Deepwater-Reservoir Elements: Sheet Sands and Sandstones
Published:January 01, 2006
2006. "Deepwater-Reservoir Elements: Sheet Sands and Sandstones", Introduction to the Petroleum Geology of Deepwater Setting, Paul Weimer, Roger M. Slatt, Renaud Bouroullec, Richard Fillon, Henry Pettingill, Matthew Pranter, Gabor Tari
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Sheet sands and sandstones are considered to be some of the best high-rate, high-ultimate recovery (HRHU) reservoirs in deepwater (Chapter 2). This is due to their tendency towards the simplest reservoir geometries: good lateral continuity, potentially good vertical connectivity, high aspect ratio, narrow range in grain size (and thus greater porosity and permeability: Chapter 13), and few erosional features. Because of their initial successes as reservoirs in the northern deep Gulf of Mexico, sheet sands and sandstones have been studied in great detail by industry to better understand them, and, hence, to find more of them. One problem, however, is that reservoirs initially interpreted as sheet sands were later determined to be amalgamated channel sands.
Sheet sands are deposited from decelerating flows at the terminus of channels. Sheet sands and sandstones reflect the sediments that have bypassed through updip channels (confined flow) and are deposited in primarily an unconfined setting. They are characterized by high aspect ratio reservoir sand bodies (>500:1), markedly different in aspect than the updip channels that feed them (30:1 to 300:1). Unlike other deepwater reservoir elements, the areal extent of sheet sands is commonly larger than the area of the trap. Sheet sands and sandstones are most prevalent in mixed mud-sand to mud dominated systems (Richards and Bowman, 1998). Sheet sands and sandstones are not as common in sand-rich to gravel-rich systems (Chapter 1 and Chapter 5).
Sheet sands and sandstones are characterized by their tabular
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Introduction to the Petroleum Geology of Deepwater Setting
This publication is intended to provide the working geologist, geophysicist, and petroleum engineer with a broad overview of the petroleum systems of deepwater settings. Deepwater depositional systems are the one type of reservoir system that cannot be easily reached, observed, and studied in the modern environment, in contrast to other siliciclastic and carbonate reservoir systems. The study of deepwater systems requires many different remote observation techniques, each of which can only provide information on one part of the entire depositional system. As a consequence, the study and understanding of deepwater depositional systems as reservoirs has lagged behind that of the other reservoir systems, whose modern processes are more easily observed and documented. For this reason, geoscientists use an integrated approach, working in interdisciplinary teams with multiple data types. The types of data used in the study of deepwater deposits include: outcrop studies, 2D and 3D seismic-reflection data (both for shallow and deep resolution), cores, conventional and specialized log suites, biostratigraphy, and well test and production information. These data sets are routinely incorporated into computer reservoir modeling programs for production performance simulation and forecasting. Technologies for deepwater exploration and development are improving rapidly. The intent of this publication is to provide information that will be usable even as the technologies advance beyond what we present here.