Plug depths, plug counts, and cement volumes come from geometry and the Railroad Commission's own rulebook — the same calculation an inspector would run by hand. Here's exactly what we work out for each plug, and why §3.14 requires it.
Drilling leaves a mile-deep hole that runs straight through the fresh water Texans drink and the oil-and-gas zones below it. When the well is done, that hole is a highway — salt water and hydrocarbons can travel up it. Plugging means setting cement across every hazard so nothing gets past. The math answers two questions:
Question 1 — the rulebook
§3.14 names every feature that has to be sealed and how far the cement must reach past it. Rules, not guesswork.
Question 2 — the geometry
Once a plug runs from one depth to another in a hole of a known width, the amount of cement is just the volume of a cylinder.
Read it top-down — ground level at the top, total depth at the bottom. Each shaded band is a plug, tagged with the rule that puts it there.
The §3.14 general rule is simple to say: for each thing that could leak, set cement reaching at least 50 ft above and 50 ft below it — a 100-ft column centered on the hazard. That margin is the cushion against a cement job that doesn't land perfectly.
§3.14(d)(1) — casing-shoe plug
A shoe is the bottom end of a run of steel casing — a seam between cemented pipe above and open hole below, and a natural leak path. Wherever a pipe ends, we cap the joint.
§3.14(d)(3) — producing-zone plug
Perforations are the holes shot through the casing to let oil and gas in — the most direct line from a pressured reservoir to the wellbore. We plug across the interval, plus 50 ft each side. Already-squeezed perforations are left alone.
§3.14(d)(2) — fresh-water plug
The most important depth in the whole filing — the bottom of the fresh water worth protecting, read from your state GAU letter. When the surface casing already shields it, a 100-ft plug is centered right there.
§3.14 — special case
On many older wells the surface casing was never run deep enough to protect the water. A single plug isn't enough, so one unbroken column of cement is poured from the surface all the way down past the water — and it takes the place of the separate fresh-water and surface plugs, with nothing double-counted.
§3.14(d)(6) — surface plug
The last 50 ft up to ground level, so the wellbore is sealed at the top and can be cut off below grade.
Once we know a plug runs from one depth to another inside a hole of a known width, the cement it holds is grade-school geometry: the space inside a pipe is a cylinder, and a cylinder's volume is its cross-section times its length.
100 ft of cement inside 8⅝-inch surface casing, set inside casing so no washout allowance:
| Step | What we do | Result |
|---|---|---|
| Cement per foot | circle area of an 8-inch bore | 0.35 ft³/ft |
| Over the plug length | × 100 ft | 35.0 ft³ |
| Washout allowance | inside casing → none | 35.0 ft³ |
| In barrels | for the mixing crew | 6.2 bbl |
| In sacks | for procurement | 33 sacks |
The same 100 ft in the wider open hole below the shoe would take more cement and the washout allowance — which is exactly why the plug is split at the shoe and the two halves are added up.
Enter an API number and watch the plug program and cement volumes compute — free to draft, no account needed to start.
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