Drilling Fluids

Drilling Fluid (Mud) & Functions

Drilling mud which is one of the essential need in drilling operations. Drilling Mud is a semi liquid fluid just like a pap which consists of liquid, water or oil, with solids in suspension. It is used to cool and clean off the bits as it rotates to the bottom of the earth. On the drilling rig, mud is pumped down through the drillstring where it spray out through the nozzles on the drill bit, cleaning and cooling off the bit in the process. Its then carry drill cutting up through the annulus where it is being filter out using a shale shaker. After filtration of the mud, it is then return to the mud pit where they are being treated by addition of chemicals and other substance. The mud can be reused by pumping it downhole and further re-circulated. Drilling mud can also be called drilling fluid. Drilling fluid also makes drilling operation easy for the drillers.

Drilling mud are categories into three section.

1. Water based mud(WBM)
2. Oil based mud
3. Gas based mud (GBM)

   WATER BASED MUD (WBM)

   
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   WBM comprises of water, clay and other chemicals. Its looks like chocolate milk and malt in resembrance when it is an homogenous mixture. A good example of this is bentonite. Water based mud are classified as:
   
   • Non-Inhibitive such as clay water, Native, Bentonite/water, Lignite/Ligno-Sulfonate (Deflocculated).
     
   • Inhibitive can be calcium based, salt water based or potassium based.
     
   • Polymer such as Non-Dispersed, High temperature deflocculated.
     
   Water based fluids are the most extensively used drilling fluids. They are generally easy to build, inexpensive to maintain, and can be formulated to overcome most drilling problems.
   

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   Non-Inhibitive Fluid or Mud

   Non-inhibitive fluids are generally used as spud muds. Those which do not significantly suppress clay swelling, are generally comprised of native clays or commercial bentonites with some caustic soda or lime. They may also contain deflocculants and/or dispersants such as: lignites, lignosulfonates, or phosphates. Native solids are allowed to disperse into the system until rheological properties can no longer be controlled by water dilution.
   

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   Inhibitive Fluid or Mud

   Those which appreciably retard clay swelling and, achieve inhibition through the presence of cations; typically, Sodium (Na+), Calcium (Ca++) and Potassium (K+). Generally, K+ or Ca++, or a combination of the two, provide the greatest inhibition to clay dispersion. These systems are generally used for drilling hydratable clays and sands containing hydratable clays. Because the source of the cation is generally a salt, disposal can become a major portion of the cost of using an inhibitive fluid.
   

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   Polymer Fluid or Mud

   These fluids can be inhibitive or non-inhibitive depending upon whether an inhibitive cation is used. Polymers can be used to viscosify fluids, control filtration properties, deflocculate solids, or encapsulate solids. The thermal stability of polymer systems can range upwards to 400°f. In spite of their diversity, polymer fluids have limitations. Solids are a major threat to successfully running a cost-effective polymer mud system.
   

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   OIL BASED MUD (OBM)

   OBM is a petroleum product which is used as a drilling fluid. example of OBM is diesel fuel, mineral and Non-Petroleum Hydrocarbon. OBM is used in the drilling operation for several reason such as increasing the lubricity of a tool, increasing cleaning abilities with less viscosity and enhanced shale inhibition.
   A primary use of oil-based fluids is to drill troublesome shales and to improve hole stability. They are also applicable in drilling highly deviated holes because of their high degree of lubricity and ability to prevent hydration of clays. They may also be selected for special applications such as high temperature/high pressure wells, minimizing formation damage, and native-state coring. Another reason for choosing oil-based fluids is that they are resistant to contaminants such as anhydrite, salt, and CO2 and H2S acid gases.
   Cost is a major concern when selecting oil-based muds. Initially, the cost per barrel of an oil-based mud is very high compared to a water-based mud system. However, because oil muds can be reconditioned and reused, the costs on a multi-well program may be comparable to using water-based fluids.
   Today, with increasing environmental concerns, the use of oil-based muds is either prohibited or severely restricted in many areas. In some areas, drilling with oil-based fluids requires mud and cuttings to be contained and hauled to an approved disposal site. The costs of containment, hauling, and disposal can greatly increase the cost of using oil-based fluids.
   

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   SYNTHETIC BASED FLUID (SBM)

   SBM which is also known as Pneumatic fluid is mostly used on offshore rigs because of its properties which consists of Oil based mud but the toxicity of the fluid fumes are much less than the oil based mud. SBM are sometimes called low toxicity oil based mud (TOBM). SBM consists of synthetic oil. Examples are dry gases, mist, foam and gasified mud.
   Pneumatic (air/gas based) fluids are used for drilling depleted zones or areas where abnormally low formation pressures may be encountered. An advantage of SBM fluids over liquid mud systems is use in increasing penetration rates. Cuttings are literally blown off the cutting surface ahead of the bit as a result of the considerable pressure differential. The high pressure differential also allows formation fluids from permeable zones to flow into the wellbore. Air/gas based fluids are ineffective in areas where large volumes of formation fluids are encountered. A large influx of formation fluids requires converting the pneumatic fluid to a liquid-based system. As a result, the chances of losing circulation or damaging a productive zone. Another consideration when selecting pneumatic fluids is well depth. They are not recommended for wells below about 10,000 ft because the volume of air required to lift cuttings from the bottom of the hole can become greater than the surface equipment can deliver.
   

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   Function of Drilling mud.

   Generally, Drilling mud serves as a muti purpose function in the oil and gas industries. Download to device or Review. Below is the overall functions of a drilling mud.
   
4. Drilling mud serve as a cooling agent to cool and lubricate the bit and drill string.
   
5. It is also used to clean the bit while rotating.
   
6. Its help to transporting cuttings and carvings from the well to the surface.
   
7. Its transmit energy to tools and bit which help drilling easier for the drillers.
   
8. Drilling fluid is used to control sub-surface and formation pressure.
   
9. Assist in the gathering of subsurface geological data and formation evaluation.
   
10. It helps to support and maintain stabilization of wellbore and control corrosion on drillstring and casing.
    
11. Its makes cementing and completion operation easier.
    
12. Minimize lost circulation.
    
13. Drilling mud provide medium for wireline logging.
    
14. Improve penetration rates.
    
15. Its ensure formation evaluation and seal formation pressure.
    
16. It reduces friction of the drill string.
    
17. Reduce pressure Losses.
    
18. Support weight of tubulars.
    
19. Drilling fluid reduce stuck pipe.
    
20. Reduce environmental impact.
    
21. Improve Safety.
    

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PROPERTIES OF A DRILLING MUD ARE:

1. Density or Weight (lbs/gal)
   
2. Viscosity: it’s resistance to flow
   
3. Yield  Point
   
4. Solids content
   

Do not think that a drilling mud or fluid is the same as a completion fluid. Is totally a different fluid. A completion fluid is a fluid used when a well is being completed, that why it's called a completion fluid. It is selected not only for its ability to control formation pressure but also for the properties that minimize formation damage.