A 1D  geomechanical model (again, consisting of stress magnitudes and orientation, pressure and mechanical properties) is constructed from wellbore data, along the path of that wellbore and is used to quantify stresses (magnitudes and orientation), rock mechanical properties (deformability and strength) and  pore pressure local to that wellbore. These data are typically presented as log traces of the given parameter, e.g., Sv, Shmax, Shmin, Young’s modulus, Poisson’s ratio, UCS (Unconfined Compressive Strength) and friction angle, as a function of depth (most often ft-TVD or m-TVD). Whenever possible, the 1D geomechanical model results are calibrated to, using a wellbore stability model, reproduce the failure events observed in the wells. 

At OFG, we build and calibrate the 1D geomechanical model for our projects following state-of-the-practice workflows and state-of-the-art tools (proprietary and commercial) with information gathered from well logs (e.g., GR, sonic, density, resistivity, image, and caliper); injectivity test data (e.g., DFITS, mini-fracs, LOTs, XLOTs, Step rate tests, and well testing); rock mechanics laboratory data (e.g., from cores and analogs); pore pressure data (e.g., from logs, RFTs, and MDTs); and drilling data (e.g., WOB, ROP, cavings).

Wellbore stability predictions of stresses around a wellbore for a specific depth (left; higher compressive stress is warmer color) and the minimum mudweight to prevent collapse for any well trajectory, for a given well depth (right; warmer color is higher mudweight). These plots were developed from 1D geomechanical model data and are used for model calibration.
In this project, analytical tools were used to calibrate the 1D geomechanical model by comparing predicted well failure (track 5, far right) with failure observed in the actual wellbore from caliper data (track 4). The 1D geomechanical model input data for the wellbore stability evaluations are shown in tracks 1-3 developed from log data taken on the particular well.

Drilling Event Analysis

A necessary step in building a calibrated 1D geomechanical model is to perform the Drilling Event Analysis.

The Drilling Event Analysis is a geomechanical evaluation of drilling data (most often, daily drilling report) in which we document: pore pressure indicators (e.g., gas inflows, kicks, and drill breaks); cuttings load and geometry; instability indicators (e.g., lost circulation – well was fractured or presence of natural fractures; tight hole; stuck pipe; high torque; reaming; excessive failure in the wellbore and excess cuttings volumes; and differential sticking); instantaneous or time dependent instability events; and operational or fluid-related well events.

These data are combined and evaluated in order to calibrate/validate the 1D geomechanical model and assist in a wellbore stability analysis.

This is a typical Drilling Event Analysis plot. The x-axis represents the date, the left y-axis represents measured depth (MD) and the right y-axis represents the mudweight (often in ppg, here shown in specific gravity, SG). The dark blue curve represents the depth of the well at a given data and the dark red curve represents the mudweight for a given date. Reported drilling events (inflows, lost circulation, tight hole, etc.) are plotted at the depth and date of occurrence.
Example presentation of Drilling Events presented (rightmost track) with drilling parameters: ROP, Torque, WOB, ECD, hydraulics, fluid conditions, solids, and gas. In this case, at deeper parts of the well the fluid rheology deteriorated and the fluid hydraulics were not enough to clean the hole and remove the high volume of cavings. The  consequence was a stuck pipe. Time dependent events (during tripping) may also indicate shale instability because of fluid-rock interaction problems.