Modern Well Log Interpretation
Duration: 
5Days
Location: 
Abu Dhabi, United Arab Emirates
Organizer: 
Mobility Oil & Gas (UK) Limited

Who Should Attend
The course is intended for entry-level engineers and geologists/geophysicists, as well as for experienced geo-scientists and technical assistants working with, or needing to understand better, the principles of log interpretation and/or to update themselves on the range of log measurements and techniques now available to them.
Although the course is appropriate for both engineers and geologists/geophysicists, the emphasis and level can be changed depending upon the participants’ requirements and backgrounds.

Training Method and General Remarks
This course presentation is modular and covers the topics listed below, using many generic examples for the participants to work on themselves as each topic is covered. Participants develop their own interpretation of 2 sets of logs (one wireline, one LWD) as the course progresses, and (most of) the last day is taken by working in teams on a further set. If possible, the latter example will be chosen from the area of the course (We have examples from Gulf of Mexico, Alaska, India, Nigeria, Kazakhstan & the North Sea).

Although the course concentrates mainly on wireline measurements, equivalent LWD measurements are also covered, remarking upon the differences and their advantages/disadvantages, with examples. The range of measurements discussed is comprehensive, so participants are also presented with an up-to-date “shop window” of the wireline & LWD tools & techniques now available to the industry.

Great emphasis is placed on the fact that log interpretation is still largely based on empirical relationships, the applicability of which may depend on local factors, and course participants are constantly reminded that reliance on “black box” interpretation methods can lead to serious mis-interpretations. Thus, the computers provided for the course are largely there to enhance the speed of computation of the data points manually chosen by the participants, using a simple Excel spreadsheet program implementing standard relationships, rather than for pushing un-screened log data through a pre-set interpretation package.

Efforts are also made broadly to cover the technologies offered by the various different service vendors, rather than only those from a single supplier.

Documentation
The course handouts include a hardcopy manual, exercises and a CD with the worked course examples and a selection of standard texts on log interpretation:
Log Interpretation Charts (Halliburton)
NMR Logging Principles & Applications (Halliburton)
Log Interpretation Openhole & Cased Hole Principles (Schlumberger)
Log Interpretation Chartbook (Schlumberger)
Introduction to Wireline Log Analysis (Baker Atlas)

Course Outline
Day 1: General Topics and Resistivity Measurements
Introductions: Course Leader, Course Participants,
Acknowledgement of Texts, Course Outline

Brief Overview of Requirement for Wireline & LWD Measurements to determine Reservoir Lateral & Vertical Extent, Pore Volume, Fluid Content, Fluid Moveability/Permeability/Pressure, Lithology/Mineralogy and Electrical Lithofacies

Overview of Basic Petrophysical Models & Relationships Used in “Clean” formation interpretation (these are discussed in detail as the course progresses):
(i) Porosity Model
Lithology/Mineralogy, total & effective porosity definition
Effect of clay minerals, difference between clay & shale
(ii) Invasion Profile Model
Why resistivity?
Definitions of Rm, Rmf, Rmc, Rw, Rxo, Rt (Ro), di, etc
(iii) Need to find the basic unknowns: Porosity, Rmf, Rw, Rxo, Rt
(iv) Linking Porosity and Resistivity by Formation Factor
(v) Determination of Water Saturation using Archie relationship
Water saturation, irreducible water saturation, effect of clay minerals

Either (covered in course for Geoscientists)
Overview of Basic Geological Models & Signatures obtainable from well logs
Measurement resolution vs. Geological features
Electro-sequence analysis
Use of dipmeters and imaging logs
Note: these topics are discussed in detail during Day 4 (see below)

Or (covered in course for Engineers)
Overview of Basic Applications of Wireline & LWD Methods for Well Completions and Reservoir Monitoring
Cement Bond Evaluation
Casing Corrosion Monitoring
Time-lapse monitoring of reservoir fluid levels
Perforation methods & Productivity Index enhancement
Note: these topics are discussed in detail during Day 4 (see below)

Depth Measurements & Control
Wireline depth control: use of calibrated wheels, magnetic marks
LWD depth control: pipe tally, tie-in with wireline
Typical wellsite depth measurement problems; perforating depth control
Measured depth, deviation, true vertical depth and the extreme importance of good depth control

Conductivity in Electrolytes and Derivation of Rmf at Formation Temperature
(i) Resistance, resistivity, conductivity
(ii) Well temperature profile and determination of temperature at zone of interest
(iii). Use of correction charts to determine fluid resistivities at desired temperature

Use of SP for Geological Interpretation and to determine Rw
Origin of SP: combination of electrochemical potentials
Relationship between SP magnitude and Rmf/Rw ratio, effect of shaliness
Use of SP for Geological Interpretation
Determination of Rw using SP

Resistivity Measurements to Determine Rt , Rxo and invasion profile
(i) Deep-reading Resistivity Measurements to determine Rt
Induction Logs (evolution from 6FF40 to Array & 3-D tools)
Laterologs (evolution from LL3/7 to Deep/Shallow/Imager/Array measurements)
LWD resistivity measurements (Propagation, RAB, Induction, Azimuthal Resistivity for hole navigation)
(ii) Pad-type Resistivity Measurements to determine Rxo
Microlog
Microlaterolog/Proximity Log
MicroSpherically- & MicroCylindrically-focused logs
(iii) Mandrel-type Resistivity Measurements to determine Ri
Early Electric logs, 16” Normal
Spherically-focused logs, LL-8
Tornado chart corrections & implications of the “step-profile” and other invasion profile assumptions

Gamma Ray
Origin: natural radioactivity, Th, U, K main components
API Calibration
Radioactive decay & statistical noise
Relationship with grain size, shaliness

Caliper Measurements
Mechanical Calipers and their use in log quality control
Acoustic Calipers
Borehole profile anomalies (breakouts, fractures, “rifle-bore” holes)
Present-day Stress Azimuth determination

Identification of Potential Zones of Interest using SP, GR and Resistivity
(i) SP - Used in identifying porous and non-porous formations
(ii) Gamma Ray - Used in shale/non-shale discrimination
(iii) Resistivity - Combination with SP & GR to identify tight and/or non-permeable zones

[This section is mainly the participants working through a series of log examples to illustrate the selection of zones of possible interest]

Day 2: Porosity and Mineralogy/Lithology Measurements

Measurements for Determination of Porosity & Mineralogy/Lithology
Density Measurements
Measurement principle & tool technology evolution (W/L & LWD)
“Spine & Ribs” calibration, mud & mudcake effects
Density/porosity/mineralogy relationship
Neutron Measurements
Measurement principle, fluid & mineralogy effects
Tool technology evolution from single detector to accelerator (W/L & LWD)
API Limestone calibration, calibration in other minerals is tool-type specific
Porosity determination, effect of gas, shale, mud constituents
Acoustic Measurements
Measurement principle & tool technology (W/L & LWD)
Dtp, Dtshear, Dtstoneley determination with array-type measurements
Washout, compaction/stress, shale alteration effects
Porosity/mineralogy determination (Wyllie, Raymer-Hunt)
Use of Dtp/Dts for gas detection, lithology
Brief remarks on rock strength prediction, fracture identification, permeability from Stoneley attenuation
(Azimuthal/radial stress analysis is discussed in an optional module at end of course)
Pe Measurements
Additional lithology identification from Pe & Density
Effects of mud-type
Crossplot methods for porosity & lithology determination
Compatible log scaling for quicklook overlays
2-D crossplots
M-N crossplots
MID plots (#1 & #2)

Gamma Ray Spectrometry and Core Sampling for Enhanced Mineralogy Determination
Spectral Gamma Ray
Use of T, U, K components for mineralogy
Elemental Capture Spectrometry
Use of Capture GR emission analysis for mineralogy
Percussion & Mechanical Sidewall Coring
As alternative to fullsize cores for fluid/porosity/permeability and mineralogy analysis

Day 3: Linking Resistivity with Porosity/Mineralogy Measurements

Linking Porosity, Formation Factor and Water Saturation
The link between Porosity & Formation Factor, and derivation of “m”
The link between Formation Factor and Water Saturation
Verification of simple Archie formula, and derivation of “n”
Effect of clay minerals conductivity in shaly formations

Determination of Water Saturations in Virgin and Flushed Zones
Archie formula
Crossplots (Pickett, Hingle)
Quicklook Rwa, F-Ratio methods
Quicklook logarithmic overlays
Moveable Oil Plot

Completion & review of 1st example set of logs (“Clean Sand” example) which the group has been working on in teams over the first 3 days. Review of GoM LWD set of logs (“Homework” example) given to participants for their study after course hours.

Day 4: Miscellaneous Measurements for Petroleum Engineering and Geological Applications

Pressure Measurements, Fluid Sampling & Analysis using Formation Testers
Overview of formation tester tool technology
Pressure sampling
Fluid analysis
Permeability/mobility measurements

Nuclear Magnetic Resonance Measurements
Overview of NMR principles, definition of T1, T2 relaxations
Overview of NMR tool technology (W/L & LWD)
Bound-fluid/Free-fluid discrimination using T2
NMR as supplement/alternative to resistivity/porosity measurements in shaly sands
T2 – permeability relationships
NMR & produceability
NMR diffusion for fluid-type discrimination using T1, T2 relaxations

Permeability Determination from Logs & Pressure Measurements
Permeability, relative permeability, core measurements
Derivation from irreducible water saturation
Derivation from pressure drawdown, buildup
Derivation from NMR measurements

Overview of Computer Log Interpretation Methods
Underdetermined, uniquely determined and iterative solutions
Iteration and error minimization, neural networks

Alternative Topics for Geologists’ Course:

Other Geological Applications of Resistivity, Porosity & GR Spectrum Measurements
Source Rock Evaluation
Sequence Evaluation
Using log measurements for geological applications (texture, overpressures, anisotropy)
Combination of Electrical Log & Other Data for Lithological Interpretation

Dipmeters, Imaging Logs & Paleomagnetic Logs; using logs for Geological Interpretation
Overview of electrical, acoustic and nuclear tool technologies for imaging
Recent developments in imaging from W/L & LWD measurements
Paleomagnetic logging
“Squaring” of logs for geological & thin-bed interpretation, sand count issues
Lithofacies zonation of logs using histograms, principal component analysis, paleoflow energy, wavelet spectrogram
Discussion of examples & applications

Alternative Topics for Engineers’ Course:

Cased-Hole Logging Measurements
Thru-Casing Logging for Porosity and Resistivity
Monitoring Fluid-level Changes using Pulsed-Neutron & Gravity Methods
This section includes participants interpreting an Openhole & Casedhole Time-Lapse example from northern Europe
Cement Bond Evaluation
Corrosion Prediction, Detection and Monitoring
Perforation, Skin and Productivity Index Enhancement
Overview of Production Logging Measurements (see also below)

Day 5: Log Quality Control, Interpretation of Final Example

Overview of Some Log Quality Control Issues
Recap of Uncertainties and Assumptions in Log Measurements

Participants work in groups on 2nd example set of logs, preferably from general area of course, otherwise using a standard example from the North Sea (“Forties” example)

Review of interpretation of 2nd set of logs, final summary and prize-giving, award of certificates

Other Topics on Special Request, or as Time Permits:
Recent Developments in Measurement Technologies
Overview of Dipole Sonic Measurements

Electromagnetic Propagation Measurements

Log Interpretation in Complex Environments
These topics take the form of Overviews of some of the issues and difficulties of making log interpretations in more complex geological & completion environments
Overview of Shaly Sand Interpretation

Overview of Log Interpretation in Thin Sand/Shale sequences

Overview of Log Applications in Shale - Oil/Gas Formations

Overview of Log Interpretation in Complex Carbonate Reservoirs

Overview of Different Approaches to Cement Bond Evaluation

Overview of Production Logging in Horizontal Wells

Participants will also be expected to do about an hour of “homework” each evening

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