Fiona Whitaker¹, Anwar Al-Helal¹, and Yitian Xiao²
¹Department of Earth Sciences, University of Bristol, Bristol, England
²ExxonMobil Upstream Research Company, Houston, Texas, USA
Reactive transport models (RTMs) can provide a comprehensive, quantitative and ultimately predictive treatment of diagenetic processes, and their effect on flow behaviors and recovery in carbonate reservoirs. They allow simultaneous integration of the major regulatory processes responsible for fluid-rock interaction across a wide range of time and space scales, and can bridge the gap between fundamental, process-oriented research and applied research. Here we explore opportunities offered by RTM, informed by our recent simulations of dolomitisation and associated diagenetic reactions.
A major strength of RTMs is that they integrate experimental, observational, and theoretical knowledge about fluid flow and reactions. Whilst operation of these processes in shallow modern systems can be constrained by field data, reconstructing diagenesis in ancient carbonates constrained by a limited number of vertical wells is rather more challenging. Using carefully designed suites of RTM simulations enables reduction of this uncertainty by quantitative assessment of both the relative importance of the various forcing mechanisms on the system behavior and the sensitivity of an environmental system to changes in any of these forcing processes.
RTMs allow us to explore the complex interplay between competitive reaction-transport processes controlling the operation of the diagenetic system. Thus we can evaluate the combined effect on mineralogy and the pore system in a manner which is difficult using and field and experimental data alone. Thus, where the permeability structure permits sufficient fluid flow, dolomitisation preferentially affects fine grained sediments with higher effective reactive surface area. However, as flow rates decline, reactions become focused in the more permeable although less reactive components of the system. High resolution simulations at the inter-well scale demonstrate how spatial variations in sediment texture result in diagenetic geobodies with complex geometries, reflecting a balance between supply of reactive fluids and reaction rate, and quantifies the impact of these changes on water breakthrough and hydrocarbon recovery
By considering the inherently complex dynamics of water-rock interactions in carbonate systems, RTMs can assist in improving the predictability of the spatial and temporal heterogeneities of diagenesis in carbonate rocks. Specifically, they can provide a platform for developing better conceptual models and hypotheses, and also generate predictions of diagenetic trends and geobodies which can be used to populate reservoir models.
AAPG Search and Discovery Article #120034©2012 AAPG Hedberg Conference Fundamental Controls on Flow in Carbonates, Saint-Cyr Sur Mer, Provence, France, July 8-13, 2012