The Drilling Process Step by Step – From Spud to TD
From the outside, drilling an oil well looks like one long job: a rig shows up, spins pipe for a few weeks, then leaves. From the inside, it's a string of separate phases, each with its own hazards and its own reasons. Miss why one step comes before the next, and the whole thing stops making sense. So how does the drilling process work, step by step, from spud to TD?
The drilling process runs in a set order: plan and permit the well, build the location, rig up, spud the well, drill and case the surface hole, install and test the blowout preventer, drill deeper sections and case each one, then drill the final section to total depth (TD), log it, and run and cement production casing. Each hole section is drilled, then protected with steel casing and cement before the next, smaller section starts. That's why a well looks like a telescope. Once the production casing is set, the drilling rig moves off and the completion crew takes over.
Here are the oil well drilling steps in order:
- Planning, permits and well design
- Site preparation and the conductor
- Rig up
- Spud and drill the surface hole
- Run and cement surface casing
- Nipple up and test the BOP
- Drill out and test the shoe
- Drill intermediate hole and set casing (if needed)
- Drill the production hole to TD
- Log the well
- Run and cement production casing
- Rig down and hand off to completions
What Happens Before the Rig Arrives?
Most of the thinking happens before anybody touches a pipe. Geologists pick the target. Engineers design the well: hole sizes, casing points, mud weights, the directional plan and the cement program. The operator secures the lease and gets a drilling permit from the state or federal regulator.
Then comes the dirt work. A crew builds the road and the pad, levels it and lays down a base that can carry heavy loads. They dig a cellar, a pit under where the rig floor will sit, so there's room for the wellhead and BOP stack.
The conductor pipe usually goes in during site prep too. It's a large-diameter pipe driven or drilled in a short distance to keep the loose surface soil from caving in and to give returns a path back to the surface. Some areas drill it with a small rig ahead of time, some let the main rig do it.
Phase 1: How Does the Rig Get Ready to Drill?
The rig arrives in loads and gets rigged up over the conductor. The substructure goes down first, then the mast goes up. The crew hooks up mud pumps, tanks, solids control, generators and every hose and line that ties them together.
Before drilling starts, the crew runs through inspections and function tests. The company man, toolpusher and crew hold a pre-spud meeting to go over the well plan, the hazards and who does what. On a good rig, this meeting is short and everybody already knows the answers. On a bad one, you learn a lot fast.
Phase 2: What Does It Mean to Spud a Well?
Spudding is the moment the bit first starts making new hole for the well. It marks the official start of drilling, and the spud date gets reported to regulators and tracked by the operator. If you want the full story on that first day, read our article on spudding a well.
The surface hole is the first section drilled by the main rig. It's usually a big bit, drilled down far enough to get below the fresh groundwater zones and into competent rock. That depth is set by the well design and by state rules that protect drinking water.
Surface hole tends to go fast. The rock is softer and the hole is shallow. But fast doesn't mean careless. Shallow gas, loose formations and lost circulation can all show up near the surface, and the BOP isn't installed yet, so a diverter is often used to route any flow away from the rig floor.
Phase 3: Why Is Surface Casing So Important?
Once the surface hole reaches its planned depth, the crew pulls the drill string out and runs surface casing, joint by joint, to bottom. Then the cement crew pumps cement down the casing and up the outside, filling the space between the pipe and the rock.
Surface casing does three big jobs:
- Seals off freshwater zones so drilling fluids and hydrocarbons can't reach them.
- Supports the loose upper part of the hole so it doesn't cave in.
- Gives the BOP and wellhead something solid to sit on.
The crew waits for the cement to set up before going further. That wait is called "waiting on cement," and it's one of the few times a drilling rig is quiet on purpose.
Phase 4: When Does the Blowout Preventer Go On?
After the surface casing is cemented, the wellhead gets installed on top of it, and the BOP stack gets nippled up on the wellhead. The BOP is the stack of rams and valves that can close the well if formation fluids start flowing in uncontrolled.
The BOP gets pressure tested before drilling ahead. The choke manifold, kill line, valves and the accumulator that closes the rams get tested too. This is not paperwork. Every test is a check that the equipment holds when you need it most.
The blowout preventer is the last line of defense, not the first. The first is the mud weight, which holds formation pressure back. But when the mud isn't enough, the BOP has to work every time.
Phase 5: What Is a Shoe Test?
The next bit runs in the hole and drills out the cement and float equipment at the bottom of the surface casing, plus a short stretch of new formation. Then the crew does a formation integrity test or leak-off test, usually called a shoe test.
In a shoe test, the crew closes the well and pumps a small amount of fluid to raise the pressure. That tells the engineers how much pressure the rock just below the casing shoe can take before it fractures. That number sets how heavy the mud can get in the next section and how big a kick the well can safely handle.
Phase 6: How Is the Intermediate Section Drilled?
Not every well has an intermediate section. Shallow wells might go straight from surface casing to the production hole. Deeper wells, or wells with trouble zones like weak formations, salt or high-pressure intervals, often need one or more intermediate casing strings.
This is where most of the work of making hole happens on a deep well. The crew drills ahead, making a connection every time the kelly or top drive runs out of room. The mud system carries cuttings out, cools the bit and holds back pressure. Mud loggers watch returns and gas. The driller watches weight, torque, pump pressure and the pit levels for any sign of a kick.
When the section reaches its casing point, the crew trips out, runs casing, cements it, tests and drills out again. Each new section uses a smaller bit than the last, so it fits inside the casing above.
Phase 7: How Do Crews Drill to Total Depth?
The production hole is the last section, and it's the one that reaches the reservoir. On a vertical well, it's a straight shot down. On a directional or horizontal well, this is where the directional driller earns their money, steering the bit through the curve and along the lateral in the target zone.
Drilling ahead is the day-to-day rhythm of a rig. Make hole, make a connection, check surveys, keep the mud in shape, watch the trip tank and pits. Bits wear out and have to be changed, which means a round trip: pull the whole string, change the bit or bottomhole assembly, and run back in.
OSHA's guide to hazards while drilling ahead covers the risks during this phase, from rotating equipment to slips and falls. A lot of people get comfortable during the long middle of a well. That's when you need to stay sharp.
When the bit reaches the planned final depth, the well is at TD. The crew circulates the hole clean and gets ready to evaluate what they found.
Phase 8: How Is the Well Logged at TD?
Logging measures the rock and fluids along the wellbore. Many wells are logged while drilling, with tools built into the bottomhole assembly that send data to the surface as the bit goes. Others get open-hole wireline logs after TD, where a logging crew runs tools down on a cable and records them on the way out.
The logs tell the geologists and engineers where the oil and gas are, how porous the rock is and whether the well is worth completing. Sometimes they confirm what everybody hoped. Sometimes they don't, and the well gets plugged instead of completed.
Phase 9: Why Run Production Casing?
If the well is a keeper, the crew runs production casing, the final and smallest full string, to bottom or through the target zone. Then it gets cemented, isolating the reservoir from the zones above it.
Production casing is what the completion crew will perforate and, in many shale wells, fracture through. It has to hold high pressure for the life of the well, so it's designed and tested with that in mind. A bad cement job here can haunt a well for years.
Phase 10: What Happens After the Drilling Rig Leaves?
After the production casing is cemented, the drilling rig's job is done. It rigs down and moves to the next well, or walks to the next slot on the pad. The well is left with a wellhead and a temporary cap or valve.
Then the completion crew moves in. They perforate the casing, stimulate the well if needed, run tubing and install the Christmas tree that controls flow at the surface. Only after all that does the well start producing. A lot of people think the drilling rig pumps the oil. It doesn't. It just builds the hole.
What Can Go Wrong During the Drilling Process?
Plenty, and every hand learns the list sooner or later. Most problems fall into a few families, and the well plan is built to avoid them or deal with them fast.
- Kicks. Formation fluid enters the wellbore because the mud weight isn't holding it back. The crew shuts in on the BOP and circulates it out.
- Lost circulation. Mud flows away into weak or fractured rock instead of coming back up. Pits drop, and the hole can lose its pressure balance.
- Stuck pipe. The drill string gets held by the hole, by cuttings packing off around it, or by pressure pinning it to the wall.
- Hole instability. Shale swells or sloughs in, and the hole gets tight or washes out.
- Equipment failures. Pumps, top drives and downhole tools all break eventually, usually at the worst time.
Honestly, most trouble gives you a warning first. Pit gain, torque creeping up, drag on a connection, a change in the cuttings on the shaker. The crews that stay out of trouble are the ones who notice small changes and speak up before they turn into big ones.
How Long Does the Whole Drilling Process Take?
It varies a lot. A shallow vertical well in easy rock might be drilled in a few days. A deep or complex well can take weeks or months, and some offshore wells take far longer. Hole depth, rock hardness, the number of casing strings, the directional plan and how much trouble the crew runs into all decide the clock.
The phases don't change much, though. Whether it's a short well or a long one, you still spud, drill, case, cement, test and repeat until you reach TD.
The Drilling Process, Step by Step: Spud, Case, Repeat, TD
The drilling process comes down to a simple loop wrapped in a lot of careful work. Prepare the site, rig up, spud, drill a section, case and cement it, test, and drill the next one smaller and deeper. At TD, log the well, run production casing, and hand it off to completions.
If you're new on a rig, learn where you are in that loop every tour. Knowing what comes next tells you what tools to have ready, what can go wrong and where to stand. That's how a hand turns into a driller.