Well Logging for Earth Scientists
Prof. Thilo Bechstädt
(GeoResources STC, Heidelberg, Germany & Jagiellonian University, Krakow, Poland
The lessons will be held at Room M2, via Mezzocannone 8
February, 18-20 09:00:12:30 - 14.30:15.30
February, 23-24 09:00:12:30 - 14.30:15.30
Prerequisites: No mathematics beyond basic algebra is required.
Program of the Course:
Part I: Lithology and Porosity Logs
February 18-20, 2015, 9:00-12:30, 14:00-ca. 17:30. 5 CFU
Part II: Resistivity, Dipmeter, and Borehole Imaging
February 23-24, 2015, 9:00-12:30, 14:00-ca. 17:30. 3 CFU
“Part II” is recommended but optional for PhD students.
The different chapters of the course consist of lectures and exercises.
Program of Part I:
Basics of Drilling and Well Logging, Gamma Ray (GR) Log, Spontaneous Potential (SP) Log
Basics of Rotary Drilling; drilling fluid (mud) and its objectives; impact of drilling mud on the borehole surroundings; basics of coring and logging; mud log; types and methods of borehole logging: open hole logging, measuring and logging while drilling. Log header; depth scale; resolution of different log-types. Formation temperatures and geothermal gradient.
Basics of GR; radioactive lithologies and their GR log response; use of composite GR; shale and sand base line; log patterns and facies interpretation; spectral GR; use and evaluation of spectral GR; types and fabrics of clay content; shale volume calculation.
Basics of SP; components of SP; log presentation; parameters influencing SP values and curve patterns; magnitude of SP; SP and SSP; shale and sand base line; log corrections; calculation of SSP and shale volume; determination of formation water resistivity; Petrophysical mapping techniques: Mapping from the SP and the GR log.
February 19, 20
Basics of porosity and permeability, Sonic Log, Density Log, Neutron Log, Nuclear Magnetic Resonance Log, Evaluation of porosity logs
Rock properties, porosity and permeability: porosity definition; effective and uneffective porosity; permeability definition; Darcy´s law; absolute and relative permeability; permeability anisotropy; lithology and mineralogy; water saturation in pores; irreducible water saturation.
Sonic Log: Basic principles of measurements; types of logging tools; log presentation; sonic velocities, lithology and porosity; analysis of different, e.g. Stoneley waves; reliability, specifics pitfalls with sonic porosity; hydrocarbon effects; array sonic log. Well to seismic tie.
Density Log: basic principles of measurements (Compton scattering and photoelectric effect). Different types of density tools: classic density tool; log presentation; use of density log; corrections; litho-density tool (photoelectric tool); lithology from photoelectric tool; barite problem; matrix density; density porosity; fluid density; hydrocarbon effects; shale volume calculation.
Neutron Log: Basic principles of measurements; types of logging tools; log presentation; units of measurement; gas effect; clay effect.
Nuclear Magnetic Resonance Log: Measurement principles and device designs; transmission frequencies; spin echo trains; polarization; TE, T2, TW; porosity and T2 distribution of spin echo trains, NMR permeability; log presentation of NMR data, porosity, pore size, permeability, immoveable (irreducible) water, free moveable water. Permeability determination: Coates permeability model and SDR permeability model; polarization time of different fluid types. Water and HC saturation determination: time domain analysis, diffusion analysis; gas detection. Pore size distribution. NMR tools specifications and limitations; NMR and logging while drilling; log quality control.
Evaluation of porosity logs: Multiple log overlay methods (GR/neutron/density/PEF; log patterns and offsets); limestone porosity units and density; neutron/density combination and gas effect; rock properties.
Porosity and lithology crossplots: Neutron-density lithology plot; neutron-sonic lithology plot; density-sonic lithology plot; M-N lithology plot; mineral identification plot (ρmaa vs. Δtmaa); mineral identification plot (ρmaa vs. Umaa). Determination/calculation of parameters. Mapping from the results of different crossplots; well to seismic tie.
Program of Part II:
Resistivity logs and their basic evaluation
Resistivity definition; borehole environment and resistivity; mud invasion; resistivities of rocks, of drilling mud and of formation fluids (water, hydrocarbons); basic resistivity relations; Archie´s equation; resistivity, water saturation and salinities (flushed zone, invaded zone, transition zone, uninvaded zone, resistivity profiles, depth of invasion); resistivity measurements and distance from borehole. Examples of water-bearing and hydrocarbon-bearing zones.
Resistivity measurements (electrode and induction tools), unfocused and focused measurements.
Electrode tools: old electrode tools (lateral tool, short and long normal tools), more modern electrode tools and their depth of investigation. Microresistivity tools: Measurement principles and device designs; micronormal & microinverse measurement; tool combinations; measurement limitations; microspherically focused log (MSFL); measurement limitations. Laterologs: Measurement principles and device designs; log presentation; laterolog, dual laterolog, MSFL, and combinations; log quality control; environmental corrections; calibration and operation.
Induction logs: Measurement principles and device designs; log presentation; induction log deep; dual induction tool; high frequency measurements and dielectric properties. Induction tool limitations; skin effect; tool combinations; depth of investigation; environmental corrections; calibration and operation.
Resistivity tool limitations: electrode or induction tool? Resistivity arrays.
Interpretation: Quick look and simple methods: General reconnaissance; ratio method of water saturation; resistivity of the flushed and the uninvaded zone (Rxo and Rt); apparent water resistivity (Rwa); conductivity-derived porosity; wet resistivity; bulk volume of water (BVW); saturation crossplots.
Dipmeter, Borehole Images
Measurement principles and device designs; usage.
Electrical (microresistivity) dipmeter measurements; dipmeter patterns. Electrical borehole tools; dipmeter data versus electrical borehole images. Data acquisition: tool types, limitations and requirements.
Acoustic borehole images: measurement principles; data acquisiton; tool types; limitations and requirements.
Processing of electrical and acoustic data; orientation; 3D to 2D data; accelerometer corrections; depth corrections; bin values and colour codes; static and dynamic processing; processing practice.
Interpretation: Structural (bedding, fractures) and sedimentological interpretation; types of presentation; comparison electrical to sonic devices.
Downhole video images: data acquisition, processing, limitations. New techniques, data integration<>