One major challenge of integrating borehole image and geophysical measurements is to bridge the gaps between their dissimilar horizontal and vertical resolutions and depth of investigation. Identifying and characterizing geological features like bedding contacts and fractures, by combining high-resolution Borehole Imaging (BHI) with Deep Shear Wave Imaging (DSWI) technology, helps to overcome this challenge. It reveal sub-seismic features in the reservoir section that ultimately lead to a more accurate structural model of the subsurface.
In this paper, we present a case study showing the full integration of both imaging methods. Picked reflectors in the deep shear wave image allow correlation with corresponding geological features on the borehole image. Identifying the dip and azimuth of a reflector from the measured orientation of the corresponding feature on the borehole wall enables the rotation of the tool reference frame to be aligned with the sagittal plane from the deep shear wave image (i.e., the plane in which the reflection occurs. Note that the strike of the reflector equals the azimuth of the sagittal plane). With this borehole image-based adjustment the sagittal plane of the deep shear wave image is shown at its correct azimuth and therefore positioned "correctly" in the subsurface. Accordingly, our understanding and interpretation of the DSWI result improves significantly. Although this azimuth can also be obtained via the four component DSWI data (Tang 2004), this is not always as robust as the method proposed here. However, if possible, it is good practice to compare both methods, also because an "event" picked from a borehole image log does not necessarily have to coincide with a similar event in the DSWI image. The borehole image event may not continue away from the wellbore and/or the resolution of this borehole image event is far above the DSWI resolution.
High-resolution borehole images are suited to identify fractures, bedding, dip and azimuth information, facies types and other properties along the borehole. Besides coring, this evaluation method reveals the highest resolution geological details, resolving features down to circa 0.2 inch (Paillet et al. 1990). However, due to their small wavelength (in the sub inch scale) ultrasonic waves, for example, are strongly affected by attenuation when propagating into the formation. Consequently, this method does not allow for the imaging of geological features away from the wellbore, but is optimized for the identification at the borehole wall.
