Lag Time & Bottoms-Up Calculator: Bottoms-Up Strokes and Mud Return Time

How It Works

1. Enter Wellbore Geometry

   Input the hole diameter, pipe OD, and section depths for each local annular section: open hole, cased hole, and riser if offshore. Verify actual dimensions from the well program, caliper, BHA, and rig records before operational use.

2. Enter Pump Data

   Input pump output from liner and stroke data or measured flow. Pump efficiency is a planning input and should be checked against counters, pit-volume observations, and current rig conditions.

3. Review Lag Time Screen

   The screen divides local annular volume by pump output. Results are shown in minutes and pump strokes for planning and review, not as an approved operating procedure.

4. Check Source Gaps

   Review the warning and source-gap notes before using the numbers in mud logging, drilling, trip, or well-control workflows.

Built For

• Planning mud-logging sample-lag discussions before field calibration
• Checking local annular-volume and pump-stroke arithmetic against well geometry inputs
• Comparing marker observations to the local calculated stroke count
• Reviewing how washout, BHA, riser, and pump-output assumptions change a planning estimate
• Preparing a source-aware calculation packet for qualified drilling or mud-logging review
• Documenting preliminary displacement volumes for non-final planning discussions

Features & Capabilities

Multi-Section Annular Volume

Screens annular volume separately for open hole, cased hole, and riser sections from entered local geometry.

Lag Time in Minutes and Strokes

Displays both time and pump strokes from the same local annular-volume screen.

Mud Pump Output Screen

Enter liner diameter, stroke length, efficiency, and pump type, or use direct measured flow inputs.

Section-by-Section Breakdown

Shows which entered sections dominate the planning volume and where washout assumptions matter most.

Calibration Input

Compares marker-depth calculated strokes to observed strokes so the source gap is visible.

PDF Export

Export the planning screen with warnings, assumptions, and source pointers for review.

Assumptions

• Borehole diameter, casing or riser ID, pipe OD, BHA, and washout are entered planning inputs.
• Pump output is a local assumption or measured input and is not automatically verified against rig counters.
• Single-acting pump output uses cylinder count, liner area, stroke length, and entered volumetric efficiency.
• All annular sections are treated as concentric local geometry screens unless field data says otherwise.

Limitations

• Borehole washout, tool joints, stabilizers, surface-system volume, and gas-detector delay can change observed lag.
• Pump efficiency, leakage, pressure, compressibility, liner or valve condition, and pump changes can change output.
• Cuttings beds, inclination, rheology, losses, gains, gas behavior, and MPD/backpressure are not modeled.
• The screen does not approve trip conditioning, well-control action, gas-detection timing, or mud-logging depth correlation.
• Marker observations require field procedure, rig context, and qualified review before changing operating assumptions.

References

• IADC drilling formula source pointer for annular-volume and pump-output context.
• API RP 13D source pointer for drilling-fluid rheology and hydraulics context.
• IADC WellSharp and WellCAP source pointers for terminology and well-control boundary context.
• NIST source pointer for unit-conversion context.

Frequently Asked Questions