Applied Mechanics and Advanced Materials Research Group ...
Transcript of Applied Mechanics and Advanced Materials Research Group ...
Dr Zahid Qamar, Prof Tasneem Pervez, Dr Farooq al-Jahwari
Applied Mechanics and Advanced Materials Research Group (AM)2R
Mechanical and Industrial Engineering Department
Sultan Qaboos University, Muscat, Oman
International Gas Union Research Conference (IGRC-2020), 24-26 February 2020, Muscat, Oman
Engineering is the art of modeling materials we do not wholly
understand, into shapes we cannot precisely analyze, so as to withstand
forces we cannot properly assess, in such a way that the public has no
reason to suspect the extent of our ignorance.
A R Dykes
MOTIVATION AND SIGNIFICANCE
Technology shapes society and society shapes technology.
Robert W. White
In some oil wells, viscosity of the crude is very high (heavy oil)
Steam is injected to increase fluidity and mobility of the oil
Steam injection heats the crude oil in the formation, lowering its viscosity and vaporizing some of the oil to increase its mobility
Polymer Pipes in Oil Drilling
Schematic of steam injection process
Cyclic Steam Stimulation (CSS) is a staged technique using Vertical
Injection and Production
Polymer Pipes in Thermal Wells
Steam injection requires large quantities of water, generally transported from nearby fields
Some oilfields in the Gulf region, especially in Oman
Water-bearing sandstone is highly fragmented
Sand screens are required for sand control
Sand screens made of carbon-steel are not reliable
Quickly undergo serious corrosion
Some oilfields have started to try out non-metallic materials
Such as strengthened polymers (eg hard PVC)
Because of their non-corroding nature
Based on a hit-and-trial approach (in Oman)
Around 15% wells have reported failure due to screen collapse
Petroleum Development Oman (PDO) wanted to obtain more information on strength of these pipes
Experimental testing facility designed and developed at Sultan Qaboos University (SQU)
For integrity assessment of large-diameter hard polymeric pipes
Included design and construction of test setup and required jigs and fixtures
Types of tests
Pipe behavior under tensile loads
Pipe behavior under compressive loads
Collapse behavior
Testing of Polymer Pipes
Scientific understanding of different strength parameters of new pipe materials (high strength PVC)
Prequalification of polymer pipes for appropriate field conditions
Major savings in cost and time for thermally assisted oil wells
Once sufficient confidence is built with PVC concept, this well design can be introduced PDO wide
Major Contributions
Currently PDO drills approximately 30 shallow water supply wells per year
Drill-site water, camp supply, R/O & frac unit supply, water-flood, steam generation
Company-wide switch from carbon steel to PVC for water supply wells
Savings of approximately 150k-200k USED per well
Annual saving of 4.5-6.0 mil USD
Savings of 20-30 mil USD over a 5 year period
Financial Upside
EXPERIMENTAL WORK
To satisfy requirements of international standards
Polymer pipes had to go through a 2-3 month ageing process before mechanical testing
In brine solution matching the salinity of the water field (1.02 sg, equivalent to 35 PPT)
Testing under tensile loads
PVC pipe sections of 1m length and 280 mm dia
Three types of pipe sections
Plain
Built-up (pipe with threaded connection in the middle)
Slotted (screen)
3 samples tested in each case
Testing Scheme and Parameters
The three types of PVC pipes for tension testing: plain, built-up, and slotted
Tension tests conducted on a Dartech universal testing machine (UTM)
Capacity of 2000 kN in tension mode and 4000 kN in compression mode
Loads and deformations (elongation) directly recorded by machine
Pipe dimensions measured before each test (length, outer diameter, thickness)
For more precise and complete data recording, strain gages used
Another advantage: transverse (hoop) strains can also be recorded; measure of anisotropy behavior (Poisson’s ratio)
Machine readings converted into stress-strain data
Stress-Strain Measurements
Expecting that deformations may be large (polymer pipe), very special high-deformation strain gages (TML company) procured
All strain gages hooked up to Dartech machine thru a data logger and computer
Two sets of strain gages (3 axial, 3 hoop) fixed on each test pipe, on top and bottom positions, on opposite sides of the pipe
Marked as TA1 (top axial-1), BH1 (bottom hoop-1), etc
Stress-Strain Measurements
Sets of strain gauges in axial and hoop directions, near top and bottom ends of pipe
SALT WATER AGEING
Soaking to be done for
3 PVC pipes of 7-m length (collapse)
18 sections of 1-m length (tension + compression)
All of 280 mm diameter
Required almost 5000 liters of saline water (roughly 1500 US gallons)
Very difficult and time consuming to
Produce this amount of distilled water
Dissolve enough salt to get required salinity
Soaking in Salt Water
Alternate (unique) solution
SQU desalination research unit near the sea
Seawater can be directly pumped through an underground tunnel and pumping system
Judicious mixing of normal drinking water and high-salinity seawater
Required salt concentration
Soaking in Salt Water
Challenges
Pumping of large amount of seawater (5000 liters)
Transportation from desalination plant to SQU
Special containers to be arranged to keep 18 pipes of 1-m length and 3 pipes of 7-m length under this saline water
Soaking in Salt Water
Transportation and storage of saline water
Immersion of 18 sections of 1-m PVC pipe (plain, built-up, and slotted) in saline water for 2-3 months soaking
DESIGN AND CONSTRUCTION OF EXPERIMENTAL SETUP
The proper study of mankind is the science of design.
Herbert Simon
Tension tests; Dartech universal testing machine
Main challenge; gripping of pipes
Three major issues or design constraints
Pipe dia was too large to go inside the gripping system of the machine
PVC surface was too smooth to provide enough friction for good grip
Too much load could not be applied in the grip region, or the PVC material would fracture here rather than in the main pipe section
Various gripping fixtures were designed, constructed, and tried out
Design and Construction of Tensile Test Setup
Idea based on application used in civil construction industry
Grout: a chemical resin mixed with water that is used for extra high strength reinforcement in concrete structures
A set of inside and outside metallic ring supports on each end of the PVC pipe
Prescribed gap between metal and PVC to pour in the grout mixture
After curing, grout would become a solid mass, exerting a large pressure and creating strong friction between metal and PVC
Hopefully, joint would not shear off under the maximum tensile load needed to fracture the main section of the pipe
Grout could be single-sided or double sided
Single-grout design would be tried out first, being more efficient in terms of time, cost, material, and effort
Grout Design
Design sketches for single-grout and double-grout designs
Exploded view of single-grout design for tensile test gripping fixture
Exploded view of double-grout design for tensile test gripping fixture
Exploded view of extended-length single-grout design for tensile test gripping fixture
Grout design was successful for slotted PVC pipes
Lowest tensile strength
Grout design failed in the case of plain and built-up pipes
Another gripping fixture designed and constructed
Based on the idea of a threaded contact between PVC pipe and inner support ring
Thread Design
Sketch of threaded-contact design for tensile test gripping fixture
Exploded and assembled views of threaded-contact design for
tensile test gripping fixture
TESTING UNDER TENSILE LOADS
Single-grout design used successfully for slotted PVC pipes
Both single and double grout designs failed for plain and built-up pipes
Grout connection sheared and broke off before pipe could fracture
Threaded connection also failed
PVC pipe fractured near the last thread of grip area rather than in the main pipe body
Various stages in preparation of single-grout tensile test fixture
Assembly of tensile fixture components
Pouring of grout in the gap between metal ring and PVC pipe
Grout curing
Assembly after grouting, etc.
Tension Testing
Single-grout tensile test setup; different stages of preparation and assembly
Testing of plain PVC pipe using single-grout fixture; grout assembly failed before pipe could fracture
Testing of plain PVC pipe using double-grout fixture; grout assembly
failed before pipe could fracture
Components of threaded-contact tension fixture, and different stages of
initial assembly
Various stages of final assembly of threaded-contact tension fixture
Testing of plain PVC pipe using threaded-contact fixture; pipe failed near last thread of grip area rather than in the main pipe body
RESULTS AND DISCUSSION
The system records force (kN), elongation/displacement (mm), and micro-strain data for each test
Later; data converted into plots of stress vs strain
Using average values of pipe dimensions measured before each test
Length, outer diameter, thickness
Pipe properties extracted from these graphs
Fracture stress
Fracture strain (ductility)
Elastic modulus
Poisson’s ratio or anisotropy (ratio of hoop strain to axial strain)
For elasticity value (Young’s modulus)
Curve fitting done for roughly 10% (initial linear portion) of graph
Tensile Test Results
Testing of slotted PVC pipe using single-grout fixture; pipe fractured in the middle section or near the end
Stress-strain plots for slotted pipe, without
aging; top and bottom positions; pipe-1 and
pipe-2
Stress-strain plots for slotted pipe, after
aging; top and bottom positions; pipe-1 and
pipe-2
Summary of Test Results
Good to observe that average values of stiffness of slotted PVC pipes are almost the same before and after aging
Value of elastic modulus determined by considering only linear portion of stress-strain curve, and fitting a straight line through these data points
Polymer pipes (not metallic); no portion of stress-strain diagram is really linear
So this straight-line fit is rather approximate
Discussion of Results
Effect of salt-water soaking on anisotropy behavior is not significant
Poisson’s ratio for slotted pipe (before and after ageing) remains in the 0.43-0.44 range
Decrease in pipe diameter (deformation in hoop direction) would be roughly 43-44% of increase in pipe length (deformation in the axial direction) under tensile loading
Discussion of Results
Surprisingly, tensile strength (maximum stress that slotted PVC pipes can withstand before tensile failure) after aging is almost 46% higher
This is of course good news for the field engineers
Discussion of Results
Acknowledgements
Authors acknowledge the support of Sultan Qaboos University (SQU) and Petroleum Development Oman (PDO) for this work.
Science never solves a problem without creating ten more.
Bernard Shaw
Many a thank!