Print this pageSediment Diagenesis Simulation Using Open and Closed System Water-Rock Interactions Simulators NEWKIN and DIAPHORE II: The Brent Group Sandstone, North Sea Example
PARK, ANTHONY J., OLIVER BILDSTHIN, and ETIENNE BROSSE
The simulators NEWKIN and DIAPHORE II and their applications to the diagenesis problems encountered in reservoirs are presented. NEWKIN is a one-cell type of a water-rock interaction program implementing kinetically controlled slow mineral-water reactions coupled with fast, equilibrium reactions among aqueous species. It can be run in either a closed-system or an open-system configuration. The simulator DIAPHORE II is a multi-dimensional simulator based on NEWKIN and a reservoir engineering simulator, and was developed to address the mass-transport and water-rock interaction phenomenology associated with diagenesis in reservoir-scale systems.
Both NEWKIN and DIAPHORE II were used to model the diagenesis of the Brent Group sandstone reservoirs of North Sea. It was originally assumed that the water compositions may provide much needed key for differentiating among different diagenetic paths a sediment may experience. To visualize this the activity-activity diagrams were used to monitor the evolution of the water compositions. Although based on equilibrium-condition reactions, these diagrams provide the necessary reference fields of chemical behavior where the progress of the non-equilibrium systems can be compared.
Thus, the simulators were used to study the varying behaviors of the water by changing the initial fluid compositions. Simulations using NEWKIN provided straight-forward pathways of water composition change. With the results of DIAPHORE II, the use of activity-activity diagrams demanded more in-depth understanding of the different mechanisms active in different regions of the system due to the open-system conditions and the non-uniform mineralization patterns.
Other simulations were carried out where the reaction rate constants were altered selectively, and was found to have very strong influences on diagenesis pathways in closed-system simulations while having less significant effects in open, multi-dimensional system simulations.
Given above observations the next task is to correlate the water composition evolution histories with the petrographic observations. It promises to be a difficult task, but when accomplished, it may provide much needed insight into how two reservoirs of the same original compositions and slightly different present-day water compositions might have experienced two different paragenetic histories.