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Abstract

Unconventional Borehole Seismic Services encompass techniques that go beyond conventional seismic methods like generation of a seismic trace (like Density+ Sonic calibrated with a Check-

shot, and Z-VSP), seismic images 2D and 3D (like the O-VSP, Walk away-VSP, and 3D-VSP). In all of them, the acquisition tool is inside the well and the sources are on the surface.

These unconventional services include:
I) Walk Away VSP for AVO Calibration (Amplitude Variation with Offset): This technique

involves placing sensors close to a specific geological horizon (sources are at regularly distributed in one azimuth). Its primary purpose is to calibrate Amplitude Variation with Offset responses obtained in Surface Seismic.

II) Walk-around VSP for the detection of Horizontal Transverse Isotropy (HTI) anisotropy in formations. This technique places the tool close to a specific geological horizon (sources are regularly distributed at constant distance to the well). It is a method used to gain information about the formations anisotropic behavior, being important for reservoir characterization and drilling decisions.

III) Borehole Acoustic Reflection Survey (BARS): BARS is designed to image reflections near the wellbore. It typically employs a Sonic Scanner tool, which emits acoustic waves and records their reflections from the surrounding formation. By extending the distance between the tool and the far monopole, BARS can capture reflections from greater distances away from the well.
IV) X-Well Survey: This technique is used to establish correlations between two different wells. It involves placing seismic sources in one well and sensors (geophones) in another well. By analyzing the travel times of seismic waves and the recorded data, geoscientists can determine velocity changes and identify reflections. X-Well Surveys are valuable for imaging and characterizing subsurface features between the two wells.

V) Microseismic Monitoring: Microseismic monitoring is employed to track the development of hydraulic fracturing (fracking) operations. During fracking, fluid is injected into a treatment well to stimulate the extraction of hydrocarbons. This process generates microseismic events (small earthquakes) in the rock formation. Sensors placed in monitoring wells detect these microseismic events, allowing operators to map the growth of the fracture network, assessing the effectiveness of the treatment.