Taberner, Conxita¹, Mateu Esteban² 
(1) Institute of Earth Sciences "Jaume Almera", CSIC, Barcelona, Spain 
(2) Carbonates International Iberia, S.L, Caimari, Mallorca E 07314, Spain

ABSTRACT: Observed Patterns in Late Burial History

The studied carbonate reservoirs have recorded: standard burial cementation trend (Stage 1), hydrothermal-thermobaric alteration (Stage 2) and/or late burial corrosion (Stage 3). Stage 1 reflects a gradual temperature increase and is dominated by chemical compaction and cementation, interrupted by minor corrosion events. Large amounts of primary and near-surface secondary porosity are destroyed during this stage. 
Stage 2 is recorded as a local, sudden, anomalous influx of higher temperature, fracture-fed fluids. Two different pathways are observed: (i) hydrothermal karst with massive calcite cementation (plumose, botryoidal) or.(ii), coarse dolomite replacement, with local saddle-zebra dolomite cement. Any inherited porosity was enlarged and redistributed. New porosity is developed by fracturing, hydraulic brecciation and re-opening of stylolites. 
Stage 3 is defined by generalized corrosion of previous fabrics, interpreted as result of mixing and/or cooling of brines with organically-derived CO₂. Precipitation of variable amounts of fluorite, dickite, quartz, feldspar, sulphides and celestite is characteristic. Two different pathways are observed: (i) abundant late poikilotopic calcite or anhydrite, (ii) minor late calcite or anhydrite cements, with major porosity development. 
Diagenetic pathways of Stage 3 are largely dependant on the previous burial history and lithologies.. Stage 2 provided a preferred setting for the development of Stage 3 (i.e.: mechanical discontinuities, brittleness, conduits, barriers), but it may be locally absent. Late poikilotopic calcite cements appear related to calcitization of previous dolomites. The combination of the different stages and pathways contribute to the explanation of the present-day distribution of reservoir properties.

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