Abstract Lower Cretaceous skeletal and non-skeletal carbonate sands associated with mud-dominanted, caprinid rudist mounds comprise much of the reservoir facies of the Black Lake Field in central Louisiana. Porosity and permeability distribution within the sand facies is controlled by the original depositional setting and resultant sediment fabric, and the subsequent strati graphic and diagenetic history. The dominant porosity type associated with the sand facies is primary interparticle, and the major porosity occluding mechanism is the presence of a mi critic matrix. Other porosity occluding mechanisms include minor cementation and compaction. Deposition of thick overlying shales, along with updip lagoonal muds, apparently formed a diagenetic seal in the Black Lake Field. This seal prevented the downdip migration of calcite cementing meteoric fluids from entering the reservoir, and resulted in the preservation of most primary interparticle porosity within the carbonate sand facies.

Abstract The Guayanilla superhighway outcrop section of southwestern Puerto Rico offers an unusual chance to examine the development and diagenesis of an Oligocene fringing reef and carbonate platform. The stratigraphic section embodies a complex sequence of three cycles of reef development. Reef cycle 2, some 48 m (150 ft) thick, comprises the development of a major fringing or barrier reef at this locality. Reef growth in cycle 2 was inhibited by intermittent ecological stress, perhaps by upwelling colder waters, so that rhodolite-paved ramps replaced shelf margin framework. Tectonic downwarp drowned the reef tract, replacing it by deep open shelf conditions, but a shallowing cycle due to uplift led to establishment of a third cycle of reef growth. Despite the substantial thickness of reef framework, reservoir quality porosity and permeability are low, primarily due to pervasive lime mud matrix. The paleoecological and sedimento-logical models derived from a study of the Guayanilla reef sequence will serve as a standard of comparison for other Tertiary reefs, both in the subsurface and surface.

Abstract Coring of the Mariana Limestone on the Orote Peninsula of western Guam has created an opportunity to examine in detail the porosity evolution of a Pleistocene reef complex. Four cores acquired for study are composed predominantly of skeletal packstones, grainstones, and rudstones, with only minor bound-stone development. Deposition occurred within the reef-flat to proximal back-reef sand apron facies. Considerable primary interparticle and intraparticle porosity has been occluded by multiple-generations of submarine cementation and internal sediment infilling within the marine environment. In some instances, multigenera-tion, radiaxial to radial fibrous, Mg-calcite, isopachous rim cements have completely occluded all primary interparticle porosity within a Halimeda /coral rud-stone to Halimeda grainstone microfacies. Further porosity reduction has resulted from the precipitation of blocky and dog-tooth sparry calcite cement under freshwater meteoric conditions. Minor, secondary biomoldic porosity developed from the preferential dissolution of aragonitic Halimeda plates and some coral and molluscan debris within the meteoric realm. Study of the Mariana Limestone indicates that considerable porosity reduction may occur within the marine environment of many reef complexes. Only through significant leaching, dolomiti-zation, and fracturing, can such complexes be rendered porous.