Casing Design Calculator

Casing design is one of the most critical aspects of well construction. The casing string must withstand three primary loads throughout the life of the well: burst pressure (internal pressure exceeding external pressure), collapse pressure (external pressure exceeding internal pressure), and axial tension (the weight of the casing string hanging in the wellbore). Proper casing design ensures wellbore integrity, zonal isolation, and safe operations from drilling through production and eventual abandonment.

The burst load scenario represents the worst-case condition where internal pressure is maximized. The most severe burst case for production casing is typically a gas kick or displacement to gas, where formation pressure at total depth is transmitted to surface through a gas column. The net burst pressure at any depth equals the internal pressure minus the external backup pressure (typically the pore pressure or mud pressure behind the casing). The casing burst rating, as published by the manufacturer per API specifications, must exceed the net burst load multiplied by the burst design factor, which is typically 1.0 to 1.25 depending on the operator's standards and risk tolerance.

The collapse load is the reverse scenario: external pressure exceeds internal pressure. The worst case for collapse is typically a lost-circulation event where the mud level inside the casing drops to zero (empty pipe) while the full mud column remains in the annulus. This creates maximum differential pressure at the casing shoe. Collapse design factors are usually 1.0 to 1.125. Note that API collapse ratings are based on empirical formulas that account for yield strength, D/t ratio, and manufacturing tolerances.

Axial tension is evaluated at the surface where the hanging weight is greatest. The buoyancy factor (1 - mud_weight / 65.4) reduces the effective weight of the casing string when submerged in drilling fluid. The tension design factor is typically the highest of the three, ranging from 1.4 to 1.8, because tension failures can be catastrophic and difficult to recover from. Some operators also include an overpull allowance (50,000 to 100,000 lbs) above the buoyed weight for contingency operations such as freeing stuck casing.

The classic casing design chart plots pressure on the x-axis against depth on the y-axis (inverted), showing the burst load line, collapse load line, and the corresponding casing ratings as vertical lines. The region between the load line and the rating line represents the safety margin. If the load line exceeds the derated casing rating at any depth, the casing selection fails for that load condition. This tool performs all three checks automatically, generating the design chart and a depth-by-depth table showing design factors at every 1,000-foot interval.

All calculations run entirely in your browser — no data is sent to any server. Built by Groundwork Analytics, an AI and engineering company that builds digital tools and deploys AI agents for the energy industry. We help operators, service companies, and engineering teams automate workflows, optimize operations, and make better decisions with their data. Get in touch or email us at info@petropt.com. Mehrdad Shirangi (Stanford PhD) specializing in reservoir simulation, drilling optimization, and AI/ML applications for upstream oil and gas.