SUBSEA MINING â MAJOR CHALLENGES
SUBSEA MINING – MAJOR CHALLENGES
Dr. Ir. Sritama Sarkar Saipem UK
CONTENTS Seafloor
Minerals Major Challenges Potential Subsea Miners Subsea Cutting Production and Power Subsea Cutting Forces, Weight and Stability Gathering Challenges Environmental Impact Transport Challenges Locomotion Challenges Launch and Recovery Challenges 2
SEAFLOOR MINERALS 3
Offshore Diamonds
•Established industry •Maximum water depth 400m •Placer pockets in overburden (sand) overlaying clay/ bedrock Polymetallic Nodules
•Extensive R&D since 1970s •Ni, Cu and Co •Water depth 5000m to 6000m •Abyssal plains
4
Methane Hydrates
•Exploration •Water depth 500m to 2000m •Soft sediments in Arctic environment •Slope and rise sediments in continental margin Cobalt Crusts
•Research •Water depth 400m to 4000m •Volcanic island arcs/ Volcanic seamounds – as very thin crusts 5
Seafloor Massive Sulphide (SMS) Deposits
•Exploration and planned commercial exploitation •Cu-Zn-Ag-Au` •Water Depth 1500m to 5000m • Very hot hydrothermal fluids, slightly acidic • Edges of tectonic plates
6
MAJOR CHALLENGES 7
SUBSEA MINING PROCESSES Mechanical Cutting
Cutting Hydraulic Cutting
Transport (Hydraulic)
Gathering (Hydraulic)
Locomotion 8
Seafloor Mining Challenges Vs. Minerals Minerals
Mn Nodules
Co Crust
+++
+++ (Phase dissociation)
No cutting
++ (Very thin crust)
Gathering
++ (Hydraulic)
+++ (Hydraulic)
+++ (Phase dissociation)
+ (Mechanical + Hydraulic)
+++ (Hydraulic)
Transport (Hydraulic)
+
++
+++
+++
+++
Locomotion
+
+++
++
++
++
Processes
Cutting
Offshore Diamonds + (Insignificant cutting)
SMS
Methane Hydrates
Relative Rating in Terms of Challenges More ‘+’ sign, more difficulty
9
POTENTIAL MINERS 10
POTENTIAL CUTTERS: DREDGING INDUSTRY
Dredge cutter And Dredge pick Cutter Suction Dredger
Drag Head Trailing Suction Hopper Dredger
Courtesy: Van Oord, Vosta LMG
11
POTENTIAL CUTTERS: DREDGING INDUSTRY
Transverse Cutter: Rotavator • Surgical cutting, resulting in less environmental impact, Ref. Sarkar, M.K. 2012 • Possibly suitable for Cobalt Crust (Thin) 12 Courtesy: EEM (P) Ltd., India
POTENTIAL CUTTERS: LAND MINING Road header
Radial pick
Point attack pick
13
Continuous Miner Courtesy: Sandvik
POTENTIAL CUTTERS: LAND MINING
Surface Miner
Position of drum cutter important for cutting force and stability of miner. Road Miner 14 Courtesy: Trencor and Wirtgen
SUBSEA MINER CONCEPTS
Courtesy: Aker Courtesy: IHC
Bulk Miner Preparatory Machine
Gathering Machine
15 Mining the Seafloor with Robots Ref.: www.iaarc.org/news/a_news_2012_09_11.pdf
CUTTING PRODUCTION AND POWER 16
CUTTING PRODUCTION
Average production = f(External factors, Manageable factors) Instantaneous production = f(Average production, Uncontrollable factors) 17
CUTTING RODUCTION(SOLIDS ) – )CASE STUDY UTTINGPPRODUCTION (SOLIDS
Production Envelope - Example Based on Nautilus Minerals estimated Annual Production = 1.8Million Tonnes (dry) from Solwara 1 Ref: http://www.nautilusminerals.com/s/Home.asp NAT005_Solwara_1_Offshore_Production_System_Definition_and_Cost_Study_Rev_3_21_June20 10
18
CCUTTER RIVE POWER UTTERDDRIVE POWER Dynamic factor(DF): Ratio between peak and average cutting force For hydraulic drives: Hydraulic efficiency and gear box efficiency Hydrodynamic efficiency: Hydrodynamic drag of rotating cutter Recirculation efficiency: Regrinding of excavated material
Instantaneous Production =
Specific Energy = 19
SPECIFIC ENERGY (LAND): EVAN’S MODEL
20
ROCK FAILURE: SUBSEA CONDITIONS
Specific Energy (Subsea) = f(In-situ UCS, Hyperbaric Factor) Disturbed sample: Decompression effect on UCS Hyperbaric factor = f(Rock properties, Cutting parameters, Cutting tool geometry and lacing)
21
CUTTER DRIVE POWER: GENERIC EXAMPLE Cutter Drive Power for Sp. En. = 10kJ/m^3
Cutter Drive Power for Sp. En. = 20kJ/m^3
Calculation Approach
Required Ins. Solids Production (m^3/hr)
Optimistic Approach
Min Max
130 200
900 1500
1900 3000
Conservative Approach
Min Max
135 220
1000 1600
2000 3300
Cutter drive power determines weight of the subsea miner If specific energy increases challenges in subsea power technologies (voltage levels etc.)need to be addressed Design of Launch and Recovery System is dependent on weight of the subsea miner Option for multiple subsea miner
22
CUTTING FORCES, WEIGHT AND STABILITY 23
CUTTING FORCE: DREDGE CUTTER
F_h: Horizontal Force, F_v: Vertical Force, F_a: Axial Force
24
CUTTER POWER TO WEIGHT: ROADHEADER
Single Roadheader can’t meet the production requirement Roadheaders are critical in yaw stability and sliding stability 25 Courtesy: Sandvik
CUTTER POWER TO WEIGHT: DRUM CUTTERS
Approximate Cutter Drive Power: Miner Weight Ratios (Air) Continuous Miner = 4:1 Surface Miner = 6:1
26
RESULTS – DRUM CUTTERS Continuous Miner (Cutter Power : Weight = 4:1) Sp. Energy 10MJ/m^3 20MJ/m^3
Sp. Energy 10MJ/m^3 20MJ/m^3
Cutter Drive Power
Machine Weight
(kW) (Te) 900 to 1600 240 to 400 1900 to 3300 480 to 820 Surface Miner (Cutter Power : Weight = 6:1) Cutter Drive Power
Machine Weight
(kW) 900 to 1600 1900 to 3300
(Te) 160 to 270 300 to 550
Largest subsea vehicles: Rock Trencher RT1 (Deep Ocean) Weight = 200Te (Air) Total power = 2.3MW Total cutter power in 3 chain cutters = 250kW, 2*400kW Operating depth = 500m Pipeline Plough PL3 (Saipem) Weight = 240Te (Air)
Peak Force (Hor. And Vert.) (Te) 20 to 35 40 to 70 Peak Force (Hor. And Vert.) (Te) 20 to 35 40 to 70
Courtesy: Sandvik
27
SUMMARY – CUTTING
Compressive strength and specific energy of cutting very important Laboratory tests In-situ tests
Uncertainty in cutter drive power estimation reduced by accurate determination of ore properties
Cutter drive power and cutter mounting position determines weight of the subsea miner
Stability of subsea miner controlled by cutting forces generated and machine design parameters 28
GATHERING CHALLENGES 29
GATHERING CHALLENGES
The rock mass properties and cutting methodology determines particle size distribution of excavated ore
The suction velocity should be sufficient to gather as much as possible of the excavated ore
Environmental impact should be minimum
Suction velocity should match the riser transport velocity – hence impacts the design of riser pump(s) and diameter of riser 30
ENVIRONMENTAL IMPACT 31
ENVIRONMENTAL SENSITIVITY Habitat
assessment
Plume
generation due to cutting and gathering devices – impact on species existing in mine area
Noise
generation
32
TURBIDITY MEASUREMENT
33 Courtesy: Dr. Mridul Kumar Sarkar, Dr. Neil Bose, Dr. Suhong Chai, Dr. Kim Dowling Australian Maritime College, Tasmania; EEM (P) Ltd. , India; University of Ballarat, Australia
TRANSPORTATION CHALLENGES 34
TRANSPORTATION CHALLENGES
Involves transportation of the excavated ore as a slurry from the seabed to the surface support vessel
Research work – ongoing on vertical transport of slurry by various universities and research institutes
Variation in the slurry density will change the catenary shape of the riser (if flexible riser used)
With the variation in the slurry density additional forces will be transferred to the connection point with the subsea miner
Riser wear needs to be investigated 35
LOCOMOTION CHALLENGES 36
LOCOMOTION CHALLENGES Topography of the terrain Slope of the terrain Rock – Reduced friction of wet rock, e.g. SMS and Cobalt crusts Soft sediments – Bearing Capacity, e.g. Methane hydrates, Polymetallic nodules Proper assessment of cutting forces necessary for sliding stability assessment Additional devices to balance cutting forces when friction is low
37
OTHER LOCOMOTION DEVICES Rotating yoke
Leg Eductor pump
Dipper
Ladder boom Cutter module
Foot
Courtsey: IHC Deep Sea Mining
Suction mouth
Ref: Dr. S Sarkar, Dr. N. Bose, Memorial University of Newfoundland, Canada and Dr. M.K.Sarkar, EEM (P) Ltd. India 2002-2007
Ref: Dr. M.K. Sarkar, EEM (P) Ltd. , India Dr. N. Bose, Australian Maritime College, Tasmania, 2008- 2012
38
LAUNCH AND RECOVERY SYSTEM Support Vessel Umbilical
Riser System
Lifting Wire
Subsea Miner Courtesy: Saipem, Wellstream (GE), Seatools, Certex
39
LARS Requirement: Oil and Gas
Transfer Lines
Risers
Static subsea system Once installed the subsea structure is not recovered
Flowlines
Jumpers
LARS Requirement: Subsea Mining
Dynamic subsea component – since the subsea miner is continuously moving The subsea miner needs to be recovered frequently for scheduled/ unscheduled maintenance 40 Courtesy: Wellstream and Nautilus Minerals
LAUNCH AND RECOVERY SYSTEM:CRITICALITIES
Support vessel – DP operated or moored
Weight of subsea miner and DAF will control design of LARS
Management of the riser during operation and movement of the support vessel in the mine
Wave, Current
Shape of riser determined by environmental load, slurry density and movement of subsea miner – pipeline integrity Accurate estimation of weather downtime 41
FOOD FOR THOUGHT
Design of suitable devices for in-situ determination or ore properties
Wear estimation of cutter tooth and riser system
Robotic change of cutter tooth subsea Wave, Current
Riser integrity monitoring during subsea mining operation
42
QUESTIONS ???
43
Dr. Ir. Sritama Sarkar Saipem UK
CONTENTS Seafloor
Minerals Major Challenges Potential Subsea Miners Subsea Cutting Production and Power Subsea Cutting Forces, Weight and Stability Gathering Challenges Environmental Impact Transport Challenges Locomotion Challenges Launch and Recovery Challenges 2
SEAFLOOR MINERALS 3
Offshore Diamonds
•Established industry •Maximum water depth 400m •Placer pockets in overburden (sand) overlaying clay/ bedrock Polymetallic Nodules
•Extensive R&D since 1970s •Ni, Cu and Co •Water depth 5000m to 6000m •Abyssal plains
4
Methane Hydrates
•Exploration •Water depth 500m to 2000m •Soft sediments in Arctic environment •Slope and rise sediments in continental margin Cobalt Crusts
•Research •Water depth 400m to 4000m •Volcanic island arcs/ Volcanic seamounds – as very thin crusts 5
Seafloor Massive Sulphide (SMS) Deposits
•Exploration and planned commercial exploitation •Cu-Zn-Ag-Au` •Water Depth 1500m to 5000m • Very hot hydrothermal fluids, slightly acidic • Edges of tectonic plates
6
MAJOR CHALLENGES 7
SUBSEA MINING PROCESSES Mechanical Cutting
Cutting Hydraulic Cutting
Transport (Hydraulic)
Gathering (Hydraulic)
Locomotion 8
Seafloor Mining Challenges Vs. Minerals Minerals
Mn Nodules
Co Crust
+++
+++ (Phase dissociation)
No cutting
++ (Very thin crust)
Gathering
++ (Hydraulic)
+++ (Hydraulic)
+++ (Phase dissociation)
+ (Mechanical + Hydraulic)
+++ (Hydraulic)
Transport (Hydraulic)
+
++
+++
+++
+++
Locomotion
+
+++
++
++
++
Processes
Cutting
Offshore Diamonds + (Insignificant cutting)
SMS
Methane Hydrates
Relative Rating in Terms of Challenges More ‘+’ sign, more difficulty
9
POTENTIAL MINERS 10
POTENTIAL CUTTERS: DREDGING INDUSTRY
Dredge cutter And Dredge pick Cutter Suction Dredger
Drag Head Trailing Suction Hopper Dredger
Courtesy: Van Oord, Vosta LMG
11
POTENTIAL CUTTERS: DREDGING INDUSTRY
Transverse Cutter: Rotavator • Surgical cutting, resulting in less environmental impact, Ref. Sarkar, M.K. 2012 • Possibly suitable for Cobalt Crust (Thin) 12 Courtesy: EEM (P) Ltd., India
POTENTIAL CUTTERS: LAND MINING Road header
Radial pick
Point attack pick
13
Continuous Miner Courtesy: Sandvik
POTENTIAL CUTTERS: LAND MINING
Surface Miner
Position of drum cutter important for cutting force and stability of miner. Road Miner 14 Courtesy: Trencor and Wirtgen
SUBSEA MINER CONCEPTS
Courtesy: Aker Courtesy: IHC
Bulk Miner Preparatory Machine
Gathering Machine
15 Mining the Seafloor with Robots Ref.: www.iaarc.org/news/a_news_2012_09_11.pdf
CUTTING PRODUCTION AND POWER 16
CUTTING PRODUCTION
Average production = f(External factors, Manageable factors) Instantaneous production = f(Average production, Uncontrollable factors) 17
CUTTING RODUCTION(SOLIDS ) – )CASE STUDY UTTINGPPRODUCTION (SOLIDS
Production Envelope - Example Based on Nautilus Minerals estimated Annual Production = 1.8Million Tonnes (dry) from Solwara 1 Ref: http://www.nautilusminerals.com/s/Home.asp NAT005_Solwara_1_Offshore_Production_System_Definition_and_Cost_Study_Rev_3_21_June20 10
18
CCUTTER RIVE POWER UTTERDDRIVE POWER Dynamic factor(DF): Ratio between peak and average cutting force For hydraulic drives: Hydraulic efficiency and gear box efficiency Hydrodynamic efficiency: Hydrodynamic drag of rotating cutter Recirculation efficiency: Regrinding of excavated material
Instantaneous Production =
Specific Energy = 19
SPECIFIC ENERGY (LAND): EVAN’S MODEL
20
ROCK FAILURE: SUBSEA CONDITIONS
Specific Energy (Subsea) = f(In-situ UCS, Hyperbaric Factor) Disturbed sample: Decompression effect on UCS Hyperbaric factor = f(Rock properties, Cutting parameters, Cutting tool geometry and lacing)
21
CUTTER DRIVE POWER: GENERIC EXAMPLE Cutter Drive Power for Sp. En. = 10kJ/m^3
Cutter Drive Power for Sp. En. = 20kJ/m^3
Calculation Approach
Required Ins. Solids Production (m^3/hr)
Optimistic Approach
Min Max
130 200
900 1500
1900 3000
Conservative Approach
Min Max
135 220
1000 1600
2000 3300
Cutter drive power determines weight of the subsea miner If specific energy increases challenges in subsea power technologies (voltage levels etc.)need to be addressed Design of Launch and Recovery System is dependent on weight of the subsea miner Option for multiple subsea miner
22
CUTTING FORCES, WEIGHT AND STABILITY 23
CUTTING FORCE: DREDGE CUTTER
F_h: Horizontal Force, F_v: Vertical Force, F_a: Axial Force
24
CUTTER POWER TO WEIGHT: ROADHEADER
Single Roadheader can’t meet the production requirement Roadheaders are critical in yaw stability and sliding stability 25 Courtesy: Sandvik
CUTTER POWER TO WEIGHT: DRUM CUTTERS
Approximate Cutter Drive Power: Miner Weight Ratios (Air) Continuous Miner = 4:1 Surface Miner = 6:1
26
RESULTS – DRUM CUTTERS Continuous Miner (Cutter Power : Weight = 4:1) Sp. Energy 10MJ/m^3 20MJ/m^3
Sp. Energy 10MJ/m^3 20MJ/m^3
Cutter Drive Power
Machine Weight
(kW) (Te) 900 to 1600 240 to 400 1900 to 3300 480 to 820 Surface Miner (Cutter Power : Weight = 6:1) Cutter Drive Power
Machine Weight
(kW) 900 to 1600 1900 to 3300
(Te) 160 to 270 300 to 550
Largest subsea vehicles: Rock Trencher RT1 (Deep Ocean) Weight = 200Te (Air) Total power = 2.3MW Total cutter power in 3 chain cutters = 250kW, 2*400kW Operating depth = 500m Pipeline Plough PL3 (Saipem) Weight = 240Te (Air)
Peak Force (Hor. And Vert.) (Te) 20 to 35 40 to 70 Peak Force (Hor. And Vert.) (Te) 20 to 35 40 to 70
Courtesy: Sandvik
27
SUMMARY – CUTTING
Compressive strength and specific energy of cutting very important Laboratory tests In-situ tests
Uncertainty in cutter drive power estimation reduced by accurate determination of ore properties
Cutter drive power and cutter mounting position determines weight of the subsea miner
Stability of subsea miner controlled by cutting forces generated and machine design parameters 28
GATHERING CHALLENGES 29
GATHERING CHALLENGES
The rock mass properties and cutting methodology determines particle size distribution of excavated ore
The suction velocity should be sufficient to gather as much as possible of the excavated ore
Environmental impact should be minimum
Suction velocity should match the riser transport velocity – hence impacts the design of riser pump(s) and diameter of riser 30
ENVIRONMENTAL IMPACT 31
ENVIRONMENTAL SENSITIVITY Habitat
assessment
Plume
generation due to cutting and gathering devices – impact on species existing in mine area
Noise
generation
32
TURBIDITY MEASUREMENT
33 Courtesy: Dr. Mridul Kumar Sarkar, Dr. Neil Bose, Dr. Suhong Chai, Dr. Kim Dowling Australian Maritime College, Tasmania; EEM (P) Ltd. , India; University of Ballarat, Australia
TRANSPORTATION CHALLENGES 34
TRANSPORTATION CHALLENGES
Involves transportation of the excavated ore as a slurry from the seabed to the surface support vessel
Research work – ongoing on vertical transport of slurry by various universities and research institutes
Variation in the slurry density will change the catenary shape of the riser (if flexible riser used)
With the variation in the slurry density additional forces will be transferred to the connection point with the subsea miner
Riser wear needs to be investigated 35
LOCOMOTION CHALLENGES 36
LOCOMOTION CHALLENGES Topography of the terrain Slope of the terrain Rock – Reduced friction of wet rock, e.g. SMS and Cobalt crusts Soft sediments – Bearing Capacity, e.g. Methane hydrates, Polymetallic nodules Proper assessment of cutting forces necessary for sliding stability assessment Additional devices to balance cutting forces when friction is low
37
OTHER LOCOMOTION DEVICES Rotating yoke
Leg Eductor pump
Dipper
Ladder boom Cutter module
Foot
Courtsey: IHC Deep Sea Mining
Suction mouth
Ref: Dr. S Sarkar, Dr. N. Bose, Memorial University of Newfoundland, Canada and Dr. M.K.Sarkar, EEM (P) Ltd. India 2002-2007
Ref: Dr. M.K. Sarkar, EEM (P) Ltd. , India Dr. N. Bose, Australian Maritime College, Tasmania, 2008- 2012
38
LAUNCH AND RECOVERY SYSTEM Support Vessel Umbilical
Riser System
Lifting Wire
Subsea Miner Courtesy: Saipem, Wellstream (GE), Seatools, Certex
39
LARS Requirement: Oil and Gas
Transfer Lines
Risers
Static subsea system Once installed the subsea structure is not recovered
Flowlines
Jumpers
LARS Requirement: Subsea Mining
Dynamic subsea component – since the subsea miner is continuously moving The subsea miner needs to be recovered frequently for scheduled/ unscheduled maintenance 40 Courtesy: Wellstream and Nautilus Minerals
LAUNCH AND RECOVERY SYSTEM:CRITICALITIES
Support vessel – DP operated or moored
Weight of subsea miner and DAF will control design of LARS
Management of the riser during operation and movement of the support vessel in the mine
Wave, Current
Shape of riser determined by environmental load, slurry density and movement of subsea miner – pipeline integrity Accurate estimation of weather downtime 41
FOOD FOR THOUGHT
Design of suitable devices for in-situ determination or ore properties
Wear estimation of cutter tooth and riser system
Robotic change of cutter tooth subsea Wave, Current
Riser integrity monitoring during subsea mining operation
42
QUESTIONS ???
43
