CHAMBAL – HARD ROCK AT 140M DEPTH
In 2015, Contractor Trenchless Engineering Services Pvt. Ltd. (TESPL) set a new record in India for the vertical depth of a river crossing in rock using Horizontal Directional Drill (HDD). The installation was for a gas pipeline which was laid to a depth of 140 meters below ground level. Trenchless Engineering Services, based in New Delhi, is the largest trenchless service provider company in India with over 2 decades of experience in the field for projects Oil and Gas, Water and Sewer, Power and Telecommunications. Clients have included GAIL India Ltd, Indian Oil Corporation Limited, Oil India Limited, ONGC Ltd. Gujarat State Petronet Ltd, Lanco Infrastructure Ltd, I&LFS in India, INGL of Israel, PetroBangla, Titas Gas Ltd., Gas Transmission Co Ltd of Bangladesh, Fernas – Turkey, Mears Inc. USA, Enikkom Construction, Zakhem in Nigeria, SNC Lavellin in Madagascar, Cherrington Inc. USA and China Petroleum Corporation in Taiwan. The company has a qualified workforce, under the guidance of Chairman and Managing Director, Vipin Gupta (who provided this article), and over 14 HDD rigs ranging from 30 t to 400 t capacity as well as Laser Guided TBMs, Auger Boring Machine (for installing casing pipes under roads and railways), Pipe Ramming, Pipe Jacking and Box Pushing systems for railways.
CHAMBAL CROSSING PROJECT
The record breaking project called for the installation of a 16 in (400 mm) diameter pipeline from Kota to Bhilwara, crossing the Chambal River near Kota as part of the Vijaipur-Kota Pipeline. The pipeline alignment on either side of Chambal River falls under National Chambal Gharial Wildlife Sanctuary. The extent of wildlife sanctuary is approximately 2,400 meter including part of the Chambal River. The ground conditions at the crossing site comprised hard rock with the presence of boulders with rock having a compressive strength of 220 MPa. Project included the installation of three 16 in (400 mm) diameter pipes. One of 1,400 m, one of 480 m and one of 530 m. There was also a requirement to install a 6 in (150 mm) diameter conduit pipeline as an HDPE duct which would carry an OFC Cable sub-ducted inside the HDPE pipe. Ultimately the three main pipelines were to connected to the main gas pipeline on either side of the crossing.
With the project falling under the auspices of the National Chambal Gharial Wildlife Sanctuary which is a highly environmentally sensitive area, high level planning and execution of the project was required and implemented to meet the necessary timeline. A topographic survey was started in the 2nd week of January 2015 to check the feasibility and optimum route for the pipeline installation under the Chambal River. There was an elevation difference of more than 100 m between the river bed and the rig site and the crossing profile was designed to reach 140 m deep. A major challenge for Trenchless Engineering was the decision about which drilling rig and support equipment should be deployed for crossing given that moving the rigs bentonite slurry and cuttings from more than 140 m depth would a mammoth task and required a high pressure head mud pump for circulation of the bentonite drilling fluid. It was decided that any rig selected would need more torque capacity than pulling force, so a rig with torque of up to 170 kNm was selected. Premium grade drill pipes and high gelling bentonite were used to reduce unwanted stress in the drill pipes while drilling. Ultimately Trenchless Engineering deployed a rig with 320 t pulling capacity utilising S-135 grade drill pipes of 65⁄8 in diameter drill pipes with 121⁄4 in (312 mm) diameter drill bits from the USA, Europe and Russia being used. Two high pressure 600 gal/min (2,270 l/min) capacity mud pumps and two 1,000 gal/min (3,785 l/min) capacity fluid recycling systems were used. Guidance control was achieved using a Paratrack P-2 steering system.
Once the pilot bore was completed two levels of hole opening were undertaken, one at 18 in (450 mm) and one to 24 in (610 mm) diameter.
The bore profile was designed to ensure minimum stresses on final pipeline and to minimise pull-in load. The entry angle for the pilot bore was set at 14 o with the exit angle on the reception side set at 11 o . The curve radius of the bore was 700 m with a total length of bore along the route being 1,424.04 m. With this profile the bore ran to a depth of 40 below the river bed and a total of 140 m below ground level.
Mobilisation of all equipment and heavy machines, as required, was started in the first week of February 2015. Site setup including anchoring of the HDD Rig which was completed by 8 March 2015 after receiving permission for the construction work from the Forest Department and other agencies involved. The pilot bore was started on 9 March 2015.
Paratrack guidance system was used to check the bore profile using a surface coil which was laid on the ground to check the position of drill bit. With drilling being in a very sensitive Ecological zone, special care was taken with respect to flora and fauna.
The daily penetration rate for pilot bore was much lower than anticipated due to the aggressive and abrasive character of the rock. A single drill rod could take more than 2 to 3 hours to complete.
Multiple trip-out and trip-in occurrences had to take place due to the effects on the drill bit and mud motor. Approximately 990 m of the pilot bore was completed by 13th June 2015. A lot of boulders were encountered while drilling in this ground layer at a depth of about 120 m from ground level at the rig.
Pilot hole drilling for the 6 in (150 mm) diameter conduit pipeline was completed on 10 August 2015 and the 6 in (150 m) conduit pipeline was successfully pulled in on 16 August 2015.
MAIN PIPELINE INSTALLTIONS
After successful completion of the 6 in (150 mm) diameter pipeline the HDD Rig was dismantled and repositioned on the alignment of the 16 in (400 mm) diameter pipeline profile to commence the pilot bore which started on 21 August 2015. Approximately 870 m of this pilot bore was completed by 9 September 2015. Unfortunately the bore then encountered large boulder quantities in the ground and the crew was forced to abandon this bore. A new pilot bore was started on 13th September 2015 which, after analysis and discussions, it was decided to take to a greater depth of 140 m. Good viscosity bentonite fluid was maintained and pumped through the bore to bring out cuttings from the very deep bore. This pilot bore was successfully completed on 27 October 2015.
REAMING AND PULLBACK
After successful completion of the pilot bore, the lead tooling and survey wire was removed from the drill pipes. Reaming was completed in two stages as previously mentioned. The first hole opener was 18 in (450 mm) diameter and the second was 24 in (610 mm) diameter. High grade bentonite is continuously pumped through the reamers to flush cuttings and stabilise the hole. The 18 in diameter ream was completed on 31 May 2016 and the 24 in on 8 August 2016 After preparing the product pipe and aligning it with the now reamed hole the pull-in of the 16 in (400 mm) diameter pipe over 1,400 m was successfully completed on 17 October 2016. Trenchless Engineering’s experienced crew and officials were deployed to supervise all activities during this project phase to ensure a smooth process.
The project was not run-of-the-mill and tested the contractor’s ingenuity and innovation at every step. In the beginning, ‘BEST IN TRADE’ tooling was mobilised, but it was soon evident that this project needed innovation to complete the project. Off-the-shelf hole openers did not work on the project which meant that Trenchless Engineering had to improvise and fabricate tooling in its yard.
The new design hole openers were made bi-directional to negotiate falling rocks or boulders in the hole during trip-outs. Furthermore, drill bit selection took time to fine tune because the available hole openers, which came with Aggressive Tooth profiles, were being sheared off in the inclined and fractured strata. New hole openers were fabricated with IADC 747/837 material which increased the life of the tool but decreased the penetration rate.
As for the drilling itself, a very disciplined drilling programme was designed and followed. After a calculated time drilling, the bit or hole opener was withdrawn and replaced with a new tool. This was because the ‘cost’ of losing a cone in the hole could have set the project back both in terms of time and money.
With the Chambal river crossing occurring inside the National Chambal Sanctuary zone, special care was taken to minimise environmental impact and hazards. Hydraulic Oil and other kinds of spills were regularly checked and removed from the working surface. All fuel tanks were placed inside bunds to avoid pollution of surface or groundwater in the event of a spillage on-site. The pipeline alignment was finalised so as to have the least impact on flora and fauna within the Sanctuary as well as excavation being restricted to minimise the impact of the construction activities on nearby flora and fauna. A constraints assessment was done at the planning stage of the project to identify designated areas for construction activities. Unwanted access of people to the work site and wildlife areas was restricted by marking an access boundary. Ecological data collection and environmental assessment was done as part of the site selection process.
Existing habitats where possible were retained and the aim was to keep natural site features in context rather than in isolated fragments. Special attention was also given to field boundaries and hedgerows and preserve wildlife corridors and habitat links.
FINAL HOOK UP
Immediately after pulling in the main, two crews were mobilised with two independent sets of rock breaking equipment to tie in the three crossings and main line on either end. Due to the extreme hardness of rock, the connection trench was established with controlled blasting.
From pull-in completion to final application of gas to the pipeline including pit cleaning, rig demobilisation, trenching of 200 m in hard rock, string welding, four tie-ins with bends, pigging, hydro testing, dewatering and swabbing, EGP, drying to achieve the dew point took just 15 days.