Page 42 - Geology of Carbonate Reservoirs

Influence on Reservoir Performance Large pores may have major impact on reservoir porosity, but connectivity may be poor; fabric similar to “ vuggy ” porosity formed by dissolution diagenesis; recovery efficiency may be poor Shrinkage and fenestral pores may have major impact on total porosity but permeability may depend more on “ matrix ” pore

Environmental Association Reefs, algal and microbial mats in intertidal or subtidal zones, and in detrital carbonates with high content of large bioclasts forming shelters Subaerial exposure surfaces as in supratidal zone, perimeter of water bodies, intermittent lagoons, playa lakes, etc.; commonly associated with evaporites in arid climates; and with

Descriptive Characteristics Voids (pores) of irregular size and shape formed by organic growth in reefs, voids conforming to size and shape of skeletal component, as sheltered beneath a bivalve shell, or algal – microbial laminae Broken laminae in lime mudrocks and algal laminated carbonates; meter - scale polygons with mudcrack boundaries; irregular, wrinkled lami

Sedimentary Structures Constructed voids, shelter voids, skeletal growth fabrics, and patterns of organic lamination (e.g., algal laminae); includes Stromatactis cavities Mud cracks, desiccation polygons (related to “ teepee ” structures), desiccation wrinkles in algal laminae, and fenestral or bird ’ s - eye fabric uid Contorted bed

Formative Processes Biological growth patterns Desiccation Slope failure and uidization Compaction

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