Mud Logging – A Combination of Direct and Indirect Measurements
MUDLOGGING, CORING AND CASED HOLE LOGGING BASICS
LEARNING OBJECTIVES
By the end of this lesson, you will be able to:
Understand the process of mudlogging including hydrocarbonshows and lithology determination.
Identify the components of the drilling mud system anddescribe where cuttings samples and gas samples are collected.
Identify lithology and hydrocarbon type (oil or gas) fromMudlog in a hydrocarbon bearing zone.
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MUD LOGGING
Traces of fluids that were contained in the formation penetrated by the bit.
The drill cuttings that are circulated up the annulus and carried to the shale shaker by the drilling mud.
Diluted gas drawn from Gas Trap agitator inmud returns
Hot wire and Chromatograph analyze streamfor hydrocarbons Total combustible gas using hot wire Chromatograph with FID for specific hydrocarbons (C1
-C6) Drill cuttings collected from shale shaker Washed, described by mud logging engineer Lithology, oil shows, fluorescence, compared to gas
data Sample and gas lag times must be measured
or calculated Interpreted log combines ROP, lithology, HC
gas readings, and detailed cuttingsdescriptions, all plotted vs. depth
Two primary sources of Mudlog data:
MUD LOGGING APPLICATIONS
Lithology determination Formation fluid typing Well positioning within stratigraphy Selection of casing and/or coring points
Detection of geo-pressures Geopressures are subsurface pressures that are higher than
“normal” pressures. Normal pressure gradient is about 0.465 psi per foot
Drilling Optimization Bit selection; hydraulics Polycrystalline Diamond (PCD) bits
Notes: Cuttings lithology when intervals drilled with PCD bits Fluid typing, ROP, pressure, bit runs still useful
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THE DRILLING MUD SYSTEM
Where are drilling mud
samples collected?
DRILL CUTTINGS SAMPLES COLLECTED AT THE SHALE SHAKER
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MUD LOG PROCESSING FLOW
Sampledat theshaker
Agitator/ Gas Trap in Possum Belly
Hot Wire (Total Combustible)
Gas Detector
Chromatograph(Gas Components
by FID + GC)
InterpretiveMudlog Output (ASCII/LAS) or
graphic formats
Drill Cuttings Interpretation
Drilling Engineering Data
Log
MUD LOGGING WELLSITE UNITS
Photo courtesy of BakerInteq
Combination Digital, Analog Unit Digital Unit
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LOGGING UNIT
GEOLOGY SIDE
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MUD LOGGING: EVALUATION
How does the subsurface team use the Mudlog?ROP log used for well-well correlation
Cuttings lithology
Gas Analysis
Oil staining on cuttings (e.g., chlorothene solvent cut): Water zone: no staining Oil zone: more heavy components Gas zone: only light components
Excellent clue is the color of
fluorescence when sample is
wetted with solvent and
viewed in UV light
MUD LOGGING COMPONENTS
Sample, gas for analysis Samples each
5-30 feet as requested Continual total gas Components each 12-15
minutes
Data output is graphic, digital Spreadsheet ASCII LAS
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ANALYSIS OF TOTAL GAS − COMPONENTSHydrogen generator
PC withIChrom
Igniter Glow Plug 24 volt
Oiler
FID Detector BlockHeated to 250C
Jet
Metal Tube tocatch Ions – 240 volts(Collector)
Balston Filter
Possum belly or ditch• Gas trap• Agitator motor• Gas lines• Condensate bottle
Pneumatics panel• Vacuum pump• Moisture Filters• Flow regulators
HP6890 Gas Chromatograph• Total gas• Gas chromatography
Courtesy of BakerInteq
LITHOLOGY DETERMINATION TAKES PRACTICE!
Large cuttings are cavings Fine cuttings of Woodford shale with no cavings
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MEASURING TIME – DEPTH SAMPLE LAG
Lag time
Methods to determine lag time include:
Calculate the lag time from the borehole geometry
Put a tracer in the mud and calculate the amount of time it takes to circulate the tracer mud from the bit until it is observed on the shale shaker
Knowledge of the lag time allows the mud logger to post the lithology at the correct depth on the mudlog
All mud logs should be lagged
DRILLING RATE/POROSITY RELATIONSHIP
Be Careful! When drilling in
shale, faster drilling can mean higher pressures which can lead to
a blowout!
Slower formations
Faster formations
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HYDROCARBON SHOW TESTS ON CUTTINGS
Various techniques to identify hydrocarbon shows from drill cuttings are:
Staining, bleeding oil, odor:(direct evidence of HC)
Natural fluorescence (UV): Distribution, intensity, color 5 = strong... 0 = nil
Solvent cut test (Chlorothene): Minerals will not produce cut fluorescence
Acetone test (light oil): Hydrocarbons cause milky white solution
Acid test: Bouncing motion of cutting if HC present Pyrolysis test (“burn it”) Hot water test: Oil film at surface
GRAPHICAL MUD LOG EXERCISE
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WERE WHOLE CORES TAKEN IN THIS WELL? IF SO, AT WHAT DEPTH?
WERE ANY OIL BEARING ZONES ENCOUNTERED?
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WHAT CAUSED THE BIG GAS SPIKE AT 5420 FEET?
WHAT IS THE DOMINANT LITHOLOGY IN THE OIL SHOWS?
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HYDROCARBON FLUORESCENCE
API°
(45°) blue-white to violet
(35-45°) white
(25-35°) yellow to cream
(15-25°) orange
(below 15°) brown
Sample fluorescence (approximate)
NOW… IS THIS A GOOD SHOW?
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LEARNING OBJECTIVES
Understand the process of mudlogging including hydrocarbonshows and lithology determination.
Identify the components of the drilling mud system and describewhere cuttings samples and gas samples are collected.
Identify lithology and hydrocarbon type (oil or gas) from Mudlogin a hydrocarbon bearing zone.
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