--> Abstract: Early Karstic Porosity Development or Late Burial Related Corrosion in a Middle East Giant Field (Natih Fm; #90063 (2007)

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Early Karstic Porosity Development or Late Burial Related Corrosion in a Middle East Giant Field (Natih Fm., Oman): Implications for Reservoir Properties Distribution

 

Taberner, Conxita1, Volker C. Vahrenkamp2, Cathy Hollis3, Mateu Esteban4, Alia Bahry2, M. Rejas5, Mike Caputi6, Abhijit Mookerjee7, Yaduo Huang6, Peter Eadington8 (1) Shell International Exploration and Production B.V, Rijswijk (ZH), Netherlands (2) Petroleum Development Oman, Muscat, Oman (3) Shell International E&P, Rijswijk, Netherlands (4) Carbonates International Iberia, S.L, Caimari, Mallorca E 07314, Spain (5) Institute of Earth Sciences, CSIC, Barcelona, Spain (6) Shell International Exploration and Production, Rijswijk (ZH), Netherlands (7) Petroleum Development Oman, (8) CSIRO Petroleum, Kensington, WA, Australia

 

Porosity and permeability distribution in Natih Fm. carbonate reservoirs (North Oman) has traditionally been interpreted as resulting from recurrent subaerial exposure at the top of several reservoir layers and major exposure at the top of the Natih Fm. In this scenario, reservoir properties should follow top to bottom distribution patterns, layer conform or disruptive. This interpretation was mostly based on limited available diagenetic information and was model driven, as core recovery was poor especially in high production intervals. A significant shift in the interpretation of the reservoir properties distribution was proposed during the last few years based on better core recovery during a recent coring campaign: 1) early diagenesis related to subaerial exposure actually caused cementation at the top of reservoir units; while 2) extensive porosity was created below cemented cycle tops later during the circulation of late burial corrosive fluids. The stacking of small-scale cycles composed of bed-bound fractures in cemented layers and extensive leaching right below these layers has created high permeability zones with significant impact on reservoir behavior. This finding is corroborated by a variety of evidence from cores, petrographic observation and detailed geochemical analysis. Key factors for the shift in the conceptual model are: 1) continuous core recovery, 2) multi-disciplinary core workshops and 3) integration of results (sedimentologists, petrophysicists, reservoir engineers) and groups (PDO, SIEP, Universities and vendors). Main target of ongoing diagenetic work is to constrain parental fluids and plumbing systems to lead to a better prediction of porosity and permeability distribution in the reservoir.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California