Extreme Overbalance, Propellant OR Extreme ?· Extreme Overbalance, Propellant. OR . Extreme Underbalance…

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  • When and how EOP, Propellant or EUP could effectively improve the wells perforation

    Extreme Overbalance,Propellant

    OR Extreme Underbalance

  • 1865, Tin torpedos filled with gunpowder, later with nitroglycerin 1910, the single-knife casing ripper 1948, shaped charges 1970s, under-balance 1980s propellant 1993, extreme over-balance

    The first 130 years of perforating



  • Overbalanced CompletionBefore Flowing



    Mud-damaged zone

    Virgin formation

    Charge debris

    Crushed and compactedlow-permeability zone

    Overbalanced CompletionAfter Flowing

    Part of low-permeability zonestill exits

    Perforation partially pluggedwith charge debris

    Ideal Underbalanced Completion

    Immediately After FlowingLow-permeability zone andcharge debris expelled bysurge of formation fluid

    Perforation Clean Up Concepts



  • Overbalanced perforating creates a crushed zone with substantial flow restrictions

    Underbalanced perforating helps to remove debris and crushed formation fragments from the perforation tunnel

    Cleanup efficiency is a function of applied differential pressure and transient flow velocities in the rock

    Perforation Clean Up Concepts



  • Why EOP The remaining reservoir pressure or underbalance is insufficient to

    effectively clean the perforations The formation competence is questionable and the risk of sticking

    perforating assemblies is greater, sufficient underbalance pressure is notpossible

    To address the perforation damage in these cases, extremeoverbalance perforating technique has been applied EOP is a near-wellbore stimulation technique EOP perforating also provides perforation breakdown in preparation for

    other stimulation methods; and therefore, eliminates the need forconventional perforation breakdown methods

    The Extreme Overbalance Perforating technique was developedindependently by Oryx Energy and ARCO

    Extreme Overbalance Perforations (EOP)



  • EOP Technique Pressuring the wellbore with compressible gases

    (the gases have a high level of stored energy) above relatively small volumes of liquid

    Typically Nitrogen is pressured up to levels significantly higher than the formation break-down pressure

    The formation is instantaneously exposed by perforating the casing or shearing a plug placed in the tubing bottom

    Compressed N2 provides the energy to drive the wellbore fluid into the formation to create short fractures around the wellbore

    Proppant carriers have also been incorporated into the perforation assembly to introduce proppantsinto the flow path as the gun detonates.



  • Energy stored in tubular creates shock wave opposite

    perforated zone.

    Energy impact and injection rates are significantly higher

    than during hydraulic fracturing.

    Overbalance pressure needs to be above 1.4 psi/ft.

    Expansion of N2 creates short fractures.

    Fracture propagation and width are function of pressure

    sustenance above fracture initiation pressure.

    EOP fracture initiation pressure is always higher.

    EOP Fundamentals



  • Effectiveness of EOP is a function of: Type of fluid across target formation

    Size of tubular (i.e., amount of finite energy available)

    Length of perforated interval, size, and gun phasing

    In-situ stress, , and permeability, k

    Applied overbalance pressure gradient

    Effectiveness of EOP



  • Opening existing (damaged or plugged) perforations

    Removal/bypass of skin damage and fines migration

    Stimulation of well where other treatments are impractical

    Pre-stimulation to permit reservoir evaluation tests

    Upfront hydraulic fracturing operation

    Stimulation of intervals with proximity to water/gas layers

    EOP Candidate Selection



  • More than 500 jobs performed: 88% showed negative skin after EOP Most treated reservoirs with k < 10md Maximum treated interval length 300 ft Success depends on overbalance gradient > 1.4 psi/ft If reservoir does not respond to EOP, it will not respond to more

    expensive treatments. Reserves do not increase but are recovered in a shorter time Clean fluids are a key to technique 80% of fractured wells showed lower fracture pressures Decline in use to less than 100 jobs a year (TCP operations are more

    than 8,000 per year)

    EOP Results Worldwide



  • In a real case, two jobs with EOP were performed Neither of the jobs resulted in a commercial success:

    In first case the perforation guns went off prematurely and forcedcompletion brine into the formation the well never producedanything measureable.

    In second case EOP surge did increase production from 1.5MMscfd to 2.4 MMscfd. Based on pressure transient test, skinreduced from 33 to 18. No long term test results available.

    The jobs proved that EOB with surface and downhole pressures of15,000 psi and 19,000psi were operationally possible.

    Cost for EOP much higher than conventional methods, economicjustification is still questionable????

    Field Experience of EOP



  • Safety: High pressure gas at surface (well depth), well hardware andequipment ratings

    Logistics - Nitrogen and pumping units Very high instantaneous flow rate.may exceed 100 bbl/min Very high surface pressure. has to be increased to more than 10,000

    psi Liquid cushion .up to maximum of 1000 ft Minimize fluid volume inside tubing, preferably 100% N2 to reduce

    friction losses Erosional effects are significantly higher Large diameter perforations and perforation phasing are more

    important than penetrationcompletion limitations for various gunoptions

    Pressure buildup before and after EOP EOP creates multiple fractures near the wellboreif no fracture is

    created, perforations are plugged.completely

    EOP Limitations and Issues



  • Propellant



  • It is an Oxidizer and a Fuel

    It burns very quickly

    It generates gas

    Post-perforation Propellant Pulse System delivers the maximum energy produced to the formation to enhance near wellbore treatments

    the generated pressure pulse is powerful enough to break the formation

    Conveyable on wireline, tubing, or coiled tubing, it is run stand-alone or in combination with a perforating gun system for a one-step process

    What is a Propellant?



  • Invented late 1970s (DynaFrac by Chuck Godfrey of

    Physics International)

    Extensively studied by Sandia (US DOE) Predicted fractures of 100s feet

    Extensively evaluated by Mobil and other majors

    1980s and discarded as an acceptable stimulation


    History of Propellants



  • Expanding bubble increases localized pressure This in turn fractures the rock

    What Propellant Does??



  • Propellant Pulse



  • Energy application rates and resulting fracture patterns for various fracture stimulation technologies

    Fracture Patterns for Various Techniques



  • Performs a mini fracture on the formation by: Using a high energy pressure wave to drive a fluid piston into the

    formation to initiate a fracture Short non-propped, bi-wing fracture created

    Potential short-term increase in production rates Results can determine whether conventional frac job is needed or not Fractures tend to stay in zone (zonal isolation) Fracture past wellbore/formation damage Fracture past perforation damage Potential communication with natural fractures

    Propellant Uses



  • At its peak 1,000 jobs per year comparedto more than 40,000 hydraulic stimulationjobs per year

    Propellant Results



  • Pressures at least 1.4 psi/ft or .6 plus frac gradient Intervals up to 300 feet (< 50 feet most common) Fluids in wellbore can vary Completion brine

    Acid - mini acid wash Resin - for sand control (more failures than successes) Minimum liquid column required for propellants to prevent tool

    movement and to initiate propellant NO liquid to surface for propellants otherwise wellhead will be blown


    Risk of completion damage such as unseating packers or splitting casing

    Will destroy hydraulic cement bond

    Propellant Operations



  • Safety No liquid to surface

    Well hardware and equipment ratings

    Splitting casing

    Packer movement

    Collapsing guns with propellant sleeves

    Formation damage If no fracture initiated, perforations are plugged

    Propellant Limitations



  • Extreme Under-balance



  • Perforation cleanup occurs in about the first 10 msec from generation

    of perforation tunnel (SPE 30081).

    Optimum underbalance to achieve clean perforations is a function of

    permeability, porosity, reservoir strength and type /size of charge

    (SPE 30081).

    Less than optimum underbalance results in variable perforation

    damage skin and variable flow rate/perforation (SPE 22809 & SPE


    Under-balance Perforation; Some Fundamentals



  • EUP jobs were performed employing modular gun system. This

    technique takes the underbalance perforating to the extreme.