This $US23.3 billion gas pipeline project involves the construction of the 8,704 kilometre pipeline that will connect Horgos, located in Xinjian Uygur Autonomous Region, with the Hong Kong Special Administrative Region after traversing 14 provinces, autonomous regions and municipalities. The trunk pipeline is estimated to cost $US10.3 billion, while the network is expected to cost $US13 billion.

The pipeline is being designed with a capacity of 30 billion cubic metres of gas per annum. Construction commenced in late 2008 and is expected to be completed by 2011.

HDD in Tianjin

On the second West – East natural gas transmission project the Tianjin pipeline bureau organised the installation of pipe near the Tianjin West Outer Ring No.10 Bridge district. The contractors selected horizontal directional drilling because the anti-corrosion steel pipeline crossed nearly 400 metres of green belt land, as well as a sewage canal and waste high-voltage towers. The length of the directional drilling crossing was 510 metres with a design depth of 15 metres.

Project contractor Mr Xing identified some of the major challenges of the crossing. “The main difficulty was overcoming the strong local interference, such as the magnetic declinations that are different along the path.”

The river banks in the green belt were of smooth topography. The river is approximately 110 metres wide, and the riverbed elevation is approximately four metres. Ground condition on the crossing consisted of clay and sand.

• Clay layer: 1.6–25 metres in depth
• Clay/sand: 17–20 metres
• Sand: 25 metres below.

The contractors used a ZT-150 HDD rig and SST guidance system, applying several technical measures to successfully finish the project and overcome the influence of the interference. The crossing started on 16 May 2009, with the pipeline pullback completed on 6 June.

In order to determine the placement of the drilling rigs, the entry point and exit point needed to be set to the central axis. In this particular project it was very difficult to set out the central axis because of the large tracts of green belt. The contractors used GPS to overcome this challenge.

The completion of the pilot hole, the key to the entire project, used a ZT-150 horizontal directional drilling rig. The drilling tool combination included the non-magnetic drill bit, the non-magnetic probe house, the non-magnetic sub, the non-magnetic drill collar and the Φ127 drill pipe. The guidance system used was the SST orientation system. The drill bit was buried with a designed nine degree angle, with the drilling completed in strict accordance to the design requirements.

The first challenge was the inability to use basic magnetic declination due to the widely varied magnetic declination along the drill path. The Drillto engineers used the SST system to take the magnetic declination at shore as its reference. A computer was then used to control the azimuth and pitch, in order to guide the bore under the river. After the drill crossed the river ground tracking continued to be used.

At approximately 50 metres from the exit point each drill pipe must carefully follow the drill pipe inclinometer to ensure accuracy, points around the pipe were excavated to prevent interference. Finally the bit with the angle of 6° broke through just in the centre line. The pilot hole

The thrust and torque were in normal condition and, by suitably adjusting the pump volume and mud viscosity, the pilot hole was completed smoothly.

After the pilot hole was completed the contractor set down the non-magnetic drill string, then did the grading reaming, with a final bore diameter of 1,000 mm. The first successful bore extended back the 500 mm diameter barrel reamer. When the 700 mm barrel reamer was extending back, both the pulling force and torque increased significantly. Through careful observation, Drillto engineers found mud viscosity was too low to lead the cuttings back. The 700 mm diameter pulled back to expand rapidly following the adjustment of mud viscosity. The 900 mm and 1,000 mm diameter reamed smoothly.

The 1,000 mm diameter reamer first washed the hole, adjusted the mud viscosity to 45s to ensure a clean hole, while the second washing used high-quality mud and increased the mud lubrication performance to ensure a low friction co-efficient. Throughout the reaming process appropriate adjusted mud displacement, controlled pullback speed, and attention to the pump pressure, torque, and the changing back drag force ensured the successful completion of the crossing.

The final step, to pull back the pipeline used a combination of a 900 mm reamer, a 150 T swierl, 5 T U-clip and the 711 X 14.2 mm diameter pipeline. The pullback was achieved by carefully observing drill rig tension, torque, mud return back and control of the pullback speed.

Conclusion

Magnetic orientation can be achieved by using other functions to solve signal interference problems or magnetic declination difference. Furthermore, the correct proportion of mud helped to ensure the successful completion of the project. In future, construction project priorities will include observing the drilling rig, mud return back, and promptly adjusting the mud. Mr Xing said “Thanks a lot to the engineers from Drillto Company, who used their experience and technique to help complete the project successfully.”

The pipeline is expected to increase the share of natural gas in China’s energy consumption by one to two per cent and play a significant role in boosting the country’s domestic natural gas demand, facilitate the improvement of China’s machinery manufacturing, improve the nation’s energy structure and promote economic and social development to the adjacent regions along the pipeline. Pipeline progress

The project has been divided into eastern and western sections with Zhongwei, located in Ningxia Hui Autonomous Region, designated as the pipeline’s midpoint. The western section, running 2,461 kilometres from Horgos to Zhongwei, commenced construction in February 2008 and the welding work on the principal parts of the trunk line is now complete. The eastern section, running 2,477 kilometres from Zhongwei to Guangzhou with a designed pressure of 10 MPa, commenced construction in December 2008. The eastern section is expected to connect into the Turkmenistan – China Gas Pipeline, which is currently under construction and is scheduled to be commissioned in 2011. On16 November the tunnelled crossing of the Changjiang River was successfully completed. The crossing was a key engineering project for the Second West – East Gas Pipeline. The crossing took place between Jiujiang City in Jiangxi Province and Wuxue City in Hubei Province, with a horizontal crossing span of 2,590 metres.