Compaction of Basin Sediments as a Function of Time-Temperature History

James W. Schmoker, Donald L. Gautier

Processes that affect burial diagenesis are dependent on time-temperature history (thermal maturity). Therefore, the porosity loss of sedimentary rocks during burial may often be better treated as a function of time-temperature history than of depth. Loss of porosity in the subsurface for sandstones, carbonates, and shales can be represented by a power function ^phgr = A(M)^B, where ^phgr is porosity, A and B are constants for a given sedimentary rock population of homogeneous properties, and M is a measure of thermal maturity such as vitrinite reflectance (R_o or Lopatins's time-temperature index (TTI).

Regression lines of carbonate porosity and of sandstone porosity upon thermal maturity form an envelope whose axis is approximated by ^phgr = 7.5(R_o)^-1.18 or, equivalently, by ^phgr = 30(TTI)^-0.33. These equations are preliminary generic relations of use for the regional modeling of both carbonate and sandstone compaction in sedimentary basins.

The dependence of porosity upon time-temperature history incorporates the hypothesis that porosity-reducing processes operate continuously in sedimentary basins and, consequently, that compaction of basin sediments continues as long as porosity exists. Calculations indicate that subsidence due to loss of porosity through time (with depth held constant) can produce a second-stage passively formed basin in which many hundreds of meters of sediments can accumulate and which conforms with the structure of the original underlying basin. Such sediment accumulation results from the thermal maturation of thick sequences of sedimentary rocks rather than from global sea level change or tectonic subsidence.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.