GEOL 40310 Fossil Fuels and Carbon Capture & Storage Lecture A8 (PDF)

Geol 40310 Fossil Fuels and Carbon Capture & Storage (CCS) Lecture A8: Appraisal 3: Reservoir Pressures and Fluid flow T. Manzocchi, University College Dublin Autumn 2023-24 1 1 Lecture A8 - Appraisal 3: Reservoir Pressures and Fluid flow Reservoir fluid pressures and oil saturation Phase pressur...

Geol 40310 Fossil Fuels and Carbon Capture & Storage (CCS) Lecture A8: Appraisal 3: Reservoir Pressures and Fluid flow T. Manzocchi, University College Dublin Autumn 2023-24 1 1 Lecture A8 - Appraisal 3: Reservoir Pressures and Fluid flow Reservoir fluid pressures and oil saturation Phase pressure and capillary pressure Repeat Formation Testing (RFT) Finding Fluid/Fluid Contacts Permeability Darcy’s Law Radial flow and the well productivity index Drill Stem Testing (DST) 2 2 GEOL 40310 Lecture A8 1 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? 3 3 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? This lecture: Next lecture: Fluid compositions and PVT properties, Formation volume factors, Gas:Oil ratio, Reservoir andvary spatially?Drive mechanisms and viscosity.Pressures How does these Not only theflow hydrocarbons are significant – for example: factors Fluid recovery 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? 4 4 GEOL 40310 Lecture A8 2 Pressure / depth plots Hydrostatic: Lithostatic: Weight of water Weight of rock Pressure (MPa) 0 50 100 150 Water Sediment 0 500 1000 1500 Depth (m) 2000 2500 3000 𝑃𝐻𝑦𝑑𝑟𝑜 = ρ𝑤𝑎𝑡𝑒𝑟 𝑔ℎ 𝜎𝑣 = 𝜌ҧ𝑏𝑢𝑙𝑘 𝑔ℎ 3500 4000 4500 Pore pressure: 𝑃𝐻𝑦𝑑𝑟𝑜𝑠𝑡𝑎𝑡𝑖𝑐 ≤ 𝑃 ≤ 𝑃𝐹𝑟𝑎𝑐𝑡𝑢𝑟𝑒 Overpressure if 𝑃 > 𝑃𝐻𝑦𝑑𝑟𝑜𝑠𝑡𝑎𝑡𝑖𝑐 5000 5 5 Pressure / depth plots 𝜎𝑣 𝜎ℎ𝑚𝑖𝑛 Shallow depth: vertical fractures as minimum stress is horizontal 𝜎ℎ𝑚𝑖𝑛 Shallow 𝜎𝑣 Deeper: horizontal fractures as minimum stress is vertical 𝜎𝑣= 𝜎𝑚𝑖𝑛 𝜎ℎ 𝜎ℎ Deep 𝜎𝑣= 𝜎𝑚𝑖𝑛 6 6 GEOL 40310 Lecture A8 3 Pressure-depth requirements for oil preservation Central North Sea database Retention capacity (psi) Dry hole discovery Ikon Science: http://www.ikonscience.com/geopressure/seal-breach-analysis Retention capacity: fracture pressure minus pore pressure 7 7 Pressure / depth relationship in a reservoir Pressure (MPa) 0 50 100 Top Seal (water saturated) 150 0 500 1000 1500 Depth (m) 2000 Oil + Water Sand grain Water Oil 2500 3000 Free water Level 3500 4000 Water 4500 5000 Oil is less dense than water, so oil pressure in a 8 reservoir is greater than water pressure 8 GEOL 40310 Lecture A8 4 Capillary pressure Top Seal PC = (o −  w )gh pc Oil + Water Height above FWL (h) Pressure o gh w gh Free Water Level Depth Water Capillary Pressure: Oil pressure minus water pressure 9 9 Wettability Water-wet reservoir rock Top Seal Oil-wet reservoir rock Oil + Water Free water Level Reservoirs are water-wet while filling. They can become oil-wet over geological time. Water 10 10 GEOL 40310 Lecture A8 5 Interface between two fluids and a solid: Contact angle, wettability. Water wet Air wet air water 11 11 Interface between two fluids: curved if the fluids are at different pressure Young Laplace Equation:  1 1  PO − PW =   +  R R  1 2 Capillary pressure R2 R1 Principal radii of curvature PO Interfacial tension (property of the fluid/fluid combination) Units: mN/m ≡ dyne/cm 𝑃𝑊 For the same interfacial tension, smaller radius of curvature at higher capillary pressure 12 12 GEOL 40310 Lecture A8 6 Capillary pressure and water saturation Capillary pressure For the same interfacial tension, smaller radius of curvature at higher capillary pressure Capillary entry pressure: The capillary pressure needed for the non-wetting phase to enter the largest pore throats Capillary entry pressure 0 1 Water saturation 13 13 Drainage capillary pressure curve: a function of grain size Coarse grained: Large pore throw radii Fine grained: small pore throw radii Capillary pressure: oil pressure minus water pressure Capillary pressure (psi) Reservoir filling along drainage capillary pressure curves 20 40 60 80 100 Water saturation (%) Shephard (2009) 14 14 GEOL 40310 Lecture A8 7 Drainage and imbibition Increase capillary pressure and oil saturation Drainage: non wetting phase (oil) increases its saturation through the largest pore throats Decrease capillary pressure and oil saturation Imbibition: Wetting phase (water) increases its saturation by expanding grain edge film thickness. “Snap-off” across pore throats traps the non-wetting phase. 15 Drainage and imbibition Drainage: Decrease of the wetting phase saturation Imbibition: Increase of the wetting phase saturation A. B. water C. water Migration and trapping: DRAINAGE oil Oil Recovery: IMBIBITION (if water-wet reservoir) B. Capillary pressure oil Hysteresis: the property depends on historical as well as current conditions Drainage Imbibition 0 C. Water saturation Capillary entry pressure A. 1 16 16 GEOL 40310 Lecture A8 8 Pressures and pressure gradients in a water-wet reservoir Pressure (psi) 4000 8000 4200 4400 4600 4800 Irreducible (connate) water saturation Capillary threshold pressure 8200 Crest 900 oil 8600 Oil: 0.33 psi/ft 8800 9000 800 Height above FWL GOC Depth (ft) gas Gas: 0.08 psi/ft Height above FWL 900 8400 Gas: 0.37 psi/ft 700 600 500 400 Oil: 0.12 psi/ft 300 200 9200 600 500 400 300 Transition zone 200 0 0 0 water 700 100 100 OWC FWL 800 100 200 Capillary pressure (psi) 9400 overpressure 300 0 0.5 1 Water saturation Height of the transition zone and shape of the water saturation profile depends on the drainage capillary pressure curve of the reservoir rock. 17 17 Finding the oil-water contact without considering pressure Depth (Feet) below sea level B 5900 1 A 6500 1km A B 18 18 GEOL 40310 Lecture A8 9 Finding the oil-water contact without considering pressure Depth (Feet) below sea level B 2 5900 1 A Well 2 6500 1km ODT (oil down to) A B 19 19 Finding the oil-water contact without considering pressure Depth (Feet) below sea level B 2 5900 3 1 A Well 2 6500 1km Well 3 ODT (oil down to) OWC (oil water contact) A B 20 20 GEOL 40310 Lecture A8 10 Repeat Formation tester (RFT) - RFT is a tool run down a well on a wireline to record the fluid pressure present. - Pressure measurements at different depths are used to establish likely fluid contacts 21 21 Using RFT data in oil exploration B B 6000 5900 A A 1km 6500 22 22 GEOL 40310 Lecture A8 11 Using RFT data in oil exploration Proven Hydrocarbon B Probable hydrocarbon ODT: 5816’ Untested B 6000 5900 A A 1km 6500 FWL: 6170’ 23 23 Fluids contacts and RFT in the Bruce Field during field appraisal Gas condensate field, North Viking Graben. Discovered 1974, development plan approved 1990. Complex structure, reservoir and fluids Appraisal history: Fluid and reservoir distribution Beckley et al. (1993) 24 24 GEOL 40310 Lecture A8 12 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? 25 25 “Les Fontaines Publiques De La Ville De Dijon”: Henry Darcy, 1856 26 Dijon: Place de la Republique. 26 GEOL 40310 Lecture A8 13 Darcy’s Law Henry Darcy’s experiments (1856). Water flow through sand filters: q=K h1 − h2 q h1 − h2 A L q: Volumetric Flow rate, (m3/sec) K: Filter-specific constant In general: A h1 q= h2 q L Darcy’s law: k P  L A k: Rock property: permeability μ: Fluid property: viscosity L q q A P + P q P 27 27 Analogies to Darcy’s law Ohm’s Law Darcy’s Law Applied pressure Applied voltage R0 =  E A I0 L Electrical Resistivity k = P A q L Current Resistance to flow Flow rate Darcy velocity (q/A) : 0.3 m/day is a representative flow rate away from wells. 28 28 GEOL 40310 Lecture A8 14 Permeability q= Darcy’s law: k P  L A  = 1 cp Units of permeability: the Darcy k =1D if: q = 1 cc/sec P / L = 1 atmos/cm A = 1cm2 Dimensions of permeability: Length2 1 mD = 9.869 10−16 m2 29 29 Porosity and Permeability Porosity: Fraction of bulk volume occupied by void space. Permeability: The ability of the rock to transmit fluid. 100 μm Sandstone (McCann and Sothcott (2009) 5μm Chalk (Stand 2007) 30 30 GEOL 40310 Lecture A8 15 Porosity and Permeability Simple cubic: 48% porosity Body-centred cubic (Rhombohedral): 26 % porosity Pores control the porosity. Pore throats control the permeability Similar permeability as pore throats are similar sizes 31 31 Porosity and Permeability Simple cubic: 48% porosity Body-centred cubic (Rhombohedral): 26 % porosity Pores control the porosity. Pore throats control the permeability Similar permeability as pore throats are similar sizes Smaller grains size: Identical porosity Much lower permeability. 32 32 GEOL 40310 Lecture A8 16 Porosity and Permeability: Grain size and sorting 33 Slatt (2006) 33 Small-scale permeability from core plugs Slabbed core Horizontal plug Vertical plug Pyrcz and Deutsch (2014) 34 34 GEOL 40310 Lecture A8 17 Large-scale permeability from well tests 35 35 Large-scale permeability from well tests Reserves, Resources and Economic Assessment of the Assets of Faroe Petroleum plc; Senergy GB Ltd, July 2016). 36 36 GEOL 40310 Lecture A8 18 Darcy’s Law: Incompressible radial flow Darcy’s law: kA dP q=  dL PR Expressed for flow across a hollow cylinder of thickness dr and radius r: Pwf rw q= re dr k 2rh dP  dr Total flow across all cylinders: 2h PR r dr q r e =  dP w r  Pwf h Integrating: qln(re ) − ln(rw ) = 2kh  PR − Pwf  Solution for flow into a well: For steady state flow into a well in an infinite, homogeneous reservoir q=  2kh PR − Pwf   ln(re rw ) 37 37 Well productivity Index Solution for flow into a well: 𝑞𝑔 (Mscf/day) q= 𝑞𝑜 (bbl/day)  2kh PR − Pwf  ln(re rw )  PI = productivity index  q = PI PR − Pwf  Reservoir Pwf Bottomhole flowing pressure PR Reservoir Pressure Pressure drawdown: reservoir pressure minus flowing well pressure: 𝑃𝑅 − 𝑃𝑤𝑓 PI is typically in range 1 - 50 bbl/day/psi. NB: this assumes the fluid is incompressible: a reasonable assumption for oil, but not gas. The PI for gas is different. 38 38 GEOL 40310 Lecture A8 19 Drill Stem Tests (DST) Shut-in configuration Flowing configuration Running in configuration Running in: Tester valve is closed, ports are open. Drilling mud passes easily through tool, with pressure gauges recording pressure of mud. Once in place: Packers are expanded to isolate test interval. Ports are closed Flowing period: Tester valve open, creates a pressure drop in the tool, formation fluids flow in, potentially up to surface. Flow rate and flowing bottom hole pressure is measured. Shut in period: Tester valve closed, sample taken. Pressures monitored for shut-in period. 39 Dahlberg (1994) 39 Drill Stem Tests (DST) Continuous pressure monitoring during a DST Pressure drawdown Flow rate Flowing bottom-hole pressure Pressure build-up Time Closed Open Closed Open Closed Both drawdown and build-up tests are performed and analysed. Analysis results are used to estimate reservoir pressure, permeability, size. 40 40 GEOL 40310 Lecture A8 20 Semilog plots of DST and production data Pressure drawdown Pressure build-up (Horner plot) “Horner time”: This decreases as real time increases Ideal permeability from semilog plots Δt Build-up Tiab and Donaldson (2012) drawdown tp 41 41 Well testing analysis methods Analysis of pressure drawdown and build-up data is highly specialist and evolving rapidly. AI & machine learning 42 Gringarten (2008) 42 GEOL 40310 Lecture A8 21 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? This lecture: Next lecture: Fluid compositions and PVT properties, Formation volume factors, Gas:Oil ratio, Reservoir Pressures and Drive mechanisms and viscosity. How does these vary spatially? Not only theflow hydrocarbons are significant – for example: factors Fluid recovery 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? 43 43 44 GEOL 40310 Lecture A8 22