Video summary

Formation Pore Pressure by Alfa Drilling School

Main summary

Key takeaways

Educational

Main ideas & lessons

  • Drilling needs safe “limits” for pressure

    • The speaker compares choosing drilling conditions to staying in the middle of a race track: if you drift too far left/right, you hit an unsafe boundary.
    • In drilling, the key limits are:
      • Pore pressure (PP)
      • Fracture pressure (FP)
    • The “safe window” between them helps prevent:
      • Blowouts/kicks (when mud is too light relative to PP)
      • Fracturing / excess loss of wellbore integrity (when mud is too heavy relative to FP)
    • The emphasis is that it’s not enough to be “tight” near one limit—you must avoid both extremes.

  • Why pore pressure increases with depth

    • The Earth’s sedimentary layers are described as stacked “rooms/houses” filled with fluid.
    • Compaction: as burial depth increases, pore spaces are squeezed, making fluid escape harder → pressure builds up.
    • This relates to overburden / vertical stress:
      • More rock buried → higher load.
      • Higher stress + trapped fluid → increased pressure with depth.
    • Analogy: pressure increases when there is no escape route.

  • Geologic context: formation, rock types, and stress concepts

    • A formation/rock layer is framed as a lithology unit containing rock types such as:
      • Igneous
      • Sedimentary
      • Metamorphic
    • Sedimentary settings are described as basins (“bowls”) that collect sediments regionally or locally.
    • Pressure behavior depends on region-specific normal conditions, not a single universal gradient:
      • Different sedimentation histories produce different “normal” pressure gradients.

  • Rock properties used in geomechanics

    • To interpret PP/FP behavior, the lecture highlights key rock properties:
      • Porosity (space between particles)
      • Permeability (ability to transmit fluids through connected pore pathways)
    • Strength parameters:
      • Compressive strength
      • Tensile strength
      • Shear strength (linked to triaxial/shear behavior)
    • Elasticity parameters:
      • Modulus
      • Poisson’s ratio (lateral expansion under loading)

  • Pressure window terminology and the “normal vs abnormal” concept

    • Distinctions:
      • Normal pressure
      • Abnormal high pressure (commonly linked to pressure seals, salt structures, or other mechanisms)
      • Subnormal low pressure (e.g., depletion/produced zones, lost circulation)
    • Abnormal pressure can lead to kicks, with drilling indicators including:
      • Higher torque
      • Higher drag
      • More back-off
      • Changes in gas/background gas percentage (rising unexpectedly)

  • How PP and FP are predicted before drilling

    • Primary prediction method mentioned: wireline logging data (prior to drilling).
    • The lecture references several commonly used models, with the most famous attributed to Bowers (name stated as “Banden/Band…”).
    • Alternative models/people mentioned depending on company/practitioner:
      • Kelly
      • Hobert (name heard; likely referring to another established method)
    • Example wireline-log inputs include:
      • Resistivity
      • Neutron porosity / neutron values
      • Bulk density
      • Sonic log (sonic transit time)
    • The speaker stresses the sonic log as especially useful:
      • It helps predict pore pressure, and can be extrapolated to infer related rock properties (e.g., porosity, modulus, Poisson’s ratio).
    • Workflow:
      • Use predictions to draw a pore pressure line
      • Derive a fracture pressure line
      • Validate after drilling and adjust as needed

  • Limitations of a PP/FP-only approach

    • After studying geomechanics, PP and FP may be viewed as not fully optimal.
    • Next-step concepts introduced for later lessons:
      • Collapse pressure
      • Minimum stress

  • Geometric depth concept

    • The lecture emphasizes TVD (True Vertical Depth):
      • Even if MD (Measured Depth) is longer due to deviation, pressure relationships should align using TVD.
    • PP/FP should be treated as uniform/linear within the same stratigraphic layer, tied to formation depth.

Methodology / instruction-style content (as presented)

  • Goal: determine a safe mud weight window

    • Identify/estimate:
      • Pore pressure (PP)
      • Fracture pressure (FP)
    • Use PP/FP to guide mud weight so wellbore pressure stays:
      • Above PP → avoid kicks/blowouts
      • Below FP → avoid fracturing/losses
    • Later (after geomechanics study), replace/adjust using:
      • Collapse pressure
      • Minimum stress

  • Predict PP/FP before drilling using wireline logging

    • Collect wireline logging data.
    • Apply a pore-pressure prediction model (speaker emphasizes):
      • Bowers method (most famous)
    • Consider variants depending on practitioner:
      • Kelly / Hobert (as mentioned)
    • Use log inputs such as:
      • Resistivity
      • Neutron porosity
      • Density / bulk density
      • Sonic log (highlighted as best)
    • Output:
      • A pore pressure line vs. depth
      • A fracture pressure line
    • Validate after drilling and update if needed.

  • Monitor for abnormal pressure while drilling (indicators)

    • Abnormal/high pressure signs:
      • Increasing torque and drag
      • Increased back-off
      • Rising gas/background gas percentage (example progression given)
    • Subnormal/low pressure signs:
      • Entering/depleting production zones
      • Lost circulation / depletion behavior

  • Use depth properly

    • Use TVD as the key depth reference for PP/FP pressure relationships rather than MD when appropriate.
    • Concept example: in deviated wells, MD can be greater than TVD, so pressure lines should correspond to TVD.

Speakers / sources featured (as mentioned)

  • Mr. Ali (and “Mr. Ali’s son” mentioned)
  • Terzaghi (referenced in connection with an equation relating stress and pressure)
  • “Mr. Geomechanics” (referenced as a geomechanics expert/role; not named)
  • Bowers (pore pressure prediction method)
  • Kelly
  • Hubert (name heard; mentioned as another method/person)
  • Instagram / Alfa Drilling School / Alfa (channel/lecturer branding referenced)
  • “Alfa Drilling School” / “Alfa … Lecturer” (institution/lecturer identity referenced; exact personal name not clearly stated)

Original video