Chapter 2 Petroleum Geology and Reservoirs ( 石油地質及儲油層 ) 2008

1. Chapter 2 Petroleum Geology and Reservoirs(石油地質及儲油層)2008

2. References石油地質及儲油層 (Petroleum Geology and Reservoir) Textbook 1 Fundamentals of Petroleum, Petroleum Extension Service, The University of Texas at Austin, Austin, Texas,1979. – chapter 1 Textbook 2 Archer, J. S., and Wall, C.G., Petroleum Engineering—principles and practice, Graham & Trotman, MD, 1986. – chapter 2 TextBook 3 Donohue, D.A.T., and Lang K.R., A First Course in Petroleum Technology, International Human Resources Development Corporation, Houston,1986 – chapter 4.1; 4.2

3. Petroleum Geology (石油地質) Geology (地質) ---研究(1)地球的歷史及構造 (2)記錄在岩石的生物(命)形式 Petroleum Geology(石油地質) ---研究地質以預測石油累積之處所

4. 地球的形成及構造 • 地球的形成 —40～50億年前由宇宙塵(Cosmic dust)的凝結而成 • 地球內部大構造 — • Core--- heavy (4,400 miles) • Mantle--- Lighter (1,800 miles) • Crust--- 10~30 miles

5. 地球內部大構造 Core-- heavy (4,400 miles) Mantle-- Lighter (1,800 miles) Crust--- 10~30 miles

6. 地球表面的變化 -- Rock cycle 噴出 形成 Primeval(初期的) Atmosphere(大氣) 地球內部 Water vapor and gases Magma (岩漿) 地殼冷卻 heat Cool 地殼收縮變形而皺摺 Metamorphic rocks Igneous rocks (火成岩) erosion 下雨 heat pressure erosion erosion Sedimentary rocks Sediments (沉積物) pressure cementation

7. 沉積岩的分類

8. Prorsity Permeability Reservoir Rock Sandstones (SiO2) Carbonates Limestones (CaCO3) Dolomites (CaCO3, MgCO3) Reservoir Rock (Sedimentary Rock)

9. 地球的歷史 • 寒武紀(Cambrian)【約5.5億年前】開始在海洋裡有大量的生物(生命) 在寒武紀之前為前寒武紀(Precambrian) • 地質年代自寒武紀開始 > 地質代年表(Geologic Time Scale) • 泥盆紀(Devonian)時期【約3.3億年前】陸上有大量植物及動物

10. Geological Time Scale

11. 地層年代表

13. Petroleum accumulation(石油累積)Petroleum reservoir(石油油藏;油藏;油層) • Petroleum accumulation必須具備 (1)Oil ＆ gas 之來源 (2)具有孔隙(porosity)及滲透率(permeability)之Reservoir Rock (3) 要有trap(封閉)以阻擋流體的流動

14. 石油的來源

15. 石油的來源 • －石油來自沈積岩的有機物質 • －海洋裡大量的生物不停的，緩慢的掉落到海底。 雖然在掉落的過程中，有部分被吃掉或被氧化掉， 但另部份(動物或植物)掉落海底而埋在沼澤或泥濘之 海底 • －海底繼續被Sand(砂)，Clay(黏土)及debris等沈積物埋沒 一直到幾千英呎 • －沈積物的壓力開始作用。 • 細菌由殘餘的有機物質中，用掉氧而分解物質， 使其僅存碳及氫 • －在高度的壓力及重量的地層影響之下， Clays變成Shales → 石油產生

16. Petroleum formation requires that organic source clays become mature by subjection to pressure and temperature.

17. 石油形成的重要條件 • 225℉ < temperature < 350℉ 有利條件 • temperature < 150℉ 不可能形成石油 • temperature > 500℉ 有機物質碳化， 不能形成石油

18. Generation of gas and oil

20. In geology and oceanography, diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration (weathering) and metamorphism.

21. Catagenesis can refer to: • Catagenesis (geology)– The cracking process in which organic kerogens are broken down into hydrocarbons; • Catagenesis (biology)– Retrogressive evolution, as contrasted with anagenesis.

22. Metamorphism can be defined as the solid state recrystallisation of pre-existing rocks due to changes in heat and/or pressure and/or introduction of fluids i.e without melting. There will be mineralogical, chemical and crystallographic changes

23. Prolonged exposure to high temperatures, or shorter exposure to very high temperatures, may lead progressively to the generation of hydrocarbon mixtures characterized as condensates, wet gases and gas. • The average organic content of potential source rocks is about 1% by weight. The Kimmeridge clay, the principal source rock for North Sea oil average about 5% carbon (~7% organic matter) with local rich streaks greater than 40%. The hydrogen content of the organic matter should be greater than 7% by weight for potential as an oil source.

24. It is a rule of thumb that for each percentage point of organic carbon in mature source rocks, some 1300~1500 cubic meters of oil per km2-m (or 10~40 barrels of oil per acre-ft; or 56-225 ft3/ 43560 ft3) of sediment could be generated. • (12~52 : 10,000) (1:833 ~ 1:200) It is not, however, necessarily true that all the oil generated will be expelled or trapped in porous rock.

25. 經過porous bed 有permeability 石油形成 ( in source rock) Migration Traps＆Reservoir Rocks 由於Compaction of Source bed and ………. 石油移棲 • The migration process involves two main stages, namely from the source rock and then through a permeable system.

26. Migration of petroleum -- from the source rock

27. Migration of petroleum -- from the source rock ** Capillary effect ** Microfractures Since the generation of petroleum is accompanied by volume changes which can lead to high local pressures, there may well be an initiation of microfractures which provide an escape route into permeable systems such as sedimentary rocks or fault planes. The source rock microfractures are believed to heal as pressures are dissipated.

28. Migration of petroleum --through a permeable system ** Fluid potential gradient or gravity effect In the permeable system the transport occurs under conditions of a fluid potential gradient which may take the hydrocarbon to surface or to some place where it becomes trapped. It might be assumed that less than 10% of petroleum generated in source rocks is both expelled and trapped, as shown in the example of Fig. 2.5.

30. Petroleum traps(石油封閉) • The characteristic forms of petroleum trap are known as structural traps(構造封閉) and stratigraphic traps(地層封閉), with the great majority of known accumulation being in the former style.

31. Erosion － Sedimentation Uplift － wearing down Strata or bed Unconformity －disconformity －Angular unconformity Upward downward Upper crust movement Arches (or upfold) → anticlines Traughs (or downfold) → synclines Fault Folds Normal Reverse Thrust Lateral Important to petroleum accumulation 地質構造（Geological Structures）

32. 造山運動之應力所造成 沉積過程所造成 Figure 1.13. Basic hydrocarbon reservoirs are structural and / or stratigraphic traps. Figure 1.12. Two general kinds of unconformities are disconformity (A) and angular unconformities (B) and (C).

33. Structural traps－an arched upper surface Stratigraphic traps---up-dip termination of porosity (permeability) 封閉(traps) Anticline trap Fault trap Dome and plug trap Structural traps Disconformity Angular unconformity Unconformity traps Lenticular trap Stratigraphic traps 封閉(traps) Combination traps

34. Cap rock and fluid distribution • Impermeable rocks provide seal above and below the permeable reservoir rocks. • At equilibrium conditions, the density differences between the oil, gas and water phases can result in boundary regions between them known as fluid contacts, i.e. gas-oil and oil-water contacts.

35. Structural trap (構造封閉) -- Anticline Longitudinal view of a typical anticline. The oil cannot escape upward because of the impervious shale bed above the oil sand; neither can it travel downward because of the water that is associated with an accumulation of this type. Anticlines－ Of the many types of structural features present in the upper layers of the earths crust that can trap oil, the most important is the anticlines－the type of structure from which the greater part of the word’s oil has been produced. Anticlines are upfolds of beds in the earth’s crust, and, when the proper conditions are present, oil accumulates within the closure of there folds.

36. Structural trap-- Anticline Plan view of a typical anticline, showing locations of longitudinal view A-B and lateral view C-D. Lateral, or end view, of a typical anticline.

37. Structural traps Figure 1.7. Schematic cross section shows deformation of earth’s crust by bucking of layers into folds Figure 1.8. Simple kinds of folds are symmetrical anticline (A), plunging asymmetrical anticline (B), plunging syncline (C), and dome with deep salt core (D). Figure 1.9. Simplified diagram of the Milano, Texas, fault.

38. Structural traps– dome & anticline Figure 1.15. Oil accumulates in a dome-shaped structure (A) and an anticlinal type of fold structure (B). An anticline is generally long and narrow while the dome is circular in outline. (Courtesy of American Petroleum Institute)

40. Structural traps -- faults Figure 1.10. Simple kinds of faults are normal (A), reverse (B), thrust (C), and lateral (D). Figure 1.11. Variations of normal and reverse faulting are rotational faults (A) and upthrust faults (B).

41. Structural traps Figure 1.14. Common types of structural traps

42. Structural trap – fault & anticline Figure 1.16. Gas and oil are trapped in a fault trap-a reservoir resulting from normal faulting or offsetting of strata. The block on the right has moved up from the block on the left, moving impervious shawl opposite the hydrocarbon-bearing formation. (Courtesy of American Petroleum Institute) Figure 1.17. Shown in map view, fault traps may be simple (A) or compound (B).

43. Stratigraphic traps(地層封閉)

44. 造山運動之應力所造成 沉積過程所造成 Figure 1.13. Basic hydrocarbon reservoirs are structural and / or stratigraphic traps. Figure 1.12. Two general kinds of unconformities are disconformity (A) and angular unconformities (B) and (C).

45. Stratigraphic traps Unconformity －Disconformity －Angnlar unconformity Pinctout Sand lenses Changes in sedimentation

46. Figure 1.22. Oil is trapped under an unconformity. (Courtesy of API) Figure 1.23. Lenticular traps confine oil in porous parts of the rock. (Courtesy of API)

47. Stratigraphic trap A stratigraphic trap where sand lenses are interspersed in a shale bed. The shale acts as a permeability barrier An example of a stratigraphic trap where the oil zone pinches out.

48. Stratigraphic Traps A stratigraphic trap where changes in sedimentation act as a permeability barrier. An angular unconformity as an oil trap. The flat-lying shale bed above the oil zones acts as a permeability barrier.

49. Stratigraphic traps • Stratigraphic traps result when a depositional bed changes from permeable rock into fine-grain impermeable rock (Fig. 2.8).