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Histeresis
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An Experimental Investigation into Explosive Decompression of Progressing Cavity Stator
Elastomers Due to Gas Infiltration
Society of Petroleum EngineersPCP Applied Technology Workshop
September 16, 2002
Presented by: Mike Guidry, Jr.
September 16, 2002PCP Applied Technology Workshop
Definition
Explosive Decompression
– Occurs when the internal pressure applied to a material by a trapped fluid exceeds the tear strength of that material upon the reduction of external pressure.
September 16, 2002PCP Applied Technology Workshop
History
Field experience
– Well bore gases can infiltrate the elastomers in down hole service.
– Severe explosive decompression damage can result when there is rapid pressure loss.
• Uncontrolled shut down situations
• Ordinary well service
September 16, 2002PCP Applied Technology Workshop
Theory
This discussion only concerns materials which are inertrelative to each other.
September 16, 2002PCP Applied Technology Workshop
Definition
Infiltration (Permeation)
– The migration of fluid into or through a lattice.
September 16, 2002PCP Applied Technology Workshop
Theory
Elastomers are permeable.
– Permeability varies with the compound structure, properties of the contact fluid, and environmental conditions.
September 16, 2002PCP Applied Technology Workshop
Theory
Typical Elastomer Structure
– Elastomer compounds are generally an amorphous lattice of long chain molecules.
– The long chain molecules are sparsely cross-linked by other atoms.
September 16, 2002PCP Applied Technology Workshop
Theory
Typical molecular structure of a carbon-hydrogen back bone elastomer with sulfur cross-links
September 16, 2002PCP Applied Technology Workshop
Theory
Two highly compressible fluids common topetroleum wells are:
– Methane
– Carbon Dioxide
September 16, 2002PCP Applied Technology Workshop
Theory
Methane
– Methane is a tetrahedral molecule
September 16, 2002PCP Applied Technology Workshop
Theory
Tetrahedral molecular structure of methane
September 16, 2002PCP Applied Technology Workshop
Theory
Carbon Dioxide
– Carbon dioxide is a linear molecule
• Linear molecular structures have the smallest cross-section of the typical molecular structures.
September 16, 2002PCP Applied Technology Workshop
Theory
Linear molecular structure of carbon dioxide
September 16, 2002PCP Applied Technology Workshop
Theory
Fluid pressure exceeding the pressure applied bythe elastomer typically results in one or more of thefollowing:
– Deflection
– Tearing
– Infiltration
September 16, 2002PCP Applied Technology Workshop
Theory
Carbon dioxide infiltrating the elastomer lattice
September 16, 2002PCP Applied Technology Workshop
Theory
Explosive decompression occurs when:
– The rate of decompression exceeds the rate of permeation
– The pressure of the infiltrate fluid exceeds the tear strength of the elastomer
September 16, 2002PCP Applied Technology Workshop
Testing
Can explosive decompression damage be minimizedthrough compound selection and field implementationtechnique?
September 16, 2002PCP Applied Technology Workshop
Testing
Test Method
– Samples of different 5 compounds were prepared in the form of a progressive cavity stator.
– 1 sample of each compound was loaded into 5 separate test cylinders.
– Each cylinder was then loaded with the test fluid and rotated for the duration of the test.
September 16, 2002PCP Applied Technology Workshop
Testing
Figure 1. Test Sample
September 16, 2002PCP Applied Technology Workshop
Testing
Test Parameters
– 1000 PSI (6.895 MPa)
– 75°F (24°C)
– 71 hours
September 16, 2002PCP Applied Technology Workshop
Testing
Fluid Composition by Volume Fraction
– Cylinder A water 100%
– Cylinder B water 80% carbon dioxide 20%
– Cylinder C water 70% carbon dioxide 30%
– Cylinder D water 60% carbon dioxide 40%
– Cylinder E water 70% carbon dioxide 30%
September 16, 2002PCP Applied Technology Workshop
Testing
Decompression Rates
– Cylinders A-D -- controlled decompression rate
– Cylinder E -- maximum decompression rate
September 16, 2002PCP Applied Technology Workshop
Results
Cylinder A -- 1 Hour Post Decompression
Compound 1 Compound 2 Compound 3
Compound 4 Compound 5
September 16, 2002PCP Applied Technology Workshop
Results
Cylinder C -- 1 Hour Post Decompression
Compound 1 Compound 2 Compound 3
Compound 4 Compound 5
September 16, 2002PCP Applied Technology Workshop
Results
Cylinder C -- Post Decompression Time Dependence
1 hour 6 hours 70 hours
Com
poun
d 4
C
ompo
und
1
September 16, 2002PCP Applied Technology Workshop
Results
Post Decompression Volume Fraction Dependence
0% Carbon Dioxide
20% Carbon Dioxide
Compound 1 Compound 4
September 16, 2002PCP Applied Technology Workshop
Results
Post Decompression Volume Fraction Dependence
30% Carbon Dioxide
40% Carbon Dioxide
Compound 1 Compound 4
September 16, 2002PCP Applied Technology Workshop
Results
Compound 4 -- Decompression Rate Dependence
1 hour
70 hours
Cylinder C Decompression Rate Cylinder E7 psi/min 400 psi/sec
September 16, 2002PCP Applied Technology Workshop
Conclusion
Explosive Decompression Damage Factors
– Volume fraction of compressible, infiltrate fluid
– Rate of decompression
– Duration at lower pressure
– Elastomer compound
September 16, 2002PCP Applied Technology Workshop
Conclusion
Reducing Explosive Decompression Damage
– Select the proper elastomer compound
– Minimize the rate of decompression
– Minimize the duration at low pressure
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