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Tempelet (Svalbard)

Silicified Carbonates. Carbonates. chalk. Tempelet (Svalbard). Loggelinje. Midterhuken (Svalbard). Loggelinje. 1) Porosity. Cubic packing.  = 47.6 %. Rombic packing.  = 26 %. Cubic packing, different grain size.  = 12.5 %. water. oie. Sand grain. Ideal. Porosity:.

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Tempelet (Svalbard)

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  1. Silicified Carbonates Carbonates chalk Tempelet (Svalbard) Loggelinje Midterhuken (Svalbard) Loggelinje

  2. 1) Porosity Cubic packing  = 47.6 % Rombic packing  = 26 % Cubic packing, different grain size  = 12.5 % water oie Sand grain Ideal Porosity: Vp = pore volume Vmatrix = grain volume Vtot = bulk volume Porous sandstone Pore size: 10 - 50 m 3

  3. tot = eff + res Total porosity: Typical effective porosity: Sandstone:  = 10 - 40 % depending on grain shape Limestone and dolomite:  = 5 - 25 % depending on fractures Effective porosityeff is the porosity of interconneceted pores Residual porosityres is the porosity of the remaining pores How do we measure the porosity eff ? 1. In situ measurements in the reservoir (well logging) 2. Core analysis: drilling cores from the reservoir followed by laboratory analysis • Drilled cores (d = 2,5 - 5´´) • Drilling sylindrical core plugs (d = 1,5´´, h = 3 ´´) • Clean and dry plugs 4

  4. 2) Saturation Water saturation: Oil saturation: Gas saturation: OIP = V So = V(1 - Swc) unit Rm3 Oil In Place (OIP): STOOIP = OIP /Bo=V(1 - Swc)/Bo unit Sm3 A porous medium (reservoir or core plug) usually contains several fluids: water, oil, gas Saturation = the fraction of the total pore volume Vp which contains the actual fluid Normally, the entire pore volum will be filled be fluids, hence: The porosity determines the amount of oil in the reservoir V = the totale pore volume (PV) So = the oil saturation Swc = “connate water” – the original water saturation Stock Tank Oil Originally In Place (STOOIP): Bo = “oil formation volum factor” = the ratio between the oil volume in the reservoir and the oil volume in the stock tank at the surface (Rm3/Sm3). Often Bo > 1 because gas is released from the oil when brought to the surface. 5

  5. a) water and oil are immiscible The van der Waals force is larger between like molecules. 3) Miscible and immiscible fluids The molecules in a liquid is held together by electrostatical forces (van der Waals forces) acting between the molecules b) water and alcohol (ethanol) are miscible The van der Waals force is larger between unlike molecules. 6

  6. 4) Wettability Pipette with water Oil Water drop The wettability is defined by the wetting angle   oil wet Neutrally wet Water wet water oil oil oil   180o water Vann water solid solid solid   180o  = 0  = 90o water oil Sand grain Wettability is the ability of one fluid to spread on a solid surface in the presence of other fluids Most oil reservoirs are water wet: • = 0 - 30o strongly water-wet • = 30o - 90o preferably water-wet •  = 90o – neutrally wet •  = 90o - 150o preferably oil-wet •  = 150o - 180o strongly oil-wet Wettability may also be quantified by capillary pressure properties. We will return to this later. 7

  7. v F y 5) Viscosity Viscosity is internal fluid friction Shear forces act between different fluid layers and between the fluid and container walls The velocity gradient in the y-direction: Shear tension: Empirical studies shows that for most fluids:  = the viscosity coefficient or simply the viscosity This is a Newtonian fluid Unit: 1 Pas = 1 Ns/m2 = 10 P (poise) 8

  8. L core plug A Q pA pB 6) Darcy’s law og permeability A pressure difference p isneeded for a fluid to flow through a porous medium. Henri Darcy (1856) discovered that the volume flow rate Q through a filter of cross section A: where the proportional constant a depends on both the fluid and the filter The modern version av Darcy’s law for fluid flow in a porous medium (e.g a core plug): Q = volume per unit time (volume flow rate) K = the absolute permeability of the medium  = the fluid viscosity Permeability unit This is a rather large unit. Therefore we define a new unit der:1 darcy (D) 9 1 millidarcy (mD) = 10-3 D = 0.98692·10-15 m2

  9. water along the pore walls (water wet) Sand grain Sand grain oil olje Sand grain Sand grain 7) Relative permeability Single phase flow: The absolute pemeabilitty K i Darcy’s equation is independent of the fluid, and depends only on the properties of the porous medium. Multiphase flow: Several immiscible fluid phases (water, oil, gas) flow simultaneously through the porous medium A sentral question arises: Does Darcy’s law and the permeability concept also apply when there are more than one fluid flowing in the porous medium? The flow possibility for one fluid may then depend on the saturation of the fluids present Water will flow more easily than the oil Oil may flow more easily in this case: than here: oil We see that the oil will flow more easily when more oil is present (large So) 10

  10. One simple capillary tube oil water A battery of tubes with varying radius and therefore varying capillary pressure: Height; Cap. press oil oil Water/oil contact (OWC) water 0 Fre water level (FWL) Siw 1.0 Water sat. (Sw) water small large Tube radius (R ) Capillary pressure curves in capillary tubes • There is a linear relation between capillary pressure pc and height h. • The total water saturation Sw below h in all tubes decrease when the tubes get thinner 11

  11. Darcy’s equations Equations of state Viscosity Continuity of equation Saturation The capillary pressure Total 14 equations

  12. From the continuity equations we have: Hence Introduce This is called the saturation equation Finally we get: 2. order partiell differential equation for Sw(x,t); non-linear with coeffisients which are functions of the independent variable Sw . The equation must be solved numerically. When Swhas been found, we may calculate fw and uw og uo, and finally pw the po, all as functions og x and t.

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  14. tool Reservoir Well logging Goal: Petrophysics as function of depth in reservoir • lithological (rock type) • porosity • saturation A tool with instrumentslowered into the borehole. The instruments in the probe measures the propertiesof formation and transmits data via mud to the surface

  15. Silicified Carbonates Carbonates chalk Tempelet (Svalbard) Loggelinje Midterhuken (Svalbard) Loggelinje

  16. Two methods Logge- sonde Kraft- kilde Bore- krone Slam- motor Øvre transmitter Øvre transmitter Mottaker antenne Gamma- sensor Resisitivitets- sensor a) Measurement While Drilling (MWD) Logging While Drilling (LWD) Tool at the bottom of the drill string. Signals transmitted as pressure waves through mud. b) Wireline Logging Drill string is pulled up and the probe is sent down with a wirethat transfer data to / from the logging instruments.Expensive, less common

  17. Log tools must withstand:  high reservoir pressure, 1000 atm  high reservoir temperatures, 120 ° C  large mechanical stresses  For time-efficient electronics The tools measure into the formationoutside invasion zone for drilling fluids Drilling Fluids (mudfiltratet) penetratesthe formation (invasion). This may give false results.

  18. Formation Sonde Clamp n n n Neutron source n n Gamma- detector  1. Neutron-log Atom nuclei consist of positively charged protons and neutrons without chargeProtons and neutrons have roughly the same mass. • Neutrons with energy 3-4 MeV sent into the formation • from a source in the tool (1 MeV = 1.6 ° 10-13 Joules) • Neutrons lose energy when colliding with atomic    nuclei, hydrogen, in the formation • When the energy is reduced to a • they may be “captured” by nuclei Si kjerne • This excited nuclei emit gamma rays • This radiation can be detected in a gamma-   detector in the tool

  19. Formation Sonde Clamp p p n n p p n n Neutron- source n Si kjerne Gamma- detector  Most effective if the neutrons collide with protons (p),ie hydrogen nuclei Much hydrogen ….. Increased gamma radiation. If the detector detects gamma radiationwe have a neutron-gamma log Most probes simultaneously measure the epithermalneutrons (En> 1 eV). It is called the neutron-neutron log The response from nøytronloggen is a measure of hydrogen-containing fluid (oil, water, gas) in the formationie, hydrogen index (HI) Since these fluids are located in the pores, it is a measure of porosity. Problem 1:Response from all hydrogen. Also from water bound to clay.. Problem 2: The gas has a low HI, - underestimation of porosity. - Detect gas layer.

  20. Formatjon  40K nuclei Sonde 238U nuclei  Gamma- detector 2. Gamma-log It measures naturally occurring radioactivity in the formation.Only gamma-rays have sufficient penetration ability in the formation ofreaching the detector in the logging tool Radioactive isotopes: • Occur in the earth (crust) • Type and rate of radioactivity depends on the mineral type • Depends on rock type, occurs particularly in shale • Radioactivity is a "finger print" of great interest to the   lithologic and stratigraphic description of the reservoir

  21. 40K - + 40Ca E=1.46 MeV 40Ar Important isotopes 1) 40K ; T1/2 = 1.3·1010 year 2) 232Th ; T1/2 = 1.4·1010 year Thorium-series: 232Th   + 228Ra      208Pb 3) 238U ; T1/2 = 4.5·109 year Uranium-series: 238U   + 234Th  8 6   206Pb

  22. The most important minerals that may contain radioactivity are: 1) Quartz [SiO2] (sandstone) – Clean regular lattice – little room to accommodate radioactive isotopes 2) Carbonates (chalk) [ CaCO3 ] – Deposits of living organisms - clean 3) Dolomitt [ CaMg(CO3)2 ] – Traces of Uranium 4) Feltspat [KAlSi3O8] and mica  clay and shale - Crystalline, containingAl, K, Na, Ca, Ba – silicates poor crystal structure, ie foreign atoms (eg. radioactive)          can take place: thus much radioactivity

  23. Petrophysics from gamma-log: 1) Lithology (rock type) – Identify shale and clean sand (in addition to mud log) 2) Clay content. Gamma-index: 0 < IGR < 1 GRmin = intensity of the clean zone (without clay / shale)GRmax = intensity of the assumed pure clay zoneGRlog = intensity of the current zone 3) The turning points in the IGR-curve defines the transition     between the layers. 4) Depth Reference. Can be used to determine casing need.

  24. mud Formation clamp Gamma- detectors tool Radioactiv source led Bore- hole 3. Density log (gamma-gamma log) Principal: A radioactive source (60Co, 137Cs) - gamma radiation. Gamma radiation (photons) scattered from electronsof atoms in the formation. Photons lose energy.Those who lose the most energy are those scattered backthe probe. This decreases the number of electrons with the originalenergy recorded in the detectors. Absoprbsjonskoeffisienten is proportional to the numberelectrons in the Z atom (molecule) which in turn dependsmass density b . Gamma-gamma log measures density in formation

  25. Bulk Mass of formation is the sum mass of pore volume (liquid)and matrix (rock) : Porosity: The matrix density m and the fluid density ftil reservoir fluids is known, porosity may be found vi by measuring b with the density log. We must expect that the density-log records: • High density of shale and cemented layers • Greater density in the oil-bearing sandstone layers than the layer of gas • Greater density in lower porosity layers • Slightly greater density in the water zones than in the oil zones

  26. Gamma-log Density-log Neutron-log Tak- berg- art Shale Sand- stone Gas Semented Sand- stone Oil Semented Shale High  Oil Sand- stone Low  Semented Vann Coal Sand- stone Shale: high radio activity, A lot of water (bound in clay), high density • gamma-log: • high for shale • fingerprint for minerals • identify layers Sandstone: low natural gamma Low neutron pga gas (low HI) Cemented sandstone: high density Sandstone with oil: HI high, high neutron-log, high density • Neutronlog: • high for oil/water • low for gas • high for shale Cemented sandstone: high density Shale: high gamma, much water Sandstone with oil: density log and neutron log depends on porosity Increasing effect on the density log the transition to the water zone • Density-log (gamma-gamma log): • high in shale • and cemented layers • higher in oil/water compared to gas Cementert sandstone: high density Coal: high water content, inc. neutron Sandstones with low porosity, Increased density, less water

  27. Phase Coherency

  28. CPMG Sequence

  29. Slow Relaxation Fast Relaxation T2 is a measure of Poresize

  30. Poresize Distribution -NMR

  31. i = 1,2 NMR 1H 1H

  32. Azimuthal Deep Resistivity (ADR) tool PTEK100 H2011 - Boreteknologi MWD forts … 33

  33. BAT Sonic tool 34

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