MUDLOGGING, CORING AND CASED HOLE...

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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