Unstable Formation and Sand Control

Unstable Formation and Sand ControlOutcomesTowards the end of lecture, you should be able to:

Explain causes of sand productionDescribe consequences of sand productionDescribe methods to predict sand productionDescribe sand control techniques

DefinitionSand control is..the limitation of sand production to an acceptable levelWells completed with sand control are designed to: retain load bearing solidsbut produce fines

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

Factors Increasing Sand Production4Whats Influences Sanding?High velocity of viscous fluid can move sandRock stresses can cause sand failure10kPSIWater can weaken sand Rock StrengthOil or Gas

The pore pressure supportsthe sandHelix RDS LimitedSand Management Training Course5Causes of Sand Production (I)Time Dependencedecreasing reservoir pressure increases the effective stress on the grains (overburden is constant)Fluid Flowfluid velocity and viscosity contributes to the pressure drop near the wellbore (drag force)production induces stress on the formation sandinduced stress > formation stress sand production

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Causes of Sand Production (II)Geological Factorstertiary age reservoirs, usually shallow depths unconsolidatedImpairment on Natural Consolidationhigh compressive strengthinternal pore pressure supports the overburden7

Causes of Sand Production (III)Mutiphase FlowWater production may dissolve natural cementing materials weakening the intergranular bonds;Water production may mobilize fines resulting in plugging of the pore structure.8Consequences of Sand ProductionAccumulation downholeAccumulation in surface equipmentErosion of downhole/surface equipmentCollapse of the formation

Sanding Prediction - WhySand ControlSand ControlSand Control? Zero strengthVery very weak Very weak Weak Dry sand Damp sand Weakly-cemented Stronger cement high F lower FPrediction of sand failureWhen a well is drilled in un-consolidated (loose-grained) sand, sand is produced together with well fluid.Sand production canerodeEquipmentWellboreplug flowlines11Prediction 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 equipmentWithout sand control, oil production of wells will lead to uneconomical.Therefore, Sand exclusion methods are required.12Prediction 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.13Prediction of sand failure 14How to predict sand failure?

Formation strength testSonic logPorosityDrawdownMultiphase flow

Prediction of sand failureExperienceAnalogySpecial Well TestCore Inspection and Testing

MeasurementsLog InterpretationCorrelations

Sand Control TechniquesMaintenance and workoverRate restrictionSelective completion practicesPrevent sand production mechanically by screen or gravel pack.Chemically consolidate the formation sand near the wellbore using resinous material.Inject resin-coated gravel into the perforations to pack and stabilize the perforations.

16Question ??Thank You