Park, Anthony¹, David Budd², Geoffrey Thyne³, Peter Ortoleva⁴
(1) Geo-Chemical Research Associates, Inc, Bloomington, IN 
(2) University of Colorado, Boulder, CO 
(3) Colorado School of Mines, Golden, CO 
(4) Lab. for Computational Geodynamics, Indiana University, Bloomington, IN

ABSTACT: Diagenesis and Mechanical Compaction in Clastic and Carbonate Sediments: Sediment Heterogeneity and Mass-transfer

The most significant porosity and permeability reducing mechanism in natural conditions is mechanical compaction, followed by diagenesis. Diagenetic alteration necessitates centimeter- to sub-kilometer-scale mass-transfer. Depth and temperature regions where these two processes dominate vary depending on sediment composition, texture, and burial history. 
A number of simulations have been carried out using WRIS.TEQ and CIRF.B simulators for several basins. Results indicate that sediment heterogeneity is a critically important geologic feature that controls the extent and timing of compaction and diagenesis. The results were compared and validated against observations. CIRF.B is a basin-scale simulator that accounts for visco-elasto-plastic rheology, fracturing, fluid flow, gas/oil generation, water-rock interactions, mass-transfer, and dynamic texture model. WRIS.TEQ is a subset of CIRF.B that simulates reservoir-scale problems. A composite medium-approach used in the programs allows simulations of mixed carbonate and clastic sediments. 
Simulation results and observations indicate that extent of mechanical compaction and diagenesis in low temperature regime is sensitive to detrial compositions, and can result in selective heterogeneity enhancement and sealing. Carbonate sediments are particularly strongly affected by early diagenesis associated with water flux history as well as compaction, while clastic sediments are more typically affected by early compaction and later diagenesis. Up to 100% of carbonate minerals may reprecipitate within first 15my of sedimentation. For clastic systems quartz overgrowth is an accessory event to early feldspar and later clay reactions. Feldspar and clay reactions are, predictably, strongly controlled by burial and thermal history. Detrital heterogeneity has a particularly strong implication on late-phase diagenesis and clay reactions.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.