Basics of Logging - Revised.pptx
- 1. 2.2- Basics of Logging History of logging, Modern logging tools, Multi-well correlations , the logging process, porosity and lithology, the Archie Equation, rock permeability, the invasion process, vertical resolution and enhanced vertical resolution.
- 2. History of logging First well logs recorded in 1927 The recording system The cable winch The stationary point- by-point log 3
- 3. History of logging Old Current V3 Resistivity Tools V1 emits a current from a surface generator. The voltage measured at V2 is proportional to the formation resistivity. V2 is measured relative to a return at V2 the surface ( V3 ). V1 This electrode configuration is the Normal tool. The distance between the V1 and V2 electrodes determines the depth of investigation and hence the resistivity being read. 4
- 4. Modern logging Tools Maxis (MCM) acquisition system Wireline Engineer Acquisition Equipment Unit Engine Client (“Witness”) Winch man Cable drum Wireline cable to downhole tools 5
- 5. Modern logging Tools Modern Logging Truck Modern Surface equipment : High powered computers Controls downhole logging Changes signal configuration to obtain acquisitions Includes surface database to optimise results and for well- to-well correlations Used also for forward- modelling Includes also all the well configurations- depth, casing, formations, etc.. 6
- 6. Modern logging Tools Logging Tools Modern Tools Sensors used in modern logging: Electrical Electromagnetic Magnetic Flux Induction Acoustic Ultrasonic Nuclear: Neutron Nuclear: γ- Rays Nuclear: Nuclear Magnetic Resonance Imaging (MRI) Every potential signal source have been used in modern-day logging 7
- 7. Modern logging Tools Modern Logs Modern logs have more measurements but the principle is the same 1600 Shading is often added to make the log curves easier to read. Additional outputs can be made: 1700 Invasion Profiles Facies Layering Gamma Ray (GR) (GAPI) 1:220 Ft Pad -180 Rt from HALS RX18 0 150 200 0 180 1 1 1000 1000 0 5 1 2 5 2 SP (SP) (MV) 0 FXND (PU) Rt from AITH (OHMM) 1 43 51 08 00 50 1 1000 Mud Resistivity from HALS 1 1 1000 1000 0 Mud Resistivity from AITH (OHMM) 8
- 8. Multi-Well Correlations Multiwell Plots Well-to-well correlations 9
- 9. Logging Cables Armour Conducting cable Insulator • 1 Conductor cable • Diameter: 0.5 cm • 7 Conductor cable • Diameter: 2.5 cm • Used mainly for cased hole logging • Cable sends power to the tool • 1000’s of signal can be sent back to the surface on the same line • Used mainly for open hole logging • Cable sends power to the tool • 1000’s of signal can be sent back to the surface 10
- 10. The Logging Process Open Hole Measurements : Wireline Logging. LWD (Logging While Drilling) Logging on Drill Pipe (TLC) Logging Using Tractor Wireline LWD TLC Tractor 11
- 13. As the tool moves, the recording of data is also made at a pre-determined sampling rate (e.g. every ½ ft.) The Logging Process 500 600 700 14
- 14. Porosity and Lithology Petroleum System: Reservoir Areservoir rock is any rock that has enough porosity and permeability to both store and allow the production of hydrocarbons The vast majority of reservoir rocks worldwide are either sandstone or carbonate rocks 15
- 15. Porosity and Lithology Why we log ? • Lithology (reservoir rock?) • Resistivity (HC,water,both?) • Porosity (how much HC?) • What type of HC • Formation mech. properties • Permeability / cap pressure • Shape of the structure • Geological information • Geothermal • Unconventional applications 16
- 16. Porosity and Lithology 1- Definition of Porosity Hydrocarbon Sand The Matrix could be complex ϕ. Sw= Carbonate Shale Anhydrite Volume of Water ϕ . (1-Sw) = Volume of oil 17
- 17. Porosity and Lithology Porosity (Continued) A rock can be made up of small grains or large grains but have the same porosity Porosity depends on grain packing, not the grain size 18
- 18. the Archie Equation Water saturation (dimensionless) Connate water (or water saturation) refers to the water that exists in the reservoir when it is discovered Water saturation is a measure of how much water is in the reservoir Hydrocarbon saturation Shc = 1 – Sw Sw calculated from wireline resistivity data usingArchie’s equation 19
- 19. Permeability Permeability Definition Parameters Area: A K = permeability, in Darcies. L = length of the section of rock, in centimeters. P2 L Q = flow rate in centimeters / sec. P1 P1, P2 = pressures in bars. A = surface area, in cm2. µ = viscosity in centipoise. K = Q. µ . L / { A . ( P1 - P2 ) } 22
- 20. Invasion Profile Resistivity of zone Resistivity of the water in the zone Water saturation in the zone Mud Rm Adjacent bed Rs . The invasion process creates a zone where the main water is filtrate Uninvaded zone h mc Flushed zone Zone of transition or R t R mc dh (Bed thickness) Rw annulus Mudcake Rxo Sw . This invaded zone also has less HC than the virgin zone h Rmf S xo Rs d d i j Adjacent bed . This fluid (Invasion diameters) displacement is an indication of fluid mobility rj d h Hole diameter 23
- 22. The Invasion Process The Invasion process Progressive invasion Mudcake is formed from solids in mud This creates an impermeable barrier Although Phydraustatic > Pformation little no invasion will take place Progressive filtrate invasion and mud-cake build-up 25
- 24. Vertical Resolution Volume of measurement The various tools have different: . Sampling rate . Depth of investigation . Vertical resolution . Statistical sampling effects 27
- 25. Enhanced Vertical Resolution Volume of measurement – vertical resolution 28
- 26. Enhanced VR 29
- 27. Enhanced Vertical Resolution GR GR has better vertical resolution compared with SP SP 30