A Multidisciplinary Workflow to Detect Fractures at Multiple Scales by Integrating Borehole Images, Core and Seismic Data, Case Studies From Saudi Arabia

Abstract

Detection of fractures and their orientation within reservoirs can significantly impact field development and well placement, but cannot be achieved by a single discipline or measurement. Seismic techniques can detect fracture corridors between wells. Seismically-derived fracture information complements information from borehole image logs and core but is often inconclusive because of limited vertical resolution. Borehole image logs provide continuous high vertical resolution detection of fractures near and around wellbores. Core data helps determine fracture geometry, fracture frequency and fracture fill. Therefore, a rigorous workflow for integrated interpretation of seismic, borehole image log and core data to detect fractures at multiple scales must accommodate the limitations of each technique. We applied this workflow to a low permeability Jurassic carbonate reservoir comprising shelf-margin clean limestones from onshore Saudi Arabia to detect subvertical fracture zones. The dip magnitude and orientation of the fracture clusters detected on borehole image log and core is consistent with NNW-SSE Najd fault trend striking fracture corridors identified on seismic. Most natural fractures detected on image logs and cores dip steeply (~75°) and might be extensional in origin, few compaction and tectonic stylolites are observed. Application of this workflow to Cretaceous carbonates from offshore Saudi Arabia detected medium to low density fracture corridors with high uncertainty from the relatively poor quality seismic data, however borehole image logs and cores (unslabbed core and 360 core scan) revealed NW-SE Zagros fault trend, vertical to sub-vertical mineralized and partially mineralized natural fracture clusters. These two example encompass 9 wells with a total of 16786 ft of borehole image data, 1352 ft of core and 700 sq km of seismic data. These results demonstrate that a multidisciplinary workflow achieves more accurate detection of fracture occurrence and orientation. By detecting and separating different fracture orientations using borehole image log and core data, this workflow helped clarify several poorly-understood structural fracture trends that had been detected by seismic interpretation. We infer that the three methodologies are consistent and give a reliable view of fracture detection at multiple scales. The workflow is valid for conventional and unconventional reservoirs, but the latter requires geomechanics and microseismic inputs.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017