An introduction to wireline logging for geotechnical ...geoss.sg/geoss/event_image/07122016-172557-ef.pdf · ROBERTSON GEOLOGGING Innovation, global support & services Introduction

ROBERTSON GEOLOGGINGInnovation, global support & services

Introduction to wireline loggingfor geotechnical applications

Agenda

Robertson Geologging

PS Suspension Logging

Density/Gamma Logging

Image Logging – Acoustic & Optical Televiewers

New Developments

Capabilities

Established 1979, in North Wales

Design, develop and manufacture of downhole tools and surface equipment

Develop software

Provide contract logging service & supply wireline & surface tools

Support hotline and replacement service

Training & commissioning

Believe in maintaining a large development program for a forever changing market

The only ISO9001 certified mineral logging manufacturer

Robertson Geologging (USA)Sales, support & rentals

Robertson Geologging (ASIA)Sales, support & rentals

Operations

Operations supported by over 45 agents worldwide

UK Headquarters

Onsite test borehole, mechanical & electrical assembly, pressure & temperature testing, calibration facilities, R&D, product development

Technology & Services

PS logger

Developed by OYO Corporation Japan for domestic use in earthquake engineering

Introduced to the USA, Golden Gate Bridge & San Francisco Airport projects

2007 OYO transferred technology over to Robertson Geologging for further development

and commercialisation

Recent projects include; shallow oil/gas projects in Russia, offshore wind farm surveys

across Europe, Australia, the Mediterranean and South America, earthquake engineering

in Asia and land & offshore projects in the Arabian Gulf

PS logger - advantages

Needs only a single uncased borehole

Surveys can be performed immediately after drilling

Very mobile, moved rapidly between stations

Minimises survey time and risk of BH collapse

High vertical resolution, locate and resolve thin layers

Transmitter and receiver in the BH noise is reduced

PS Logger - operations

PS Logger - operations

Telemetry

Receivers

Filter

Source

Source driver

Weight

PS logger - operations

Powerful source, monopole and directional receivers separated by acoustic damping

tubes

Measurements typically shot at 1m intervals (1 minute)

Once fired the resultant fluid motion produces a tube wave at the BH wall

Waves propagate parallel to the BH axis, setting up corresponding fluid movements

that are detected by 3D hydrophone receivers – allowing the wave velocity to be

directly measured

Open water filled BHs between 75 – 150mm diameter. Will work through PVC with

adequate grouting – does not work with steel casing

PS logger - deliverables

Waveforms are examined and first arrival picks are made

Left and right oriented S waves are derived and averaged

Digital filtering can be used to attenuate random noise

Deliverables:P wave and S wave waveformsP wave and S wave velocity profilesVp/Vs ratio profileTabular data of arrival times, velocities and Vp/Vs ratio

If bulk density is known, the following can be derived:Shear modulusBulk modulusYoungs modulus

PS logger - picking first brake

PS logger - interpretation

Final calculation of Vp and Vs after picking first arrivals

PS logger - interpretation Bulk, Shear and Young moduli, measured in Mpa.These are automatically calculated if density profiles are loaded

Final calculation of Vp and Vs after picking first arrivals

PS Logging

Formation Density Sonde

Formation Density - sonde

Diameter 50 mm

Length 3.02 m (with source)

Temperature rating 0 – 70°C extended range available

Pressure range 0-20 Mpa

Weight 20 kg

Source type 100 mCi 137Cs

Supported cable type mono or 4 conductors

Borehole diameter range 65 to 300 mm

Formation Density - applications

The in-situ measurement of electron density

Conversion of data to calculate formation bulk density & Poisons ratio

Mineral studies (coal identification)

Porosity

Fracture identification (comparison with PS Logger)

Identification of Lithological layers

Support to acoustic impedance sections and elastic moduli estimate after Sonic Log measurements

Formation Density - theory The sonde employs a radioactive source which ‘bombards’ the formation with gamma rays

The detectors measure the abundance of gamma rays

At a fixed distance from the source, the gamma count will be proportional to the formation density

The phenomenon is called Compton scattering. Gamma rays collide with electrons multiple times, gradually losing energy, until eventually they are absorbed. In denser rocks, counts are lower because most gamma rays are absorbed before they get to the detector

This process logs electron density and that is all. Whereas the geologist will measure density by establishing the weight and volume of a sample, the logger estimates the concentration of nucleons (protons and neutrons) via the electron count (one electron per nucleon pair). Denser rocks have more nucleons per volume

The relationship between electron density and bulk density is fairly constant for the major rock-forming elements like silicon, aluminium and magnesium. The Z/A ratio, electrons (and so protons)/total nucleons is about 0.5. So the conversion from electron density to bulk density is, theoretically, straightforward

Formation Density - theory

One detector very close to the source (28 cm apart), called “high resolution detector” (HRD)

One “long space detector” (LSD) bigger in size, 48 cm off whose use allows for compensation

Optional “bed resolution detector” (BRD), 14 cm from the source to resolve thin layers

The distance between the source and the detector affects the volume (depth) of investigation and the resulting cps (and density) readings

Formation Density - theory

The long spaced detector (LSD) will record lower gamma rays count because of the greater distance of this detector from the source but it will refer to a bigger volume.It is less sensitive to borehole diameter changes (ie voids, caving and mud panel) and fluid

HRD (and BRD) is more prone to borehole variations (caving, rugosity) and more influenced by borehole fluid type

Although presenting improved vertical resolution it should be filtered and mostly used as qualitative response, comparing it with calliper profile

Formation Density - theoryFactor affecting density readings:

Borehole diameter and borehole fluid density (especially for the HRD/BRD), even if the sonde is sidewall constructed and a user function is introduced to reduce borehole effect

Cavities/borehole wall roughness as well as air or light mud (< 1 g/cc) underestimate density while heavy drilling fluids overestimate the response

Deposits with very high Natural Gamma readings (Uranium ore) as introducing additional counts thus lowering final density calculation. This channel should be monitored

Certain minerals may lead to overestimate or underestimate of density.For example clays present a wide range of density and when intercalated with other lithologies amplify uncertainties

Gas saturated formation may lead to porosity overestimate while the Neutron Porosity would have lower readings

Formation Density - compensation

To achieve measurement precision in a range of borehole conditions, the logger mustemploy a logging system that provides reliable borehole compensation. That is the cruxof the issue, the difference between an average density sonde and a good one.Compensation includes the above

Televiewer - HiOPTV

HiOPTV - operations

Best results in clear water or air filled borehole

Thick/heavy muds and debris can obscure borehole wall images

Should allow 24-48 hours of settlement after drilling

Typically log at 2m/min, running slowly can cause the centralisers to stick and not move

fluently

If centralisation is not properly achieved, features & true orientation (azimuth and

inclination) cannot be assessed in post processing software (RGLDip or Wellcad)

HiOPTV - applications

Fracture identification and characterisation in term of dip and azimuth (local stress

studies)

Stratigraphic studies (very thin layer detection)

Lithology characterisation

Core orientation and borehole deviation studies

Casing studies

.

HiOPTV - examples

Lithology discrimination(layers/bands & intrusions)

Televiewer – HiRAT (high resolution acoustic televiewer)

Karl Jones, Business Development Manager Robertson Geologging

High resolution acoustic pulses - 1.5 MHz frequency – are generated by fixed a piezo-electric resonator and then transmitted along the tool axis to be reflected by a rotating planar mirror

Beam is ultra-focused to achieve the highest resolution and signal cleanliness

After mirror reflection the pulses propagate orthogonally to the sonde body through the acoustic window (nylon construction for acoustic impedance) then through the borehole fluid to be reflected by the wall of the boreholefollowing an almost normal incidence

HiRAT - operations

)

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Integration of HiRAT, OPTV and 3-arm calliper profiles

HiRAT – full borehole data despite poor core recovery

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HiRAT – borehole deviation

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HiRAT - interpretation

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Stick-plot Arrow-Plot BH deviationNotes

Wireline workshop issue 16 March 2016

New developments/other applications

Increased horizontal logging capability (up to 1000m)

Memory module to alleviate the need to use a wireline for directional logging

New 4” pressure meter

Thank youSteve [email protected]+852 65033486

Karl Jones MScBusiness Development & Sales Manager Europe and [email protected]+44(0)771 482 5357

www.geologging.com