MD to TVD Converter

Measured depth (MD) is the distance along the wellbore path from the reference point, which is what the drill pipe measures. True vertical depth (TVD) is the vertical distance from that same reference down to the point of interest. In a perfectly vertical well the two are equal; in a horizontal well MD keeps increasing while TVD barely changes. Pressures, formation tops and fluid gradients all depend on TVD, not MD.

TVD cannot be derived from measured depth alone — it needs the survey. Using the minimum curvature method, the change in TVD between two stations is (ΔMD ÷ 2) × (cos I₁ + cos I₂) × RF, where I is inclination and RF is the ratio factor (2 ÷ β) × tan(β ÷ 2) for dogleg angle β. Add that change to the TVD at the first station.

The ratio factor corrects for the wellbore following a circular arc rather than a straight line between survey stations. Without it you get the balanced tangential result, which is close over short intervals with little angle change but drifts as the dogleg grows. The error accumulates station by station, so it matters most through build sections — precisely where accurate TVD matters most.

Not from a single depth. TVD depends on the whole survey path above the point, so you need at least two survey stations and a known TVD at the first. To convert a full survey set you apply this calculation to each consecutive pair, carrying the TVD forward — which is what GeoMaster does automatically across the survey as the well is drilled.