The technique adopted is to mix quantities of mica flakes and granular bentonite into special batches of mud which is pumped down the hole. The drill pipe is then withdrawn and the hole left undisturbed for a time being. Mica flakes tends to plate out on the walls at the lost zones and reduce the size of the holes through which the mud can pass. After a short interval, the plug is strong enough to permit circulation to resume without loss. Drilling then proceeds normally until a depth well below the lost circulation zone.
|Appearance||Flexible, non-adhesive, pearly silver flakes.|
|Specific Gravity||2.2 – 2.8|
|Density||270-320 Kg/m3 (0.17-0.20 gm3/cc)|
|Moisture @ 100oC||Less than 0.25%|
|Water Solubility (BS 1775)||Virtually insoluble|
|Reactivity||Inert. No reaction with hydrocarbons, acids, brines and water|
|Oil Absorption (BS 1775)||60-75 gms/oil|
|Effect on Mud||No adverse effect on properties and components of oil or water base muds.|
There are three grades of MICA FLAKES which are normally used for specific purposes:
(1) Coarse Mica Flakes: Suitably used for sealing openings. Apparent density = 0.17kg/ltr. Particle Size : Max 10% retained on 9.50mm B.S.Sieve. Material retained on Sieve 4.75mm + material passed through 1.70 mm = 30-40% Max.
(2) Medium Mica Flakes: Generally used to combate mild circulation in porous formations. Apparent density=0.18 kg/ltr. Particle size: Max 10 % retained on 3.35 mm B.S.Sieve. Material retained on 1.70 mm + material passed through Sieve 0.425 mm = 30-40% Max.
(3) Fine Mica Flakes: Suitable for use when a sealing agent is needed to be small enough to pass through a shaker screen without interfering with the operations. Apparent density=0.20 kg/ltr. Particle size : Nil retained on 0.850 mm B.S.Sieve. Matertial retained on Sieve 0.425 mm + material passed through sieve 0.15 mm = 30-40% Max.