THE HABITAT OF HYDROCARBONS IN SEDIMENTARY BASINS (cơ sở KHOA học địa CHẤT dầu KHÍ SLIDE TIẾNG ANH)

Chapter 08: THE HABITAT OF HYDROCARBONS IN SEDIMENTARY BASINS Content Introduction 8.1-The Sedimentary Basin Concept 8.2-Sedimentary Basin Classification 8.3-Distribution of petroleum – rich basins Introduction There are approximately 600 sedimentary rock basins in the world A quarter of them are producing petroleum Before exploitating in a new area, attemting to locate drillabe prospects, it is necessery to establish the type of basin, what productive horizons it may contain and where they may be broadly located • Even though petroleum reserves can be found in rocks of all ages, most giant fields and most of the world's reserves occur in sequences, of Late Mesozoic and Cenozoic age ( Figure 01) Paleozoic rocks probably had potential to generate hydrocarbons equal to that of these younger rocks, but there has been more time in which to destroy all or part of the petroleum through uplift and erosion (Halbouty et al, 1970) Fig: 01 • Worldwide reserves can be related to their location within a petroleum basin, regardless of its basin type (Figure: 02) Fig: 02 8.1-The Sedimentary Basin Concept • A general term for any large area of tectonic origin with a thick accumulation of sedimentary rocks • A basin is a geological structure with a unique sequence of rocks that are dissimilar to those outside the basin • A low area with no exterior drainage • Include both depression itself and the thickerthan-everage sediments that fill it Fig: 03 Idealized pattern of a sedimentary basin Fig: 04 Sedimentation patterns over arch, shelf and basin Main content: 1.Geometry of Sedimentary Basins 2.Sediment Fill 3.Tectonic Processes and Timing 4.Basin-Forming Mechanisms 5.Sedimentary Basin Classification 10 Fig: 47 Generalized cross-section through the Arabian-Iranian basin 75 Table 10.6 Downwarp Basin • • • • • • • • • • A Open- related to pull-apart, passive margins B Closed- related to foreland basins C Trough- related to foreland basins Distinguishing features basement and depositional downwarp dipping into small oceans, inland seas or linear suture zones; intermediate crust Depositional History mixed, interfingering shallow marine facies, either carbonate or clastic-prone Reservoir carbonate (C); or mixed (A,B) with sandstone (A) or carbonate (B) dominant Source overlying, interfingering and basin-center shales; limestone and marls important in B Cap mostly shale; both shale and evaporites in B Trap anticlines; salt flow; combination; reefs, pinch-outs and unconformities Geothermal Gradient normal to above average Hydrocarbons intermediate to mixed gravity crudes; sandstones more paraffinic, carbonates more aromatic; average to high natural gas Risks maturation; leakage; deformation too intense; igneous activity; poor reservoir properties Typical Reserves 4- 40 billion bbl hydrocarbon/basin (A); 10- >50 (B), 5- (C) 76 Tertiary Deltas In a sense, tertiary-age deltas are not true basins but later overprints onto other basin types They can form in any coastal setting, and are found about equally over convergent and divergent margins 77 Fig: 48 Idealized pattern of a Tertiary age delta 78 Fig: 49 Major delta basins of the world 79 Fig 50: Generalized cross-section through the Niger delta of west Africa 80 Table 10.7 Tertiary Delta   Distinguishing features: circular depocenter basin; on plate triple junction where failed arm rift meets ocean basin, particularly at divergent or transcurrent margin Depositional History: prograding wedge of land-derived clastics with Type III kerogen Reservoir: sandstone (pro-delta facies) Source: shale Cap: shale Trap: roll over anticlines; growth faults, mud or salt diapirs; sand lenses Geothermal Gradient: low Hydrocarbons: paraffinic to paraffinic-naphthenic crude; very high natural gas Risks: small trap size, adequate caprock Typical Reserves: to 20 billion bbl hydrocarbon/basin; few fully developed 81 8-3-DISTRIBUTION OF PETROLEUM – RICH BASINS Together the 25 sedimentary basins in the world, which are the richest in terms of known petroleum reserves, contain nearly 90% of the world's oil and gas 82 8-3-DISTRIBUTION OF PETROLEUM – RICH BASINS (cont.) A breakdown of these petroleum-rich basins by basin type shows that eight of them belong to the downwarp basin class, and an additional seven are large foreland basins Of the remaining ten, three of the basins are rifts and two are deltas Finally, there are five convergent margin basins, including three non-arc, one back-arc, and one collision basin type Only three basin types are not found among the world's richest petroleum basins: the interior, the pullapart, and the fore-arc basins 83 Fig: 51 Richest petroleum basins 84 Fig: 52 85 Fig: 53 Histogram divides the total world sediment volume 86 Fig: 54 Distribution of P.reserves with depth for each of the basin types 87 Fig: 55 Percent of all P producing basins within each basin type that contains giant fields88 Exercise 89 ... basins of the world Fig: 20 Major interior basins of the world 35 Table 10.1 Interior Basin (Intracratonic, sag) • Distinguishing features simple, single cycle; no uplands; in continental interiors... elevation and the interplay between the rate of subsidence and the rate of sedimentation 13 Tectonic Processes and Timing • An important aspect of sedimentary basins is the nature and timing of tectonic...Content Introduction 8.1 -The Sedimentary Basin Concept 8.2 -Sedimentary Basin Classification 8.3-Distribution of petroleum – rich basins Introduction There are approximately 600 sedimentary rock basins