Abstract
The Nukhul reservoirs of Egypt’s Eastern Desert typically have low porosity, low permeability, and relatively heavy oil. Hence, hydraulic fracturing is key to enhancing reservoir producibility, and an understanding of fracture geometry is important to determine reservoir drainage.
To measure hydraulic fracture height at the wellbore, shear wave anisotropy data were acquired in casing with an advanced acoustic tool. Hydraulic fracturing post-job pressure matching also provided estimates of fracture geometry. Shear wave anisotropy data confirmed that the Thebes and Rudeis formations acted as fracture barriers and confirmed the fracture confinement in the Nukhul formation, which was the fracturing job objective.
Although, overall, the post-fracturing shear wave anisotropy measurement and the post-job pressure matching delivered similar results for fracture height at the borehole, the shear wave anisotropy data showed uneven levels of anisotropy across the fractured reservoir interval, indicating that the fracture might not have as simple a geometrical shape as was modeled by the post-fracturing analysis.
Based on wireline data, a newly constructed and calibrated mechanical earth model obtained detailed rock elastic properties and stress profiles. These geomechanical properties defined 26 zones across the reservoir (instead of the initial 6) and were input into the fracturing modeling software.
Fracture geometry obtained through this enhanced modeling closely matched the shear wave anisotropy results—the modeled fracture width corresponded to the variations of shear wave anisotropy observed across the fracture height. The fracture was narrower in the upper part of the reservoir and wider in the lower part, with a half-length of 300 ft in the lower part and almost 400 ft in the upper part.
In this case study, we demonstrate how full use of available data, application of the latest acoustic technology, and integration of multiple disciplines (acoustics, geomechanics, stimulation) can lead to better fracture geometry description and achievement of greater accuracy in reservoir description.
