LECTURE 17

LECTURE 17

1. PETROLEUM SYSTEM

   • Elements
     • Source rock
     • reservoir rock
     • SEAL rock
       • prevent migrate of H/C through reservoir + force H/C accum. in trap
       • low permeability, non-porous, small pore throats - trap H/C
       • Types
         • Fine-grained rocks
           • siltstones, shales, mudstones
           • cappillary seal (completely seal)
           • susceptible to breaching by fracturing
           • may be source rocks as well as seal rocks
         • Clay smear/fault gouge in fault zone
           • capillary seal
           • may provide fault seals
         • Evaporites
           • non-permeable
           • self-sealing (ductility) - high sealing integrity
       • Modes
         • cap seals
           • Potential depends
             • Capacity
               • max. capillary pressure/ column height
               • displacement pressure
                 • pressure required to form a filament of mercury through pore space
               • Capillary pressure vs. buoyancy
                 • capillary increase-column height increase-buoyancy increase at top of reservoir-H/C invade seal through large pore where cap. pressure is lower
                 • upward migrate H/C driven by buoyancy (density difference betw. fluids) oppose cap.pressure
                 • Migration change depth+shape reservoir
                 • Buoyancy press. > displacement press - seal leak
             • geometry (seal closure)
               • thickness + areal extend
             • Seal intergrity
               • Mechanical properties, lithological+ structural homogeneity, ductility
         • fault seals
           • Types
             • Damage
               • processes (grain crushing)- membrane seal (limestone)
               • sand:sand windows across fault due
                 • shale gouge
                   • ductile shale beds either side of fault entrained in fault zone
                 • cataclasis
                   • grains breaks+crushes -fine grained gouges -loss pores
                 • cementation
                   • fluid flow along once permeable fault
             • Juxtaposition
               • fault juxtaposes sealing rock again reservoir rock- juxtaposition fault seal
               • sand:sand high risk, sand:seal low risk
             • Reactivation
               • fault reactivate after trap charged-high risk H/C migrate along active fault zone
               • stick-slip-stick
               • fault seal valving with periodic pore pressure rise then fluid release
       • Quality
         • Good (perfect)- capillary seal
         • Poor- rate seal
     • Overburden rock
   • Processes
     • trap formation
     • H/C migration
     • H/C accum..
     • trap&H/C preservation
     • H/C generation