Bridging Scales of Fracture Characterization Through Conventional Log Measurement
Authors:   Sonatrach, Benaida Amar , Cherif Nadjib ,   Sonatrach, Bouzida Yasmina ,   Baker Hughes, Zhunussova Gulzira Z. ,   Baker Hughes, Riou Jeremy ,   Baker Hughes, Salter Tim ,   Baker Hughes, Caeneuve Eduardo A. ,   Baker Hughes
Published: October 2022

Resistivity and acoustic near-wellbore characterization techniques are increasingly used to provide structural definition and fractures identification. The two log types are complementary, often showing ability to compensate for borehole conditions and lithology uncertainty. Image logs have a limited depth of investigation, and it is appealing to be able to link the detailed wellbore information to other lower resolution imaging such as seismic. By using dipole shear acoustic measurements like Deep Shear Wave Imaging (DSWI), it is possible to identify features (azimuth and dip) in the near-wellbore region, in many cases up to 100 to 110ft (depending on formation properties). With this new information that helps to bridge the scales between Borehole Imaging (BHI) and seismic, it is feasible to build a hierarchy model of the main events to better characterize the reservoir, this will provide the understanding of their chronological importance order and its role on the producibility of these wells. A case study is presented from the Ordovician Age, Hamra Quartzites of SE Algeria. Data was acquired in two horizontal wells, drilled parallel to each other. The objective was to reduce the uncertainty on structural characterization by combining both BHI and the DSWI to augment their strengths and offset their individual tool limitations. Although BHI logs present a very detailed image of the events that are cutting the borehole and can be comparable to core data, its measurement is very shallow, while the DSWI it has a deeper depth of investigation, but low detail compared with BHI. Another benefit of integrating DSWI is to detect features that are not intersecting the wellbore and cannot be captured by BHI. The main challenge was to understand and quantify the log response of different features seen on each measurement sets and so attribute them to a sub-seismic feature. Geomodelling software allowed for 3D visualization, correlation of the results and interpretation. The image log observations which are wellbore centered are combined with DSWI observations up to 100ft away in these wells. It is observed that those depth intervals commonly with reduced image quality (hindering traditional image-based dip picking), were near vertical fracture corridors intersecting the borehole and extended at least 60ft away from the boreholes. DSWI has also confirmed stratal boundaries matching image features that also display shear movement and possible fault drag away from the borehole, so identifying likely fault zones. In addition, based on the gas index, mud losses and open-hole data it seems that the lithology has a significant control on the fracture properties and plays a significant role in controlling their producibility. The data integration process provide insight for the asset team to propose hierarchical reservoir characterization model. Likewise, beyond the fact that DWSI bridges the scale between BHI and Seismic, it has confirmed the existence of BHI fracture clusters and their spatial extension.