Borehole Logging

COMMERCIAL BOREHOLE LOGGING PAUL SPIELMAN September 2007

From Warrior Energy Services Website, www.warriorenergyservices.com

TYPICAL WIRELINE TRUCK

From Welaco

TYPICAL WIRELINE SKID UNIT

Welaco Unit at Ormat’s Puna Geothermal Venture in Hawaii

TYPES OF LOGS • Geophysical Logs – – – – – –

Resistivity Porosity Gamma Ray Dip Meter Borehole Imaging Other

• Production Logging – – – –

Pressure Temperature Spinner Fluid Density

• Well Inspection – – – – – –

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Sonic Caliper Electro-magnetic Ultrasonic RA Tracer Video

RESISTVITY LOGS • • Measure bulk resistivity of formation • Laterlog – The original well log – Electrodes direct current into formation to ground electrodes on surface

• Induction – Magnetic field induces current in formation – Used with low conductivity well fluids

• Porosity can be calculated if water salinity is known • Oil or gas saturation can be calculated if porosity and water salinity are known

POROSITY LOGS • Neutron tool – Neutron source – High energy neutrons are slowed down by hydrogen atoms in water (or oil) and detected by tool – Porosity is function rock type and slow neutron count

• Density tool – – – –

Gamma ray source Electrons reflect gamma rays back to detector in tool Electrons in formation proportional to density Porosity is function of rock type and density

• Sonic tool – Measures speed of sound in formation – Porosity slows sound – Porosity is function of rock type and measured speed of sound –

GAMMA RAY LOG • Gamma ray detector measures natural radioactivity of formation • Mostly due to Potassium in Shale – Shale has porosity but no permeability

• Uranium and Thorium – Less common sources natural radioactivity – Detected by more sophisticated tools that measure gamma ray energy

• Run with other tools to correlate logs

DIP METER AND BOREHOLE IMAGING • Dip Meter – Four or six arms with few buttons measure small scale resistivity – Wellbore inclination and orientation – Map bedding planes of sedimentary formations

• Imaging Tools – Resistivity imaging tools • FMI - Schlumberger, EMI – Halliburton • Pads with many buttons map small scale resistivity

– Ultrasonic imaging tools • USIT – Schlumberger, CAST – Halliburton • Spinning ultrasonic transducer measures I.D. and sonic impedance

– Borehole image • Dip and orientation of fractures • Structure and stress of formation – Borehole breakout – Drilling induced fractures

OTHER GEOPHYSICAL LOGS • Mineral identification – Pulsed neutron source stimulates gamma ray emissions – Tool measures energy spectrum of returning gamma rays – Percentage of elements (silica, calcium, etc.)

• Magnetic resonance – Detects free water – Determine permeability –

GEOTHERMAL APPLICATIONS • Geophysical tools designed for sedimentary formations – Algorithms for sandstone, shale, limestone, dolomite – Special algorithms required for crystalline rock

• Resistivity tool is sufficient to quantify porosity when water salinity is known • Sonic tool puts seismic surveys on depth • Density tool calibrates gravity surveys • Formation imaging tools map fractures and quantify stress regime • Neutron and density tools can identify lithology, – if samples are available to create correlations – if there is variation in rock type

Schlumberger Litho-Density Log

COMPANIES The Big Three

Geothermal Production Logging

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• SCHLUMBERGER • HALLIBURTON • BAKER ATLAS • Worldwide Geophysical, Production & Inspection Logging

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Video • DOWNHOLE VIDEO – Oxnard CA • many other companies 

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WELACO – Bakersfield CA PACIFIC PROCESS SYSTEMS – Bakersfield CA SCIENTIFIC PRODUCTION SERVICES – Houston TX INSTRUMENT SERVICES INC. – Ventura CA

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Pressure-Temperature-Spinner & some other services 

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Sell and service equipment

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Many other companies in Japan, New Zealand, Philippines, Iceland, Kenya (KenGen), etc.

PRODUCTION LOGS • Very useful in geothermal wells • Can be run with simple or sophisticated equipment • Temperature surveys are essential for exploration work • Pressure & Temperature surveys are more useful for well testing and production

TEMPERATURE LOGS • Most important parameter in geothermal wells • Thermocouple wire – easiest for shallow holes

• RTD – most accurate

• Mechanical tool – Only option for deep hot wells 10 years ago

• Electronic surface readout tool in thermal flask – Requires high temperature wireline

• Electronic memory tool in thermal flask – State of the art – Slick line or braided cable

• Fiber Optics – Instantaneous temperature profile of entire wellbore – Good for measuring transients

• High temperature electronics – Not yet commercial

TEMPERATURE PROFILE SURFACE

DEPTH

CONDUCTIVE GRADIENT

HYDROTHERMAL SYSTEM OUTFLOW ZONE UPFLOW TEMPERATURE REVERSAL

CONDUCTIVE HEAT SOURCE TEMPERATURE

PRESSURE LOG •

Second most important reservoir parameter – pressure drives flow – producing drawdown indicates reservoir productivity (or injection buildup) – drawdown curves analyzed to determine reservoir permeability

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Water level, easily measured – used in hydrology but less useful in geothermal systems – dependant on wellbore temperature and gas or steam pressure above water

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Mechanical pressure tool – common ten years ago

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Capillary tubing filled with nitrogen or helium – reservoir pressure is measured at surface – good for long term reservoir pressure monitoring of hot wells

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Electronic surface readout tool in thermal flask – requires high temperature wireline

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Electronic memory tool in thermal flask – state of the art – slick line or braided cable

STATIC PRESSURE AND TEMPERATURE PROFILES PRESSURE 0

50

TEMPERATURE 100

150

200

250

0

200

400

DEPTH

WATER LEVEL 600

800

1000

1200

STATIC PRESSURE

STATIC TEMPERATURE

300

350

STATIC AND FLOWING PRESSURE AND TEMPERATURE PROFILES PRESSURE 0

50

TEMPERATURE 100

150

200

250

300

0

200 FLOWING TEMPERATURE

DEPTH

400

600

800

STATIC PRESSURE

STATIC TEMPERATURE

FLASH DEPTH

FLASH DEPTH PRESSURE DRAWDOWN

1000 FLOWING PRESSURE 1200

350

SPINNER LOG • Propeller measures flow in wellbore • Identifies production (or injection) zones • Calculate fluid velocity from series of up and down runs at different cable speeds

FLOWING SPINNER SURVEY Log down 100 fpm

Log up 100 fpm

SPINNER COUNTS -10

0

10

20

0

200

DEPTH

400

600 FLASH DEPTH 800

1000

1200

MAIN PRODUCTION ZONE

30

40

50

TYPICAL SHALLOW WELL LOGGING UNIT

From USGS website, nc.water.usgs.gov

TYPICAL SLICK LINE WINCH

From BOP Controls Inc. website, bopcontrols.net

WELL INSPECTION LOGS •

Sonic Cement Bond Log (Same tool as sonic porosity log) – – –

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Caliper – –

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Measures metal loss Detects corrosion, holes and parted casing

Ultrasonic (same as imaging tool) – –

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Measures I.D. of casing Detects corrosion, scale, washouts, parted casing

Electro-magnetic – –

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Measures quality of cement on outside of casing Difficulty with large geothermal well casing Difficulty with micro-annulus caused by temperature and pressure changes

Measures I.D. and thickness of casing, and impedance of material behind casing Detects corrosion, holes and cement

RA Tracer – – –

Injects slug of iodine 131 into wellbore Gamma ray detector measures radioactive slug Detects leaks in casing and flow behind pipe

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Identify well problems Requires very clear water

Video

PRESSURE CONTROL Should be used there is any possibility of well flowing

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Pack-off

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– Rubber cylinder tightens around wireline – Few hundred psi

Grease out Low pressure

Lubricator

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– Length of pipe below pack-off – Necessary to run tool in pressurized well

Blow out preventor

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– Valve below lubricator that closes around wireline – Useful if pack-off fails or wireline gets stuck in pack-off

Grease tubes for high pressure

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– Placed below pack-off Grease in – For thousands of psi High pressure – Grease pumped in high pressure end flows to low pressure

PRESSURE-TEMPERATURESPINNER TOOLS FOR SALE • MADDEN SYSTEMS (Odessa, TX) – Flasked surface readout and memory tools

• KUSTER COMPANY (Long Beach, CA) – Mechanical tools – Flasked surface readout and memory tools –

Anyone with a slickline or braided cable winch can run memory tools.

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GEOPHYSICAL LOGGING TOOLS AND WIRELINE WINCHES FOR SALE 

• Companies that used to make tools and sell wireline systems went out of business in the 1990’s • • Companies that sell systems now are on the internet