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I have used KCl-Polymer mud for most of water-based mud I’ve ever work with. As hole problem gets more challenging, the KCl-Polymer mud seems obsolete. It need some additives to prevent clay and shale formation of being troublesome. I have run some additional products such as PHPA (partially-hydrolized polyacrylamide), glycol, lime mud, and premium grade amine mixture (some companies have different name). These worked fines mostly, however I used “Silicate Mud” lately and it brings the shale inhibition to a whole new level. So happy!
In a nutshell, silicate mud is very inhibitive. It expects the drill cutting to be large (in a good way of course 🙂 ) and firm and most of them will be removed at shaker and has no issue with cutting integrity. Consequently, the MBT will remains low as drilling progresses meaning that just a little amount of drilled solid gets into the mud system. How lovely it is 🙂
Actually, there is still a controversy within the industry, regarding the specific theoretical inhibition mechanism of silicate. But, there is one, which in my point of view, is quite make sense.
Inhibition is mainly provided by :
- Direct chemical bonding of the silicate polymers with the silanol surfaces of the formation and the drill cuttings,
- Silicate polymerisation
- Precipitation of the silicate with divalent ions
——- will present some illustration later on. I promise ——
This multiple interaction results in an effective chemical and pressure seal preventing fluid and colloidal solids from invading the pore spaces of the formation.
- Maintain the pH at 10.5 – 11, once less than that, some silicate may precipitate thus decline its effectiveness. some polymer might be degraded, but still ok at some level.
- Monitor the MBT. a good silicate mud has to be able to keep the MBT at almost constant value. Typically MBT less than 10 ppb is decent, somehow 12.5 ppg is a little bit acceptable. Once exceeded, there may be silicate ion has decline that causing the cutting integrity in a low level. Typically, when MBT spikes, its ineffective to mix Silicate Liquid into. It tends to flock. So, better mix in the low solid in separated tank (e.g. reserve tank) or considering dump and dilute the mud.
- Keep an eye of Solid Control Equipment. Once you find broken shaker screen, replace it promptly. Make sure Desander-desilter work. If needed, Run centrifuge.
Have a good day, mud-minded people!