LECTURE 21

LECTURE 21

1. WELL LOGGING

   • Conventional Logs
     • Spontaneous potential (SP)
       • Measures natural electric potential, porosity, well correlation
     • Resistivity (LLD and LLS)
       • measure: electric resistivity, deep+shallow logs (flushed zone vs. virgin zone), pemeability, pore fluid type
     • Gamma-ray (GR)
       • measure: decay of natural radioisotopes, lithology, grain size, well correlation
     • Sonics (DT)
       • Measure: slowness of rock, lithology, porosity
     • Caliper (CAL)
       • Measure: borehole diameter, washouts, mudcake, stress-induced failure
     • Neutron (NPHI)
       • measure: hydrogen atoms (water content), lithology, porosity
     • Density (RHOB)
       • measure: electron density, bulk rock density, lithology, porosity
     • Dipmeter
       • measure: orientation of dipping surfaces, structural+ stratigraphic analysis
     • Measurement/logging while drilling (MWD/LWD)
       • log measurement detector can also be mounted in the drill colars behind bit
       • Pros: real-time logging while drilling, minimise invasion effects, safer, easier, possible in horizontal/deviated well
       • Cons: some not as high quality as wireline logging
   • Measurement of physical properties of rocks+fluids vs. depth in a well
   • many logs to identify rock types, porosity, oil/water filled
   • wireline logging
     • housed in pipe (protection), several assemble tools, cable for power+send data back
     • data records as tool move up+down holeat maintain speed to measure depth (200-2000m/hr)
   • Logging truck
     • mounted with cable, winch, depth measurement + computerise record + processing equipment
   • reading: measured property/volume (dimension of volume control: resolution, radius of investigation)

2. Specialist Logs

   • High resolution electrical + acoustic logs
     • pseudo-images of borehole walls
     • high resolution image of borehole: sedimentary structure, fractures, irregularities
   • Small-scale structural + stratigraphic analysis
   • Stress-induced failure of borehole (collapse)
   • Drilling-induced fractures (fluid loss)