Characterization of petrophysical flow units in carbonate reservoirs

A procedure for identifying and characterizing petrophysical flow units helps resolve some of the key challenges faced in exploration for and production of carbonate reservoirs. The application of this model reveals that one key to understanding and predicting the performance of carbonate reservoirs is to represent them as combinations of different flow units, each with uniform pore-throat size distribution and similar performance. If a relationship exists between depositional facies and flow units, one can develop a common geological and engineering zonation. Parasequences can then be characterized in terms of petrophysical flow unit types. Combining the water saturation, hydrocarbon column height, and relationships of these flow units with the interpreted sequence stratigraphy of the area provides a useful tool for mapping reservoir performance cells to predict the location of stratigraphic traps. This approach can also be useful in managing producing reservoirs to develop bypassed pay and to establish presimulation performance predictions. To illustrate this method, we use five examples: a Middle East limestone, where the model is used to identify reservoir zones with significantly different performance that are less evident from log porosity alone; the Madison carbonate of the Williston basin, where we demonstrate the potential to predict a stratigraphic trap in dolomitic grainstone; a mid-continent Lansing Kansas City moldic limestone, where the model is used to identify productive pay below zones with high water saturation in wells without modern logs or core; a San Andres dolomite from the Howard Glasscock field in the Permian basin, where bypassed pay potential is identified within a mature production setting; and in another Permian basin example, interpretation of the Cisco dolomite at Dagger Draw field demonstrates how to use the model in a secondary porosity reservoir to help identify parasequences and to predict an oil-water contact.