Print this pageFault Influence on fluid Flows and Reservoir Diagenesis
LEE, M., J. LEWANDOWSKI, and K. KRONMUELLER
We present an integrated methodology for reservoir heterogeneity study in complex geological settings. In the study area, the quality of reservoirs is heterogeneous, and is jointly influenced by facies, structural and diagenesis.
The main producing sands of the study field are the Schneverdingen, the Dethlingen, and the Wustrow within the Upper Rotliegend (Lower Permian) in NW German Basin. Although the Schneverdingen is mostly located in the water zone, it has the best quality and is currently the best producer of the field. A high degree of reservoir heterogeneity exists for both Wustrow and Dethlingen sands, but could not be correlated with facies alone.
Detrital grains of the Wustrow and the Dethlingen were altered more extensively in samples near the EW trending, fractured/faulted transfer zones than in samples near the graben center. Four alteration zones are recognized, where cement compositions change gradually. Integrated evidence shows the effects of acidic, highly evolved, and CaCl[2]-rich saline fluids during cementation at temperatures around 140 to 170 degrees C. During two separate episodes, peaked at around 205 and 180 MA, diagenetic fluids entered the reservoir through fractured fault-transfer zones, and altered nearby Wustrow and Dethlingen sandstones. Away from the entry zones, sandstones in the paleo-HC zones were protected from further alteration. The Schneverdingen suffered only limited alteration due to the fact that the sands were sealed from lateral fluid movement by tight fanglomerates which extended into the fluid entry zone. Timing of the two events can be correlated to active rifting on the both sides of early Atlantic ocean and in NW Europe, when hydrothermal fluids were active.