Mud Logging

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Exploration Technique: Mud Logging

Exploration Technique Information
Exploration Group: Downhole Techniques
Exploration Sub Group: Well Log Techniques
Parent Exploration Technique: Well Log Techniques
Information Provided by Technique
Lithology: Lithological layers are identified from drill cuttings
Stratigraphic/Structural: Porosity of rocks
Hydrological: Fluid content of the borehole while drilling can be determined
Cost Information
Low-End Estimate (USD): 1,300.00130,000 centUSD
1.3 kUSD
0.0013 MUSD
1.3e-6 TUSD
/ day
Median Estimate (USD): 1,450.00145,000 centUSD
1.45 kUSD
0.00145 MUSD
1.45e-6 TUSD
/ day
High-End Estimate (USD): 2,000.00200,000 centUSD
2 kUSD
0.002 MUSD
2.0e-6 TUSD
/ day
Time Required
Low-End Estimate: 1 days0.00274 years
24 hours
0.143 weeks
0.0329 months
/ job
Median Estimate: 1 days0.00274 years
24 hours
0.143 weeks
0.0329 months
/ job
High-End Estimate: 1 days0.00274 years
24 hours
0.143 weeks
0.0329 months
/ job
Mud Logging:
Mud logs enable the geological description and analysis of rock cuttings suspended within the returned drilling mud and can provide a variety of useful information regarding reservoir parameters.
Other definitions:Wikipedia Reegle

Mud logging is the analysis of the drilling mud that has been cycled down the borehole and returned to the surface during drilling operations. The drill mud carries rock fragments from the bottom of the borehole and these rock fragments are used to determine the downhole lithology. A mobile laboratory is set up near the drilling rig so that mud logging can give close to real time data of the lithology and borehole fluid during a drilling operation. Mud logging is also important for monitoring the drill fluid volume so the drill operator knows if fluid is being lost to a formation. Mud logging is a standard practice during drilling operations and normally a third party mud logging company is hired to perform the task.
Use in Geothermal Exploration
Mud logging is common practice in geothermal drilling. It is important for geologic monitoring and lithological record keeping.

Field Procedures
Samples from the drilling mud are taken at predetermined intervals. The samples are taken to the onsite laboratory and the drilling mud is separated from the drill cuttings. The drill cuttings are dried and viewed under a microscope then geologic descriptions are written up describing the lithology of the cuttings. Drill cuttings are often displayed in order of depth they were received from so that the change in lithology relative thickness of strata can be viewed and documented.

Mud logger collecting a sample.[1]

Data Access and Acquisition
Example of a mud log.[2]

Best Practices
Mud logging is standard practice during drilling operations and is important for documenting the geology that a well passes through. Preserving and storing the rock cuttings in an organized filing system is normal procedure.
Potential Pitfalls
-The depth that the rock cuttings originated from is not always 100% accurate. Calculations can be made that determine the time it takes for the drill cutting to reach the surface, this is called “lag time”. Some assumption have to be made in the calculations because not all rock cuttings are the same size and density so there can be some error in calculating the depth that the cuttings originated from.

-A small degree of mixing occurs in the mud before it reaches the surface, so the rock cuttings in a particular sample may a mixture of cuttings from a range of depths.

-Contamination can sometimes be a problem when making interpretations of samples. There can be metal contaminates in the drilling mud from fragments of the drill bit or drill string. Cement from well casings may get into the drilling mud. Sometimes different materials may be mixed into the drill mud to help loss of circulation and these can sometimes be misinterpreted as mica flakes, calcium carbonate, or various other minerals.[3]

  1. Schlumberger. Schlumberger Office Photos [Internet]. 2013. [cited 2013/10/14]. Available from:
  2. Geotech Logging Servces LLC. Geotech Logging Services [Internet]. 2013. [cited 2013/10/24]. Available from:
  3. eltayeb Shaa. What is mudlogging [Internet]. [cited 2013/10/14]. Available from:

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