Fundamentals of petroleum Geology_1.pptx

This PPT explains fundamentals of Pteroleum Geology

1. Fundamentals of Petroleum Geology

2. Historical Petroleum products have been used for at least 8000 years Herodotus 450 BC – natural seeps Egyptians – mummification/ Victorian medication Ancient Greece everlasting flame in the sacred Oracle at Delphi Persian Temples built around natural gas sources Early uses: medication, waterproofing, warfare Up to mid 19 th century: all oil produced from seeps, shallow pits and hand dug shafts James Young: extracted oil from carboniferous shales , Scotland 1847: “oil- shales ” 1st Natural gas : Sichuan Province China several thousand years ago Bamboo tools and pipes – salt production 1 st oil-seeking well = Pechelbronn , France, 1745 1 st well to produce oil: Oil creek, Pennsylvania by “Colonel” Drake

3. The Demand for Oil Products Increased greatly by WWI (1914-18) By 1920 the oil industry dominated by the “seven sisters (oil companies)” Post WWII, oil companies began to risk profits from one productive area to explore for another. 1960: Organization of Petroleum Exporting Countries (OPEC) formed in Baghdad (Iraq) Objective: control the power of the independent oil companies by price control & appropriation of company assets

4. The science of petroleum geology Chemistry Geochemistry is a major component of petroleum geology Detailed knowledge of the mineralogical composition of rocks – reservoir quality Pore-fluid chemistry – reservoir degradation/ enhancement Organic geochemistry: biomarkers, fingerprinting Physics Geophysics contribute to Understanding the earth’s crust Understanding the structures involved in trapping: folds, faults Identifying the position of such traps: magnetics, gravity, seismics Understanding the wells: wireline logs, lithology, porosity.. Biology Study of fossil life: Palaeontology contributes Dating/ stratigraphic characterization Environmental characterization (fossil environments, palaeoecology ) Biochemistry: transformation of plant and animal tissues into kerogen and through to oil and gas.

5. The physical and chemical properties of oil and gas Hydrocarbon: composed of H and C Gases Liquid Oil, Crude Plastic Asphalts, Coals, Kerogen Wet ethane, propane Dry methane

6. Natural Gas Liquid (NGL) Classified into Hydrocarbon Gases Methane (dry) Ethane (wet) Propane Butane ORGANIC ORIGIN Inert Gases Helium Argon Krypton Radon Nitrogen Also Carbon dioxide Hydrogen sulphide INORGANIC ORIGIN

7. Crude Oil “ a mixture of hydrocarbons that existed in the liquid phase in natural underground reservoirs and remains liquid at atmospheric pressure after passing through surface” Highly variable in composition and in appearance Primarily carbon, hydrogen and minor oxygen, nitrogen, sulphur , vanadium, nickel… Color: yellow, green, brown to dark brown & black Oil at the surface tends to be more viscous, most oils are less dense than water: generally measured as the difference between its density and that of water: (API= American Petroleum Institute) Thus light oils have API < 10° and heavy oils are more dense than water. °API = 141.5 SG 60/60°F - 131.5

8. The Five main components of an oil accumulation Must be an organic-rich source rock to generate the oil/ gas The source rock must have been heated sufficiently to yield its petroleum There must be a reservoir to contain the expelled hydrocarbons. This must have: Porosity , to hold the hydrocarbons Permeability , to allow fluid flow The reservoir must be sealed by an impermeable Cap Rock to prevent upwards escape of the hydrocarbons to the earth’s surface Source, reservoir and seal must be arranged in such a way that the petroleum is Trapped

9. Formation of an oil accumulation Burial of adequate organic source material. most petroleum is derived from the accumulation of trillions of individual micro-organisms. Burial to the appropriate depths. depths of 2-6 km and temperatures of 60-160º C. Presence of a reservoir-quality rock. a porous storage space. Sandstone and limestone are the most common reservoir rocks. To be a reservoir they must have: Porosity , to hold the hydrocarbons Permeability , to allow fluid flow Presence of an adequate seal A seal is an impermeable bed (such as a shale or a bed of salt) that sits on top of the trap and prevents the hydrocarbons rising any further . Presence of a trap In order to prevent the hydrocarbons rising to the surface and escaping they must be caught in a confined space, termed a trap. i.e. the source, reservoir and seal must be arranged in such a way that the petroleum is trapped.

10. The Petroleum System

11. In addition to the five components, a further two events are essential: Timing : no trapping unless the traps are present when migration is occurring Maturation : no petroleum if the source rock OM does not mature Migration : no accumulation if the petroleum doesn’t migrate

12. The Source Rock This shale typically contains >1% of organic carbon, by weight. The shale is very widespread, underlying much of Britain and most of the North Sea, and is by far the most important source rock for the oil that has been found in the North Sea Basin.

13. The Reservoir Rock: Sandstone An outcrop of pebbly sandstone (at base of cliff) overlain by red sandstone. The Budleigh-Salterton pebble beds, of Triassic age. A few kilometres to the east these beds dip into the subsurface, and form part of the oil reservoir at the Wytch Farm Field, which is Britain’s largest onshore oil field.

14. The Reservoir Rock: Sandstone The Jurassic Bridport Sand. Another of the reservoir sandstones important in the Wytch Farm field of southern Britain. The layering in this sandstone may be the result of rhythmic climatic changes in the shallow sea where this sandstone was deposited.

15. The Reservoir Rock: Dolomite The Cairns Formation, of Devonian age, exposed near Canmore , in the Front ranges of the Rocky Mountains, just east of Banff, Alberta. This is one of the more important reservoir units in the subsurface of Alberta.

16. The Reservoir Rock: Dolomite This is an example of an important reservoir rock type. Fossil stromatoporoids have been hollowed out by the chemical conversion of limestone to dolomite, creating pore spaces so large that they are sometimes called “ cavernous porosity ”

17. Making reservoirs today: limestones An exposure of modern limestone in the Florida Keys. This limestone is only a few hundred years old. It shows the structure of coral and other organic remains . Burial of this limestone would probably lead to reduction in porosity as a result of cementation. Good quality reservoir rocks, such as the dolomite shown in another picture, are created by dissolution of some of the rock. This usually occurs many millions of years after the initial formation and burial

18. The Seal Commonly evaporites, chalks and shales. Relatively impermeable

19. The Trap: Stratigraphic Stratigraphic traps are traps created by the limits of the reservoir rock itself, without any structural control. Here is an example of a reef trap. The diagram shows a vertical slice (cross-section) through the reservoir and overlying rocks. Stratigraphic traps are also formed in clastic rocks: here, in a cross-section through a continental margin, two sandstone beds form traps within muddy coastal deposits. River channels may form long, thin traps corresponding to the former position of the river or delta distributary. Beach sands may form sheet-like bodies along an ancient shoreline etc.

20. The Trap: Structural Structural traps are formed where the space for petroleum is limited by a structural feature Tilted fault-block traps are formed where the upward flow of the petroleum is prevented by impermeability along the fault plane and by an overlying cap or seal: common in the North Sea. Anticlinal traps are formed by folding in the rocks. Unconformity traps are generated where an erosional break in the stratigraphic succession is followed by impermeable strata.

21. The Trap: Structural This type of structural trap is very common in fold-and-thrust belts at the front of mountain ranges like the Rocky Mountains of Alberta, where older rocks are pushed sideways over younger rocks (e.g., the yellow unit is here pushed over the light-blue unit). Oil is pooled in anticlinal folds. The traps may also be partly faulted, as in the upper one shown here.

22. The Subsurface Environment

23. Temperature in the subsurface Increases towards the earth’s core: geothermal gradient Different lithologies will conduct heat differently: thermal conductivity Additional heat added by decay of radioactive species Heat Flow = Geothermal gradient x thermal conductivity Mineral Thermal conductivity Halite 5.5 Limestone 3 – 3.5 Sandstone 2.5 – 4 Coal 0.3

24. Pressure in the subsurface The force per unit area acting on a surface Overburden pressure (S) = lithostatic pressure (p) + fluid pressure (f) Column of freshwater = 0.43 psi/ ft : normal Abnormal ( overpressured ) = >0.43 psi/ ft Abnormal ( underpressured ) = <0.43 psi/ ft Grain-grain contact Hydrostatic (imposed by a column of fluid at rest) Hydrodynamic (fluid potential gradient caused by fluid flow)

25. Temperature – Pressure Relationship Boyle’s Law: (P x V)/T = constant Fluid may exist in either the liquid or gaseous form depending on the PT conditions. Above the critical point: only 1 phase may exist liquid gas c condensation evaporation PRESSURE TEMPERATURE

26. Modern Organic Processes at the Earth’s Surface Surface 82% C locked into CO 3 in carbonates 18% occurs as organic C in coal, oil & gas When death occurs, a plant or animals remains are normally oxidized and CO 2 / H2O released Subsurface When death occurs, a plant or animals remains are normally oxidized and CO 2 / H2O released Under exceptional conditions: organic matter is buried and preserved in sediments The composition of the organic matter strongly influences whether the organic matter can produce coal, oil or gas.

27. Basic components of organic matter in sediments PROTEINS More abundant in animals: O, C, N, H CARBOHYDRATES Occur in both. C n (H 2 O) n sugars, cellulose, starch LIPIDS (Fats) Occur in both: C, H, O Fats, oils, waxes (e.g. leaf cuticles) LIGNIN Occurs in plants: complex aromatic ring structures, large molecules All of these + Time + Temperature + Pressure = KEROGEN

28. Types of Kerogen Type I : algal kerogen “best” oil source Lipid-rich Type II : herbaceous kerogen Good oil source Includes zooplankton (sapropelic) Type III : woody kerogen (coaly) Good gas source Rich in humic components Type IV : amorphous kerogen

29. What happens when we subject kerogen to subsurface conditions? KEROGEN Diagenesis Catagenesis Metagenesis Shallow subsurface Normal pressure and temperature Released: CH 4 , CO 2 , H 2 O Overall decrease in O Overall increase in H and C Deeper subsurface Increased pressure and temperature Released: oil & gas Overall decrease in H and C Metamorphism High temperature and pressure Only C remains: becomes graphite

30. When is oil expelled?

31. Migration of hydrocarbons Primary From source rock to “carrier bed” Secondary Through the carrier bed/ structure to the reservoir How? As long as the oil droplets expelled are < pore throats, buoyancy will migrate the droplets until they reach a throat through which they cannot pass. Further movement can only occur when the displacement pressure of the oil exceeds the capillary pressure of the pore This process progresses until the oil column reaches a rock whose pores are so small that the oil column pressure cannot force further movement: the oil is trapped against a CAP ROCK (seal)

32. The Reservoir Rock Must have sufficient porosity ( F ) to store the oil Must have sufficient permeability (K) to allow fluid flow F % = (volume of voids / total volume of rock) x 100 Effective F = total volume of voids that are interconnected K: measured in Darcy units (commonly miliDarcy) Often measured as Kv and Kh due to grain orientation/ heterogeneity issues The perfect Reservoir rock: 10 – 30% F and 500 – 1000mD Well sorted, medium-coarse grain size Laterally continuous with no poor RQ intervals/ facies Kv Kh x Kh z

33. The Trap A subsurface obstacle to flow of petroleum to the earth’s surface. Classified (broadly) into Structural Traps Formed by tectonism, diapirism, gravitational and compactional processes, e.g. folds and faults. Stratigraphic Traps Trap geometry is essentially inherited from the original depositional architecture, e.g. pinchout and unconformity traps Hydrodynamic Traps