Fracture Characterization and Evaluation Using Fault Likelihood Technology Reveals Sub-Seismic Deformation Zones and Reduces Drilling Uncertainties in Abu Dhabi Unconventional Plays, United Arab Emirates

Abstract

Abstract The main objective of this study is to maximize the efficiency of characterizing and evaluating naturally fractured unconventional reservoirs in the Emirate of Abu Dhabi, United Arab Emirates. Using routine 3D seismic interpretation methods in these highly fractured geological settings has previously led to the misinterpretation of seismic noise as fractures and potentially overlooking a great deal of sub-seismic detail. Consequently, a more advanced Fault Likelihood technology was used to overcome the challenges associated with this goal. This objective is intended to reduce drilling uncertainties, minimize the risk of drilling geohazards, and optimize hydrocarbon productivity in areas of dense natural fracture swarms. An advanced Fault Likelihood approach was used in this study by calculating semblance across adjacent 3D seismic traces in elongated fault-like windows at different azimuthal and dip directions. The quantified semblance values are then used to locate possible faults at low semblance values between seismic traces after integration with dip and azimuthal values. A structural coherency filter was used to smooth seismic data along the main reflection dips without altering discontinuous surfaces, including possible faults. Fault Likelihood, azimuth, and dip volumes were incorporated to obtain a tracking volume. The presence, shape, geometry, orientation, and distribution of each seismic-scale and sub-seismic fracture was possible to outline by using detailed analysis of the resulting fault likelihood volumes and visualization in the three-dimensional domain. Additionally, automatic fault extraction was applied to create more robust seismic maps of key horizons. Resultant numerous, low-uncertainty faults and fracture objects are to be used in the fault modeling workflow as part of static reservoir modeling. Results of this study are intended to be used in creating low-uncertainty, highly detailed fracture models that are of primary importance in the dual porosity nature of the unconventional reservoirs in the United Arab Emirates. Routine manual fault interpretation is a tedious and subjective process in 3D seismic interpretation. If the subject area has many fractures and faults of various scales, structural interpretation will be very time-consuming and will not identify sub-seismic discontinuities. Therefore, automated fault interpretation and extraction is a better option. Alternative methods of routine edge-detection automated fault interpretation often give generic results that can misinterpret seismic noise as genuine geological surface discontinuities while overlooking a great deal of fracture presence and distribution. To resolve this challenge, the fault likelihood approach provides a breakthrough by improving fault attribute quality using three-dimensional seismic data.