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Gre composite material for well completion solution
REFERENCE DOCUMENTATION
An erosion study has been carried out for the Zohr field development project (Offshore Egypt).
Erosion is estimated over the service life of 5” Xtrees and production tubing, using DNV’s recommended practices RP-O501 (Det Norske Veritas – Norwegian certification company).
Erosion, especially during exploration phase, could become a challenge in the unlikely event that Zohr wells produce high amounts of sand or particles made of quartz, which are much more erosive than carbonate minerals.
Should this prove to be the case, erosion will remain within the design limits of the completion equipment as long as the solid loading remains moderate (below 0.09 - 0.14 lb/MMscf) and particls remain small (<50 microns).
Usually, in this scenario, high chrome content material is applied, with consequent very high cost and long delivery time which could remarkably impacts on the project. For this job, the opportunity of the GRE composite material application has been evaluated.
Direct Impact Test and Flow Loop slurry erosion tests have been arranged at PoliMi in order to verify the GRE suitability in harsh conditions.
An erosion study has been carried out for the Zohr field development project (Offshore Egypt).
Erosion is estimated over the service life of 5” Xtrees and production tubing, using DNV’s recommended practices RP-O501 (Det Norske Veritas – Norwegian certification company).
Erosion, especially during exploration phase, could become a challenge in the unlikely event that Zohr wells produce high amounts of sand or particles made of quartz, which are much more erosive than carbonate minerals.
Should this prove to be the case, erosion will remain within the design limits of the completion equipment as long as the solid loading remains moderate (below 0.09 - 0.14 lb/MMscf) and particls remain small (<50 microns).
Usually, in this scenario, high chrome content material is applied, with consequent very high cost and long delivery time which could remarkably impacts on the project. For this job, the opportunity of the GRE composite material application has been evaluated.
Direct Impact Test and Flow Loop slurry erosion tests have been arranged at PoliMi in order to verify the GRE suitability in harsh conditions.
Introduction to Well Construction
A well is a borehole designed to produce petroleum hydrocarbons to the surface. For a production well, the target is optimizing the fluids management in order to maximize the reservoir drainage.
The well is created by drilling a hole into the earth using a drill string. After the hole is drilled, sections of steel pipe (casing) and cement are placed in the wellbore. The casing provides structural integrity to the drilled wellbore, in addition to isolating potentially dangerous high pressure zones from each other and from the surface.
In order to safely produce oil or gas up to surface, a Completion string (tubing) is run into the casing.
In conclusion, the production stage is the most important stage of a well's life, when the oil and gas are produced.
A well is a borehole designed to produce petroleum hydrocarbons to the surface. For a production well, the target is optimizing the fluids management in order to maximize the reservoir drainage.
The well is created by drilling a hole into the earth using a drill string. After the hole is drilled, sections of steel pipe (casing) and cement are placed in the wellbore. The casing provides structural integrity to the drilled wellbore, in addition to isolating potentially dangerous high pressure zones from each other and from the surface.
In order to safely produce oil or gas up to surface, a Completion string (tubing) is run into the casing.
In conclusion, the production stage is the most important stage of a well's life, when the oil and gas are produced.
Case study
Zohr is the largest gas discovery ever made in Egypt and in the Mediterranean Sea and will be able to satisfy part of Egypt’s natural gas demand for decades to come. The field is currently producing 2 bcfd (approx. 57k m3/d), equivalent to approximately 365.000 barrel of oil equivalent per day. This level of production was achieved thanks to the start-up of the fifth production unit, backed by the 8 gas producers and a new 30” x 218 km sealine.
The Shorouk Offshore Block is located in the East Nile Delta offshore and belongs to the East Mediterranean Basin. The total Block area is 3765 km2, in a water depth of 1100-1700 m and around 100-200 km far from shore.
The first committed well of the first exploration period is Zohr-1, a multi target structure to test a completely new play in the Nile Delta Basin. The main target is Miocene in age, while the second and deeper target is Lower Cretaceous in age and foresees carbonate platform faces (to be reached in future appraisal campaign).
The proposed Zohr-1 well has encountered the main target, the Miocene build up, around 3800m (+/-75m).
Zohr is the largest gas discovery ever made in Egypt and in the Mediterranean Sea and will be able to satisfy part of Egypt’s natural gas demand for decades to come. The field is currently producing 2 bcfd (approx. 57k m3/d), equivalent to approximately 365.000 barrel of oil equivalent per day. This level of production was achieved thanks to the start-up of the fifth production unit, backed by the 8 gas producers and a new 30” x 218 km sealine.
The Shorouk Offshore Block is located in the East Nile Delta offshore and belongs to the East Mediterranean Basin. The total Block area is 3765 km2, in a water depth of 1100-1700 m and around 100-200 km far from shore.
The first committed well of the first exploration period is Zohr-1, a multi target structure to test a completely new play in the Nile Delta Basin. The main target is Miocene in age, while the second and deeper target is Lower Cretaceous in age and foresees carbonate platform faces (to be reached in future appraisal campaign).
The proposed Zohr-1 well has encountered the main target, the Miocene build up, around 3800m (+/-75m).
Erosion
From an engineering point of view, the study has been approached considering sensitivities in terms of particle load, particle size and flow rate. Results are based on test parameters 175 MMscf/d flow rate and 50 μm quartz particles (more erosive than calcite, that would be the best representation of Zohr Carbonate reservoir).
From an engineering point of view, the study has been approached considering sensitivities in terms of particle load, particle size and flow rate. Results are based on test parameters 175 MMscf/d flow rate and 50 μm quartz particles (more erosive than calcite, that would be the best representation of Zohr Carbonate reservoir).
Particle load sensitivity
- Low 0,05 lb/MMscf: the total erosion in the Blinded Tee Downstream Choke for this lower sand load is slightly over 1 mm over the service life of the tree, which is well within the design limit. Erosion in other locations is very low and will thus not be an issue at this particle load.
- Medium 0,14 lb/MMscf: this can be defined as the maximum particle load that can be allowed while staying below the 3 mm erosion threshold. The highest erosion rate is located at Blinded Tee Downstream Choke.
- High 0,86 lb/MMscf: Due to the extremely high particle load, the erosion in both turns downstream the choke exceed the design limit.
Particle size sensitivity
Test parameters: 175 MMscf/d flow rate, 0.1 lb/MMscf particle load, quartz particles
- Small Particles (20 µm): the erosion rate is much reduced and within the design limit (2-3 mm cumulative erosion).
- Medium Particles (50 μm): erosion could become an issue if the average particle size exceeds 50 μm at the sand load assumed here.
- Large Particles (150 μm): particles erode 6.5 mm in the first turn downstream of the choke over the service life of the tree, which exceeds the tree’s design limit.
Flow rate sensitivity
Test parameters: 0.1 lb/MMscf 50 micron quartz particles.
- Low Particles (250 MMscf/d): the cumulative erosion in the first turn downstream the choke is 5 mm, which exceeds the tree’s design limit (2-3 mm cumulative erosion).
The tests were stopped: the erosion rates in the 250 MMscf/d case start out very high at around 0.2 mm/year and remain at that level until 2032. According to the erosion model, after 2032 production is choked back to base case conditions (175 MMscf/d).
For wells that are produced at high rates near the design limit, their solids production should therefore be carefully monitored and production constraints may be required to maintain erosion at acceptable levels in case of high sand production rates (>0.1 lb/MMscf) and/or production of large particles (>50 μm).
GRE – Glass Reinforced Epoxy resin
Due to the high potential erosion issues in the Zohr Wells, high content Cr material can be considered the typical solution responding with its characteristics. GRE has been evaluated as a suitable cheaper alternative. GRE system is a lined pipe combination of two materials, namely, a carbon steel tubing with a Glass Reinforced Epoxy internal liner. Carbon Steel guarantees the mechanical resistance of the system and the internal GRE liner assures the corrosion/erosion resistance.
Due to the high potential erosion issues in the Zohr Wells, high content Cr material can be considered the typical solution responding with its characteristics. GRE has been evaluated as a suitable cheaper alternative. GRE system is a lined pipe combination of two materials, namely, a carbon steel tubing with a Glass Reinforced Epoxy internal liner. Carbon Steel guarantees the mechanical resistance of the system and the internal GRE liner assures the corrosion/erosion resistance.
For oil well applications, the system consists of a glass-fibre reinforced epoxy resin composite liner inserted inside a low alloy carbon steel tubing with a cement grout. The grout transfers the pressure directly to the steel tubing even if there is little or no bonding between the liner, the grout and metal. Alkalinity of the cement is then beneficial to the corrosion rate of Carbon Steel by neutralizing the low pH of acid gases migrating in the system annulus. The end of the liner is protected from mechanical damage by a GRE end cap or a T-end flange. A polymeric Corrosion Barrier Ring (CBR) usually provides the continuity of the corrosion barrier across the coupling between two adjacent flares. The lining is generally lightweight: it adds no more than 13% of the weight of the steel pipes, which eliminates the need for additional lifting equipment.
GRE has an outstanding erosion resistance evaluated throughout specific tests in Polimi Laboratories.
Erosion depth ed, normalized by the corresponding average experimental measurements ed, exp, at four points along the deepest bucket section (left), four points along the bucket outlet (center), and average value along four sections (right). The red lines, lower and upper box bounds, and whiskers represent the median, 25th and 75th percentiles, and extreme values, respectively. (Leguizamón et al., submitted to Renewable Energy, 2019.)
Tests on GRE:
Wet direct impact tests
A total of 23 direct impact tests have been performed, for varying nozzle-to-specimen angles, jet velocities, and testing times. The solid volumetric concentration varied within 0.76% and 1.02% among the tests, and, it was approximately constant during each experiment. The tests allowed obtaining a comprehensive characterization of the resistance of GRE to slurry erosion. Some representative pictures of the eroded GRE specimens are provided here below for the high velocity jet (35 m/s).
Wet direct impact tests
A total of 23 direct impact tests have been performed, for varying nozzle-to-specimen angles, jet velocities, and testing times. The solid volumetric concentration varied within 0.76% and 1.02% among the tests, and, it was approximately constant during each experiment. The tests allowed obtaining a comprehensive characterization of the resistance of GRE to slurry erosion. Some representative pictures of the eroded GRE specimens are provided here below for the high velocity jet (35 m/s).
From left to right: 5’, 15’, and 30’ for 90° and 35 m/s.
Straight pipe results
The test has been performed in the slurry flow loop. The GRE pipes have been installed within the testing line of the flow loop; they are connected to the 3” steel pipes of the loop through specific steel connections.
The slurry flow rate was kept at about 21.5 l/s, corresponding to a velocity of about 8.5 m/s in the pipe (considering an inner diameter of 2.23”). The pressure, measured 0.96 m upstream the inlet flange of pipe 1, was within 3÷7 bar. The temperature of the flow during the tests was within 23÷36 °C. The measured concentration during the tests was within the 0.31 ÷ 0.72% range. After the test, the GRE pipes were removed from the loop. A segment of pipe of about 34 cm of length was cut from the pipe 2. The inner diameter of the pipe segment was measured with a caliper; the mean measured value of pipe diameter was 56.3 mm (2.22”), which is very close (even smaller) to the one given by the manufacturer. Therefore, there is no measurable variations of the inner diameter.
The test has been performed in the slurry flow loop. The GRE pipes have been installed within the testing line of the flow loop; they are connected to the 3” steel pipes of the loop through specific steel connections.
The slurry flow rate was kept at about 21.5 l/s, corresponding to a velocity of about 8.5 m/s in the pipe (considering an inner diameter of 2.23”). The pressure, measured 0.96 m upstream the inlet flange of pipe 1, was within 3÷7 bar. The temperature of the flow during the tests was within 23÷36 °C. The measured concentration during the tests was within the 0.31 ÷ 0.72% range. After the test, the GRE pipes were removed from the loop. A segment of pipe of about 34 cm of length was cut from the pipe 2. The inner diameter of the pipe segment was measured with a caliper; the mean measured value of pipe diameter was 56.3 mm (2.22”), which is very close (even smaller) to the one given by the manufacturer. Therefore, there is no measurable variations of the inner diameter.
Visual inspection of the internal surface of the GRE coating did not reveal any sign of erosion, further confirming the absence of measurable/detectable mass removal.
Completion Design
Zohr Wells have been completed with 7” slotted Liner System in a 8 ½” Open Hole. The single 7” 28Cr Upper Completion String is run inside the 9 5/8” Casing.
The overall completion architecture responds to double safety barrier criteria.
- Retrievable Packer system isolate zones by packing off the annulus between casing and tubing.
- Safety Valve System blocks uncontrolled flows in case of Xtree failures. This type of Safety Valve incorporates two independent operating systems, which offer redundancy to maintain dependable valve operation and ensure fail-safe operation in critical applications.
- Two Chemical Injection Lines are installed at different depths in order to provide the downhole injection service (i.e. scale inhibitor, hydrates, paraffins, corrosion etc.).
- Downhole Pressure and Temperature gauge is installed in a dedicated mandrel, close to the packer depth.
- A Subsea Wellhead & Xtree system ensures a safe connection to production subsea facilities.
