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Unstable Formation and Sand Control
S. Raja Rajeshwary
OutcomesTowards the end of lecture, you should be
able to:1. Explain causes of sand production2. Describe consequences of sand production3. Describe methods to predict sand production4. Describe sand control techniques
DefinitionSand control is…..
the limitation of sand production to an acceptable level
Wells completed with sand control* are designed to:
• retain load bearing solids
• but produce fines
*The term “exclusion” can be misleading
Experience with Sand~70% of the Malaysian fields have sanding
problems
In Malaysia, we have :sand production from both oil and gas fieldsno issues with the water injectorsaccess to most equipmenthomogeneous and heterogeneous sandsrun various types sand control: IGP, ESS, SAS,
SCONno experience of horizontal GPs
Areas Requiring Sand ManagementSand control usually required in areas with
newer sediments:
Malaysia Brunei Australia China UKCS Nigeria West Africa Gulf of Mexico Venezuela
Process Of Sand Management
Sanding anticipated
Sanding not anticipated
Sanding possible
Exclusion (maybe control)
Control (maybe
exclusion)
Maybe control (exclusion
unlikely)
Prediction
Control
Completion, Fit For Purpose
Selection:- Longevity- Productivity- Functionality- Cost
• Decline of reservoir presssure (increase of overburden pressure)
• Cementing Material, Degree of Consolidation
• Fluid Viscosity, Production Velocity, Drag Forces
• Increasing water production (destroys intergranular cementing material)
• Formation damage (increases drawdown)
Factors Increasing Sand Formation
What’s Influences Sanding?
High velocity of
viscous fluid can move
sand
Rock stresses can cause sand
failure
10kPSI
Water can weaken sand
Rock Strength
Oil or Gas
The pore
pressure
supports
the sand
Causes of Sand Production (I)Time Dependence
decreasing reservoir pressure increases the effective stress on the grains (overburden is constant)
Fluid Flow fluid velocity and viscosity contributes to the
pressure drop near the wellbore (drag force) production induces stress on the formation sand induced stress > formation stress sand production
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Causes of Sand Production (II)Geological Factors
tertiary age reservoirs, usually shallow depths unconsolidated
Impairment on Natural Consolidation high compressive strength internal pore pressure supports the overburden
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Causes of Sand Production (III)Mutiphase Flow
Water production may dissolve natural cementing materials weakening the intergranular bonds;
Water production may mobilize fines resulting in plugging of the pore structure.
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Consequences of Sand Production1. Accumulation downhole2. Accumulation in surface equipment3. Erosion of downhole/surface equipment4. Collapse of the formation
Sanding Prediction - WhySand Control Sand Control Sand Control?
Zero strength Very very weak Very weak Weak
Dry sand Damp sand Weakly-cemented Stronger cement
high F lower F
Prediction of sand failureWhen a well is drilled in un-consolidated (loose-grained) sand, sand is produced together with well fluid.
Sand production can
I. erode
Equipment
Wellbore
II. plug flowlines
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Prediction of sand failureAt low rates, little or no sand may be produced.
At high rates, large quantities may be produced.
In flowing wells, sand can erode chokes and can
be accumulated in separators.
In pumping wells, sand can erode down-hole
pumping equipment
Without sand control, oil production of wells will
lead to uneconomical.
Therefore, Sand exclusion methods are required.15
Prediction of sand failure Sand production is a two stage process
1- Failure of the rock
2- Transport of the failed materials into the
well bore
Sand production will only be observed once
both these processes have occurred.16
Prediction of sand failure
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How to predict sand failure?
1.Formation strength test2.Sonic log3.Porosity4.Drawdown5.Multiphase flow
Prediction of sand failureExperienceAnalogySpecial Well TestCore Inspection and Testing
MeasurementsLog InterpretationCorrelations
Sand Control Techniques1. Maintenance and workover
2. Rate restriction
3. Selective completion practices
4. Prevent sand production mechanically by screen or
gravel pack.
5. Chemically consolidate the formation sand near
the wellbore using resinous material.
6. Inject resin-coated gravel into the perforations to
pack and stabilize the perforations.
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