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Previous HitPredictingNext Hit Previous HitPorosityNext Hit Reduction as a Function of Time, Temperature, and Burial Depth

WAPLES, DOUGLAS W., and HIROMI KAMATA, Japan National Oil Company, Chiba, Japan

Functions Previous HitpredictingNext Hit Previous HitporosityNext Hit reduction normally are dependent only on burial depth for a given rock type. However, this purely empirical approach lumps together the effects of several different Previous HitporosityNext Hit-reducing processes, some of which may depend on additional factors. Much of the Previous HitporosityNext Hit reduction in older rocks in particular is due to time- and temperature-dependent diagenetic reactions.

We have developed an empirical equation to take into account the Previous HitporosityNext Hit-reducing effects of seven different processes in limestone, shale, and Previous HitsandstoneNext Hit: repacking of grains, crushing of microfossils, ductile grain flow, pressure solution, welding following pressure solution, clay diagenesis, and cementation by minerals precipitated from moving fluids. Previous HitPorosityNext Hit reduction in limestone uses five of these processes, shales use three, and sandstones use six.

We have determined preliminary default values for the various constants in these equations for each lithology. The user need only specify the lithologic composition of the rock (including fraction of lithic + clay components for sandstones) and the relative availability of calcium carbonate and silica in pore fluids for cementation.

Our Previous HitporosityNext Hit-reduction equation can easily be incorporated into existing numerical basin models. This method should provide more accurate estimates of true porosities (and hence permeabilities) in a wide variety of basins than the current depth-dependent functions, which require local calibration.

Our model only attempts to account for the regular progression of Previous HitporosityNext Hit reduction as an aid in basin modeling and is not designed to predict anomalous events or to account for natural data scatter within a single lithologic unit. Since Previous HitreservoirTop characteristics are often strongly influenced by anomalous or local events, we do not recommend the use of our model to predict production characteristics of specific reservoirs.


AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)