New High-Definition Microelectrical Images Shed Light on Complex Paleozoic Nubian Sandstone Reservoir

Haddad, Elie; El-Defrawy, Nadia; Hussein, Mohamed; Hassan, Ahmed; Laronga, Robert J.; Hassan, El-Said; Nassar, Mohamed

The Ras Budran oilfield, operated by Suez Oil Company, was first discovered in 1978 and lies approximately 2.5 mi off the Sinai coast of the Gulf of Suez. Oil is produced from three units of Nubian Formation sandstone from a depth of 11,000-12,000 ft (3,352-3,657 m). The lower unit, of Paleozoic age, averages 10% porosity and has up to 200 md in-situ permeability. However, multiple sedimentary and diagenetic facies present within the unit result in large variations in porosity and permeability at both wellbore and reservoir scale, and make it unreasonable to consider the unit as a single hydraulic zone. Unfortunately it is impossible to recognize these facies from the evaluation of standard petrophysical logs, which have been the norm in Ras Budran until recently.

To shed new light on the problem, a new high-definition microelectrical imaging tool was logged in RB-B13 and yielded the first-ever high-resolution images of Nubian Sand, despite the well having been drilled with non-conductive oil-base mud (OBM). While microelectrical imaging technology adapted for the OBM environment has been available for the last decade, the spatial resolution, coverage, and sensitivity to formation texture offered by these devices is not sufficient for detailed evaluation of structural, sedimentary, and diagenetic features present in the field. The new high-definition imager is based on the physical design of the industry-standard imager for conductive water-base mud (WBM) and thus features the same high spatial resolution and coverage. All-new electronics featuring improved signal processing and a higher signal-to-noise ratio extend the use of the new tool to the OBM environment under specific, favorable conditions that are present in Ras Budran.

Based on formation sedimentary and diagenetic features clearly observed in the high-resolution images, six facies were clearly identified and classified over the entire sand unit, resulting in accurate flow unit delineation. Further studies presently aim to link facies to porosity-permeability relationships. In addition, multiple fracture sets were identified and interpreted as mineral-filled, implying influence as permeability baffles.

Interpretation of high-resolution formation images has allowed the operator to establish an understanding of this Nubian Sand reservoir's complexity in terms of fracturing and diagenesis. The insight gained positively impacts the operator's completion and enhanced oil recovery strategy.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013