Publications
Peer-adjacent open research published alongside welleng by Jonathan Corcutt
(Corcutt Beheer B.V., Wassenaar, Netherlands;
ORCID 0009-0008-1953-7760). Each paper is
openly deposited with a citable DOI and is accompanied by an open-source reference
implementation in welleng. For how to cite the software and these papers, see
CITATIONS.md.
The welleng software itself has a permanent concept DOI:
10.5281/zenodo.20968887.
An Open, Vectorized Closed-Form Solver for the 3D Curve-Hold-Curve Point-to-Target Problem
Jonathan Corcutt (2026). DOI: 10.5281/zenodo.21130979.
The curve-hold-curve (circle-line-circle, CLC) point-to-target problem — connecting a start station to a target station with two circular arcs joined by a straight tangent under a dogleg-severity limit — is the core construction in directional-drilling trajectory planning. This paper gives an open, vectorized closed-form solver (correcting the degree-10 resultant polynomial), together with a maximum-radius / landing / radius-sweep toolkit and a validated reference implementation.
Keywords: directional drilling, well trajectory, curve-hold-curve, Dubins path, minimum curvature, closed-form solver, dogleg severity, path planning.
Reproducing the ISCWSA Gyro Error-Model Test Cases
Jonathan Corcutt (2026). DOI: 10.5281/zenodo.20940515.
The ISCWSA gyro error model (Torkildsen et al., SPE 90408, 2004; Rev 5.13, 2023) is the industry framework for the positional uncertainty of gyro-surveyed wellbores. This paper reproduces its published test cases (SPE 90408 Appendix E), documents implementation clarifications and reference-data inconsistencies, and provides an open-source reference implementation validated against the standard wells.
Keywords: wellbore position uncertainty, gyro survey, ISCWSA error model, SPE 90408, covariance, directional surveying, MWD, reference implementation.
Making the Exact Wellbore Anti-Collision Boundary Practical
Jonathan Corcutt (2026). DOI: 10.5281/zenodo.20976872.
Wellbore anti-collision is governed by the ISCWSA separation rule (Sawaryn et al., SPE-187073-MS), which is conservative by construction. This paper presents an efficient, validated, open implementation of the exact combined-ellipsoid boundary (a mesh-free analytic Mahalanobis clearance), and quantifies the cost of the separation-rule approximation — usable as a fast broadphase filter ahead of exact narrowphase checks.
Keywords: anti-collision, wellbore clearance, separation factor, ISCWSA, Mahalanobis distance, collision avoidance, uncertainty ellipsoid, directional drilling.
A Note on the Well Trajectory Tortuosity Index
Jonathan Corcutt (2026). DOI: 10.5281/zenodo.21206271.
The Tortuosity Index (TI), a geometric well-trajectory quality metric, is conventionally combined across the inclination and azimuth domains as a root-sum-of-squares. This note shows that combination is not well-posed — the arc- and chord-length terms are the full three-dimensional quantities in both domain sums, so any curve turn detected in both is double-counted, over-stating tortuosity by up to √2. It gives the corrected 3D computation (sectionizing by curve-turn-plane continuity, capturing torsion) and a dimensionless Modified Tortuosity Index, both validated against a closed-form solution, invariants, and the ISCWSA standard wells in open-source tests.
Keywords: tortuosity index, well trajectory, directional drilling, wellbore quality, minimum curvature, modified tortuosity index, torque and drag, KPI.