Definition
Neutral Point — The neutral point is the depth in a drill string where axial stress transitions from tension above to compression below, marking the boundary that separates the pipe in tension from the weighted components that supply weight-on-bit.
Also known as: neutral point, neutral point of the string
What the neutral point is
The neutral point is the location along the drill string where the axial load is zero — above it the string hangs in tension, below it the string is in compression because weight is being transferred to the bit. Its position depends on how much weight-on-bit is applied and on the buoyed weight of the components.
Keeping the neutral point within the heavy, stiff part of the assembly — the drill collars and heavy-weight drill pipe — is a fundamental rule of BHA design. Ordinary drill pipe run in compression below the neutral point is prone to buckling and fatigue.
Why it matters
- Buckling prevention — drill pipe must stay above the neutral point, in tension.
- WOB dependence — increasing weight-on-bit moves the neutral point up the string.
- Buoyancy — the buoyancy factor of the mud shifts the effective weights and the neutral point.
Renting the weight below the neutral point
Enough collar and HWDP weight must sit below the neutral point to supply WOB without buckling drill pipe. We rent drill collars and heavy-weight drill pipe to place that weight correctly — contact us to size your BHA.