PT.       ccent Jaya Indonesia

Well testing  adalah  metode  untuk mendapatkan  berbagai  properti dari reservoir secara dinamis dan hasilnya lebih akurat dalam jangka panjang.

Tujuannya:

• Untuk  memastikan  apakah  sumur  akan   mengalir  dan  berproduksi.

• Untuk mengetahui  berapa  banyak  kandungan hidrokarbon di  dalam  reservoir  dan  kualitasnya.

• Untuk   memperkirakan   berapa    lama  reservoirnya   akan    berproduksi   dan    berapa   lama  akan menghasilkan keuntungan secara ekonomi.

Teknik ini  dilakukan  dengan  mengkondisikan  reservoir  ke  keadaan  dinamis  dengan   cara  memberi gangguan sehingga tekanan reservoirnya akan berubah.   Jika  reservoirnya sudah/sedang berproduksi, tes  dilakukan dengan cara  menutup  sumur  untuk  mematikan   aliran  fluidanya.   Teknik ini disebut buildup test.   Jika  reservoirnya sudah  lama  idle,  maka  sumur dialirkan kembali.   Teknik ini disebut drawdown test.

When 3D  seismic has  been completed, it is  time to  drill  the well.   Normally  dedicated  drilling  rigs either on mobile onshore units or offshore floating rigs are used. Larger production platforms may also have  their own production  drilling equipment.   The  main  components  of the  drilling  rig  are  the Derrick, Floor,  Drawworks, Drive and  Mud Handling.   The control  and p ower 22  can be hydraulic or electric.

Earlier  pictures  of  Drillers  and  Roughnecks  working   with  rotary  tables  (bottom drives)  are  now replaced with top  drive and semi automated  pipe handling on  larger installations.   The hydraulic or electric  top drive hangs from the derrick crown and gives pressure  and rotational  torque to the drill string. The whole assembly is controlled by the drawworks.  Photo: Puna Geothermal Venture The Drill String is assembled from pipe segments about 30 meters (100 feet)  long  normally  with  conical inside threads  at  one  end  and  outside  at the  other.  As each 30 meter  segment  is drilled,  the  drive  is disconnected and a new pipe segment inserted in the string.   A cone bit is used to dig into the rock. Different cones are  used for different  types of  rock and at different stages of the well.  The picture shows roller cones with inserts  (on the left); other bits are PDC (polycrystalline diamond compact, on the right)  and Diamond Impregnated. Photo:  Kingdream PLC  As the well is sunk into the ground, the weight of  the  drill string  increases  and might reach  500 metric tons or more for  a  3000 meterdeep well. The drawwork  and  top  drive  must  be   precisely  controlled  not  to  overload  and break the drillstring or the cone. Typical values are 50kN force on the bit and a torque of 1-1.5 kNm at 40-80 RPM for an 8 inch cone. ROP (Rate of Penetration) is very dependant on depth and could be as much as 20 meters per hour for shallow sandstone and dolomite (chalk) and as low as 1 m/hour on deep shale rock and granite.  Directional  drilling  is intentional  deviation of a  well bore from the vertical.  It is often necessary to drill 23 at an angle from the vertical to reach different parts of the formation. Controlled directional drilling makes is possible to reach  subsurface areas laterally  remote from the point  where the bit enters the earth.  It often  involves  the use of  a  drill motor driven by mud pressure mounted directly on the cone (Mud Motor, Turbo Drill, and Dyna-Drill), whipstocks: a steel casing that will  bend between the drill pipe and cone, or other deflecting rods.   Also used for horizontal wells and multiple completions,  where one  well may split into several  bores.   A well  which  has sections more than 80 degrees from  the vertical is  called a horizontal  well.   Modern  wells  are drilled  with large horizontal offsets to reach different  parts of the structure and achieve higher production.   The world record is more than 15 kilometers. Multiple completions allows production from several locations.   Wells can be any depth from almost at the surface to a depth of more than 6000 meters.     The oil and gas typically formed at 3000-4000 meters depth, but the overlying rock can since have eroded away.   The pressure and  temperature  generally  increases  with increasing depth, so that deep  wells can have more than 200  deg  C temperature  and 90 MPa pressure  (900 times atmospheric  pressure),   equivalent  to  the hydrostatic  pressure set by  the distance  to the surface.,   The weight of  the oil in  the  production string reduces the wellhead pressure. Crude oil has a specific weight of 790 to 970 kg per cubic meter. For a 3000  meter  deep well  with 30 MPa  ownhole  pressure  and normal  crude  oil at 850 kg/m3, the wellhead  static   pressure would  only be around 4,5 MPa.    During  production the pressure would go down further due resistance to flow  in the reservoir and well.   The mud enters though the drill pipe, through the cone and rises in the uncompleted well. The Mud serves several purposes:

• Bring rock shales (fragments of rock) up to the surface

• Clean and Cool the cone

• Lubricate the drill pipe string and Cone

• Fibrous particles attach to the well surface to bind solids

• Mud weight should  balance  the downhole pressure to avoid leakage of gas and oil. Often,   the well will  drill  though  smaller  pockets of  hydrocarbons  which  may cause “a blow out” if the mud weight cannot  balance  the  pressure.     The  same  might  happen  when   drilling  into  the  main  reservoir. To prevent an uncontrolled blow out, a subsurface safety valve is often installed.

This valve  has  enough  closing  force  to  seal  the  well  and  cut  the  drill string in an uncontrollable blow-out situation.   However   unless  casing is  already also  in place,  hydrocarbons  may  also  leave though other cracks in the in the well and rise to the surface through porpus or cracked rock.            In addtion  to fire and polution hazards,  dissolved  gas in  seawater  rising under a  floating structure significantly  reduces buoyancy.  24 The mud mix is a  specialist  brew designed  to match the desired flow viscosity, lubrication properties and specific gravity.   Mud is a common name used for all kinds of fluids   used  in  drilling  completion  and  workover,  It can be Oil Base,  Water  Base or  Synthetic  and consists of powdered  clays such as bentonite, Oil, Water and various additives and chemicals such as caustic soda,  barite   (sulphurous  mineral),  lignite  (brown  coal),  polymers and emulsifiers.  Photo: OSHA.gov A special high density mud called Kill Fluid is used to shut down a well for workover.   Mud is recirculated.   The coarse rock shales are separated in a shale shaker, the mud could then pass though finer filters and recalibrated with new additives before returning to the mud holding tanks.