Chapter 7 Origin and Migration of Petroleum PDF

MKPP 1213 APPLIED GEOSCIENCE & GEOPHYSICS LECTURER: DR. CHONG AIK SHYE CHAPTER 7 Origin and Migration of Petroleum 3 Origin of Petroleum • Inorganic theories – Cosmic sources: hc’s found in meteorites • Consolidation of H and C during earth cooling. • The discovery (Mueller, 1963) of a type of...

MKPP 1213 APPLIED GEOSCIENCE & GEOPHYSICS LECTURER: DR. CHONG AIK SHYE CHAPTER 7 Origin and Migration of Petroleum 3 Origin of Petroleum • Inorganic theories – Cosmic sources: hc’s found in meteorites • Consolidation of H and C during earth cooling. • The discovery (Mueller, 1963) of a type of meteorite called carbonaceous chondrites. • Chondritic meteorites contain greater than 6% organic matter and traces of various hydrocarbons including amino acids. • The chief support is that the hydrocarbons methane, ethane, acetylene, and benzene have repeatedly been made from inorganic sources. 4 Origin of Petroleum • Inorganic theories – Reaction of metal carbides in the earth • Mendele’ve (1902) reasoned that metallic carbides deep within Earth reacted with water at high temperatures to form acetylene. CaC2 + 2H2O = C2H2 + Ca(OH)2 • Then Porfir’ev (1974) – iron carbide react with percolating water to form methane and other oil hydrocarbons. FeC2 + 2H2O = CH4 + FeO2 • There is little evidence for the existence of iron carbide in the mantle. 5 Origin of Petroleum • Organic theory • From transformation of biomatter. • The biogenic origin of petroleum is widely accepted on the basis of geochemical studies. • The deposition of an organic-rich sediment is favored by a high rate of production of organic matter and a high preservation potential. • The preservation of organic matter is favored by anaerobic bottom conditions and a rapid sedimentation rate. 6 Origin of Petroleum 7 Basic Components of Organic Matter • The principal biological components of living organisms are: • PROTEINS – More abundant in animals: O, C, N, H • CARBOHYDRATES – Occur in both. Cn(H2O)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 8 Average Composition of Biomolecules C H O S N Lipids 76 12 12 - - Proteins 53 7 22 1 17 Carbohydra tes 44 6 50 - - Lignin 63 5 31.6 0.1 0.3 83-87 10-14 0.1-1.5 0.5-6 0.1-1.5 Petroleum 9 Basic Components of Organic Matter (OM) • How do living organisms become Organic Matter?  Organism dies: decay begins  Complex molecules break down rapidly. • How then does OM accumulate in the vast quantities needed for identified oil volumes?  Accumulation of large quantities of living organisms requires Oxygen. To facilitate oil generation, the OM produced by the death of these organisms must be preserved. Preservation of large quantities of dead organisms requires Anoxia (anoxic environment). 10 Productivity and Preservation of Organic Matter • Geochemical evidence that oil source beds were deposited in four main anoxic environments in the geological record. – Large anoxic lakes – Anoxic silled basins – Anoxic layers caused by upwelling – Open-ocean anoxic layers 11 Productivity and Preservation of Organic Matter – Large anoxic lakes Permanent stratification promotes development of anoxic bottom waters, particularly in large lakes not subject to seasonal overturn. E.g. Lake Tanganyika: warm equitable conditions all year. Lake Tanganyika NW SE PERMANENT THERMOCLINE CH4 , H2S 1.5km Longitudinal section 525km 12 Productivity and Preservation of Organic Matter – Anoxic silled basins •Landlocked silled basins with positive water balance: good chance of developing anoxia. E.g. Black Sea, Baltic Sea. In arid-condition silled basins (Red Sea, Mediterranean). 13 Productivity and Preservation of Organic Matter – Anoxic layers caused by upwelling •Only develop when surface biological processes exceed deep water oxygen supply E.g. Benguela current, Peru coastal upwelling. 14 Total Organic Carbon (TOC) -Source rock evaluation • If a rock contains significant amounts of organic carbon, it is a possible source rock for petroleum or gas. • The TOC content is a measure of the source rock potential and is measured with total pyrolysis. • The table below shows how TOC (in weight percent) relates to the source rock quality. TOC Quality 0.0-0.5 poor 0.5-1.0 fair 1.0-2.0 good 2.0-4.0 very good >4.0 excellent 15 How does OM become Oil? • 2 stages: • Conversion of OM to kerogen • Conversion of Kerogen to oil and gas 16 Transformation of OM into Kerogen • As the organic matter is buried, it transforms from basic biological components into new polymeric organic compounds that eventually become kerogen. • What is kerogen? • Insoluble in organic solvents • Complex mixture of high molecular weight organic materials • Kerogen is composed of varying proportions of C, H, and O. General composition may be described as: • (C12H12ON0.16)x 17 Type of Kerogen - Source rock evaluation • It is important to identify the type of kerogen in a source rock. • Type I : algal kerogen • “best” oil source • Lipid-rich • Type II: herbaceous (liptinic) kerogen/ lipid-rich kerogen • Good oil source • Includes zooplankton (sapropelic) • Type III: woody (coaly/humic) kerogen • Good gas source • Rich in humic components • Type IV: amorphous kerogen 18 Type I Kerogen • • • • • Rare High-grade algal sediment Generally lacustrine Contains sapropelic OM Oil shales, coorongite & tasmanite, Boghead coals • H:O = 1.2- 1.7; H:C = 1.6 – 1.8 • Lipids are the dominant compounds 19 Type II Kerogen • Intermediate derivation • Commonly marginal marine • Mixture of continental and aquatic (planktonic) OM • Algal tissue, pollen, spores • Principal source for oil • H:C = about 1.4 20 Type III Kerogen • • • • Sediment containing primarily humic OM Terrestrial (woody) origin Equivalent of coal vitrinite Deposited at the oxic water/ sediment interface • Gas-prone • H:C < 1.0 (more C than H) 21 Type IV Kerogen • From any source • Oxidized, recycled or altered during an earlier thermal event • Inert carbonaceous material • H:C < 0.4 • No evolutionary path left: no hydrocarbons generated. 22 What happens to kerogen as it is buried and heated? • Large molecules crack to smaller low mol. wt. Geomonomers: 1000-6000m depth; 50-175°C – Initial products are H2O and CO2 • Increased temp and burial: – Volatile products lost (hydrogen, CH4) and liquids (C13 – C30) – O2 lost rapidly by dehydration and decarboxylation (loss of CO2 from fatty acids) – C and N lost least readily 23 What happens to kerogen as it is buried and heated? • Thus with increasing temperature: – C-content of kerogen rises – H:C ratio decreases • Two fractions are produced by thermal transformation of kerogen: – Fluid high in H (petroleum and natural gas precursor) – Residue high in C (e.g. bituminous coal, bitumen) 24 KEROGEN Diagenesis Shallow subsurface Normal pressure and temperature Released: CH4, CO2, H2O • Overall decrease in O • Overall increase in H and C Catagenesis Deeper subsurface Increased pressure and temperature Released: oil & gas • Overall decrease in H and C Metagenesis Metamorphism High temperature and pressure Only C remains: becomes graphite 25 When is oil expelled? 26 The result of this? • The amount of oil generated increases linearly with time • The amount generated increases EXPONENTIALLY with temperature. • Thus, TIME IS AN IMPORTANT FACTOR 27 Time and oil generation • The younger the source, the higher the temperature required to generate oil • RESIDENCE TIME 28 This Introduced the Concept of the OIL WINDOW • A range of temperatures through which oil generation can occur • Below 60°C: sediments are immature • Above the critical temperature (Approx 120°C): sediments are post-mature • Assumes that no migration of the oil has occurred (I.e. into lower temperature regimes) 29 The principal zone of oil formation during the thermal generation of petroleum hydrocarbons 30 Temperature is the single most important factor in thermal maturation 31 Time is the second most important factor in thermal maturation 32 Maturation of Kerogen - Source rock evaluation • Establishing the level of maturation of kerogen in the source rocks is vital in petroleum exploration. • The maturity of a source rock is a measure of the degree to which reactions have proceeded in the generation of petroleum products from organic matter. • With increasing maturity, first oil and then gas are expelled. • The rate of maturation may be dependent on temperature, time, and, possibly, pressure. 33 Purposes of Maturation Indicators • To recognize and evaluate potential source rocks for oil and gas by measuring their contents in organic carbon and their thermal maturities • To correlate oil types with probable source beds through their geochemical characteristics and the optical properties of kerogen in the source beds • To determine the time of hydrocarbon generation, migration and accumulation • To estimate the volumes of hydrocarbons generated and thus to assess possible reserves and losses of hydrocarbons in the system. 34 Maturation of Kerogen • • • • • Several techniques have been developed. Two commonly used maturation indices are: 1) Thermal maturity index (TTI) 2) Level organic maturation (LOM) TTI is calculated from a formula that integrates temperature with the time spent in each temperature interval (in increments of 10 oC) as a source rock is buried. • LOM is based on the assumption that reaction rate doubles for each 10oC increment of temperature. • LOM values of 7 – 13 (oil generation occurs), LOM = 13- 18 (gas generation occurs). 35 Maturation of Kerogen Time Temperature Index (TTI) 36 Maturation of Kerogen • Techniques for determining temperature: • Paleothermometers: two major groups of techniques are used: • 1. Chemical Paleothermometers a) Organic i. Carbon ratio ii. Electron spin resonance iii. Pyrolisis b) inorganic i. Clay mineral diagenesis ii. Fluid inclusion 37 Maturation of Kerogen • 2. Biological Paleothermometers a) Pollen coloration (TAI) -measure the color of organic matter (spores and pollen) -essential colorless and then change to yellow, orange and brown. b) Vitrinite reflectance -used a reflected-light microscope to measure the degree of reflectivity of vitrain (coal maceral). 38 Maturation of Kerogen 39 Migration of hydrocarbons • Oil (& gas) migrates from the source, through carrier beds and accumulates in the reservoir. • Primary migration – From source rock to “carrier bed”. • Secondary migration – Through the carrier bed/ structure to the reservoir. 40 Migration of hydrocarbons • How does migration occur? – 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). 41 Primary Migration • Hypotheses – 1. Migration of hc’s in clay compaction water – 2. Migration by molecular solution in water – Migration in micellar solution – Migration in gas charged solution – Migration via microfracturing of source rocks – Diffusion along kerogen network • Arguable that all of these processes are in operation 42 Primary Migration Porosity Decrease with Compaction. Shown are shale porosities from various regions. 43 Secondary Migration • Oil must be capable of continuous phase flow • Availability of continuous pore spaces allows continuous flow • Physical requirements for secondary migration are: – 1. Adequate supply of hydrocarbons – 2. Adequate continuous migration pathways – 3. Adequate pressure gradient to drive migration 44 Main Mechanisms of Secondary Migration • Migration by water drive • Migration by gas flushing • Fracture-bound migration 45 Buoyancy • Difference in densities between H2O and oil = main mechanism of secondary migration • All crude oils float on saline water, nearly all on freshwater • Thus, oil tends to migrate upwards through the heavier water • Subject to a buoyant force (Pb) 46 Gas Flushing • 2 fluids of different densities try to occupy the same trap • Heaviest fluid is displaced as lighter one moves above it 47 Secondary Migration • Different stages in the migration and accumulation of oil and gas in interconnected traps (after Gussow, 1968) 48 Next Class Chapter 8 Trapping Structure and Seal System 49 THANK YOU In the Name of God for Mankind www.utm.my