DOWNHOLE TUBING FOR GAS PRODUCTION
CAPCIS is continually testing materials to verify performance at operational limits beyond the established envelope.
In this instance, a test programme was performed for
a major Operator to verify the suitability of glass
fibre reinforced epoxy composite lined tubing for use
in a typical Middle East gas producer at a maximum temperature
of 110°C. The system has a long track record of
use in water injection service in different areas of
the world. Due to the high inherent corrosion resistance,
combined with a relatively low cost of the system, it
was considered for use in gas producing (and oil producing)
wells.
The operational downhole conditions valid for the study were:
- Shut in pressure around 300 bar
- Downhole temperature 110°C
- Gas with 0.6 mol % H2S, 2.0 mol % CO2
- Lifetime 25 years
The first part of the test program comprised accelerated ageing of
the glass fibre liner material at three temperatures,
110, 130 and 150°C to generate data for an Arrhenius-type
model using the methodology of ISO 2578. Material coupons
were exposed in Hastelloy autoclaves to three phases:
brine, liquid hydrocarbon and a gas mixture (methane,
H2S and CO2).
Samples were removed after four different exposure
times (up to 2000 hours). The mechanical properties
for the various exposure temperatures and times were
used to estimate the temperature limits of the glass
fibre liner for a 25 year service life. These limits
were clearly above the design temperature of 110°C.
An additional and potentially limiting factor on the materials performance in service is flow, which was investigated in a second phase of testing using a purpose built flow loop.
The methodology developed for accelerated ageing has subsequently been used successfully to find the temperature limits for the following test conditions:
- Very sour gas at 10% and 20% H2S and temperatures
up to 150°C.
Oxygenated seawater. The residual life during service given the predicted thermal profile for a raw seawater injector was estimated.
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