How is the weight agent Hematite seen in the fluid/mud market today? Is it being used regularly? but how common are the situations where it is needed?

from my personal experience, i'd say not so often.

Barite can weigh up to 17 PPG muds (but you have to keep good mud rheology)

we drill with 16 ppg mud all the time with barite and it's fine.

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of course there are some cases where Hematite is a must, but not often as much as you think.