PRODUCTION OF OIL AND GAS

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PRODUCTION OF OIL AND GAS
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Production Phase

• Once petroleum found well drilled operation
  enters production phase
• After oil and gas found, appraisal drilling need
  to be done to check for commercial viability
• Important to test formation to ensure profit and
  determine proper rate of extraction
• New well begins production, a potential test is
  run determine most oil and gas to be produced
  in a 24 hr period
• Most efficient recovery (MER) rate based on
  most oil and gas can be extracted for a sustained
  period of time without harming formation
• Some well under enough pressure do not need
  pumping system. Only install Christmas tree or a
  series of valves and pipes at the surface to
  produce oil and gas

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• Most well require some kind of lifting method
  depending on depth of well and whether the well
  has multiple completion
• Most common method is rod pumping
• When oil and gas reach surface they are separated
  
• Gas is sent to processing plant
• Sediment and water from oil is removed then oil
  is transported to refinery

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Glossary of Terms

• Formation
• Refers to either a certain layer of the earths
  crust or a certain area of layer.
• It often refers to the area of rock where a
  petroleum reservoir is located
• Christmas Tree
• Series of pipes and valves system for controlling
  the flow of oil from a well
• Due to high underground pressures, the oil was
  naturally lift by gas or air thus no additional
  pumps needed

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• MER (Most Efficient Recovery)
• MER rate based on most oil and gas that can
  extracted for a sustained period of time without
  harming the formation
• Generally, most well cannot work 24 hrs, 7 days a
  week could damage formation
• Multiple Completions
• Drilling single well at several different depth
  in formation
• Reason increase production from a single well

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Field Production

• Primary Recovery (Natural Methods)
• 1st method of producing oil from a well
• Solution gas drive
• pressure inside reservoir relieved when well
  punctures and gas trapped in oil forms bubbles
• Bubbles grow, exert pressure push oil to well and
  up to surface (20-30)
• Gas cap drive
• If contain gas cap, drill well directly into oil
  layer gas cap expand
• Expanding gas pushes oil into well (40)
• Water drive scenario
• Water layer press against oil layer
• Water pushes oil towards surface and replace it
  within the pores of the reservoir rock
• Highest recovery up to 75

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• Secondary Recovery
• Used to enhance or replace primary techniques
• Water flooding
• Additional injection well is drilled into the
  reservoir
• Pressure water injected
• Water displaces the oil in reservoir
• Mechanical Lift
• Reciprocating or plunger pumping called
  horsehead
• Pump barrel lowered into well on 6 inch string
  steel rod (sucker rods)
• Up and down movement force oil up to tubing

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• Tertiary Recovery
• When 2nd recovery no longer effective
• Thermal Process
• Steam Flooding steam injected, heats oil to
  flow readily
• in-situ combustion (fire flooding) air
  injected, a portion if oil ignited , combustion
  front moves away from air injection well toward
  production well
• CO2 injection
• CO2 injected, mix with oil reduces forces that
  hold oil to pores, allows easily displace by
  injected water
• Chemical recovery
• Inject polymer into water phase of reservoir
  trap, large molecule add bulk to water, water
  thicken, wash oil from pores
• Sometimes surfactant added to reduce force water
  to solid

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• Improvement of formation characteristic
• To aid 3rd recovery because production drop
• Acidizing
• Injecting acid into a soluble formation (exp
  carbonate) to dissolve rocks
• Enlarge the existing voids and increase
  permeability
• Hydraulic Fracturing
• Inject a fluid into formation under significant
  pressure to enlarge existing fracture and create
  new fracture
• This fracture extend outward from well bore into
  formation therefore increase permeability

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Petroleum Production System

• Petroleum hydrocarbon production involve 2
  districts
• Reservoir a porous medium with a unique storage
  and flow characteristic
• Artificial structures includes well, bottom hole,
  surface gathering, separation and storage
  facilities
• Production Engineering - attempts to maximize
  production in a cost effective way
• Appropriate production technology and method
  related directly with other major area of
  petroleum engineering such as formulation
  evaluation, drilling and reservoir engineering
• Petroleum Hydrocarbon
• Mixture of many compounds petroleum and natural
  gas
• Mixture depending on its composition and
  conditions of P and T occur as liquid or gas or
  mixture of 2 phase

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Reservoir Engineering Fundamentals

• Porosity
• Define Porosity Total pore volume in the rock
  sample
• Total rock sample volume (solidpore)
• Mathematically
• Range of porosity 0.1 to 0.3
• Use reservoir core to measure porosity
• Limitations
• Rock sample must be large enough to obtain many
  sand grains and many pores to be representative
• Features sample has a different type of pore
  space from sandstone

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• Fluid Saturation
• Water saturation, Sw Volume filled by water
• Total pore volume
• Oil saturation, So Volume filled by oil
• Total pore volume
• If oil and water is the only fluid present, Sw
  So 1
• In most oil fields Sw tends to increase as
  porosity decrease
• Typical value of Sw 0.1 to 0.5
• Free gas also present in oil pools,
• Free gas saturation, Sg Volume filled by free
  gas
• Total pore volume
• 3 factors should always be remembered conceiving
  fluid saturation
• It vary from place to place in reservoir rock Sw
  higher in less porous sections due to gravity
  segregation of the gas, oil and water

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• Vary with cumulative withdrawal oil produced
  replace by water or gas
• Oil and gas saturation frequently expressed in
  terms of HC-filled pore space.
• Pore space fV
• HC-filled pore space SofV SgfV (1-Sw)fV
• Therefore,
• Oil saturations,
• Gas saturations,

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Example One of the most important determinations
for an oil accumulation is the volume of oil in
place. Suppose that in geological evidence is
known that the area extent of an oil reservoir is
2 million sqft and that the thickness of the bay
zone is 30 ft. If the sand porosity and water
saturation are 0.2 and 0.3, respectively, how
much oil is present? Solution Volume of bay
2,000,000 ft3 x 30 ft 6x107ft3 Total pore
volume 0.2 x 6x107 12x106 ft3 Then SwSo1
So 1 - 0.3 0.7 Total oil volume 0.7 x
12x106 8.4x106 ft3
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• Permeability
• Measurement of the ease with which fluid flow
  through the rock
• A function of a degree of interconnection between
  pores in the rock
• The concept was introduced by Darcy in a
  classical experimental work from both petroleum
  engineering and ground water hydrology
• The flow rate can be measured against pressure
  (head) for different porous media
• The flow rate of fluid thru specific porous
  medium is linearly proportional top head
  difference btw the inlet and outlet and
  characteristic property of the medium, thus
• u kDP
• Where k permeability and is a characteristic
  property of
• the porous medium

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• Suppose a cylindrical sample (core) of a porous
  rock is fully saturated with liquid of viscosity
  m.
• Experimentally for a particular rock sample the
  expression
• Darcy Equation
• where k is constant
• Q will increase a k increases, the higher the
  value of k the more readily will liquid flow
  through the core

l
A
Q
P1
P2
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• If in flow rate contain two fluid (oil and
  water), free gas is not present then,
• If Q (cm3/s), m (cp), l (cm) A (cm2), and P1 and
  P2 (atm), the value of k in Darcy is
• 1 Darcy 10-8 cm2

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• Oil Gravity
• Commonly expressed in degree API
• The terms heavy, medium and light crude cover
  approximately the ranges 10 to 20o, 20 to 30o and
  over 30o API, respectively
• Instantaneous Water/Oil Ratio (WOR)
• Homogeneous formation produce only oil and water
  (no free gas) then
• The pressure drop in oil may differ slightly from
  that in the water owing to effect of capillary
  forces, so dividing the equations above, results
  in

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• At the surface
• Or from above equation
• (surface)
• Where Bo is oil formation volume factor
• Bo is defined as ratio of the volume of oil (plus
  the gas in solution) at reservoir T and P to the
  volume of oil at standard conditions (so-called
  stock-tank oil)

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• Instantaneous Gas/Oil Ratio (GOR)
• Homogeneous formation producing only oil and gas
  (no water production, although water may be
  present in the formation)
• Where the pressure drop across the distance dl is
  the same for both fluid, if capillary forces are
  neglected. Dividing
• Stock-tank oil rate will be qo/Bo, and surface
  free gas rate qg/Bg. In addition to free gas
  produced from the formation, each barrel of
  stock-tank oil will release a volume Rs of gas,
  then the total surface gas/oil ratio is

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• At the surface
• Therefore
• (surface)
• Productivity Index
• Bottom hole flowing pressure - producing pressure
  (Pwf) at the bottom of the well
• The difference btw this and the well static
  pressure (Ps) is

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• Ratio of producing rate of the well to its draw
  down is called Producing Index.
• If the rate q (bbl/day) of stock-tank liquid and
  draw down (psi), the productivity index (J) is
  defined as
• (bbl/day/psi)
• Productivity index is based on the gross liquid
  rate (oil rate water rate)
• Specific productivity index, Js is the number of
  barrel (gross) of stock-tank liquid
  produced/day/psi/ft net thickness