Geomechanics · Module G2
Elastic Properties from Logs
Compressional and shear sonic, together with bulk density, give the dynamic elastic moduli that every later step of a mechanical model relies on. The module covers the conversions and their units, the empirical ways to estimate shear velocity when no shear log was run, the correction from dynamic to static stiffness, and the two common definitions of brittleness.
- Level
- Intermediate
- Position
- Module 2 of 8
- Video
- About 16 minutes, narrated
- Format
- Narrated video lesson with captions and slide reading view; with the certified option, a quiz whose pass unlocks the next module.
What the module covers
- Slowness, velocity and the Vp/Vs ratio
- Dynamic Poisson's ratio and Young's, shear and bulk moduli
- Estimating shear velocity from compressional velocity
- The dynamic-to-static stiffness correction
- Elastic and mineralogical brittleness indices
- Sonic quality: enlarged hole, gas and unit errors
Learning outcomes
After the module you should be able to:
- Compute dynamic and static moduli on stated inputs, with any synthetic shear labelled.
- Compute Poisson's ratio and Young's modulus at one depth by hand
- Explain why an estimated shear log has to be labelled as estimated
A short preview
Take a sandstone with a compressional slowness of 80 µs/ft, a shear slowness of 140 µs/ft and a density of 2.45 g/cc. Dividing 304.8 by each slowness gives velocities of 3.81 and 2.18 km/s, a Vp/Vs ratio of 1.75, and Poisson's ratio depends on that ratio alone: about 0.26. The shear modulus is density times shear velocity squared, roughly 11.6 GPa, and Young's modulus is twice that times one plus Poisson's ratio, about 29 GPa. Those are dynamic values; a slow laboratory loading test on the same rock usually gives a noticeably lower stiffness.
Who it is for
Drilling, completion and reservoir engineers, petrophysicists and geoscientists who build or review pore pressure and wellbore stability predictions for well planning.
Prerequisites: None required; working familiarity with well logs helps. The hands-on steps use the Geomechanics workspace, available from the Professional plan.
Take the module in the Learning Hub
Geomechanics: Specialty course, sold separately: eight modules that build a calibrated 1D mechanical earth model from logs, from elastic properties and pore pressure to the mud weight window and its range. The lesson opens in the Learning Hub once the track is purchased; graded quizzes and the certificate come with the certified option.