Post on 04-Apr-2018
7/29/2019 Causes of Low Well Productivity Wellbore and or Reservoir Issues
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Causes of Low WellProductivity:
WellboreAnd/Or
Reservoir Issues
Iraj Ershaghi, USC
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Outline
Increasing Number of Marginal Wells Causes for low Productivity
Solution Approaches Question of Economic Feasibility
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Source EIA
More Than 60% of California Wells produce less than 15 Barrels per day
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Energy to Produce Oil
Rate of production=(Productivity index)*(Pressure Drawdown)
Reservoir Pressure, P
Wellbore
Pressure, pwf
Pressure
drawdown=p-pwf
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Drop in Pressure Drawdown
Loss of Reservoir Pressure High Wellbore Pressure
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Productivity Index
+S)
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Drop in Productivity Index
Decrease in Oil and Increase in Water or Gas Saturation Increase in Wellbore Skin (Paraffin/ Asphaltene/scale)
Increase in Oil Viscosity (Loss of Light Components)
Collapsed Tubing
Collapsed Perforation
Poor Isolation of Zones
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Need to
Understand the
Pore Structure
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What Plugs the flow Channels?
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Open Hole Cased Hole PerforationGravel Pack Hole
Damaged Interval
Damage Affecting
all Types ofCompletions
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Major Causes of Formation Damage
Mechanical
Chemical
Biological
Thermal
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Mechanical Damage
Fines Migration
External Solids Entrainment
Relative Permeability Reduction
Geomechnical Stresses-Collapsed Around the Well
Fracture/Propant Plugging
Propant Embedment
Glazing and Mashing
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Collapsed Formation
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Extraneous Solids Entrainment
Overbalanced Drilling, Completion, Kill and StimulationFluids
Solids From Overbalanced Fluid Losses
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Solid Types
Weighting Agents (barite, hematite, CaCO3)
Fluid Loss Agents
Bridging Agents (Cellulosic fibers, Oil soluble resins..etc)
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Adverse Relative Permeability Effects
Trapping of Water based Filtrate
Trapping of Oil Based Filtrate
Entrapment of water of Condensation
Kro
Krw
Sw
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Chemical Damage Mechanisms
Rock-Fluid Interactions
Fluid-Fluid Interactions
Wettability Alteration
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Fluid-Fluid Damage Mechanism
Precipitates (organic and inorganic)
Scales
Paraffins
Asphaltenes
Hydrates
Diamondoids
Chemical Adsorption
Emulsions
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Clay SwellingSubstitution of Water into a Clay Matrix
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Near Wellbore Wettability
Alteration
Oil
Water
Kro KroKrwKrw
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Biological Damage Mechanisms
Plugging
Corrosion
H2S Generation
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Thermal Damage Mechanism
Mineral Transformations
Dissolutions and Re-precipitation
Fines Migration
Wettability Alteration
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Diagnostic Techniques
Proper Analysis of In-situ Fluids and Properties
Framework Composition Study of Rock,
Wettability, Capillary Pressure and Relative
Permeability Character
Displacement Testing to Evaluate Different
Damage Mechanism because of past Drilling,Completion,and production practices
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Formation Damage
Can be a very complex process and is generally
reservoir and application specific
Several Mechanisms may be operative
Various Lab Screening or Down hole Surveys
May be necessary
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Scale Buildup
Completion/Workover Fluids
Fluid Production (change of pressure, temperature,
pH)
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Suitable for
Acidizing?
Suitable for Frac Pac?
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Corrective Actions Can work
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Case Study Data
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Another Example
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Example from a Service Company
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Another Example
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Well Testing-ToDiagnose Damage
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Evidence of Skin from
Well Test Data
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Diagnostic
Plots
Indicating
Skin
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Production Data Diagnostic PlotsWell Operation history-Gross Vs. Net
Offset Well ComparisonProduced Fluid/Solid Samples
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Check the HistoryOne time Pressure Transient Test may not be
diagnostic of the source of the problem
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Historical Perspectives
Use of Dirty Completion Fluids
Lack of Good Perforating Practice
Failure to Recognize Precipitating Oil Mixtures or
Incompatible Waters
Failure to Inhibit Fluids Against Clay Swelling inSandstone Formation
Use of Painted Tools and Rusty or Scaled Pipes
Excess Use of Thread Dope
Use of Impure Additives
Use of Fresh Water Buffer
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HistoricalUse of Corrosion Inhibitors
Use of Scale Inhibitors
Deposition of Asphalt
Plugging of Gravel Packs
Damage When Cutting Paraffin or Asphaltenes
Damage From Acidizing or Fracturing Fluids
Damage During Perforation
Damage During Casing or Cementing Operations
Damage During Drilling
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Summary- Formation Damage
Drilling Damage-clays, Weighting Agents, Lost Circulation Agents Drilling Fluid Filtrate
Cementing Damage
Perforation Damage
Completion and Workover Fluids Damage
Damage in Gravel Packs
Damage During Production
Fines Migration Loss of Rock Compressive Strength
Precipitation of Organic or Inorganic Materials
Change in Wettability
Damage From Stimulation Fluids
Damage From Water Control Polymers
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Formation DamageImplicationsUnrealized Production
Unrealized Stimulation Potential
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Attitudes About a Marginal Well
Negative
Technologically Beyond Repair
Not Economical to Fix Keep on With Reasonable Prices-Shut Down Otherwise
Positive
Still Much Oil Left to Be Produced
Explore Ideas
Seek Cost Share to Fix Wells
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Drop in Pressure Drawdown
Loss of Solution Gas Los of Gas Cap
Small Size or No Aquifer
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Drawdown Corrective Measures
Pressure Maintenance Water Injection
Gas Injection Steam Injection
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Blessings of Gravity Drainage
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Solution StrategyUse Material Balance to Roughly Estimate
What may be left in the ground
(Do not use Decline Curve of Marginal Wells)
If If some fractional recovery of remaining oil
justifies investment, focus on both wellborecleanup and pressure maintenance
Investment in Risky Unexplored Areas vs.
Investment in a Secure ProvenDevelopment Areas
Study the history of the wells to assess the extent of
the damage
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Partners
Producers Government Support
Service Companies
Student Interns