Influence of reservoir character and architecture on hydrocarbon distribution and production in the miocene of Starfak and Tiger Shoal fields, offshore Louisiana
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Reservoir properties and production performance have been assumed to be controlled by their sequence stratigraphic position and the systems tract in which they are found. This hypothesis has been tested in a dataset from two mature gas fields, located ten miles offshore Louisiana. Available data included several decades of production history, various geophysical logs of 155 wells, sidewall core and special core analyses, which provide full information on hydrocarbon distribution and type, reservoir lithology, porosity, permeability, and production characteristics. The systems tracts of the Miocene study interval (60 fourth-order and 10 third-order sequences) were characterized with thickness and net sand maps, facies interpretation, and production evaluation. The three systems tracts of the fourth-order sequences (lowstand, transgressive, and highstand) show different trends in rock properties, such as porosity, permeability, or sand content. Each systems tract can be characterized with a typical range of values for its reservoir properties. These reservoir characteristics are clearly different for each of the three fourth-order systems tracts. In contrast, the data of the third-order sequences show high variability. The values of porosity of the three systems tracts do not differ significantly from each other and prediction is impossible with high confidence. The sequence stratigraphic framework was linked to production information by (1) analyzing the average monthly production rate per perforated foot of fourth-order systems tracts and by (2) correlating to producing facies of each fourth-order systems tract. The strongest producers were found in facies of lowstand and highstand systems tracts and ranked highest. The incorporation of depositional facies interpretation into the fourth-order framework allows more detailed production estimation. Facies data also confirm the general picture of the systems tracts regarding rock properties, but they reveal differences among the facies types that could not be detected during the analysis of entire fourth-order systems tracts. One end product of this research is a database that stores all the information collected during the research, with customized search options that present a quick overview of systems tracts information. The application of this database is limited to stratigraphic units produced by similar depositional environments.