By Safar Mohammad Khan, Deputy General Manager, HDD, Apollo Techno Industries
Horizontal Directional Drilling is a steerable guided method of Installing underground utilities (viz OFC, PC, Gas Pipe line, Water & Sewerage Pipe Line etc) in a prescribed bore path using surface launched HDD Machines.(Apollo, Vermeer, Ditch Witch, XCMG, Drilto, Goodeng, Dilong, American Augur, herrenknecht, etc). Apollo has created a niche in the small and mid-size segment and is doing rigorous and extensive work in the technical upgradations with the quality components in manufacturing of MAXI RIGS ( >45-ton Rigs). Recently, Apollo developed an outstanding Maxi Rig model A1200 which is gaining popularity especially for drilling in rocks by using the Mud Motor and other advanced tools. A prescribed boring is used when an open trench or open excavation is not possible.
The tools and technique used in the HDD method have high demanding technology in Gas Pipeline Projects (viz: LDPLP- Long Distance Pipeline Project, CCPLP-Cross Country Pipeline Project, and GPLDP- Gas Pipeline Distribution Project). The HDD machine is now commonly used for laying OFC, power cable, water and sewerage pipeline of Telecommunication companies, SEB and City Municipals, respectively. Due to expansion of CGD (city gas distribution work), LDPLP (Long distance pipeline project) and cross-country pipeline projects (CCPLP) will accelerate the technological innovations of quality HDD rigs in the near future.
Apollo (made in India) has already taken the initiative to offer technically sound rigs with complete solutions to customers (both Retail & Corporate) across the country. Prompt delivery of indigenously developed HDD Machines with the best safety features and equipped with world-class components is a great step towards developing pipeline infrastructure - without dependency on China and other countries.
Installation of a pipeline string by HDD is accomplished in the following six stages:
- Soil Investigation
- Drill path design
- Drilling the Pilot Hole
- Pre-reaming the horizontal Boring or Reaming
- Pull back operation
- Installation of Conduits
Different types of drilling bits/drill heads (diamond bit/Tungsten bit/VCP bit/hard face bit) are used in the pilot-bore process. Selection of drill bit depends on the type of soil strata. The purpose of soil testing is not only to determine the feasibility of HDD crossing, but also to establish the most efficient way to accomplish it. If the strata becomes very hard (>90 MPA) then one has to use the rock cutting tools accordingly - like Mud Motor, Air Hammer, ARMOR etc. The geo-tech information governs the determination of best crossing route, along with selection of drilling tools and execution methodology.
Soil identification is done to locate rock, rock inclusions, gravelly soils, loose deposits, hard morum, boulders, brittle rock, black laterite, pebble stones, mountain blend, fast stak and bluff stones, etc.
Soil strata investigation is performed by analyzing the soil sample extracted from bore-holes drilled along the pipeline route - called bore log data. For big crossings, bore logs are typically taken at 200 m intervals. For short crossings (which are less than 300 m length), as few as three bore logs may be sufficient. The borings should be near the drill-path to give accurate soil data, but sufficiently far from the borehole to avoid pressurized mud from following natural ground fissures and rupturing to the ground surface through the soil-test bore hole. A thumb rule is to take borings at least 10m to either side of bore path. Although these are good general rules, the number, depth, and location of boreholes are best determined by the engineer.
Drill path design
One of the key considerations in the design of the drill-path is creating as large a radius of curvature as possible within the limits of the right-of-way. Small radius of curvature induces bending stresses and increases the pullback load due to the capstan effect. The capstan effect is the increase in frictional drag while pulling a pipe around a curve due to a component of the pulling force acting normal to the curvature. Higher tensile stresses reduce the pipe’s collapse resistance. Curvature requirements are dependent on the site’s geometry (crossing length, required depth to provide safe cover, staging site location, etc.), but the degree of curvature is limited by the bending radius of the drill rod and the minimum elastic bending radius of the pipe.
The designed drilling profile consists of a series of straight lines and curves. The straight lines are referred as tangents. The straight sections are those in which the drilling hole curvature is ideally zero. This implies that any pipe section can be considered as a straight section if the curvature of that section is less than that necessary to make the pipe deviate beyond the walls of the hole, which is roughly 1.5 times larger in diameter than the pipe itself.
Drilling the pilot hole
The guidable steering tool is placed within the Bore Hole Assembly (BHA). Generally, the BHA is made up of non-magnetic drill collars. The ‘lead collar’ of the BHA is placed on the alignment of the particular crossing. After the alignment, the steering probe is energized with electrical current (wire-line steering) and a bearing for the drill path is established and logged into the surface computer. The drilling rig is set precisely on line with a transit. The non-magnetic lead collar (with steering probe) and the directional deviation tool are started exactly at the designated entry point. In most cases, one Non-Magnetic Drill Collar (NMDC) is used behind the BHA. A 10 m non-magnetic collar shall serve as a buffer between the steering probe (in the lead collar) and the steel drill pipe. Drill pipe is often highly magnetized due to the continual making up and breaking out the tool joint connections and can affect the tool parameters.
Pilot hole drilling typically is considered the most challenging and time-consuming step. As each piece of drill pipe is advanced, the next drill pipe is fitted with a wire inside. This wire is attached to the corresponding wire of the drill pipe previously drilled. This internal wire is the vehicle used for the signal to be sent from the steering probe located in the Bottom Hole Assembly (BHA) to the surface computer. This process is repeated until the bit is advanced along the predetermined path and comes out at a predetermined exit location - as per the designed drilling path.
Pre-Reaming the Horizontal Boring/Reaming operation
Once the drilling bit exits (punch out) the pilot hole, the lead pieces/drill pipes are unscrewed. The hole opener/reamer is then attached to the leading pipe to start reaming operation. The reaming operation consists of using an appropriate tool to open the pilot hole to a slightly larger diameter than the carrier pipeline. The percentage oversize depends on many variables including soil types, soil stability, depth, drilling mud, borehole hydrostatic pressure, etc. Normal over-sizing may be from 1.4 to 1.5 times the diameter of the carrier pipe. While the over-sizing is necessary for insertion, it means that the inserted pipe will have to sustain vertical earth pressures without significant side support from the surrounding soil.
Good grade of bentonite is continuously pumped through the reamers to flush the cuttings and stabilize the hole. Similar procedure is repeated for all stages of reaming.
The pullback operation involves pulling the entire pipeline string in one segment (usually) back through the drilling mud along the reamed-hole pathway. The pulling equipment is attached to the leading end of the drill pipes string, and the prepared pipe string is fed gently into the bored hole. Proper pipe handling, cradling, bending minimization need to be followed. Axial tension force readings, constant insertion velocity, mud flow circulation/exit rates, and footage length installed should be recorded. The pullback speed ranges usually between 1 to 2 feet per minute in MAXI Rigs and 7-8 feet per minute in Mini rigs.
Pipeline projects in India
A lot of pipeline projects for the expansion of gas, crude oil, CNG, LPG, water and sewerage are underway, while many are still awaited or stalled due to the Covid-19 lockdown. Most of the projects are delayed and many are in the bidding and tendering phase.
Gas pipeline project
The share of Natural Gas in India’s energy basket is 6.2% as against 23.4% globally. Gujarat alone has 25%. The country aims to achieve 6.2 to 15% of natural gas. Gujarat, Goa and Haryana and the UTs of Delhi, Chandigarh, Diu & Daman and Dadra Nagar Haveli are fully authorized for development of CGD networks. About 53% of India’s area and 70% of its population spread over 402 districts in 27 states and UTs would have access to CGD networks for supply of natural gas.
The following winning entities will be developing the gas pipelines and gas distribution in the cities: Torrent Gas, Adani Gas, Gujarat Gas, Indian Oil-Adani Gas, Hindustan Petroleum Corporation, Bharat Gas Resource, IOCL, Gail Gas, Unison Enviro, Thinkgas, Assam Gas Company, Maharashtra Natural Gas, ESSEL, Megha Engineering & Infrastructure, Tripura Natural Gas Company, Green Gas, and IGL. These companies will be working on city gas distribution pipeline installation work with the help of HDD method and open trench, depending on the circumstances. PNG and CNG pipes will be parallelly laid beneath the soil depth up to 1.65 mtrs to 2.00 mtrs. Total distribution work will probably be for 1,12,696 kms across India.
State-owned gas utility GAIL India will invest over ₹45,000 crore over the next five years to expand the National Gas grid and city gas distribution network. GAIL currently operates 11,000-km of pipeline network and markets two-thirds of all-natural gas sold in the country. Out of the ₹45,000 crore investment, ₹32,000 crore would go into pipeline laying and another ₹12,000 crore in city gas distribution (CGD) networks for retailing of CNG to automobiles and piped natural gas to households.
Adani Gas will invest up to ₹9,000 crore in setting up city gas distribution network over the next 10 years to retail CNG to automobiles and piped cooking gas to households. Adani Gas Ltd (AGL) on its own and in a joint venture with state-owned Indian Oil Corp (IOC) has won a city gas license for 38 geographical areas spread over 71 districts in 15 states.
GAIL is looking to put up 400 CNG stations and give out a record of 10 lakh piped natural gas (PNG) connections to household kitchens in the next 3-5 years.
Cross Country Pipeline Projects
Some of the major players in India who are making cross country pipeline installation through the HDD method and their technology innovations include ONGC, IOCL, OIL, GSPL, IGL, GSPC, Adani, Avantika, and PNRGB.
Recent HDD Cross Country projects executed or under execution by Apollo A1200 HDD Machines
1. Project: IOCL-ADANI of gas pipeline project executed by Guru Construction Company.
Gas Pipeline Dia-20” + 6” bundle pulling
Location: Bhadreshwar at Sakra River/Ch.No-37860
Driller: Bibhuti Kr. Mandal
HDD Machine used: A1200.
2. Project: GIGL (Gujarat State Petronet Limited)
Executed by: SNS Trechless Engineering, Bharuch; Dia-30” CS
Location: Talwandi, Bhatinda
HDD Machine used: Apollo A1200, Shot Length-294 m, Soil – normal soil with sand impression.
Challenges: None, except the site management.
HDD Machine Apollo A1200
Apollo’s A1200, a powerful made in India HDD Machine is equipped with world class specification which makes the machine fast and reliable. It is even capable of drilling in black rock bed at Sakra River beneath 14 metres. Its 800 LPM big Mud Pump makes the water flow high. It has joystick control systems and 6000 PSI operated hydraulic pumps, along with the 6000 PSI rotation. All the HDD processes have been observed to be very effective and fast due to the high quality specifications, and along with a trained driller they enable installation highly successful. The only challenges were site preparation and management. A quality mud motor along with all the site preparations are required (viz. mud mixing system, mud recycling system, rock cutting reamers, diesel etc). Some interference was found in the locating systems due to the salty nature of the rock.
Benefits of Directional drilling
- Reduced soil disturbance.
- A single location area can be used to install different pipes.
- Reduces the fractures to existing rock formations.
- Reduces the contamination of groundwater pollution.
- Protects the ecosystem and adjacent areas.
- The directional drill produces twice the amount of oil or gas being extracted.
- Reduces the excavation and shoring costs.
- It is a safer operation than open cut.
- Weather will not impact directly on the process.
- Limited traffic and landscape disruption.
- Ideal for sites sensitive to surface disruption such as heavy roadways, airport runways, golf courses, etc.
- Ability to drill beneath surface obstructions or ongoing site operations.
Amongst the machine parts, the rigs segment accounted for a significant market share during the forecast period. Rising demand for well-organized rigs in HDD projects for distant pipeline installations is propelling the growth of this segment. Mini HDD rigs are mostly used for laying of power and telecommunication lines and in installing heavy pipes for gas distribution. By geography, the North America region has dominated the market during the forecast period due to the increasing number of oil and gas industries and infrastructure development projects.
A lot of infrastructure needs to be developed in India under the urban development program for smart cities, where LPG will be supplied through gas pipelines to houses. 5G network distribution is well prepared by all the telecom companies (such as Airtel and Reliance Jio) where the OFC duct will be installed by using HDD machines. Power cable giants under the SEBs will be expanded by using HDD machines. Now, the Municipal Corporations are also knowledgeable about installing water and sewerage pipelines through non-disruptive technology.