Lost Circulation Center

1What is lost circulation?

Lost circulation is the loss of whole drilling fluid from the wellbore into the formation — fluid leaving through fractures, vugs or permeable rock, not filtering through a cake. It is measured by what the pits lose, in barrels per hour.

Losses vs fluid loss — don’t confuse them. Fluid loss (API filtrate) is the small, controlled seepage of liquid through the filter cake, measured in mL. Lost circulation is whole mud — solids and all — disappearing into the formation. One is a cake-quality number; the other is a returns problem.

Operational impact: lost hydrostatic head (well-control risk), lost expensive fluid, non-productive time, and in severe cases an inability to keep the hole full. It is one of the costliest events on a well.

2Types of lost circulation

Losses are graded by rate, because the rate decides the response:

The grade is the first thing a field diagnosis establishes — it sets both the urgency and the LCM strategy.

3Common causes

Where the fluid goes tells you what you are fighting:

• Natural fractures — pre-existing open fractures that take fluid as soon as they’re intersected.
• Induced fractures — the well breaks the rock itself when ECD exceeds the fracture gradient. This is the one solids control influences most directly.
• Cavernous / vugular formations — karst, caverns and large voids that can take total losses instantly.
• Highly permeable zones — coarse sands and gravels that drink fluid through pore space (seepage to partial).
• Weak / depleted formations — low fracture resistance, easily induced once pressure creeps up.

Note the pattern: two of these — induced fractures and weak formations — are pressure-driven, and pressure is driven by ECD, which is driven by the fine-solids load. That is the SC DrillTech angle.

4Field diagnosis guide

You rarely see the loss zone — you read it from surface signs. Four signals, read together, grade the loss:

Read all four. A pit drop with full flowline returns and a falling SPP reads differently from a total loss with no returns — and the mud trend tells you whether you helped cause it at surface.

5Lost circulation & solids control

This is where SC DrillTech has something few others say. The solids-control system can either protect you from losses — or quietly make them worse and waste the LCM you’re paying for.

LCM & shale shakers

The shaker is where LCM is won or lost. Run normal screens during an LCM treatment and the deck screens out the very material you just pumped — throwing expensive fibres and flakes straight to waste. The fix is deliberate screen selection: coarsen the deck, or bypass the shaker for the LCM circulation so the material survives to the active system. See the shaker guide and screen blinding.

LCM & mud cleaners

The mud cleaner’s fine screen will also reject coarse LCM. During treatment, know when to bypass the cones / cleaner so the LCM isn’t classified out — then return to normal once the pill is placed. It’s an operational decision, not a set-and-forget. See the mud cleaner guide.

LCM & centrifuges

A centrifuge running through an LCM treatment can strip out the sized material you need in suspension, and load itself with fibrous solids it was never meant to handle. The recommendation: idle or isolate the centrifuge during active LCM work, and resume once the treatment has done its job. See the centrifuge guide.

LCM recovery & reducing unnecessary losses

Beyond protecting the pill, the bigger prize is not generating the problem: controlling ultra-fine drilled solids keeps PV and ECD down so you induce fewer losses in the first place. Better solids control upstream means fewer LCM events downstream.

Common solids-control mistakes during a loss event

• Leaving fine screens on the shaker — screening out the LCM you just bought.
• Running the centrifuge through the treatment — removing sized material from suspension.
• Forgetting to bypass the cones / mud cleaner during the pill.
• Letting LGS and PV climb unchecked — raising ECD until the formation breaks.
• Not restoring normal solids control after the pill — leaving the system half-configured.

6LCM categories

LCM is grouped by particle shape, because shape decides how it bridges and seals. An overview — sizing and selection are an expanding topic here:

Effective pills often blend all three — granular to bridge, fibrous to span, flaky to seal. Detailed selection and sizing are flagged below as coming soon.

7Economic impact

Losses are expensive on more than the fluid line. A single event compounds across the cost sheet:

• Lost mud — every barrel into the formation is barrels of base fluid and chemicals gone.
• Extra dilution & build — rebuilding lost volume, often the most expensive lever.
• Extra waste — more volume to treat and haul, especially on NAF.
• Logistics — LCM, barite and base-fluid resupply, sometimes by boat or air.
• Rig time — NPT chasing the loss is usually the biggest number of all.

Simple example: a partial loss of 30 bbl/hr on an OBM at a fully-loaded cost of a few hundred dollars a barrel runs into five figures a day before a single hour of NPT — which is why prevention at surface (controlling ECD via solids) pays for the whole solids-control effort many times over.

8Future expansion

?FAQ

→Connected across SC DrillTech