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Introduction

Deep Ocean Resources

The deep oceans have abundant mineral resources like Polymetallic nodules; cobalt rich manganese crust and hydrothermal deposits.Utilising this mineral wealth for the benefit of mankind will be the focus of ocean mining activities in future.Polymetallic nodules have economically valuable metals such as Copper, Cobalt, Nickel and Manganese and are viewed as potential resources for the depleting land resources and increasing demand.

Distribution of marine minerals

Area Allocated:

Polymetallic nodules are found in abundance at Central Indian Ocean Basin (CIOB) in depths of 5000m - 6000m. An area of 75,000 sqkm in CIOB was allocated by the preparatory commission International Seabed Authority (ISA), UN to Govt. of India as pioneer investor for exploration and development of technology to mine these Polymetallic nodules from a depth of 5000-6000m.

Background of the Project

There are 380 million tons of nodules in the retained Indian Pioneer area. Development of deep sub-sea technology for mining these resources is a major challenge, considering the high pressure environment and very soft soils. NIOT has been working on a mining concept where a crawler based mining machine collects, crushes and pumps nodules to the mother ship using a positive displacement pump through a flexible riser system.

NIOT, Deep Sea Technologies group has been given a mandate to develop an Integrated Mining System for mining Polymetallic nodules from a depth of 5000-5500 m by Ministry of Earth Sciences (MoES), Govt of India under Deep Ocean Mission (DOM) programme. The work has been taken up in phases.

Mandate

  • Design and development of new crawler based mining machine capable of collecting and pumping manganese nodules from a water depth of 6000m
  • To develop a flexible riser system for transporting mined nodules from ocean floor to the mother ship.

Integrated Mining system configuration

Deep sea Mining -Progressive developments:

Deep sea mining of manganese nodules from soft ocean floor at 5000 to 6000 metres depth is a major technological challenge. India has been working on developing this complex technology in a phased manner. To minimize development costs and associated risks, initial efforts are focused on realization and qualification of machinery for shallow waters, followed by further development of machinery in deep waters.

As a first step, an Underwater Mining system operable at 500 meters water depth was developed. An initial study was done on the various deep sea mining and flexible riser concepts. The mining machinewas designed to operate on soft seabed and has special track belts with involute track belts to compact the seabed during locomotion.Underwater mining system with a flexible riser concept was validated in the Indian seas at 410m water depth. Further the mining machine was upgraded with crusher, nodule pickup and collection unit and was demonstrated at 510m water depth off the coast of Malvan



Optimisation and design of an integrated mining system for Polymetallic nodules from depths of 5000-6000m depends on the in-situ measurements of the sea floor soil properties. An in-situ soil tester capable of operation at 6000m water depth was developed by NIOT and demonstrated at 5462m water depth at the Test mine site (TMS), CIOB and used for further survey activities.

Pumping studies

Studies were undertaken for the pumping of nodules through a vertical riser system stage wise.

Sea trials was conducted onboard ORV Sagar Nidhi during Dec 17 – Jan 18, to assess the pulsatile slurry flow behaviour in an actual flexible vertical riser system, with and without crushed natural manganese nodules. An experimental slurry pumping system with flexible riser unit was deployed from the ship to a maximum depth of 400 m. The slurry pumping unit consisted of twin-piston solids pump adapted for sub-sea applications, screw feeder with hopper for controlled feed of the crushed nodules, a hydraulic power pack unit, instrumentation and control and power system. The flexible hose (Φ 100 mm) of the riser was instrumented with pressure sensors at predetermined locations to record the inline pressure fluctuations. The sea trials intended had the following objectives:

  • Slurry flow characterisation up a flexible hose vertical riser, with reciprocating pump, ensuring that the flexible hose is without bends and kinks.
  • Evaluation of the developed improved hose deployment and deck attachment arrangements
  • The trial data would be used for validation of the analytical and numerical analysis and for scaling up the system to 6000 m depth.
  • To assess the slurry flow behavior and resultant accumulation in the vertical system at varying flow rates during pulsatile actuation.
  • Effect of flexible hose system on damping out of the pressure fluctuations.
  • Effect of ship’s heave on the suspended riser system and subsea platform.
Pump testing through a vertical riser

Locomotion demonstration at 5270m water depth

The mining machine was tested for locomotion and maneuverability at the central Indian Ocean Basin (CIOB) at the depths of 5270m. The primary objective of the trials was to test seabed locomotion/ traction capability on soft soil and the functionality of the various systems, viz. mechanical moving parts, hydraulic power unit, electrical systems and the instrumentation, at the extreme ambient hydrostatic pressures and very low temperatures of 1 - 4 deg C.The machine was operated extensively, covering a cumulative distance of over 120 m with 2.5 hours of operation on the sea bed at depths of 5270m. This achievement records the first tethered sea bed moving machine to operate at this depth.

Deployment of mining machine at CIOB (V1- 2021)

Mining Machine Locomotion on the seabed at 5270m depth

Retrieval of mining machine and deck view during operation

Proposed work:

On completion of locomotion sea trials of the mining machine at CIOB, The machine is being augmented with an indigenously designed mechanical pickup and collector system for collection and conveying of collected nodules from the sea floor to the pumping system. A crusher and pumping system is being installed on the machine to convey the crushed nodules to the pump frame which is suspended from ship by the umbilical cable. The planned mining machine, apart from the locomotion system, would have a rake type nodule collection system at the advancing end of the machine and a nodule crusher, feeder and slurry pumping system.

Initially it is proposed to conduct the sea trial without the pumping station, where the collected nodules shall be discharged locally at a height of 50-80m above sea bed. The trials will be conducted in coordination with the National Institute of Oceanography (NIO), Goa, who would be assessing and monitoring the environmental impact due to the seabed nodule collection through dedicated moored and instrumented sub-sea data buoys.

Pumping will be attempted through a 150 – 200 m long flexible hose, the slurry being discharged about 50 – 80 m above the seabed.

Schematic of the Mining Machine for nodule collection and pumping trials


Submersibles

The Deep Sea Technologies group is involved indeveloping manned and unmanned underwater vehicles for the exploration and exploitation of deep ocean mineral resources such as poly-metallic manganese nodules, gas hydrates, hydrothermalsulphides,etc and other oceanographic, polar and industrial applications


Manned and unmanned underwater vehicles:

  • Design and development of 6000 m depth rated scientific manned submersible with a capacity to carry three crew members and scientific equipment
  • Development of 6000m depth rated work class deep water Unmanned Remotely Operable Vehicle (ROSUB 6000) and utilization for deep ocean scientific exploration
  • Development of 500 m depth rated polar cum shallow water remotely operated vehicle (PROVe) and utilization for shallow water and polar scientific studies.
  • Development of deep water Wire-line Autonomous Coring System(WACS) to drill up to 100 m and collect long core samples from ocean basins up-to the maximum depth of 3000 m for Gas hydrates ground truth validation.

Deep water ROV - ROSUB 6000

Development of 6000 m depth rated deep-water work class Remotely Operated vehicles (ROV) by National Institute of Ocean Technology (NIOT)was initiated by Polymetallic Nodule Management (PMN) Board of the Ministry of Earth Sciences (MoES), Govt. of India. The system design, development and testing was completed for scientific usage. The ROV is equipped with multifunctional tools and sensors for offshore applications such as deep ocean mineral exploration, seabed imaging, gas hydrate exploration, pipeline routing, submarine cabling, well head detections, sampling etc.The ROSUB system was developed and tested up to a depth of 5289m water depth at PMN site for its envisaged functionality. The scientific explorations at Gas hydrates site in Krishna-Godavari (KG) basin, hydrothermal sulphides site - SONNE Field in South Central Indian Ridge region, Poly Metallic Nodule Mining (PMN) site in Central Indian Ocean Basin (CIOB) was conducted using deep water ROV (ROSUB 6000) up to a depth 5289m. ROSUB 6000 system was deployed and operated using imaging sonar and optical imaging at 3400m water depth for target verification of the missing Indian Air Force AN32 aircraft during September 2016.


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ROSUB 6000 system

The ROSUB system consists of deep water work class Remotely Operable Vehicle (ROV), Tether Management System (TMS), Ship based Launching and Recovery system (LARS), Power transmission and Data telemetry system, Integrated Navigation System (INS) and Control software. The submerged weight is compensated by buoyancy packs made of syntactic foam fitted to the upper part of the frame. It is fitted with a five-function grabber arm, used to position the ROV steadily in one position by holding on to a support, and a seven-function manipulator is then used to perform assigned robotic tasks. The manipulator is similar to those found in various industrial applications on-shore, having a number of joints, a rotating wrist, and a hand-like claw.

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View of ROSUB 6000 system operation

Shallow water / Polar ROV (PROVe)

Based on the experience gained from 6000 m depth rated unmanned underwater vehicle (ROSUB 6000), design and development of Shallow water/ Polar ROV (PROVe) was taken up by NIOT by indigenous way to cater the requirement of scientific and engineering usages in shallow water and polar regions. The vehicle is electrically propelled using BLDC thrusters and can be maneuvered in 4-DOF (Degrees of Freedom) in Shallow waters up to 500m water depth. The vehicle is equipped with underwater video cameras, lights, scientific sensors (CTDO), underwater spectral irradiance meter, scanning sonar, navigation sensor and ice coring devices. The PROVe shallbe used for oceanographic investigation, search and recovery in port and harbors, biodiversity mapping, coral reef monitoring, ice thickness measurement,visual support etc. Scientific explorations were conducted using the PROVe at coral reef studies at Andaman Islands and biodiversity studies at Arabian Sea up to depth of 200m. Underwater inspection of objects was conducted using PROVe for DRDO purpose in Bay of Bengal up to a depth of 90m. The PROVe was tested and qualified for its polar scientific usage at Priyadarshini lake near Maitri base station of Antarctica and Indian Barrier Ice shelf during 34th Indian Antarctic Summer Expedition up to a depth 62m .

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Underwater picture of PROVe

Deep water Manned Submersible

The DST group is involved in design and development of 6000 m depth rated scientific research manned submersible.Manned submersible allow the scientists to get down in the environment to observe the life in its natural habitat at deep-waters. The manned submersible shall have capability for deep ocean resource explorations, scientific observations in deep waters, search and rescue support activities. The vehicle has a capability to carry 3 persons with operation endurance of 12 hours at 6000 m depth and emergency endurance of 96 hours were finalised for the development of personnel sphere/human capsule, life support systems, ballast systems, propulsion systems, underwater battery, power distribution system, sensors, control hardware and navigation.

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Conceptual design of Manned Submersibles

TECHNOLOGY FOR GAS HYDRATES

Gas hydrates are crystalline combination of a natural gas and water (known technically as a clathrate) looks remarkably like ice but burns if it meets a match lit. Energy in the gas hydrates amount to twice as much as all fossil fuels combined. Gas hydrate estimated to contribute a very large amount of methane, a potential clear hydrocarbon fuel resource. Our physical, chemical, geological and geotechnical knowledge is too limited to predict about possible exploration and unwanted environmental consequences of gas hydrate production. Hence, "gas hydrates" will most certainly be subject to increased research in the years to come. In India occurrence of gas hydrates is proved during JOIDES drilling program of NGHP under Ministry of Petroleum.

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Carbon Distribution

Following are the major activities

  • Deep sea exploration technology development
  •       -> ROSUB 6000 usage with scientific payloads for gas hydrate exploration
          -> Design and Development of Autonomous Coring System for ground truth validation of gas hydrate occurrence
  • Research activities on extraction methodology/technology
  •       -> Mathematical / theoretical studies
          -> Laboratory scale experiments
          -> Development of technology for conducting experiments for methane extraction from gas hydrates

Towards exploration of gas hydrates, NIOT had developed ROV – ROSUB 6000 with necessary scientific payloads for methane hydrate exploration. Vehicle was deployed at gas hydrate site in KG basin and established the occurrence of chemosynthetic habitats at 1037 m water depth in Bay of Bengal.

Towards ground truth validation of gas hydrate occurrence, a wire-line autonomous coring system (WACS) is developed in association with Williamson & Associates, USA. The system is designed to drill up to 100 m and collect long core samples by wire-line drilling technology from ocean basins up-to the maximum depth of 3000 m. The system is integrated with pressure core sampler for the recovery of gas hydrates at in-situ pressure condition. The System is qualified for operation up to 2906 m water depth in Bay of Bengal. The WACS was deployed and drilled up to 101.5 mbsf at 223 m water depth and 60mbsf at gas hydrate site of Krishna Godavari basin in Bay of Bengal.

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WACS Deployment        Underwater Drillhead
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Magazine view                   Underwater drlling view

Extraction feasibility studies

  • Methane hydrate extractions feasibility studies were conducted using electro-thermal and depressurization based techniques with reference to the gas hydrate reservoirs such as Krishna Godavari, Mahanadi and Andaman Basins.
  • Simulations were performed using MATLAB code and reservoir modelling software TOUGH + HYDRATE to identify the efficacy of the depressurization and electro-thermal techniques.
  • To understand the formation mechanism, laboratory set up is also established for thermal conductivity and acoustic properties measurement at in-situ gas hydrate phase.