"Modeling in Carbonates: Where is the geology?"
ExxonMobil Upstream Research Company, Houston TX
Building reservoir models in carbonate reservoirs that can support reliable predictions of future reservoir performance is a well acknowledged difficulty in our industry. The complexities unique to carbonate reservoirs provide a set of challenges quite different from those in siliciclastic reservoirs. The impact of diagenesis on rock properties and reservoir geometry and continuity is complex. Additionally the impact of natural fracturing on flow behavior represents a level of complexity which is typically beyond our means to adequately describe and predict. The focus of this paper is on matrix dominated systems and will not fully address the impact and complexity of natural fracturing.
Current industry practices for carbonate reservoir characterization and modeling fail to adequately define the distribution and continuity of the permeability extremes. The ability to both map and predict the continuity of low permeability barriers to flow and the high permeability flow conduits is not an EXPLICIT output of our work flows. Rather we tend to assume that by providing detailed interpretations of rock fabric, stratigraphic architecture, EOD geometries, rock typing, petrophysics etc. we will end up with a “good” model.
When we examine modern analogues and outcrop analogues and we compare these to our geological models created using geostatistics, we see very different expressions of geometry and continuity. We have become so accustomed to looking at these geostatistical models that we no longer find them to be either unacceptable or geologically unreasonable. We should not accept these representations and we need to work towards developing capabilities to better capture our geological concepts and interpretations in our 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