LECTURE 20

LECTURE 20

1. DRILLING

   • Types
     • Onshore
     • Offshore
       • Jack-up rig
         • able to stand on sea floor, floated into place, leg jacked down onto sea floor
         • shallow water, <120m
       • Semi-submersible rig
         • <= 10,000 feet/ ~3000m
         • stable in marine, watertight pontoons below ocean, wave base, operating deck is far from waves connected to pontoon by structural columns
   • Rotating system
     • Rotary table
     • Kelly and Kelly bushing
     • Drillingstring assembly
       • Swivel
         • Decoupling of Kelley rotation and circulating system
       • Drill pipe
         • steel, 30-33 feet long
       • Drill collars
         • holds equipment for logging while drilling (LWD)
         • Measurement while drilling (MWD)
         • Add weight to drill bit
       • Drill bit
         • Tricone drill bit
         • Diamond drag drill bits
         • Decrease in well diameter with drilling depth
         • different bits used for different hardness of formation rocks
   • Hoisting system
     • Derrick
     • Drawworks
     • Crown block
     • Travelling block
       • Mud hose (circulating system)
   • Circulating system
     • Mud
       • Circulating - lubrication - cooling - cleaning of bit - removal of cutting - prevent fluids flowing into well from subsurface formations + chemical reaction with subsurface formations
     • mud pump
     • Shale shakers
       • Remove drill cuttings from drilling fluid (mud)
     • Mud tanks
     • Mud volume
       • gain
         • Blowout
         • Blowout preventers (BOPs)
       • Lost (lost circulation)
         • Fractures
         • Fluid invasion of formation
   • Conventional drilling program
     • Drill - log - case - cement - change for smaller bit+string - boost mud weight (density) - repeat...
       • Casing cement in place
         • prevent contaminations (fresh water aquifers), unstable formations from caving in
         • enable use high density fluids in deep drilling, smooth internal bore for installing equipmnet
         • isolate+ seal off high pressure zones
     • new joint in mouse hole - swinging the swivel - stabbing the joint - reconnection
     • Drill to final/total depth - cement casing & bottom hole assembly - perforate production well casting at target depths
     • Mud log
       • Geological interpretation of drill cutting, check rock types vs. prognosis
       • Gas detect, composition analysis
       • fluorescence (oil)
       • Drilling (drilling rate), mud (density, resistivity, viscosity) data
       • is basic record of drilling, cutting description of a lithology log
   • Deviated wells
     • Access issues
       • Environmental
       • Onshore to offshore areas (cheaper drilling)
       • from offshore platforms to many different parts of petroleum field
     • Relief well for blowout
     • Increased production due to
       • Greater intersection with reservoir (thin/low permeable reservoir
       • avoid fluid comming during production by gravity
       • intersect/ stimulate fracture network
       • Access multiple fuild/pressure compartments
   • Coring
     • hollow drill bit captures a core (column of rock)
     • core slabbed + interpret at surface
       • Neotectonic structures (faults, fractures)
       • sedimentary strcutures (cross/graded bedding)
       • Plugs of core extracted to investigate
         • porosity
         • permeability
         • seal capacity