Petroleum Systems of Deepwater Settings
Understanding and predicting the petroleum systems of deepwater settings are some of the most challenging aspects of deepwater exploration and production. Unlike the case with other aspects of petroleum systems (e.g., reservoirs and traps), predictions of the systems′ source, seal, generation, timing, and migration are challenging, primarily because these parameters are the least constrained scientifically and must all be imaged from seismic and other data, petroleum seeps, or modeling. Petroleum-systems modeling is a topic of active research in many companies, yet few results have been published because of the proprietary nature of the material and the important competitive advantage afforded to the companies that conduct those studies. One significant challenge in petroleum-systems modeling is that every sedimentary basin is unique in the evolution of its petroleum systems. Subtle changes in source-rock richness and distribution, timing of structures, and/or different pressure regimes can contribute to vastly different prospectivity. In general, deep-water basins are unique compared with other petroleum basins because of (1) their recent generation and migration of petroleum (during the last 5–10 million years) and (2) the fact that all elements of their petroleum systems work together from the initial evolution of the basin and are inextricably linked (their reservoirs are deposited with growing structures, etc.).
The first two elements of petroleum systems—reservoirs and traps—are described in Chapters 4 through 8 and Chapter 9, respectively. In this chapter, we address, in an extremely abbreviated manner, the four remaining aspects of petroleum systems in deep-water
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This course provides the working geophysicist with a broad overview of the petroleum systems of deepwater settings. The six main elements of petroleum systems will be covered: reservoirs, traps, seals, source rocks, generation, migration, and timing. The course is designed to teach students approximately 80% of what is important. For those interested in further study of a specific topic, each chapter has extensive references for the current literature. About 10% of the current cutting-edge information remains proprietary and cannot be included.
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 sili-ciclastic and carbonate reservoir systems. The study of deepwater systems requires many remote-observation systems, each of which can provide only one view of the entire depositional system. As a consequence, the study and understanding of deepwater depositional systems as reservoirs have lagged behind those 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 (Figure 1-1). The types of data used in the study of deep-water deposits include detailed outcrop studies, 2D and 3D seismic-reflection data (both for shallow and deep resolution), cores, log suites, and biostratigraphy. These data sets are routinely incorporated into computer reservoir modeling and simulation (Figure 1-1).
The following chapters integrate all of these data types and disciplines to characterize the many facets of deepwater systems. Technologies for deepwater exploration and development are improving rapidly. The intent of the course is to provide information that will be usable even as the technologies advance beyond what we present here.
With that in mind, this chapter introduces basic deepwater terminology and concepts for deepwater systems that will be used throughout this book.
Geoscientists routinely use several terms to describe the sedimentary processes and characteristics of deepwater settings and deposits. For the sake of consistency in this book, we define these terms as follows.
The term deep water is used informally in industry in two ways. First, deep water refers to sediments deposited in water depths considered to be “deep,” i.e., those under gravity-flow processes and located somewhere in the upper- to middle-slope region of a basin. Sediment gravity-flow processes are operative in lakes in relatively shallow water and in cratonic basins where water depths may be less than 300 m. Thus, unless stated otherwise, we use the term deepwater systems to refer to marine-sediment gravity-flow processes, environments, and deposits.