In many areas clear water cannot be used as a drilling fluid because of its effect on formations and the lack of sufficient viscosity to properly clean the hole. In these circumstances Non-Dispersed Polymer Muds may be used to closely simulate the drilling characteristics of clear water. Non-dispersed Polymer muds have found their best application in areas where formations are hard and penetration rates are slow. These polymer muds contain fewer than 5% low-gravity solids and hence are sometimes referred to as low-solids non-dispersed (LSND) muds. LSND muds do not perform well in areas with
Most Non-Dispersed Polymer Muds are composed of water with varying quantities of bentonite and polymers. Polymers are added to the system to build viscosity either through flocculation of the solids or by viscosifying the water phase. They are also added to provide filtration control. Some of the more commonly used Non-Dispersed Polymer Muds are:
BEN-EX is a powdered water-dispersible polymer packaged in 2-lb bags. It is used to increase the yield of bentonite and to flocculate drilled solids. The addition of 0.05 lb/bbl BEN-EX will approximately double the yield of bentonite. This is an advantage because fewer solids are used to produce the same viscosity. The application of BEN-EX for extending bentonite is confined to water containing less than 5000 mg/L chlorides.
Low-Gravity solids should be kept below 5% by volume. Best drilling rates are obtained in the 2-3 volume % range. Water dilution and use of mechanical separation equipment is recommended. BEN-EX acts as a flocculant for non-bentonitic clays. If settling pits are available, solids will settle out. Deflocculants should not be added unless absolutely necessary. Deflocculants should be added very cautiously because BEN-EX muds respond quickly to very small treatments.
BEN-EX can be economically used for mixing large volumes of spud mud or fresh mud when lost circulation occurs. The BEN-EX system can easily be converted to any type system as drilling progresses.
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