TI elastic-property inversion on basis of walk-away VSP and full waveform sonic

Donald, J. Adam (Schlumberger) | Jocker, Jeroen (Schlumberger) | Leaney, Scott (Schlumberger) | Dasgupta, Suvodip (Schlumberger) | Van Kleef, Franciscus (ADNOC Offshore) | Brindle, Frank (ADNOC Offshore)


The effect of anisotropy on sonic measurements within layered formations has an impact in geomechanics and geophysics workflows. A new single-well workflow is presented that uses a probabilistic approach using prior information to provide a complete continuous characterization of the transverse isotropic (TI) parameters. The workflow applies to any well orientation or structural dip and yields results that are consistent with prior information from offset wells, core measurements or walk-away vertical seismic profile (VSP) results.

Analysis of single-well sonic measurements is predominately done using deterministic models for which the orientation of the measurements must be aligned with the layering; in other words, vertical or horizontal (not deviated) wellbores must be used for flat structural dip. In addition, such models depend on strict assumptions for using the measurements to predict the missing parameters because there are not enough measured slownesses in a single well to determine the five independent moduli. Multiwell models depend on variable well orientations, usually where a combination of a vertical with multiple deviated wells are needed to characterize the relative change in slowness with dip for each associated slowness. Often, the acoustic anisotropy must be determined before these deviated wells are drilled and evaluated to impact well placement, drilling design, or stimulation plans.

The approach demonstrated herein uses prior information of TI elastic properties to determine a consistent model at each depth. The inversion uses all sonic slownesses, compressional, fast and slow shear, as well as Stoneley shear along with the fast shear azimuth and density to provide a continuous output of either stiffness moduli or velocities at each depth. The prior information can be from multiple sources such as core tests (dynamic or static), borehole seismic survey results, offset well data, or a public core database.

A case study from an offshore field in Abu Dhabi, UAE, is presented to demonstrate this new workflow using sonic and walk-away VSP data for input to velocity model calibration for prestack depth migration. Understanding the impact of anisotropy on wellbore stability calculation for adjacent fields is also of interest.

Presentation Date: Thursday, October 18, 2018

Start Time: 8:30:00 AM

Location: 205A (Anaheim Convention Center)

Presentation Type: Oral