Shorelines move in response to the balance of geodynamic processes acting on sedimentary basins; thus the stratigraphic record of shoreline migration is an important tool for reconstructing climate, tectonic, and eustatic histories from ancient deposits. Here we test whether subsidence geometry influences shoreline migration in response to sea-level change by comparing two physical experiments conducted in the Experimental EarthScape (XES) basin. The experiments had similar sediment supply, subsidence rate, and sinusoidal sea-level cycles, but one experiment had a fore-tilted subsidence profile, where subsidence rates increased with distance from the sediment source (similar to a passive-margin setting) and the other had a back-tilted subsidence profile, where maximum subsidence was close to the sediment source with subsidence rates decreasing downstream. In the recent back-tilted experiment, decreasing subsidence rates downstream resulted in a tendency for shoreline regressions to self-amplify during base-level fall, whereas increasing subsidence rates upstream caused a rapid shoreline retreat during base-level rise, causing amplified shoreline fluctuations during sea-level cycles compared to the previous fore-tilted experiment. These results indicate that the spatial pattern of subsidence in a basin has a significant effect on shoreline migration in response to eustatic cycles. Shorelines in back-tilted basins are substantially more sensitive to changes in relative sea level than comparable coastlines in passive-margin settings, all else being equal.
SUMMARY Published laboratory elastic-wave velocity versus porosity data in carbonate rocks exhibit significant scatter even at a fixed mineralogy. This scatter is usually attributed to the strong variability in the rock-frame or pore-space geometry, which, in turn, is driven by the richness and complexity of diagenetic alteration in these very reactive sediments. Yet, by examining wireline data from oil-bearing high-to-medium porosity chalk deposits, we find surprisingly tight velocity–porosity trends. Moreover, these trends are continued into the low-porosity domain by data from a location thousands of miles away from the chalk field. This congruence implies a universality of diagenetic trends, at least in the massive deposits under examination. We also find that the elastic bulk and shear moduli of the pure-calcite end member are somewhat smaller than such values reported in the literature. Using the end-member elastic constants relevant to the data under examination, we establish a theoretical rock physics model to match and generalize these data.
The Permo-Carboniferous reservoirs of central Saudi Arabia comprise important accumulations of natural gas and light oils. Some of the reservoirs exhibit low resistivity and low contrast resistivity (LRLC) phenomena. Low resistivity pay reservoirs often produce gas/oil with little or no water at very low resistivities. Low contrast resistivity pay zones, on the other hand, produce hydrocarbon at minimum resistivity contrast between hydrocarbon-bearing intervals and adjacent water-wet or shaley zones. Evaluating these types of reservoirs poses a major challenge to petrophysicists and petroleum engineers due to the difficulty in recognizing them on logs and quantifying their hydrocarbon potential when using simple resistivity-based petrophysical models. As a result, potential pay zones can be incorrectly evaluated or bypassed. The objectives of this study, therefore, are: 1) to understand the causes of LRLC pay in the study reservoirs through a detailed assessment of the textural and mineralogical composition of the rock, and 2) to validate a simple porosity-based methodology for recognizing LRLC pay in both old and new wells. To achieve the set objectives, 38 core samples and 107 thin sections were selected from two wells exhibiting low resistivity (Well-1) and low contrast resistivity (Well-2) phenomena, for detailed petrographic and mineralogical studies (SEM/XRD). Furthermore, a water salinity map was created to provide general salinity trends in the area. Well data combined with results of mineralogical and petrographic studies suggest that low resistivity and low contrast resistivity pay in the study reservoirs is the product of a complex mix of: 1) clay mineral types and its mode of distribution, 2) thin reservoirs below resistivity tool resolution, 3) significant grain size variation and microporosity, and 4) variable formation water salinities. This paper highlights the causes of low resistivity and low contrast resistivity phenomena in reservoirs in central Saudi Arabia. Furthermore, the applicability of a porosity-based methodology for recognizing LRLC phenomena was verified with promising results.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.