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

9

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

10

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.

11

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

14

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

17

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.

19