Definition
Tapered String — A tapered string is a drill or work string built from two or more sizes or grades of pipe — heavier sections up top and lighter sections below — so that each part of the string carries its loads efficiently in very deep or extended-reach wells.
Also known as: tapered string, tapered drill string, combination string
What a tapered string is
A tapered string combines more than one pipe size, weight or grade in a single string. The heaviest, strongest pipe goes near the surface where tensile load is greatest, and progressively lighter or smaller pipe is run deeper where the hanging weight below is less. This “taper” keeps each section working near its efficient capacity rather than over-sizing the whole string to the top load.
Tapered strings are common in deep, high-angle and extended-reach wells, where a single uniform pipe would either be too weak at the top or unnecessarily heavy and stiff at the bottom.
Design considerations
- Tension profile — sections are transitioned where the load drops below the next size’s rating.
- Torque and drag — smaller lower sections reduce drag in long laterals.
- Fatigue at transitions — crossovers between sizes are fatigue-sensitive and must be managed.
Renting a tapered string
Building an efficient taper requires stocking multiple compatible sizes and grades. We rent drill pipe and heavy-weight drill pipe across sizes and grades to compose a taper — contact us with your well profile.