causes of low well productivity wellbore and or reservoir issues

7/29/2019 Causes of Low Well Productivity Wellbore and or Reservoir Issues

1/46

Causes of Low WellProductivity:

WellboreAnd/Or

Reservoir Issues

Iraj Ershaghi, USC


2/46

Outline

Increasing Number of Marginal Wells Causes for low Productivity

Solution Approaches Question of Economic Feasibility


3/46

Source EIA

More Than 60% of California Wells produce less than 15 Barrels per day


4/46

Energy to Produce Oil

Rate of production=(Productivity index)*(Pressure Drawdown)

Reservoir Pressure, P

Wellbore

Pressure, pwf

Pressure

drawdown=p-pwf


5/46

Drop in Pressure Drawdown

Loss of Reservoir Pressure High Wellbore Pressure


6/46

Productivity Index

+S)


7/46

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


8/46

Need to

Understand the

Pore Structure


9/46

What Plugs the flow Channels?


10/46

Open Hole Cased Hole PerforationGravel Pack Hole

Damaged Interval

Damage Affecting

all Types ofCompletions


11/46

Major Causes of Formation Damage

Mechanical

Chemical

Biological

Thermal


12/46

Mechanical Damage

Fines Migration

External Solids Entrainment

Relative Permeability Reduction

Geomechnical Stresses-Collapsed Around the Well

Fracture/Propant Plugging

Propant Embedment

Glazing and Mashing


13/46

Collapsed Formation


14/46

Extraneous Solids Entrainment

Overbalanced Drilling, Completion, Kill and StimulationFluids

Solids From Overbalanced Fluid Losses


15/46

Solid Types

Weighting Agents (barite, hematite, CaCO3)

Fluid Loss Agents

Bridging Agents (Cellulosic fibers, Oil soluble resins..etc)


16/46

Adverse Relative Permeability Effects

Trapping of Water based Filtrate

Trapping of Oil Based Filtrate

Entrapment of water of Condensation

Kro

Krw

Sw


17/46

Chemical Damage Mechanisms

Rock-Fluid Interactions

Fluid-Fluid Interactions

Wettability Alteration


18/46

Fluid-Fluid Damage Mechanism

Precipitates (organic and inorganic)

Scales

Paraffins

Asphaltenes

Hydrates

Diamondoids

Chemical Adsorption

Emulsions


19/46

Clay SwellingSubstitution of Water into a Clay Matrix


20/46

Near Wellbore Wettability

Alteration

Oil

Water

Kro KroKrwKrw


21/46

Biological Damage Mechanisms

Plugging

Corrosion

H2S Generation


22/46

Thermal Damage Mechanism

Mineral Transformations

Dissolutions and Re-precipitation

Fines Migration

Wettability Alteration


23/46

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


24/46

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


25/46

Scale Buildup

Completion/Workover Fluids

Fluid Production (change of pressure, temperature,

pH)


26/46

Suitable for

Acidizing?

Suitable for Frac Pac?


27/46

Corrective Actions Can work


28/46

Case Study Data


29/46

Another Example


30/46

Example from a Service Company


31/46

Another Example


32/46

Well Testing-ToDiagnose Damage


33/46

Evidence of Skin from

Well Test Data


34/46

Diagnostic

Plots

Indicating

Skin


35/46

Production Data Diagnostic PlotsWell Operation history-Gross Vs. Net

Offset Well ComparisonProduced Fluid/Solid Samples


36/46

Check the HistoryOne time Pressure Transient Test may not be

diagnostic of the source of the problem


37/46

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


38/46

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


39/46

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


40/46

Formation DamageImplicationsUnrealized Production

Unrealized Stimulation Potential


41/46

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


42/46

Drop in Pressure Drawdown

Loss of Solution Gas Los of Gas Cap

Small Size or No Aquifer


43/46

Drawdown Corrective Measures

Pressure Maintenance Water Injection

Gas Injection Steam Injection


44/46

Blessings of Gravity Drainage


45/46

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


46/46

Partners

Producers Government Support

Service Companies

Student Interns

causes of low well productivity wellbore and or reservoir issues

Documents