- Mud logging
Well logging Gamma ray logging
Spontaneous potential logging
The service contracted
A mud logging technician in the modern oil field drilling operation determines positions of hydrocarbons with respect to depth, identifies downhole lithology, monitors natural gas entering the drilling mud stream, and draws well logs for use by oil company geologists. Rock cuttings circulated to the surface in drilling mud are sampled and analyzed.
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.
The oil industry representative (or "company man") (also with the tool pusher, and geologist) provides mud loggers their instruction. 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 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 geo-strata that the rig crew is about to drill through.
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 alignment by the mud logger to provide accurate readings.
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 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.
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 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 whose 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.
Mud logging includes observation and microscopic examination of drill cuttings (formation rock chips), and evaluation of gas hydrocarbon and its constituents, basic chemical and mechanical parameters of drilling fluid or drilling mud (such as chlorides and temperature), as well as compiling other information about the drilling parameters. Then data is plotted on a graphic log called a mud log. Example1, Example2.
Other real-time drilling parameters that may be compiled include, but are not limited to; rate of penetration (ROP) of the bit (sometimes called the drill rate), pump rate (quantity of fluid being pumped), pump pressure, weight on bit, drill string weight, rotary speed, rotary torque, RPM (Revolutions Per Minute), SPM (Strokes Per Minute) mud volumes, mud weight and mud viscosity. This information is usually obtained by attaching monitoring devices to the drilling rig's equipment with a few exceptions such as the mud weight and mud viscosity which are measured by the derrickhand or the mud engineer.
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 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.)
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 time log of drilled formations.
Details of the mud log
- The rate of penetration 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 mud logs, it is measured in minutes per foot.
- The porosity in (Figure 1) is represented by the blue line farthest to the left of the log. It indicates the pore space within the rock structure. An analogy would be the holes in a sponge. The oil and gas resides within this pore space. Notice 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 other drilling parameters and therefore not always reliable.
- The lithology in (Figure 1 & 2) is represented by the cyan, gray/black and yellow blocks of color. Cyan = lime, gray/black = shale and yellow = sand. More yellow represents more sand identified at that depth. The lithology is measured as percentage of the total sample, as visually inspected under a microscope, normally at 10x magnification (Figure 3). These are but a fraction of the different types of formations that might be encountered. (Color coding is not necessarily standardized among different mud logging companies, though the symbol representation for each are very similar.) In (Figure 3) you can see a sample of cuttings under a microscope at 10x magnification after they have been washed off. Some of the larger shale and lime fragments are separated from this sample by running it through sieves 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 can not be seen and must also be considered in the total estimation. With that in mind this sample would be considered to be about 90% shale, 5% sand and 5% lime (In 5% increments).
- The gas in (Figure 1 & 2) is represented by the green line and is measured in units of ppm (parts per million) 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 = C2 (ethane), purple = C3 (propane) and blue = C4 (butane). Detecting and analyzing these heavy gases help to determine the type of oil or gas the formation contains.
- Directional drilling
- Drilling fluid (mud)
- LWD (Logging While Drilling)
- MWD (Measurement While Drilling)
- Well logging
- ^ 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. ISBN 0-918062-00-4
- 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. ISBN 0872014339
- 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 ISBN
- Whittaker, Alun, 1991, Mud logging handbook, Englewood Cliffs, NJ: Prentice Hall, 531 p. ISBN 0131552686
- Articles and books on mud logging
- Hand drawn mud logs
- Schlumberger website description of log
- Maverick Energy Lexicon
- Drilling technology
- Petroleum geology
- Oilfield terminology
- Petroleum economics and industry
Wikimedia Foundation. 2010.
Look at other dictionaries:
Mud motor — (or Drilling Motor) refers to a Progressive Cavity Positive Displacement Pump placed in the Drill string to provide additional power to the bit while drilling. The PCPD Pump uses Drilling Fluid (commonly referred to as Drilling Mud, or just Mud)… … Wikipedia
Mud engineer — A mud engineer (correctly called a Drilling Fluids Engineer, but most often referred to as the Mud Man ) works on an oil well or gas well drilling rig, and is responsible ensuring the properties of the drilling fluid, also known as drilling mud,… … Wikipedia
Mud log — A Mud log is a graphical representation of the ROP (Rate Of Penetration), lithology, hydrocarbons and other drilling parameters generated while drilling an oil well. The act of gathering this information is considered mud logging and is done by… … Wikipedia
Logging while drilling — (LWD) is a technique of measuring geologic formation properties in real time while drilling an oil well.DescriptionLogging while drilling, along with measurement while drilling systems provide wellbore directional surveys, petrophysical well logs … Wikipedia
Well logging — Gamma ray logging Spontaneous potential logging Resistivity logging Density logging Sonic logging Caliper logging Mud logging LWD/MWD v · … Wikipedia
Exploration Logging Company — The Exploration Logging company was originally founded in 1952 in Sacramento, California, by a group of Stanford University geology and engineering graduates to provide geologic logging services. Exploration Logging is now part of… … Wikipedia
Density logging — Well logging Gamma ray logging Spontaneous potential logging Resistivity logging Density logging Sonic logging Caliper logging Mud logging LWD/MWD v · … Wikipedia
Drilling mud — In geotechnical engineering, drilling mud, also known as spud mud (when beginning the drilling process), is a drilling fluid used to drill boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling… … Wikipedia
Spontaneous potential logging — The spontaneous potential log, commonly called the self potential log or SP log, is a measurement taken by oil industry well loggers to characterise rock formation properties. The log works by measuring small electric potentials (measured in… … Wikipedia
Michigan logging wheels — Logs were suspended from wheel axle Gen … Wikipedia