--> Abstract: Predicting Fault Controlled Diagenesis and Porosity/Permeability Evolution in Rotliegendes Reservoir, Germany: Insights from R; #90063 (2007)

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Predicting Fault Controlled Diagenesis and Porosity/Permeability Evolution in Rotliegendes Reservoir, Germany: Insights from Reactive Transport Models

 

Xiao, Yitian1, W. L. Esch2, Joann E. Welton1, R. E. Klimentidis1, Pete Rumelhart1 (1) ExxonMobil Upstream Research Company, Houston, TX (2) ExxonMobil Exploration Company, Houston, TX

 

We developed reactive transport models (RTM) to predict the distribution of illite in the Rotliegendes tight gas play and to assist with reservoir management strategy. One proposed diagenetic model for the Rotliegendes reservoir is the “fault controlled illitization” model. This model suggests that penetration of the Rotliegendes sequence by acidic hydrothermal fluids from Carboniferous coal seams produced a zoned clay mineral halo around tectonic and stratigraphic Rotliegendes and Carboniferous contacts that is partially responsible for the poor reservoir quality.

 

We developed RTMs to predict the spatial distribution of K-feldspar, quartz, illite, kaolinite, and porosity/permeability evolution in the Rotliegendes reservoir. We investigated the effects of key natural variables on Illite formation and distribution. These variables include initial mineralogy, fluid chemistry, K, Al and SiO2 sources, temperature, fluid migration, and the location of open faults and fractures.

 

Our results are consistent with the proposed “fault-controlled illitization” model and field observations. Our results demonstrate that moderate amounts of K-feldspar (~10%) can provide sufficient K, Al, and SiO2 for illite, kaolinite, and quartz cementation. Additionally, sufficient fluid flow (> 1 cm/yr) and temperature (> 100 oC) are required to drive K-feldspar dissolution and illite formation. The diagenetic zonings are predicted to be closely associated with fluid-flow pathways emanating from faults and fractures. More acidic fluids cause faster illitization and more kaolinite formation near the fault zone. Closed faults serve as flow barriers and should not have an associated alteration halo.

 

Coupled with basin models, RQFM, and well observations, RTM can significantly improve our capability to fully evaluate all controls that influence reservoir quality.

 

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