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required for the mud and cuttings to return to the surface, a modern augmentation has come into use: Measurement while drilling. The MWD technician, often a separate service company employee, logs data in a similar manner but the data is different in source and content. Most of the data logged by an MWD technician comes from expensive and complex, sometimes electronic, tools that are downhole installed at or near the drill bit.
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at some later time (and depth) determined by the oil industry geologist's research. The mud logger may also possess logs from wells drilled in the surrounding area. This information (known as "offset data") can provide valuable clues as to the characteristics of the particular geostrata that the rig crew is about to drill through.
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rate. "D-exponents" are mathematical trend lines which estimate this internal pressure. Thus both visual evidence of spalling and mathematical plotting assist in formulating recommendations for optimum drilling mud densities for both safety (blowout prevention) and economics. (Faster drilling is generally preferred.)
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and must be considered when estimating percentages. Also, this image view is only a fragment of the total sample, and some of the sand at the bottom of the tray cannot be seen and must also be considered in the total estimation. Thus, this sample would be considered to be about 90% shale, 5% sand and
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that might be encountered. (Color coding is not necessarily standardized among different mud logging companies, though the symbol representations for each are very similar.) In Figure 3, a sample of cuttings is seen under a microscope at 10× magnification after they have been washed off. Some of the
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and well-site geologist (WSG), provides mud loggers with their instructions. The mud logging company is contracted specifically as to when to start well-logging activity and what services to provide. Mud logging may begin on the first day of drilling, known as the "spud in" date, but is more likely
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Rate of drilling is affected by the pressure of the column of mud in the borehole and its relative counterbalance to the internal pore pressures of the encountered rock. A rock pressure greater than the mud fluid will tend to cause rock fragments to spall as it is cut and can increase the drilling
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Another important task of the mud logger is to monitor gas levels (and types) and notify other personnel on the rig when gas levels may be reaching dangerous levels, so appropriate steps can be taken to avoid a dangerous well blowout condition. Because of the lag time between drilling and the time
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Mud logging technicians observe and interpret the indicators in the mud returns during the drilling process, and at regular intervals log properties such as drilling rate, mud weight, flowline temperature, oil indicators, pump pressure, pump rate, lithology (rock type) of the drilled cuttings, and
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Mud loggers connect various sensors to the drilling apparatus and install specialized equipment to monitor or "log" drill activity. This can be physically and mentally challenging, especially when having to be done during drilling activity. Much of the equipment will require precise calibration or
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within the rock structure. Oil and gas reside within this pore space. Note how far to the left the porosity goes, where all the sand (in yellow) is. This indicates that the sand has good porosity. Porosity is not a direct or physical measurement of the pore space but rather an extrapolation from
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as the quantity of total gas, but does not represent the actual quantity of oil or gas the reservoir contains. In (Figure 1) the squared-off dash-dot lines just to the right of the sand (in yellow) and left of the gas (in green) represents the heavier hydrocarbons detected. Cyan =
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Mud logging is often written as a single word "mudlogging". The finished product can be called a "mud log" or "mudlog". The occupational description is "mud logger" or "mudlogger". In most cases, the two word usage seems to be more common. The mud log provides a reliable
609:. More yellow represents more sand identified at that depth. The lithology is measured as a percentage of the total sample as visually inspected under a microscope, normally at 10× magnification (Figure 3). These are but a fraction of the different types of
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in Figure 1 & 2 is represented by the black line on the left side of the log. The farther to the left that the line goes, the faster the rate of penetration. On this mud log, ROP is measured in feet per hour, but on some older, hand-drawn
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Chambre
Syndicale de la recherche et de la production du petrole et du gaz naturel, 1982, Geological and mud logging in drilling control: catalogue of typical cases, Houston, TX: Gulf Publishing Company and Paris: Editions technip, 81 p.
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and fluid content of the borehole while drilling. Historically it is the earliest type of well log. Under some circumstances compressed air is employed as a circulating fluid, rather than mud. Although most commonly used in
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The mud logging company is normally contracted by the oil company (or operator). They then organize this information in the form of a graphic log, showing the data charted on a representation of the wellbore.
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Exlog, 1979, Field geologist's training guide: an introduction to oilfield geology, mud logging and formation evaluation, Sacramento, CA: Exploration
Logging, Inc., 301 p. Privately published with no
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exploration, mud logging is also sometimes used when drilling water wells and in other mineral exploration, where drilling fluid is the circulating medium used to lift cuttings out of the hole. In
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other data. Mud logging requires a good deal of diligence and attention. Sampling the drilled cuttings must be performed at predetermined intervals, and can be difficult during rapid drilling.
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P.W. Purcell "Chapter 16 Mud
Logging" pp. 347-354 in L.W. Leroy, D.O. Leroy, and J.W. Raese, editors, 1977, Subsurface Geology, Colorado School of Mines, Golden, 941 pp.
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Mud logging technicians in an oil field drilling operation determine positions of hydrocarbons with respect to depth, identify downhole
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and temperature), as well as compiling other information about the drilling parameters. Then data is plotted on a graphic log called a
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equipment with a few exceptions such as the mud weight and mud viscosity which are measured by the derrickhand or the
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Other real-time drilling parameters that may be compiled include, but are not limited to; rate of penetration (
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in Figure 1 & 2 is represented by the cyan, gray/black and yellow blocks of color. Cyan =
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in Figure 1 is represented by the blue line farthest to the left of the log. It indicates the
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1" (every foot) mud log showing corrected d-Exponent trending into pressure above the sand
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Whittaker, Alun, 1991, Mud logging handbook, Englewood Cliffs, NJ: Prentice Hall, 531 p.
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larger shale and lime fragments are separated from this sample by running it through
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in Figure 1 & 2 is represented by the green line and is measured in
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Mud logging includes observation and microscopic examination of
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brought up in the mud. A mobile laboratory is situated by the
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alignment by the mud logger to provide accurate readings.
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381:(formation rock chips), and evaluation of gas
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369:1" (5 foot average) mud log showing heavy (
27:Creation of a detailed record of a borehole
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526:Learn how and when to remove this message
120:Learn how and when to remove this message
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258:is the creation of a detailed record (
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765:Articles and books on mud logging
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689:MWD (Measurement While Drilling)
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780:Maverick Energy Lexicon
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69:"Mud logging"
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43:This article
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800:Well logging
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516:January 2021
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498:Please help
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442:mud engineer
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418:drill string
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391:drilling mud
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371:hydrocarbons
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313:The services
299:drilling rig
264:drilling mud
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149:Well logging
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52:Please help
47:verification
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679:Geosteering
383:hydrocarbon
342:tool pusher
289:natural gas
281:hydrocarbon
256:Mud logging
182:Resistivity
794:Categories
700:References
611:formations
574:Sample of
572:(Figure 3)
561:pore space
426:mud weight
307:drill ship
305:, or on a
80:newspapers
594:lithology
584:Louisiana
487:does not
430:viscosity
395:chlorides
393:(such as
323:geologist
319:lithology
297:near the
273:petroleum
268:lithology
171:Gamma ray
136:Inside a
110:June 2015
662:See also
580:oil well
556:porosity
548:mud logs
462:time log
428:and mud
407:Example2
403:Example1
283:surface
260:well log
647:propane
508:removed
493:sources
468:Details
436:to the
399:mud log
165:Density
160:Caliper
151:methods
94:scholar
18:Mud log
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655:butane
639:ethane
616:sieves
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675:(mud)
630:units
603:shale
361:Scope
215:(NMR)
207:(MWD)
199:(LWD)
187:Sonic
101:JSTOR
87:books
749:ISBN
744:ISBN
735:ISBN
714:ISBN
622:The
607:sand
599:lime
591:The
553:The
539:The
491:any
489:cite
73:news
625:gas
582:in
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422:RPM
414:ROP
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389:or
177:Mud
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