Well logging analysis: methods and interpretation

Well logging analysis: methods and interpretation

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  WELL LOGGING ANALYSIS METHODSAND INTERPRETATION PETROLEUM GEOLOGY II – WS 2013/14 CRISTIANO ASCOLANI
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  2 Well Logging “The productof a survey operation, also called a survey, consisting of one or more curves. Provides a permanent record of one or more physical measurements as a function of depth in a well bore. Well logs are used to identify and correlate underground rocks, and to determine the mineralogy and physical properties of potential reservoir rocks and the nature of the fluids they contain.” (SPWLA - Society of Petrophysicists and Well Log Analysts, online glossary, last modified 2010/03/02) LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14 • Downhole Sondes lowered into the well bore by a survey • On surface Core logs, mud sample logs, hydrocarbon well logs, etc.
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  3 Well Logging Commonly classifiedby the kind of energy that is input (active systems) or received (passive systems): 1. Electric Logging Techniques • Spontaneus Potential Log • Resistance Log • Microlog • Induction Log 2. Nuclear Radiation Logging Techniques • Gamma Ray (Natural Gamma) Log • Natural Gamma Spectral Log • Density or Gamma-Gamma Log • Neutron Log • Neutrino Log 3. Acoustic/Seismic Logging Technique • Sonic/Acoustic Log • Acoustic Borehole Imaging Log • Cross-Hole Seismic Test • Seismic Tomography • Borehole Optical Systems • Borehole Image Processing • System (BIPS) 4. Other Wireline System • Borehole Caliper Log • Directional Surveys • Borehole Fluid Temperature Log • Borehole Gravity Log • Magnetic Log • Flowmeter Log LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14
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  4 Electric Log Spontaneus Potential Log Itrecords the difference in potential in millivolts between a fixed electrode at the surface and an electrode in a borehole • Clays and shales generate one charge, permeable formations such as sandstone will generate an opposite one • SPs occur when two aqueous solutions with different ionic concentrations are placed in contact (brime-mud, fresh water-mud) • Hydrocarbon suppression: SP log response is reduced Resistivity Log (SP) Characterization of the rock or sediment in a borehole by measuring its electrical resistivity. • Most rock materials: non-conductor • Enclosed fluids (water based): conductor • Hydrocarbon fluids: almost infinitely resistive LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14
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  5 Electric Log (CRCLEME, 2002)(Technical Service Center, Bureau of Reclamation, 2002) LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14
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  6 Gamma Ray Log Thesimplest radioactive method in geophysical well logging is the natural gamma log. These logging tools record the level of naturally occurring gamma ray emissions from the rocks around a borehole. Different types of rock emit different amounts and different spectra of natural gamma radiation • Shales usually emit more gamma rays than other sedimentary rocks: potassium is a common component in their clay content, and because the cation exchange capacity of clay causes them to adsorb uranium and thorium. • Sandstones/carbonate rocks usually do not generate so much gamma rays. • BE CAREFUL: sometimes non-shales also have elevated levels of gamma radiation: sandstone can contain uranium mineralization, coal and dolomite may contain absorbed uranium etc.. LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14
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  7 Bulk Density Log Radioactivesource and detector are lowered down the borehole and the source emits medium-energy gamma rays into the formation. Big elements rate: gamma rays rapidly loose energy Neutron Porosity Log Radioactive source and detector are lowered down the borehole and the source emits neutrons into the formation. High H rate: neutrons rapidly loose energy 𝐵𝑢𝑙𝑘 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝐿𝑜𝑔 ∝ 1 𝑁𝑒𝑢𝑡𝑟𝑜𝑛 𝐿𝑜𝑔 LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14
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  8 Acoustic/Sonic Log They providea formation’s interval transit time, designated as ∆t, which is a measure of a formation’s capacity to transmit seismic waves. The velocity is calculated by measuring the travel time from the piezoelectric transmitter to the receiver ∆ 𝑡= 𝑡𝑓𝑎𝑟 − 𝑡 𝑛𝑒𝑎𝑟 Calculation of porosity: Wyllie’s time averaged equation 1 𝑉 = ∅ 𝑉𝑓 + 1 − ∅ 𝑉 𝑚𝑎𝑡 (Wikipedia.org) LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14
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  9 Acoustic/Sonic Log The velocitiesand corresponding travel times of the rock and matrix are: (Petrocenter.com) LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14
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  10 Caliper Log Well loggingtool that provides a continuous measurement of the size and shape of a borehole along its depth. The caliper tool measures the variation in borehole diameter as it is withdrawn from the bottom of the hole, using two or more articulated arms that push against the borehole wall (Wikipedia.org)Multi-finger Caliper, MFC model (Landau Petroleum Technology Co.). LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14
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  11 Wireline Logging: example BasicLog (Schlumberger, 2011) LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14
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  12 References • Oilfield ReviewSpring 2011: 23, no.1, Schlumberger, 2011 • Oilfield Review Autumn 2012: 24, no.3, Schlumberger, 2012 • In Papp, É. (Editor), 2002, Geophysical and Remote Sensing Methods for Regolith Exploration, CRCLEME Open File Report 144, pp 105-115. • Engineering Geology Field Manual, Second Edition, Volume II; U.S. Department of the Interior Bureau of Reclamation, 2001 • Wikipedia.org LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14