GEOL40310_LectureA04_Exploration1_2023.pdf

Geol 40310 Fossil Fuels and Carbon Capture & Storage (CCS) Lecture A4: Exploration 1: Petroleum Systems; Seismic imaging Autumn 2023-24 1 1 Exploration 1: Petroleum Systems, Seismic imaging The carbon cycle Coal Oil and gas: The “petroleum” system: Formation of hydrocarbon Source rocks Burial and...

Geol 40310 Fossil Fuels and Carbon Capture & Storage (CCS) Lecture A4: Exploration 1: Petroleum Systems; Seismic imaging Autumn 2023-24 1 1 Exploration 1: Petroleum Systems, Seismic imaging The carbon cycle Coal Oil and gas: The “petroleum” system: Formation of hydrocarbon Source rocks Burial and maturation Migration and accumulation in traps Reservoir rocks and Seal rocks Exploration, Appraisal, Development, Production Phases Seismic Acquisition and processing 2 2 GEOL 40310 Lecture A4 1 The Carbon Cycle Kroeger et al. (2011) • • • • Carbon is cycled between the atmosphere, the oceans and rocks. The surficial cycle transfers carbon (CO2) between soil, vegetation, the oceans and the atmosphere. The subsurface cycle involves organic matter burial and remobilisation as oil and gas. This migrates to surface naturally over millions of years transferring carbon (CH4) to the atmosphere. 3 3 Geological time chart Mass extinction Age of many source rocks for oil Mass extinction Age of much coal Gas source rocks are less restricted to particular ages Colonization of land by plants 4 4 GEOL 40310 Lecture A4 2 The Carboniferous Period Much of the world’s coal is the product of land-plants alive in the Carboniferous period Oil is not produced from land-plants (it is produced from algal and planktonic material). 5 5 Lignite mine Hungary Bituminous coal mine, India 6 6 GEOL 40310 Lecture A4 3 Formation of coal http://www.undergroundcoal.com.au 7 7 Global coal distribution 8 GEOL 40310 Lecture A4 4 Global coal consumption by region 1990-2022 9 Global coal trade movements 2022 10 GEOL 40310 Lecture A4 5 Top 10 emitters to the EU-ETS 2021 EU-ETS: European Union Emissions trading scheme https://ember-climate.org/ 11 11 Terminology Fossil Fuels Hydrocarbons Coal • • Petroleum (i.e. Oil) Natural Gas Coal is formed from the burial of land-plants Hydrocarbons have a more complex origin as part of a “petroleum system” 12 GEOL 40310 Lecture A4 6 Petroleum Systems • A functional petroleum systems comprises a combination of several geological processes Geometrical necessity: Stratigraphic necessities: Seal rock Trap Required Processes: Accumulation and retention Reservoir rock Migration Source rock Maturation 13 13 Formation of Hydrocarbons Photosynthesis: 6CO2 + 12H2O → C6H1206 + 6H2O + 602 Glucose converted to more complex organics within plants or animals that have eaten them. Proteins: Amino acids in animals and to a lesser extent plants. Carbohydrates - sugars, cellulose, starch present in animals and plants Cn(H2O)n. Lipids –Fats, oil, waxes present in animals and plants. C5H8 Lignin – Fibrous, structural component of land plants. The plants and animals die, followed by: - Oxidation of organic material to produce CO2 and H2O Or - Rapid burial and conversion to kerogen and, ultimately, oil or gas. 14 14 GEOL 40310 Lecture A4 7 Formation of Hydrocarbons 15 15 Kerogen types Type I Algal Type I Type II Liptinitic (phyto- and zooplankton) Type II Type III Type III Humic (land plants) 16 Selley (1998) 16 GEOL 40310 Lecture A4 8 Present-day Distribution of organic carbon in the upper sedimentary layer (0.5cm) Two factors at play: - Organic productivity - Anoxia 17 Allen and Allen (2013), after Romankevich (1984) 17 Outcrops of source rocks for oil and gas • • • Thermally matured organic rich marine clays Source rocks for conventional reserves Source and reservoir rock for unconventional “shale gas” reserves Ordovician Utica Shale, New York State Jurassic Kimmeridge Clay, Wessex Basin Michael C. Rygel via Wikimedia Commons 18 18 GEOL 40310 Lecture A4 9 Weight %, total organic carbon 0% Total Organic Carbon (TOC) 40% TOC (weight %) Poor 0 - 0.5 Fair 0.5 – 1 Good 1–2 Very Good 2 -4 Excellent >4 100m Kimmerdge Clay Formation: Source rock for may North Sea Reservoirs Source rock quality 19 Jenkyns et al. (2002) 19 Petroleum Systems • A functional petroleum systems comprises a combination of several geological processes Stratigraphic necessities: Geometrical necessity: Seal rock Trap Required Processes: Accumulation and retention Reservoir rock Migration Source rock Maturation 20 20 GEOL 40310 Lecture A4 10 Burial and maturation Maturation level assuming present-day geothermal gradient. Oligocene – recent Present day 60° isoterm Paleocene Oil Generation Cretaceous Present day 120° isoterm Jurassic Gas Generation Present day 220° isoterm Triassic Barren Permian Example for the Central Graben (UKCS). 21 Selley (1998) 21 Crude oil samples from New Zealand fields Photo: Trans-Orient Oil 22 22 GEOL 40310 Lecture A4 11 Migration and accumulation in traps Oil reservoirs trapped by gentle folds in the reservoir sequence - Oil migrates as rivulets of isolated stringers at the pore scale. - Movement is promoted by the fluid buoyancy and retarded by the widths of the water-wet pore throats. - Oil accumulates within highs in the carrier sequences (traps) 23 23 Natural Gas migration to surface “Gate to Hell”, Turkmenistan 24 Photo: somethinteresting.com 24 GEOL 40310 Lecture A4 12 Trap • A container for the oil or gas. • Hydrocarbon is less dense than water, therefore it will preferentially flow upwards and the bucket must be inverted e.g.: Fold belt, Zagros Mountains, Iran 25 25 Trap • A trap is the container for the oil or gas. • Hydrocarbon is less dense than water, therefore it will preferentially flow upwards and the bucket must be inverted Wyoming State Geological Survey 26 https://www.wsgs.wyo.gov/energy/oil-gas-resources.aspx 26 GEOL 40310 Lecture A4 13 Reservoir rocks 100 μm Sandstone (McCann and Sothcott (2009) Fractured Limestone Reservoir rocks need: - Porosity (gaps), - permeability (to allow fluid flow) 5μm Chalk (Stand 2007) A reservoir does not need to be a sedimentary rock: igneous and metamorphic rocks can provide excellent hydrocarbon reservoirs 27 27 Seal rocks • A seal must be able to prevent hydrocarbon from leaking over geological time • Effective seals have very low permeability and high ductility • Evaporite or shale deposits seal most hydrocarbon reservoirs Carnallite: (potassium magnesium chloride) mines , Yekaterinburg 28 28 GEOL 40310 Lecture A4 14 Petroleum Systems • A functional petroleum systems comprises a combination of several geological processes Stratigraphic necessities: Geometrical necessity: Seal rock Trap Required Processes: Accumulation and retention Reservoir rock Migration Source rock Maturation 29 29 Exploration 1: Petroleum Systems, Seismic imaging The carbon cycle Coal Oil and gas: The petroleum system: Formation of hydrocarbon Source rocks Burial and maturation Migration and accumulation in traps Reservoir rocks and Seal rocks Exploration, Appraisal, Development, Production Phases Seismic Acquisition and processing 30 30 GEOL 40310 Lecture A4 15 Stages of work in a reservoir Appraisal Lectures A4, A5: Exploration Lectures A6, A7, A8: Appraisal Lectures A9, A10: Development & Production 31 31 Marine seismic acquisition An energy source (watergun) pumps soundwaves of various frequencies into the subsurface. A proportion of the energy is returned (reflected) at an interface (e.g. major geological boundary). A resulting ‘picture’ of the subsurface structure is produced. 32 Bjørlykke (2010) 32 GEOL 40310 Lecture A4 16 Acoustic Impedance: Seismic Velocity * Density. 33 Bjørlykke (2010) 33 Depth Seismic reflection and Multiples Time Original seismic Section Reprocessed to remove mutiples. 34 Flesja et al. (2010) 34 GEOL 40310 Lecture A4 17 Seismic migration Not all reflectors are flat! Depth Reflections bounce off surface at 90° Time Depth Section Time Stacked section Migrated section For this surface, three reflections are recorded at certain positions. None are reflected from vertically beneath the stack location. Seismic migration shifts the source of the reflections laterally, to resolve the actual geometry of the reflector. 35 Bacon et al (2003) 35 Stacked Section Migrated Section 36 http://principles.ou.edu/seismic_explo/reflect/reflect.html 36 GEOL 40310 Lecture A4 18 Migration is non-unique, iterative and the subject of immense current technological advances. Central North Sea salt diapir Kirchhoff Migration Reverse time migration http://www.geoexpro.com/articles/2010/04/depth-imaging-seeing-the-invisible37 37 Supercomputers by processing power, June 2019 Processing power by sector Tflops / sec Top 15 industry supercomputers Petroleum E&P Other 38 38 GEOL 40310 Lecture A4 19 Regional 2D Seismic acquisition for frontier exploration Seismic line, South Porcupine Basin: Virtual Seismic Atlas 39 39 3D Seismic acquisition 40 40 GEOL 40310 Lecture A4 20 3D Seismic data for detailed planning 41 Image: Spectrum website. 41 A B Amplitude Extraction Amplitude AI Red soft, black hard. A Example: RMS amplitude extraction from specified interval. B Upper Cretaceous, offshore Norway. Jackson & Sømme (2011) 42 42 GEOL 40310 Lecture A4 21 Direct Hydrocarbon Indicators Acoustic impedance softer harder Depth Amplitude tuned to gas-sand response 43 Bacon et al (2003) 43 Stages of work in a reservoir Appraisal Lectures A4, A5: Exploration Lectures A6, A7, A8: Appraisal Lectures A9, A10, A11: Development & Production 44 44 GEOL 40310 Lecture A4 22