--> Linking Diagenetic History of Upper Cambrian Microbial Buildups to Genetic Pore Types, and Computed Tomographic Responses From Pore to Core, and Log Scales
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Linking Diagenetic History of Upper Cambrian Microbial Buildups to Genetic Pore Types, and Computed Tomographic Responses From Pore to Previous HitCoreNext Hit, and Previous HitLogNext Hit Scales

Abstract

Abstract

The pre and post salt carbonate reservoirs offshore Brazil contain large oil and gas reservoirs in microbialite facies. Very few microbialite outcrop exposures can be studied in three dimensions in the field. However, it is the case for a series of world class, newly accessible outcrops on Eagle Ridge Ranch in Mason county (Texas), where microbial well-organized build-up architecture, can be observed in multiple exposures on several pavements and cliffs along three different rivers. The outcrops generally, but not always, include three distinct phases of microbial growth, directly or indirectly interacting with the sediment accumulating between the buildups. This study aims to contrast and quantify the extent of diagenetic alteration throughout the build-up growth phases, from their initial establishment on a transgressive flat pebble lag, vertical growth and lateral expansion, and ultimate demise. Then, rock type based on Previous HitporosityNext Hit, Previous HitpermeabilityNext Hit, and the volumetric fraction of either diagenesis, depositional or fracture porosity, and mineralogy. Diagenetic mineralogy is based on the assumption that dolomite and pyrite are diagenetically precipitated, while calcite can be primary or secondary and will be described through thin section petrography. The extent of diagenetic alteration is measured from the pore scale and upscaled to the whole core scale using high resolution micro computed tomography (CT). This method quantifies the volume fraction of different pore types and mineralogical phases, and is used in upscaling to the effective atomic number (effAT#) logs generated from dual energy CT. Dual energy can be used to determine the relative distributions of calcite versus dolomite. The effAT# log lends itself to form a diagenesis log by linking the extent of diagenetic alteration, at a given depth, to the respective atomic number reading. At those depth locations, Previous HitporosityNext Hit and Previous HitpermeabilityNext Hit measurements help to link reservoir quality to degree of diagenetic alteration. The extent of diagenetic alteration at locations not sampled by CT scanning is determined via interpolation between samples using the effAT# log. Diagenesis, mineralogy, Previous HitporosityNext Hit, and Previous HitpermeabilityNext Hit logs are then generated as ultimate results of this study. This approach will yield a rock typing method that takes into consideration the extent of diagenetic alteration, Previous HitporosityNext Hit and Previous HitpermeabilityTop, while relating these measurements from the pore to core, and well log scales.