Formation Evaluation

  1. What are logs used for?
    correlate zones, assist with structure and isopach mapping, and help define physical rock characteristics such as lithology, porosity, pore geometry, permeability, identify productive zones, determine depth and thickness of zones, distinguish between oil, gas and water in a reservoir, estimate HC reserves, determine facies relationships and drilling locations
  2. Two types of logs?
    Open hole logs and cased hole logs
  3. open hole logs
    run in newly drilled, uncased wells, used to determine whether or not to run casing
  4. cased hole logs
    used to perforate the well
  5. two primary parameters determined from well log analysis are:
    porosity and fraction of pore space filled with HC (HC saturation)
  6. Three general types of logs
    Electrical, nuclear, acoustic or sonic log
  7. word log may refer to:
    a particular curve, a group of curves, the physical record of the measurements, a logging tool (sonde), or the process of logging
  8. Rock properties or characteristics that affect logging measurements are:
    porosity, lithology, mineralogy, permeability, water saturation, resistivity of the rock
  9. porosity
    ratio of voids to the total volume of the rock
  10. effective porosity
    the amount of void space that is interconnected.
  11. lithology
    used to describe the solid portion of the rock
  12. mineralogy
    describes the minerals in a particular rock
  13. lithology effect
    shale in sandstone causes log readings to change
  14. some measurements, primarily nuclear are...
    made as a result of molecular level interactions between the formation and the logging tool
  15. acoustic measurements interact...
    with the formation on a bulk level so it is more affected by lithology
  16. parameter that has been used to account for the lithology effects
    shale volume
  17. permeability
    ability of a rock to transmit fluids, controlled by the size of the connecting passages between pores
  18. absolute permeability
    ability of a rock to transmit a single fluid, when completely saturated with that fluid
  19. effective permeability
    the ability of the rock to transmit one fluid in the presence of another fluid when the two fluids are immiscible
  20. Water saturation
    amount of pore volume in a rock that is occupied by formation water
  21. Irreducible water saturation
    the water saturation at which all the water is absorbed on the grains in a rock or is held in the capillaries by capillary pressure
  22. Hydrocarbons, the rock, and the fresh water of the formation are all assumed to have a _____ resistivity
  23. _______ is the rock property on which the entire science of logging first developed
  24. ______ is the inherent property of all materials, regardless of their shape and size, to resist the flow of an electric current
  25. Salt water has a _____ resistivity
  26. The measurement of resistivity is a measure of the...
    amount of salinity of the formation water
  27. Resistivity is a basic measurement of a reservoir's...
    fluid saturation, and is a function of porosity, type of fluid, and type of rock.
  28. Laterologs
    resistivity logs run in salty mud
  29. Induction Logs
    resisitivity logs run in fresh mud
  30. First electric log was run in...
    France by the Schlumberger brothers in 1927
  31. Archie's Equations:
    Ro=F*Rw, F=a/Phi^m, where a=tortuousity factor, and m=cementation factor
  32. What is Rxo, Rmf, Sxo, Rt, Rw, and Sw?
    Rxo=resistivity of flushed zone, Rmf= resistivity of the mud filtrate, Sxo=water saturation of the flushed zone, Rt=resistivity of the uninvaded zone, Rw=resistivity of formation water, Sw=water saturation of uninvaded zone
  33. Invaded zone
    zone in which much of the original formation fluid is replaced by mud filtrate
  34. Ri
    resistivity of the transition zone
  35. The bulk resistivities are...
    Rxo, Ri, Rt
  36. Diameter of invasion
    depth of mud filtrate invasion into the invaded zone
  37. The amount of invasion that takes place is dependent on...
    the permeability of the mud cake, not the porosity of the formation.
  38. The diameter of invasion is greatest in _____ porosity rocks
  39. dj/dh for high, intermediate, and low porosity rocks.
    high=2, intermediate=5, low=10
  40. Ri, Rz, Si
    Ri=resistivity of transition zone, Rz=resistivity of the fluid in the transition zone, Si=water saturation of the transition zone
  41. If invasion is deep or moderate, the flushed zone is...
    most likely completely cleared of its formation water by mud filtrate.
  42. When oil is present in the flushed zone, the degree of flushing by mud filtrate can be determined from the...
    difference between water saturation in the flushed zone(Sxo) and the water saturation in the uninvaded zone(Sw)
  43. Usually about ___ to ___ percent of the oil is flushed out
    70, 95
  44. The ratio of the uninvaded zone's water saturation to the flushed zone's water saturation is an indicator of
    hydrocarbon moveability (MHI)
  45. There are 3 commonly recognized invasion profiles:
    Step, transition, annulus
  46. The transition profile has a _____ geometry, with two parameters:
    cylindrical, di (diameter of flushed zone) and dj (diameter of transition zone)
  47. The transition profile needs at least ____ resistivity measurements, each a different diameter away from the wellbore
  48. The 3 resisitivity measurements of the transition zone are:
    Rxo, Ri, Rt
  49. The ability to estimate the invasion in a formation was
    made possible with the introduction of the...
    dual induction log and dual laterolog
  50. “dual” means that each tool made
    tow induction or two laterolog measurements, one at medium and one at deep distance from the wellbore
  51. The dual induction and laterolog made a third measurement which was...
    shallower than the medium and deep measurements
  52. Distances for Rxo, Ri, and Rt
    Rxo=.5-1.5ft, Ri=1.5-3ft, Rt=3ft+
  53. Annulus profiles...
    only present in HC bearing zones, indicate high relative permeability to HC, will dissipate with time, and can only be observed on fresh mud resistivity logs
  54. An annulus profile is detected only by an _____ run soon after a well is drilled
    induction log
  55. Annulus profile can only occur....
    in HC bearing zones
  56. Annulus effect
    is detected by a higher resistivity reading on the deep induction log than the one on the medium induction log, Rt>Ri
  57. How many resistivity measurements does a step profile and transition profile have?
    Step-2, transition-3
  58. 3 facts about an annulus profile-
    Rt>Ri, only in induction logs, and indicates HC productivity
  59. Fresh water based mud has resistivity profile of:
  60. Salt water based mud has resistivity profile for:
  61. A saltwater mud results in a wet profile where
    shallow, medium, and deep resistivity measurements all read low resistivity
  62. 2 reasons why it is important to know lithology
    • -porosity logs require a lithology constant before the porosity of the zone can be calculated
    • -the formation factor also varies with lithology
  63. 3 parameters that vary with temperature are
    resistivities of the drilling mud, mud filtrate, and formation water
  64. The formation temperature is determined by knowing:
    formation depth, bottom hole temperature, total depth of a well, and surface temperature
  65. formation temperature is calculated by using
    linear regression y=mx+c where x=depth, y=temperature, m=geothermal gradient, c= mean annual surface temperature
  66. Arp's Formula can be used to
    correct fluid resistivities to formation temperature
  67. four most fundamental rock properties use in well logging are
    porosity, permeability, lithology, and water saturation
  68. Lithology of a formation must be known because
    it is needed to determine porosity, the formation factor varies with lithology, and water saturation varies with the formation factor
  69. The four fluids that affect logging measurements are
    drilling mud, mud filtrate, formation water, and hydrocarbons
  70. Resistivity profiles for Wet Zones:
    For fresh mud where (Rmf>>Rw)
    For salt mud where (Rmf=Rw)
  71. Resistivity profiles for HC zones:
    For fresh mud where (Rmf>>Rw)
    For salt mud where (Rmf=Rw)
    • Rxo>Ri<Rt, annulus profile: Rt>Ri, all read high
    • Rxo<Ri<Rt
  72. The SP log is used for
    determining gross lithology, to correlate zones
  73. SP log is used to:
    detect permeable beds, detect boundaries of permeable beds, determine formation water resistivity(Rw), determine the volume of shale in permeable beds
Card Set
Formation Evaluation
Test 1