Lost circulation mechanics

[soman703]

Hello everyone,

I have few questions about lost circulation.I would love it if anyone can throw light on it and help me solve these issues.

How much magnitude of mud lost classifies it under lost circulation?
If the mud weight is too high does the rock fail in tension?

does shear failure also occur in form of breakouts in it? what is shear failure by breakout?

does hole diameter reductions also happen due to swelling clays in it? what is the process of diameter reduction called and what it causes if it doesnt effect lost circulation in any way.

Thankyou.

[Tafuti]

Lost circulation hapen when the hydrostatic pressure Hp of the fluid column is higher then the pore Pp and/or frack Pf pressure of the formation.
When the Hp > Pp but < Pf then fluid enters into formation by pushing formation fluid away. Depending on circulation sytem and how fast the losses occur, this can be observed when ~2-3% of fluid has gone away. It hapends when the fluid used is too heavy or when formations are depleted, or in some other cases when formations are fractured/vugular type.
When Hp>Pp>Pf then the formation breaks down and in this case losses are big and abrupt.
Some very approximate gradients to keep in mind are Pp ~10kPa/m; Pf ~ 20kPa/m

[soman703]

Thankyou so much sir!
Very beautifully explained.

[soman703]

Thankyou so much sir!
Very beautifully explained.