GEOL 40310 Lecture A6 - Appraisal 1 - 2023-2024 PDF

Geol 40310 Fossil Fuels and Carbon Capture & Storage (CCS) Lecture A6: Appraisal 1: Drilling, and oil-in-place calculations Autumn 2023-24 T Manzocchi, University College Dublin 1 1 Lecture A6: Appraisal 1 Drilling: Drilling operations Mud weight and casing Sediments and geofluids Pore Pressure...

Geol 40310 Fossil Fuels and Carbon Capture & Storage (CCS) Lecture A6: Appraisal 1: Drilling, and oil-in-place calculations Autumn 2023-24 T Manzocchi, University College Dublin 1 1 Lecture A6: Appraisal 1 Drilling: Drilling operations Mud weight and casing Sediments and geofluids Pore Pressure Fracture Pressure Macondo Drilling disaster (Deepwater Horizon) Objectives of reservoir appraisal Equation for oil volume in place (STOIIP) and definitions of: Gross-rock volume Net:gross ratio Porosity Oil saturation Wireline logging: Gamma Log – Determination of Net:Gross Formation density log: Determination of porosity Resistivity log: Determination of saturation 2 GEOL 40310 Lecture A6 1 Stages of work in a reservoir Appraisal Lectures A4, A5: Exploration Lectures A6, A7, A8: Appraisal Lectures A9, A10, A11: Development & Production 3 3 Exploration drilling rigs Drillship Jack-up Semi-submersible 4 4 GEOL 40310 Lecture A6 2 The drill rig Drill pipe – typically 30’ long Tricone bit 5 5 The travelling block 6 6 GEOL 40310 Lecture A6 3 Making pipe on the drill-floor 7 7 Mud circulation system 8 Schlumberger Oilfield review 2012 8 GEOL 40310 Lecture A6 4 Drilling curve SPE PetroWiki 9 9 Oil well drilling and casing Cementing casing Drilling out cement Drilling mud Open Hole Drill bit As a well is drilled, the density of drilling mud is modified so that is matches the porepressure of the formation. Steel casing is cemented in place to isolate formations with different pore pressure 10 regimes. 10 GEOL 40310 Lecture A6 5 Normally pressured sediments Sea Factor driving Factor allowing compaction: compaction: Porosity 0 0.1 0.2 0.3 1000 Sediment 1500 2000 2500 3000 3500 4000 Flow of pore water Weight of overlynig sediments 0 500 4500 5000 11 11 Normally pressured sediments Pressure (MPa) Sea 0 50 100 150 0 𝜎𝑣 = 𝜌ҧ𝑏𝑢𝑙𝑘 𝑔ℎ 1500 2000 Depth (m) Water saturated Sediment 500 1000 2500 𝑃 𝜎𝑣 𝑃 = ρ𝑤𝑎𝑡𝑒𝑟 𝑔ℎ 3000 3500 4000 4500 5000 12 12 GEOL 40310 Lecture A6 6 Over-pressured sediments Sea 100 150 normally-pressured 500 1000 1500 2000 𝑃 𝜎𝑣 2500 3000 Over-pressured Very low permeability layer 50 0 Depth (m) Shale Flow of pore water sand Pressure (MPa) 0 sand Restricted flow of pore water 3500 4000 4500 5000 When the flow of water is restricted, pore pressures become elevated and the pore water starts supporting some of the weight of the grains. 13 13 Drilling mud and overpressure The density of the drilling mud in the well bore is designed to balance the pore pressure in the formation. Pressure (MPa) 0 50 100 150 0 500 1000 1500 Depth (m) 2000 2500 3000 3500 4000 4500 5000 14 14 GEOL 40310 Lecture A6 7 Drilling mud and overpressure The density of the drilling mud in the well bore is designed to balance the pore pressure in the formation. Pressure (MPa) 0 50 100 150 0 500 1000 1500 Depth (m) 2000 2500 3000 3500 4000 4500 5000 15 15 Drilling mud and overpressure The density of the drilling mud in the well bore is designed to balance the pore pressure in the formation. Pressure (MPa) 0 50 100 150 0 500 1000 1500 Depth (m) 2000 2500 3000 3500 4000 4500 5000 16 16 GEOL 40310 Lecture A6 8 Drilling mud and overpressure The density of the drilling mud in the well bore is designed to balance the pore pressure in the formation. Pressure (MPa) 0 50 100 150 0 500 1000 1500 Depth (m) 2000 2500 3000 3500 4000 Blow out: Consequence of drilling into a highly Over-pressured permeable formation with an insufficient mud weight. 4500 5000 Flow! 17 17 Transocean Deepwater Horizon Macondo Disaster: April 2010 Gulf of Mexico: Extremely rapid sedimentation rate key to generating overpressures. Macondo - Est. 4.9 million barrels of oil spilt - Cost to BP: $55 Billion (est. Feb 2016). 18 18 GEOL 40310 Lecture A6 9 Pore pressure and rock fracture Pressure (MPa) 0 50 100 150 0 The stress tensor: 𝜎1 > 𝜎2 > 𝜎3 500 1000 𝜎𝑣 1500 Depth (m) 2000 Typical pore pressure 2500 3000 Pore pressure, P 3500 4000 Stress and intrinsic tensile strength of the rock (T) are holding the grains together. If the pore pressure (P) exceeds the sum of these, the rock will fracture. 4500 5000 19 19 Pore pressure and rock fracture Pressure (MPa) 0 50 100 150 0 The stress tensor: 𝜎1 > 𝜎2 > 𝜎3 500 1000 1500 𝜎𝑣 Typical fracture pressure Depth (m) 2000 2500 Typical pore pressure 3000 Pore pressure, P 3500 4000 4500 Stress and intrinsic tensile strength of the rock (T) are holding the grains together. If the pore pressure (P) exceeds the sum of these, the rock will fracture. 5000 Fracture criterion: 𝑃 ≥ 𝜎3 + 𝑇 20 20 GEOL 40310 Lecture A6 10 Use of casing to isolate well sections Upper section: lower mud weight Pressure (MPa) 0 50 100 150 0 500 1000 1500 Depth (m) 2000 2500 3000 3500 4000 4500 5000 21 Safe drilling: Pore Pressure < mud weight < fracture pressure 21 Use of casing to isolate well sections Lower section: higher mud weight. Upper formation isolated from well behind steel casing Upper section: lower mud weight Pressure (MPa) Pressure (MPa) 0 50 100 0 50 100 150 0 150 0 500 500 1000 1000 1500 1500 Depth (m) 2500 Depth (m) 2000 2000 2500 3000 3000 3500 3500 4000 4000 4500 4500 5000 5000 Safe drilling: Pore Pressure < mud weight < fracture pressure 22 22 GEOL 40310 Lecture A6 11 Discovering hydrocarbon by drilling Trap “Top seal” Reservoir rock “Bottom seal” Appraisal 23 23 Discovering hydrocarbon by drilling Trap “Top seal” Dry hole water Reservoir rock Oil reservoir “Bottom seal” oil water OWC Saturated reservoir gas oil water Gas cap (gas & water present) GOC OWC Oil leg (oil & water present) Water saturated reservoir rock Gas reservoir gas water GWC OWC: Oil-Water contact GWC: Gas-Water contact GOC: Gas-Oil contact 24 24 GEOL 40310 Lecture A6 12 Reservoir appraisal: I have discovered a reservoir: now what? - Should I try to develop it myself, or should I sell it? - What is it worth? - How big is it? - What is in it? - How can I produce the hydrocarbon most efficiently? - What are the principal uncertainties? 25 25 Reservoir Appraisal Oil production rate Cash flow during the field life cycle 500 400 300 • A successful appraisal means that the correct development decisions are made, and the facilities designed are fit for purpose. • If the final production volume turns out to be less than expected, the infrastructure will have been overdesigned and therefore too expensive. • If potential production rates have been underestimated, the cashflow is less than it might have been given a better production design. 200 100 0 -100 -200 -300 -400 -500 100 15 20 25 Production Decommissioning 200 10 Development 300 Appraisal 400 Exploration 5 Gaining Access Cumulative cash flow (million $) 0 500 0 -100 -200 -300 -400 -500 0 5 10 15 20 25 Time (years) Jahn et al. (2008) 26 26 GEOL 40310 Lecture A6 13 Reservoir Appraisal Objectives What is the hydrocarbon in place? Gross Rock Volume: Controlled by shape of structure, dip of flanks, positions and throws of fault, Depths of fluid contacts (OWC, GOC) Net:Gross Ratio: Depositional environment, facies distributions, diagenesis Porosity: Depositional environment, facies distributions, diagenesis Hydrocarbon Saturation: Reservoir quality, capillary pressure. What is the likely performance of the reservoir during production? What hydrocarbon production rates are possible? Is the reservoir compartmentalised structurally and/or stratigraphically? What is the reservoir quality and heterogeneity? What is the pressure regime and is there pressure support? (i.e. aquifer, gas cap). What are the characteristics of the fluids? Fluid compositions and PVT properties, Formation volume factors, Gas:Oil ratio, viscosity. How does these vary spatially? Not only the hydrocarbons are significant – for example: H2S is poisonous and corrosive – is it present dissolved in the oil? Barium is a major cause of scale precipitation: what is its concentration in the formation water? 27 27 Reservoir Appraisal Objectives What is the hydrocarbon in place? Gross Rock Volume: Controlled by shape of structure, dip of flanks, positions and throws of fault, Depths of fluid contacts (OWC, GOC) Net:Gross Ratio: Depositional environment, facies distributions, diagenesis Lecture A6 Porosity: Depositional environment, facies distributions, diagenesis Hydrocarbon Saturation: Reservoir quality, capillary pressure. What is the likely performance of the reservoir during production? What hydrocarbon production rates are possible? Is the reservoir compartmentalised structurally and/or stratigraphically? What is the reservoir quality Lecture A8and heterogeneity? What is the pressure regime and is there pressure support? (i.e. aquifer, gas cap). What are the characteristics of the fluids? Fluid compositions and PVT properties, Formation volume factors, Gas:Oil ratio, viscosity. How does these vary spatially? Not only the hydrocarbons are significant – for example: Lecture A7 H2S is poisonous and corrosive – is it present dissolved in the oil? Barium is a major cause of scale precipitation: what is its concentration in the formation water? 28 28 GEOL 40310 Lecture A6 14 Hydrocarbon Volume in place (example for oil) Gross Rock Volume Formation Volume Factor Porosity Stock tank Oil Initially In Place STOIIP = GRV * NTG * φ* SO * (1/BO) Net:Gross Ratio Oil saturation Ultimate Recovery UR= STOIIP * RECOVERY FACTOR 29 29 Gross-rock volume : The volume of rock between the oil-water contact and the top seal Seal rock Water saturated Reservoir rock Top reservoir structure contour map Oil saturated reservoir rock B A’ A 2000 2200 2400 A’ A Spill point B B’ 2000 2200 Spill point 2400 B’ Contours: depth below datum of the top of the reservoir formation The maximum possible column height is controlled by the spill point. 30 30 GEOL 40310 Lecture A6 15 Net: Gross Ratio: The fraction of the volume that is productive Shale Sand Ca. 65% NTG 20m 31 31 Porosity: The fraction of the Net volume that is fluid filled Thin Section of a porous sandstone Pore Quartz Grain NB Blue is stained epoxy resin that the sample is impregnated with while the thin section is made 32 32 GEOL 40310 Lecture A6 16 Oil Saturation: The fraction of the pore space that is oil-filled. Producing OWC OWC Irreducible Water Saturation Economic OWC oil water Transition zone Oil Column 100% oil production 100% water production Oil Water contact Free Water Level FWL 0 0.5 1 Water Saturation 33 33 Formation volume factor: The volume of oil in the reservoir required to produce one unit volume of oil at surface Reservoir Surface oil water OWC Gas Oil + dissolved gas Oil Usually liquids expand at lower pressure. The oil formation volume factor, however, is usually > 1, as gas comes out of solution as the oil is depressurised. 34 34 GEOL 40310 Lecture A6 17 Hydrocarbon Volume in place (example for oil) Gross Rock Volume Stock tank Oil Initially In Place Formation Volume Factor Porosity STOIIP = GRV * NTG * φ* SO * (1/BO) Net:Gross Ratio Source of information: Seismic and drilling Oil saturation Well logging Oil Sampling (Next lecture) 35 35 Exploration, appraisal and development drilling: Ula Field, Norway Field discovered 1976 by BP Came on stream 1986. Est STOIIP: 1.1 billion bbls. Produced to 2018: 496 million bbls. Total Investment to 2018: 17 billion NOK (ca. 4 billion US$). 36 36 GEOL 40310 Lecture A6 18 Ula Field Appraisal: 9 wells, 10 years: At least 6 different OWCs 37 Heum (1996), Norwegian Petroleum Directorate 37 Hydrocarbon Volume in place (example for oil) Gross Rock Volume Stock tank Oil Initially In Place Formation Volume Factor Porosity STOIIP = GRV * NTG * φ* SO * (1/BO) Net:Gross Ratio Source of information: Seismic and drilling Oil saturation Well logging Oil Sampling (Next lecture) 38 38 GEOL 40310 Lecture A6 19 Wireline logging 39 Jahn et al. (2008) 39 The Gamma Log Records the natural radioactivity produced by the rock. Radioactive elements in sedimentary rocks: potassium, thorium, uranium (typical contribution: 30,000: 4:1) Jahn et al. (2008) 40 40 GEOL 40310 Lecture A6 20 Sequence Net:Gross Ratio from the Gamma log 41 Jahn et al. (2008) 41 Porosity from the Formation Density log Gamma rays directed into the formation from a radioactive source. The rays lose energy when they collide with electrons (“Compton scattering”). Used to measure the porosity of the formation porosity Grain density Bulk density Fluid density Jahn et al. (2008) 42 42 GEOL 40310 Lecture A6 21 Water saturation from Resistivity logs • An electric current is forced through the formation, and the resistivity is measured. • Formation water is conductive, hydrocarbon and rock grains are not. • If the porosity is know, the hydrocarbon saturation can be established. Archie’s Equation: Resitivity of formation water 1 1 R n Sw =  W    RT  porosity Formation resistivity Formation resistivity factor, often ca. 2.0 43 Jahn et al. (2008) 43 Types and resolution of different logging tools Type Measures Vertical resolution (m) Uses Electrical (SP, Resistivity) Electrical properties of rocks and fluids 1.5 – 2 Water saturation, fluids, correlation Gamma Natural radioactivity 0.2 - 0.3 Neutron Hydrogen atom density 0.4 Lithology, shale content, correlation Porosity, sometimes lithology Density Rock (incl. pore) density 0.4 Porosity, sometimes lithology Sonic Velocity of sound waves through rock 0.6 Porosity, sometimes lithology Caliper Well bore diameter and shape Dipmeter Orientation of planar features Slatt (2006) Calibration, stress orientation 0.01 Structure and depositional environment 44 44 GEOL 40310 Lecture A6 22 Hydrocarbon Volume in place (example for oil) Gross Rock Volume Formation Volume Factor Porosity Stock tank Oil Initially In Place STOIIP = GRV * NTG * φ* SO * (1/BO) Net:Gross Ratio Source of information: Seismic and drilling Oil saturation Oil Sampling (Next lecture) Well logging 45 45 Hydrocarbon Volume in place (example for oil) Gross Rock Volume Stock tank Oil Initially In Place Formation Volume Factor Porosity STOIIP = GRV * NTG * φ* SO * (1/BO) Net:Gross Ratio Oil saturation Ultimate Recovery UR= STOIIP * RECOVERY FACTOR Recovery factor depends on permeability, fluid viscosity, reservoir architecture, etc., etc. 46 46 GEOL 40310 Lecture A6 23