Mud Logging OverviewSolidsLiquidsGassesPermian Basin Mudlogging Services

Mud Logging
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OverviewSolidsLiquidsGassesPermian Basin Mudlogging Services
Overview :
Mud logging is the process of collecting, analyzing and recording the meaningful solids, fluids, and gasses brought to the surface by the drilling fluid (mud). The mud logger keys all of his data to the Geolograph on the rig floor.
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Solids:
The mud logger collects samples of the cuttings from the downhole strata on a regular basis, usually every ten feet. Collections are usually made at the shaker table for the mud system. The logger then washes and dries the cuttings, keeping them properly labeled as to depth that they represent. In order to know what depth the samples actually come from the logger must constantly calculate a "lag" time, i.e. the time it takes the samples to reach the surface from the time they were cut. The greater the depth, the greater the time for the samples to reach the surface after they were cut. In order to help with the lag calculations, the logger tracks hole size, pump strokes, and occasionally sends distinctive samples down the pipe to measure the actual lag.
The logger examines the dried samples under a binocular microscope and records the predominant rock types on a depth strip chart that has drill times and chromatograph readings also recorded on it. Rock types are often correlated with the drill times for a particular rock type, e.g. fast drill time for a porous sandstone. Obviously properly recording what rock type is being drilled at what depth is not an exact science. Some factors that affect the accuracy are logger experience in an area, improper lag times, interbedded thin layers of multiple rock types, finely-ground rock fragments, sloughing of uphole rock material, and diligence of the logger.
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Liquids:
The logger analyzes for liquids primarily in two ways: chloride content and fluorescence. Chloride content of the mud is constantly monitored. An increase in chlorides from a certain depth can indicate a strong salt water flow from a permeable formation. Samples are also viewed under ultraviolet light to check for fluorescence because most oils fluoresce. In the event that fluorescence is detected. The sample is subjected to cleaning fluid to determine whether it is hydrocarbon or mineral fluorescence.
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Gasses:
A key component of a mudlogging unit is a gas chromatograph. This unit continuously samples the gases coming out of the mud and analyzes them for methane and the heavier hydrocarbons. The presence of a 'show' of hydrocarbons on the chromatograph alerts the logger to be more alert for other evidences of hydrocarbons. Sometimes a separate "lag" must be determined for gasses as they may rise faster to the surface than the samples. A bag of carbide dropped down the drill pipe is usually used for this purpose.