The dual neutron probe provides an accurately calibrated borehole-compensated neutron porosity measurement in mud-filled open holes. It is the probe of choice for quantitative formation-fluid studies, including shallow oil and gas prospects.

Principles of Measurement

The dual neutron measurement uses two 3He proportional detectors and a detachable, sealed neutron source. Fast neutrons emitted by the source are scattered and slowed by light elements (and principally hydrogen in the formation) until they reach thermal energy levels. The ratio of the flux of thermal neutrons reaching the near and far detectors depends on the Hydrogen Index and porosity. Use of the two detectors and a ratio method provides a porosity measurement which is independent of borehole size over a range of hole diameters.

Features

Compensated porosity

Raw long-spaced neutron

Raw short-spaced neutron

Count ratio

Natural gamma

Casing collar locator

Water

Lithology identification

Engineering

Location of aquifer and aquitard

Minerals

Shale content
Fracture analysis in coals
Correlation between open and cased-hole logs
Strata correlation between wells

Borehole type

Open/cased, water-filled (qualitative measurements are possible in air-filled boreholes)

Centralisation

excentralised with bowspring

The ELOG or electric log is the classic water-well combination probe combining shallow, medium and deep penetrating resistivity measurements with
self-potential (SP) and natural gamma (optional).

Principles of Measurement

Resistivity

The down-hole ELOG probe is equipped with electrodes, measurement electronics and an insulated bridle. A low-frequency bi-directional electric current from a source electrode on the probe returns through the formation to the cable armour above the bridle. Potentials due to this current flow are measured on various sense electrodes on the probe with respect to a voltage-reference ‘fish’ normally located at the surface. The spacing between the source and individual sense electrode determines the depth of investigation of the measurement. These measurements are converted to apparent formation resistivities within the probe and digitally transmitted to the surface.

SP

The SP is a voltage measurement between a
non-polarising down-hole electrode and a reference ‘fish’ at the surface.

Digital down-hole measurement avoids errors due to cable effects in deeper boreholes

Constant-power down-hole current source give 4 decades of measurement without manual range switching

Automatic real-time correction for borehole diameter and well-fluid resistance

Optional natural-gamma measurement and temperature

16" Normal resistivity

64" Normal resistivity

Single-point resistance

Self potential (SP)

Natural-gamma

Temperature (optional)

8" and 32" Normal resistivity (optional)

Water

Determination of water quality
Indication of permeable zones and porosity

Engineering/Minerals

Bed-boundary positions
Strata correlation between boreholes

Borehole type

Open-hole, water-filled

The bridle top must be immersed in well fluid, restricting top logging depth to 10m below the fluid level. A short bridle may be used to allow resistivity logging to within 3m of the fluid surface. However, 64" normal results in this case will be qualitative. Best results are obtained in fresh mud with low to medium formation resistivities.