Shear Velocity Analysis From Challenging Near-Offset VSP Survey Used to Understand Subsurface Mechanical Properties

Process the zero offset vertical seismic profile (ZVSP) data and estimate the shear velocity (Ps) from already acquired zero offset VSP data.

In an offshore well, Weatherford experts deployed the SlimWave™ tool to conduct a ZVSP survey. This involved deploying four arrays of three-component geophones in the borehole and an air gun source at the surface.
The vertical seismic profiles with the source located near the wellhead (zero offset VSP) are a useful tool for 1D study of compressional waves (Pp) and shear waves (Ps).
The mode conversion in the subsurface generates shear waves with sufficient amplitude and it can be identified and picked for velocity analysis.
A Hodogram analysis was performed to obtain the shear velocity and maximize shear wave energy, and the reorientation of horizontal X and Y components into horizontal maximum (HR) (or radial component) and horizontal minimum (HT) (or transverse component) was performed.
Weatherford experts then used the HR data with the vertical component data (Z) to estimate the down going shear wavefield by using a parametric wavefield separation.
The shear moveout was picked and measured the lateral displacement of shear wave arrivals on the shear wavefield seismic data. Good correlation was observed between the compressional and shear velocities.

Weatherford’s VSP shear processing provided a shear velocity (Ps) profile from zero offset VSP data and its non-rig related product as well as its additional product of zero offset VSP.
The shear velocity profile helped geophysicists and geologists understand the subsurface mechanical properties of the earth by using shear velocity along with compressional velocity.
With this data, the customer was able to calibrate the shear slowness to generate the shear synthetic seismogram to study the geological structure around the borehole.

Details

Location

Middle East

Well Type

Offshore, development

Hole Size

8-1/2 in.

Casing Size

13-3/8 in. at 2,995 ft (912 m)

Measured Depth

3,865 ft (1,178 m)

Products/Services

MARS™