As part of Indradhanush Gas Grid Limited’s North East Gas Grid Pipeline Project, an HDD pipeline installation was required crossing of the mighty Brahmaputra River, in the state of Assam, North East India. The main contractor for the project was NRP Projects Private Limited (NRP), which undertook not only the practical application of the HDD technology for the pipeline installation but also the design work for the HDD and associated works required.
The new North East Gas Grid Pipeline Project is designed to meet the gas needs of the entire North Eastern states of India, leveraging the northeast region’s hydrocarbon potential. It will enhance access to clean fuels in the industrial, commercial, domestic household and transportation sectors amongst others. It will also facilitate a boost in industrial and economic development in the North East region of India.
The HDD Option
With ground comprising Sandy/Clay/Silt conditions, Horizontal Directional Drilling (HDD) technology was the preferred choice for the installation under the Brahmaputra River because the pipeline had to be laid at a depth of 47 meters from the datum level and complete a crossing of some 4,102 m in length.
The requirements of such a long and deep crossing meant that the selection of the right equipment was paramount. The design of the installation was based on the intersect method which required two pilot bores to be installed, usually at the same time such that the drill strings meet at about the halfway point in the crossing. Two pipelines were to be installed beneath the Brahmaputra River, one for the main gas pipeline and one for telemetry conduit which would run parallel to it. Ground investigation included a geotechnical survey which was carried out through the entire 4,102 m to ascertain the geology to assess the tooling required. Conventional vertical drilling was used to collect soil
samples.
To complete the set of bores required, NRP ultimately selected two spreads of XCMG XZ6600 drilling rigs for pilot and reaming and a GOODENG GS8000-LS HDD drilling rig which would be set up on either side of the river. The drilling rigs had pulling capacities of 660 t and 800 t respectively. The GS8000LS was selected on the basis of its design pull load of 638 t. A concrete Deadman was cast in addition to the conventional steel Deadman anchor which is used for any HDD projects.
The guidance system used for the bores was a PARATRACK II system. For the downhole tooling, NRP utilised 10⅝ in (270 mm) diameter drill bits for the pilot bores with in-house designed reamers for hole opening to the required diameter. Drilling fluid was handled with a Kemtron Tango 1000HDX recycling unit with BW3000, Garner Denver -PZ8, CWB2800LPM and Oilwell A1700 mud pumps. The drilling mud comprised a sodium-based bentonite with additional Soda Ash, Xantham Gum and Pac R additives. The mud mixing unit was designed in-house by NRP.
As previously mentioned, two bores were required for the project, one over a length of 4,080 m and one of 4,100 m length. The first was for a conduit pipe which was a 6 in (150 mm) o.d. pipe and the second was the for the gas main which was a 24 in (610 mm) o.d. pipe. For the conduit pipe bore, once the pilot run was completed the conduit pipe itself was pulled directly into place.
For the gas main bore, on completion of the pilot run, some five reaming stages were required including:
STAGE I – reaming up to 24 in (610 mm) diameter
STAGE II – reaming up to 36 in (914 mm) diameter
STAGE III – reaming up to 42 in (1,066 mm) diameter
STAGE IV – a clean pass run at 36 in (914 mm) diameter
STAGE V – the product pipe run with a 24 in (610 mm) diameter reamer
The pipes used for the 6 in (150 mm) conduit pipe included subducted 40 mm diameter HDPE duct and fibre optic cable, API 5l gr b seamless and a wall thickness of 10.7 mm, which was supplied by NRP. The main gas pipe was a 24 in (610 mm) diameter, API 5l gr x70 with a wall thickness of 12.7 mm, which was welded by NRP at the site and supervised by a third party, IGGL. The pipes were supplied by IGGL as 12 m lengths and welded using the SMAW Process.
The entire pipe string was floated in a trench filled with water with a total of 19 excavators being deployed to handle the string during the operation and pull-in. A good buoyancy control system was also in place to facilitate good pipe handling.
INSTALLATION TIMINGS
For the smaller diameter installation, the pilot bore started on 28 October 2022 and took 55 days to complete. The pipe pull took a further 2 days, finishing on 26 December 2022. In total some 57 days. For the gas main itself, pilot boring commenced on 7 January 2023 and took 27 days. Stage I reaming commenced on 11 February 2023 and took 15 days; Stage II took 19 days from 27 February and Stage III took 14 days from 16 March. The Clean Pass took 8 days from 30 March, with the pipe pulling operation starting on 19 April and completing just 4 days later on 21 April after pulling continuously for 56 hours. In total some 86 days.
CHALLENGES
A number challenges faced the contractor during the course of the Brahmaputra River crossing project including:
• A narrow road leading to nearby villages and then to the project location.
• Rains made it extremely difficult to haul equipment, consuming a lot of time.
• Given the size of the project and the amount of equipment required, local villagers demanded proper approach roads with these problems being solved by NRP under the guidance of IGGL with significant sums being spent to make the roads useable.
• Transporting the HDD materials from one side of the river to the other side using trailers was a daunting task due to narrow approaches through the villages.
• The river on the pipe side of the project (Jorhat) used to get filled with rain water which made it extremely difficult to move around, so additional excavators needed to be deployed.
• A short spell of rain could hamper progress for weeks, however, NRP stepped up and deployed ‘round the clock’ working to enable the target date of 21 April 2023 to be reached.
• The major challenge was to execute and complete the project within the narrow
window of 4 months to avoid entering a long monsoon period.
The entire project operated on either side of the Brahmaputra River, with Majuli (the first island district of India since 2016) on one side and Jorhat town on the other. Permissions were taken in general by IGGL and the public was made aware of the importance of the project and the benefit it would provide to their daily gas needs. The space constraint was also a significant challenge, with a lot of time being spent in making the necessary site approaches, through seeking permissions from the local village heads.
This was a challenge as they had not before witnessed such a huge fleet of equipment passing through their narrow roads, a lot of time was spent by NRP and IGGL in discussions to ensure that inconvenience to locals would be minimised, which then allowed the project
to proceed. The actions of the teams and the locals were said to be commendable. Commenting on the project the chairman of NRP, Mr J R Patel said: “Congratulations to Team NRP for the untiring efforts in executing the longest and most challenging crossing of 4,102 m by installing a 24 in and 6 in pipeline under the Brahmaputra River, India.
NRP surpassed the previous record of 4,088 m for longest HDD installation, also set by NRP, on completing this crossing of 4,102 m. Supported by the highly skilled manpower, a fleet of equipment, including two HDD Rig spreads of 660 t and 800 t, and adequate buoyancy measures, the pulling for over a period of 56 hours, the 24 in steel pipe of 4,102 m at a depth of 47 m was a smooth affair. NRP is proud to achieve the success of this longest HDD installation within 3½ months due to meticulous planning and implementation. I congratulate and thank Team NRP, including the staff, drillers and workers associated
with these crossings
