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Mud logging is a well logging process in which drilling mud and drill bit cuttings from the formation are evaluated during drilling and their properties recorded on a strip chart as a visual analytical tool and stratigraphic cross sectional representation of the well. The drilling mud which is analyzed for hydrocarbon gases, by use of a gas chromatograph, contains drill bit cuttings which are visually evaluated by a mudlogger and then described in the mud log.

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The two primary purposes of drilling mud or drilling fluids are to :

1.. Remove cuttings from the formation produced by the bit at the bottom of the hole and carry them to the surface. This is achieved by adjusting the rheology of the mud system.

2.. Maintain hydrostatic equilibrium so that fluids and gas from the formation do not enter the well bore causing the well to flow, kick or blow out. This is achieved by adjusting the mud weight (density). High-density additives (barite, hematite) are used for preparation of kill-weight fluids, which create hydrostatic pressure that prevents water entering the well or hold the oil/gas inside and prevent blowout, and to physically stabilize the formation.

Other characteristics are considered important in modern drilling. Some of these include :

a.. Safe for the environment

b.. Prevent dispersion of reactive clays (gumbo)

c.. Ability to seal formation fractures/voids

d.. Non abrasive to tools and rig equipment

e.. Seal porous rock layer, equalize the pressure, cooling the bit, flush out the cutting & lubricating the bit

Details of Use

On a drilling rig pumping it with mud pumps through the drill string where it sprays out of nozzles on the drill bit (cleaning the bit in the process), the mud then travels back up the annular space between the drill string and the sides of the hole being drilled, up through the surface casing, and emerges at the surface. Cuttings are then filtered out at the shale shaker and the mud enters the mud pits. The mud is then pumped back down and is continuously recirculated. The mud is treated periodically in the mud pits to give it properties that optimize and improve drilling efficiency.

Composition of drilling mud

Water-based drilling mud may consist of bentonite clay (gel) with additives such as barium sulfate (barite) or hematite. Various thickeners are used to influence the viscosity of the fluid, eg. Xanthan Gum, guar gum, glycol, carboxymethylcellulose, polyanionic cellulose (PAC), or starch. In turn, deflocculants are used to reduce viscosity of clay-based muds; anionic polyelectrolytes (eg. acrylates, polyphosphates, lignosulfonates (Lig) or tannic acid derivates (eg. Quebracho) are frequently used. Red mud was the name for a Quebracho-based mixture, named after the color of the red tannic acid salts; it was commonly used in 1940s to 1950s, then was obsoleted when lignosulfates became available. Many other chemicals are also used to maintain or create some of the properties listed in the section titled ‘Purpose’.

One classification scheme for drilling fluids is based on their composition, and divides them to:

a.. water-base,

b.. non-water (oil, olefin, or other synthetic fluid) base, and gaseous, or pneumatic.

c.. Oil Based and Synthetic Based muds are frequently classified seperatly due to the vast differences in regulations when using them.

Tanya – athur queen

Terima kasih pak Budhi untuk penjelasannya. Saya mau nanya lagi mengenai mudlogging unit.

– Apa saja output dari mudlog?

– Apa job desk seorang mudloger?

– Apa saja scope service yang diberikan oleh mudlog service?

Terima kasih.

Rangkuman Diskusi Mailing List Migas Indonesia bulan April 2007 dapat dilihat dalam file berikut:

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