FLOWLINES & PIPELINES
Innovation enhances deepwater pipeline
pre-commissioning and inspection
Deepwater pipeline pre-commissioning and in-line inspections are logistical and technical challenges, and vessel time is typically a major expense. The Tamar gas feld project in the Mediterranean Sea met these challenges using
specialized subsea commissioning technology to mechanically displace and introduce
pipeline fuids, and ultrasonic in-line inspection tools to assure pipeline integrity.
The long-distance, deepwater pipeline project for Noble Energy involved a subsea gas
production and transportation system connecting the Tamar gas feld to an offshore
receiving and processing platform linked to
the existing Mari-B platform. The system
produces gas from fve high-fow-rate subsea
wells through separate infeld fowlines to a
subsea manifold. Dual subsea pipelines transport production from the subsea manifold approximately 149 km (92.5 mi) to the Tamar
offshore receiving and processing platform.
The processed gas goes to the existing Ashdod Onshore Terminal (AOT) for sales into
the Israel Natural Gas Line (INGL).
Weatherford’s Pipeline and Specialty Servic-
Infeld fowline operations
es (P&SS) group was contracted to provide the
pipeline pre-commissioning and inspection, in-
cluding tieback pipelines, monoethylene glycol
(MEG) pipelines, infeld fowlines, gas and con-
densate injection pipelines, Tamar sales gas ex-
port pipeline, and utility pipelines. Integration of
these services through a single contractor was
one key to reducing logistical and scheduling
constraints for overall project success.
Challenges and solutions engaged in the
project revolved around subsea fooding, testing, and MEG injection; dewatering, MEG
conditioning, and nitrogen purging; and ultrasonic wall measurement base line inspection.
A key aspect of the pre-commissioning involved
fooding, cleaning, gauging, and hydrotesting the
5 x 10-in. deepwater ( 1,600 m to 1,800 m/5,248 ft
to 5,904 ft) infeld fowlines of 4-km to 6-km ( 2.5-
mi to 3.7-mi) lengths. These operations were
performed from the seabed using Weatherford’s
Denizen subsea pre-commissioning system.
Flowline operations were independent of the
tieback lines and jumper installation. Schedule
fexibility increased as a result, and the remote
subsea operations avoided the use of a large,
vessel-based pumping spread or deepwater
downline. Subsea pumps for the food and hy-
drotest operations were driven by high ambient
hydrostatic pressure during the pipeline free-
food phase and by ROV hydraulic power.
The Denizen pigging pump launched the
dewatering pig train with slugs of MEG. A
custom, high-volume MEG skid was deployed
subsea and connected to the fooding skid to
avoid the cost of downline intervention to inject the MEG.
Pre-launching the pigs allowed dewatering
of the 10-in. infeld lines via a jumper from the
16-in. tieback lines. As a result, all dewatering
nitrogen injection was performed from the
shallow end of the tieback lines.
Another novel subsea operation used multiple remote subsea data-logging skid packages during hydro-testing. Typically, the ROV
and pumping skid hold station at the end of
the pipeline for the full 12- or 24-hr pressure
test. This was unworkable with fve pipelines
requiring testing and hold periods.
The solution was to deploy multiple independent hydro-test logging skids. The system’s
pumping skid has a built-in hydro-test data logging system that displays pipeline pressure, temperature, and pump fow rate. A high-pressure
triplex pump, powered by the ROV’s hydraulic
system, elevated pipeline pressure by injecting
chemically treated and fltered seawater.
The logging skids were stabbed into the
pipeline and the pressure test was conducted
through them. Instead of remaining on station
during the hold period, the pump skid was
freed to pressurize the next pipeline.
Twin 16-in. pipelines
Flooding, cleaning, and gauging the twin
147-km (91.3-mi) x 16-in. pipelines was done
from a vessel at the shallow end of the 240-m to
1,700-m (782-ft to 5,576-ft) water depth run. In-line inspection surveys were conducted during
fooding. A caliper tool was pumped to verify
minimum bore followed by a UTMW tool to acquire the wall thickness baseline survey.
The inspection was followed by dewatering operations for all 5 km ( 3 mi) of the Tamar infeld and tieback pipelines. Pipeline diameter and water depth required a pressure
range of 170 to 235 bar ( 3,465 psi/17 MPa to
3,408 psi/23.5 MPa), which required specialized compression equipment. Weatherford’s
Temporary Air Compression Station (TACS)
Mark J. Slaughter
The Tamar gas field presented many
logistical and technical challenges to
pre-commissioning and inspection.