Stratigraphic Basin Analysis Models

(adsbygoogle = window.adsbygoogle || []).push({}); Stratigraphic basin analysis models are used to interpret the sedimentary history of a basin by examining the distribution and character of its sedimentary rocks. These models help geologists understand the depositional environment, source of sediment, and the tectonic and climatic events that have shaped the basin over time. Introduction The primary purpose of stratigraphic modeling in sedimentary basins is to predict the distribution of siliciclastic and carbonate lithologies. This is especially important in frontier basins where seismic data and well control are limited. The foundation for modern stratigraphic modeling is the concept of sequence stratigraphy, developed by P. R. Vail and his colleagues at Exxon Production Research Company during the late 1960s and middle 1970s. https://youtu.be/_0WcDWOe3nI (adsbygoogle = window.adsbygoogle || []).push({}); Sequence Stratigraphic Models Depositional sequences are defined as packages of genetically related units bounded by stratigraphic discontinuities (unconformities) and their correlative conformities (Mitchum, 1977). Depositional sequences (Figure 1) FIGURE 1 Depositional sequences and Figure 2 have a chronostratigraphic significance because they are deposited during a time interval limited by the ages of the sequence boundaries where they are conformities. FIGURE 2 Chronostratigraphic significance because they are deposited during a time interval limited by the ages of the sequence boundaries where they are conformities Each depositional sequence has its "own particular regional distribution, stratal geometry, thickness pattern, and geologic history", and is deposited during one cycle of rise and fall in sea level. Anstey (1992) discusses the general principles of sequence identification and lithologic prediction based on sequence models. Anstey begins with a reprise of the basic techniques for defining sequence boundaries (Figure 3). FIGURE 3 Sequence boundaries in a simple shelfal system (Figure 4), (adsbygoogle = window.adsbygoogle || []).push({}); FIGURE 4 Shelfal system and then leads the reader step by step through the sequence stratigraphic analysis of a more complex shelfal system (Figure 5). FIGURE 5 Complex shelfal system The sequence analyzed in Figure 5 lies between SB1 and SB2; each of the unconformities (and their correlative conformities) represents a period of relative sea-level lowstand. Figure 6 shows the elements affecting relative sea level, and the expected locations of sequence boundaries SB1 and SB2. FIGURE 6 The elements affecting relative sea level Anstey breaks the sequence down into separate systems tracts, each composed of sediments deposited in linked depositional systems during the different phases of sea level fall and rise that produce a sequence. He presents a series of three-dimensional models, keyed to the relative sea-level chart, which illustrate the key components of the separate systems tracts. For example, Figure 7, FIGURE 7 Figure 8, FIGURE 8 and Figure 9 show the three components of the lowstand systems tract, FIGURE 9 The three components of the lowstand systems tract (adsbygoogle = window.adsbygoogle || []).push({}); and Figure 10 FIGURE 10 and Figure 11 are summaries of the types of sediment and reservoir potential predicted in the lowstand systems tract. FIGURE 11 The types of sediment and reservoir potential predicted in the lowstand systems tract Anstey continues with models of the transgressive systems tract, highstand systems tract, and shelf margin systems tract, and builds a complete sequence analysis of the various tracts that comprise an ideal sequence. Figure 12 summarizes these tracts relative to the sea-level curve, FIGURE 12 Summarizes these tracts relative to the sea-level curve and Figure 13 FIGURE 13 Squence Stratigraphy and Figure 14 FIGURE 14 FIGURE 14 show the stratal patterns of Figure 5 interpreted in terms of likely rock type for a clastic system. (adsbygoogle = window.adsbygoogle || []).push({}); Seismic Facies Analysis https://youtu.be/ORpGB6NnuX8 (adsbygoogle = window.adsbygoogle || []).push({}); We use seismic facies analysis to interpret depositional environment and lithology within each depositional sequence in a basin. Sequence stratigraphic models provide the framework for this analysis and prediction. Seismic reflections configurations are controlled by gross stratification, and certain patterns indicate certain depositional environments and erosional processes. Using cross sections and three-dimensional models, Anstey (1992) formalizes the geological significance implied by various reflection configurations. Shell Oil Company (1987) illustrates seismic facies analysis with seismic sections from several environments. Parallel reflection configurations within sequences indicate depositional environments in uniformly subsiding basins, where rates of deposition are also relatively uniform. Figure 1, FIGURE 1 Deposition are also relatively uniform Figure 2, Figure 3, FIGURE 2 FIGURE 3 Figure 4, FIGURE 4 (adsbygoogle = window.adsbygoogle || []).push({}); and Figure 5 FIGURE 5 show variations in this type of configuration. Subdivisions are based on changes in amplitude, continuity, and frequency. We can verify environmental and lithologic interpretations using well data. Prograding clinoform reflection configurations within depositional sequences indicate lateral outbuilding of sediments. Subdivisions are related to variations in the rate of deposition and in water depth. Sigmoid patterns develop where sediment supply is low and basin subsidence/sea level rise is rapid (Figure 6). FIGURE 6 sediment supply is low and basin subsidence/sea level rise is rapid Oblique patterns (Figure 7) develop where sediment supply is relatively high, basin subsidence is slow and sea-level is at a still-stand. These conditions result in "rapid basin infill and sedimentary bypass with some erosion of the upper depositional surface." IGURE 7 Oblique patterns External reflection configurations include mounds, fills, banks, and lenses. Mounds are typically elevated above surrounding strata, and are diverse in origin. Figure 8, FIGURE 8 External reflection configurations include mounds Figure 9, and Figure 10. FIGURE 9 illustrate several mound configurations with various external and internal reflection configurations, which provide clues to the origin of the mounds. FIGURE 10 Fill configurations indicate strata infilling "negative-relief features in the underlying strata." Boundary surfaces typically show erosional truncations at the base of the fill. Internal reflections may show variations in sedimentation history within the fill strata (Figure 11 and Figure 12). FIGURE 11 (adsbygoogle = window.adsbygoogle || []).push({}); FIGURE 12 Bank configurations (Figure 13) typically mark the shelf-slope break, and basin fill onlaps the bank margin. FIGURE 13 Lens configurations (Figure 14 ) are bounded by converging surfaces. FIGURE 14 FIGURE 14 They are thick in the middle and thin towards the edges. Basin Analysis Case Studies https://youtu.be/mNHJYd3CzDE (adsbygoogle = window.adsbygoogle || []).push({}); Assessment (adsbygoogle = window.adsbygoogle || []).push({}); 1. The primary purpose of stratigraphic modeling in sedimentary basins is to predict the distribution of siliciclastic and carbonate lithologies. A .TrueB .False 2. Depositional sequences are defined as packages of genetically related units bounded by stratigraphic discontinuities. A .TrueB .False 3. ________ patterns develop where sediment supply is low and basin subsidence/sea level rise is rapid. 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