Drag to walk around it. Tap RCD, choke, separator or pump — or use the view buttons to jump inside the spread.
Drilling “mud” is a heavy fluid the rig pumps down the drill pipe (the “string”) to cool the bit and carry rock chips back up the gap around the pipe (the “annulus”). On a normal rig it just pours back out into an open channel. Here it can't escape: a seal at the top (the RCD) traps it, valves (the chokes) squeeze it, a meter weighs it, a tank splits out any gas, and it goes round again. Amber = mud coming back under pressure. Teal = mud on its way down. Tap any box.
Its job, its place in the loop and its headline specs appear here. Start at 1 and follow the numbers: that is the journey of one litre of mud.
Thirteen pieces of kit make this rig work. Every one opens with a plain-words explanation — what it does, where it sits, what it connects to — and the full engineering record (internals, connections, safety notes) is one tap inside each card. Search, or filter by job type.
Deep underground there is a safe zone for pressure. Too low — below “pore pressure”, the pressure pushing in from the rock — and the well pushes back (a dangerous “kick”). Too high — above “fracture pressure” — and the rock cracks and swallows your mud. Keeping the pressure at the bottom of the well (BHP, bottom-hole pressure) inside that zone, while everything around it changes, is the whole skill. Work the guided exercise first, then play freely.
The safe zone is set by the two gradient sliders — properties of the rock, independent of the mud you pick. Set the mud weight below the pore gradient and the well is underbalanced: watch the status change. Real wells take these gradients from offset data, LOT/FIT and the hydraulic model.
When a new pipe is added, the pumps slow down and friction fades — so backpressure (SBP) rises by exactly the same amount, and the pressure at the bottom (BHP) never moves.
| Pump speed | Friction | Backpressure needed | Pressure at bottom (BHP) |
|---|
The standard CBHP swap: ramp the pumps down in steps while the choke closes to replace lost friction with surface backpressure — then reverse it. In Auto choke the loop tracks pump rate (the Weatherford MicroFlux / SLB i-balance “lookahead” idea); in Manual, SBP stays where the slider is and you watch BHP sag. Scrub the trace afterwards like a simulator telemetry replay.
Every question is answered somewhere in the lessons before this one — the seal's real job (the RCD), what happens when the pumps pause (a “connection”), one pressure calculation (ECD, the effective weight of the moving mud), telling a real kick from its lookalike, and which method you pick when nothing comes back up. Answers check instantly, with the reasoning shown. The score lives only while this page is open.
Every method below uses the same kit you walked around in 3D — the seal (RCD), the squeeze valves (chokes), the meter, the gas tank (separator), the helper pump and the computer controller. What changes is the plan for pressure: where in the well it is held steady, and what happens to the mud that comes back up (the “returns”).
In a conventional well the gap around the pipe (the annulus) is open to the air, so the pressure at the bottom is whatever the mud column and friction happen to give you — and it swings every time the pumps start or stop. MPD seals that gap shut and holds pressure from the surface with valves (chokes), so bottom-hole pressure (BHP) becomes a number you choose and defend, second by second.
Lighter mud plus applied backpressure also means the pressure can be lowered as fast as it is raised — something mud weight can never do.BHP = Hydrostatic + Friction (pumps on) + SBP — when friction stops, SBP replaces itThe line is the pressure at the bottom of the well (BHP) across one connection — the moment a new length of pipe is added and the pumps pause. Conventional (right): friction vanishes with the pumps, pressure sags toward a kick, then spikes hard enough to crack rock on restart. MPD (left): the choke squeezes exactly enough to replace the lost friction — the line never leaves the safe zone. That one flat line is the whole idea of this app.
MPD is only for deepwater rigs.
It grew up offshore, but the fastest-growing use today is on land — the rig in this app is a land rig. Any well with a narrow pressure window can use MPD, in a desert or in deep water.
MPD removes the risk of a blowout.
MPD spots a kick earlier and smaller — it never removes the risk. The BOP, the barriers and a trained crew stay the last line of defence, and the well-control plan is written as if MPD were not there.
MPD is just drilling slightly underbalanced.
Opposite intent. MPD holds pressure at or just above the rock's pressure to keep flow out. Underbalanced drilling drops below it on purpose to invite flow in. Similar sealed kit on top, opposite plan underground.
The computer runs everything — the crew just watches.
The computer holds a number the crew chose. People set the plan, spot the weird cases and take over when it matters — both case studies in the Pressure Lab are human-communication failures, not computer ones.
MPD needs a brand-new rig and special mud.
It's mostly bolt-on kit — a seal, chokes, a meter, a helper pump and a controller — fitted to a conventional rig like this one, running ordinary mud, just mixed a touch lighter.
The full route, matching the course track at the top of every page — step 1 is the 3D Rig tour; this page is step 2.
The idea, the four variants, the connection procedure.
Trace the closed loop and where pressure is applied.
Thirteen records — job, connections, failure modes.
Hold the window, run a connection, survive the faults.
Eight questions drawn from all of it. Aim for 8 / 8.
The everyday method. Use slightly lighter mud, then top the pressure up from the surface so the pressure at the bottom of the well stays rock-steady, just above the pressure pushing in from the rock. Made for wells where the safe zone is very narrow. One precision: “constant” means constant at ONE chosen depth — the anchor point (see the glossary). Pressures above and below that point still shift a little as friction comes and goes; the anchor is what the controller defends.
For the worst ground: rock so cracked that mud poured in simply vanishes. A cap of heavy mud is held under pressure at the top while cheap fluid (often seawater) is pumped down and sacrificed — it never comes back; the rock cuttings are pushed into the cracks with it.
Two different mud weights stacked in the same well — lighter above, heavier below — so each stretch of rock gets the pressure it can take. Mostly used in deep water, with pumps on the seabed.
The cautious mode. The returning mud is kept sealed under the rig floor — for safety and so nothing is discharged — and the crew drills the normal way, bringing the pressure kit into play only if the well surprises them.
CBHP is the dominant variant — about 55–60% of the MPD market (2025, index-sourced). The bar under each card is its pressure profile against the pore → fracture window: the marker is where BHP is held.
| What the well is telling you | Pick | Why it wins |
|---|---|---|
| Pore–fracture window too narrow for mud weight alone | CBHP | BHP held at a set-point; the friction ↔ SBP swap keeps connections flat. |
| Fractured or karst formation, total losses, no returns possible | PMCD | Mud cap held under pressure, sacrificial fluid down the string — nothing needs to come back. |
| Deepwater: the riser margin eats the window at the shoe | Dual gradient | Two effective densities above / below a point widen the usable window. |
| Drillable conventionally, but containment or readiness is the concern | RFC / HSE | Closed returns under the rig floor; the spread is rigged up and ready to take pressure. |
| Conventional | MPD (CBHP) | Underbalanced | |
|---|---|---|---|
| Annulus | Open to atmosphere | Sealed by RCD, pressurised via chokes | Sealed, below pore pressure |
| BHP target | Above pore, swings with pumps | Constant, just above pore | Below pore — formation flows by design |
| Kick detection | Pit volume, flow paddle | Coriolis delta-flow — much earlier | Continuous production to separator |
| Best for | Wide windows | Narrow windows, HPHT, depleted | Productivity / evaluation |
Effective density at depth = hydrostatic + friction. MPD manages ECD, not just mud weight.
Surface backpressure held by chokes — the top-up that replaces friction when pumps stop.
The well's normal flow/pressure signature, so a real influx stands out.
Formation takes fluid under pressure, gives it back when pressure drops — can mimic a kick.
Non-return valves in the string — stop backflow when annulus is pressurised.
Max allowable surface pressure — the hard ceiling choke automation must never exceed.
The depth where BHP is held constant in CBHP — usually the bit, or the weakest / most critical point in the open hole.
Bottom-hole pressure: hydrostatic + friction + SBP. The single number every MPD decision is really about.
MPD Alpha is a playful, hands-on tour of Managed Pressure Drilling — the way modern rigs hold the pressure at the bottom of a well exactly where they want it. Instead of a textbook, you get a colourful 3D rig you can walk around, tap and take apart: follow one litre of mud around the loop, meet all thirteen machines, then try holding the pressure yourself in the Pressure Lab and prove it in the quiz.
Start with the guided tour. Everything is explained in plain words first — tap any bold term for the short version, and the engineering depth is one tap behind it when you're ready.
Use it to picture the whole MPD spread at once — what connects to what, what happens when a part fails, and the checks a supervisor runs before every connection.
The methods, the loop diagram and the fault scenarios are built to be shown to someone else — myths busted, figures sourced, nothing invented.
MPD Alpha was created by Muhammad Zain, an MPD Supervisor who wanted the subject to feel the way it feels on a good day at the rig — clear, hands-on and a little bit fun. If MPD ever looked like a wall of jargon to you, this app is his answer.
PetroMind Rig Explorer (structure & interaction model): https://rig.petromind.ai/
MPD components & closed-loop principle: https://drillingcontractor.org/shale-drilling-reaps-efficiency-gains-from-mpd-pressure-control-23264
Four MPD variants: https://drillingcontractor.org/offshore-drilling-hazard-mitigation-controlled-pressure-drilling-redefines-what-is-drillable-3178
Backpressure pump & MGS tie-in: https://drillingcontractor.org/mpd-planning-how-much-is-enough-1770
CBHP method, API 16RCD / 7NRV, BHP equations (BSEE TAP 582): https://www.bsee.gov/sites/bsee.gov/files/tap-technical-assessment-program/582ab.pdf
ECD formula & worked example: https://www.drillingformulas.com/2009/04/
Automated control & connection “lookahead” (SLB i-balance): https://www.slb.com/-/media/files/mi/product-sheet/i-balance-ps.pdf
3D models in the rig scene: “Oil pump” (pumpjack) — CC-BY, via Poly Pizza: https://poly.pizza/m/fZykGFywa5D · Pipes, Tank, Water Tank, Container and Barrel — CC0, via Poly Pizza: https://poly.pizza/m/GB6AFkoiZb
Main rig: “Oil Rig” (https://sketchfab.com/3d-models/oil-rig-ddef41323acb4fc6a1a055a52fc40745), via Sketchfab, is licensed under Creative Commons Attribution (http://creativecommons.org/licenses/by/4.0/).
Spare pipe racks (south-east yard), trip tank (west apron) and mud-pump skid (north-east apron): taken from the project's own 1500 HP land rig model — procedurally generated for this project (Blender).
BOP stack on the wellhead: “Custom BOP stack + RCD — procedurally generated for this project (Blender)”.
Choke manifold on the pad: “Custom choke manifold — procedurally generated for this project (Blender)”.
Top drive on the mast: “Custom top drive — procedurally generated for this project (Blender)”.
Separator and flare on the return line: “Custom mud gas separator + flare stack — procedurally generated for this project (Blender)”.
MPD control cabin on the south apron: “Custom MPD control cabin — procedurally generated for this project (Blender)”.
Distribution manifold on the pad: “Manifold - PV-703673” (https://skfb.ly/ovp8E), via Sketchfab, is licensed under Creative Commons Attribution (http://creativecommons.org/licenses/by/4.0/).
Surge valve cutaway by the choke manifold: “Surge Valve 02” (https://skfb.ly/oqnZO), via Sketchfab, is licensed under Creative Commons Attribution (http://creativecommons.org/licenses/by/4.0/).
Production-corner exhibits: “ESP VD AR”, via Sketchfab, is licensed under Creative Commons Attribution (http://creativecommons.org/licenses/by/4.0/).
“ESP Sand Diverter AR (Shut Down)”, via Sketchfab, is licensed under Creative Commons Attribution (http://creativecommons.org/licenses/by/4.0/).
Rig-floor details: “Power Tongs ( oil rig drilling )” (https://skfb.ly/puTFN), via Sketchfab, is licensed under CC Attribution-NonCommercial-ShareAlike (http://creativecommons.org/licenses/by-nc-sa/4.0/).
“Oil Rig Dial Machine” (https://skfb.ly/p8JuR), via Sketchfab, is licensed under CC Attribution-NonCommercial-ShareAlike (http://creativecommons.org/licenses/by-nc-sa/4.0/).
Vendor specs (RCD ratings, choke sizes, pump rates) vary by model and are marked “Not established” in the records rather than invented — the same honesty convention PetroMind uses. MPD figures above are index-sourced and corroborated across sources; treat them as learning values, not design data.
MPD Alpha is a learning overview, not an operating procedure. Real operations need a well-specific MPD plan, barrier analysis, crew competency and OEM manuals.