Feature Article
Improving Geotechnical Drilling to Reach Seafloor Massive Sulfide DepositsRovdrill 3 Completes More Than 100 Dives on Difficult Terrain To Collect Samples for Nautilus Minerals’ Solwara 1 Deposit
AUTHORS:
Product Manager, Rovdrill
Operations Manager, Rovdrill
Forum Energy Technologies
Houston, Texas
In 2007 and 2008, Nautilus Minerals Inc. (Toronto, Canada) carried out seafloor mineral exploration drilling and sampling programs at Solwara 1, a planned deep-sea mining project offshore Papua New Guinea, using the ROV-based conventional drilling systems Rovdrill 1 and Rovdrill 2 developed by Perry Slingsby Systems Inc. (Houston, Texas), now a Forum Energy Technologies company. In average water depths of 1,500 to 1,600 meters, these systems drilled up to 18 meters into the seafloor, recovering a number of core samples that were of sufficient quality to assay the mineral content and infer some basic characteristics and boundaries of the deposit field.
First-generation Rovdrill systems and support spreads had certain limitations. During the previous campaigns in 2007 and 2008, a number of holes were terminated prematurely—often considerably short of target depth—due to hole collapse. Steeply sloping terrains at the drill sites and reliability of the drill rig affected long-term productivity.
As a result of these operational constraints, large areas at Solwara 1 remained undrilled. The results from other geophysical investigations and surveys performed previously and concurrently with the drilling programs, particularly electromagnetic surveys, inferred that the depth of the ore body on Solwara 1 could be considerably greater than that indicated by the core sample recoveries.
In 2010, Nautilus Minerals began another drilling program at Solwara 1 and other surrounding deposit fields. The aim was to further establish the minimum boundary for the seafloor massive sulfide (SMS) deposit field on Solwara 1, which had not been completely defined during the 2007 and 2008 campaigns. Nautilus Minerals required a system with improved drilling efficiency and capabilities to achieve a minimum penetration depth of 40 meters below the seabed, and core recovery of at least 75 percent overall, with a target of 90 percent in massive sulfide layers.
On review of the critical functional requirements for the Nautilus Minerals 2010 SMS drilling, Seafloor Geoservices (Houston) determined the attributes and capabilities of the Rovdrill 3 system were close to meeting the Nautilus requirements. In 2010, Nautilus selected Seafloor Geoservices to provide the Rovdrill 3. Forum Energy Technologies, the parent company of both Seafloor Geoservices and Perry Slingsby Systems, sponsored the development and manufacturing of the project’s equipment.
Rovdrill 3 Development
In 2008 and 2009, Perry Slingsby and Seafloor Geoservices developed the Rovdrill 3 in Houston, Texas. The impetus for this development was mainly to build upon the previously field-proven rigs, Rovdrill 1 and 2, but with considerable redesign and enhanced capabilities to address much broader subsea geotechnical investigation applications and markets other than SMS exploration.
Unlike the first-generation Rovdrill 1 and 2, the Rovdrill 3 was not designed and built in response to a specific project requirement but rather as a result of market requirements and a survey of client groups, including potential mineral exploration clients and offshore oil and gas geotechnical investigation clients. To meet Nautilus Minerals’ drilling requirements, the Rovdrill 3 required additional upgrades and modifications, principally to the subsea drill module assembly to address and overcome the limitations experienced with the previous Rovdrill systems.
Due to the extreme environmental conditions prevalent at the target drill sites (e.g., steep gradients, loose unconsolidated formations and dense clusters of hydrothermal chimneys), the primary obstacle was to ensure that the drilling module could be landed and stabilized safely and sufficiently on or as close as possible to the 50-some initial target drill sites identified by Nautilus Minerals geologists. Using previously surveyed bathymetry data, computer-based landing simulation scenarios were developed to help establish if it was possible for the drilling module to access the target drill sites, and if not, how close the module could be deployed. This was done by importing the bathymetry data into Forum Energy Technologies’ VMAX Project Simulator software in the native one-meter pixel data set in .DXF source format. The data were then converted into 3D Studio MAX (now Autodesk 3ds Max), which allowed the development team to run accurate interactive landing simulation scenarios.
This process helped produce a concept design for the drill module landing foundation geometry and dimensions. The resulting four-legged, jack-up-type foundation module assembly interfaced to the base of the drill module and deployed as a complete subsea package.
Having successfully engineered a landing foundation solution for the drilling module, the next task was to stabilize the hole collar in the upper unconsolidated zones to ensure the borings could progress into the firmer underlying mineralized zones. This was achieved using wireline drilling and sampling and deploying multiple hole casing strings in the hole’s upper zone. By utilizing wireline drilling and sampling, the risk of hole collapse was reduced significantly because the outer drill string remained in the hole during inner sampling tube deployment and recovery. To continue this article please click here.
Allan Spencer is a professional engineer at Forum Energy Technologies who has 12 years of experience in the design, project management and offshore operation of subsea remote intervention technologies. He specializes in ROV-based geotechnologies and has held a variety of senior managerial positions in the U.K. and U.S.
Allen Ramsey is a professional engineer at Forum Energy Technologies 10 years of experience in project management and the operation of specialized remotely operated and manned subsea vehicles and equipment. He has held senior positions in the U.K. as project engineer and senior project manager, and in the U.S. as operations manager.
First-generation Rovdrill systems and support spreads had certain limitations. During the previous campaigns in 2007 and 2008, a number of holes were terminated prematurely—often considerably short of target depth—due to hole collapse. Steeply sloping terrains at the drill sites and reliability of the drill rig affected long-term productivity.
As a result of these operational constraints, large areas at Solwara 1 remained undrilled. The results from other geophysical investigations and surveys performed previously and concurrently with the drilling programs, particularly electromagnetic surveys, inferred that the depth of the ore body on Solwara 1 could be considerably greater than that indicated by the core sample recoveries.
The Rovdrill 3 drill module being recovered to the vessel on completion of a successful dive.
In 2010, Nautilus Minerals began another drilling program at Solwara 1 and other surrounding deposit fields. The aim was to further establish the minimum boundary for the seafloor massive sulfide (SMS) deposit field on Solwara 1, which had not been completely defined during the 2007 and 2008 campaigns. Nautilus Minerals required a system with improved drilling efficiency and capabilities to achieve a minimum penetration depth of 40 meters below the seabed, and core recovery of at least 75 percent overall, with a target of 90 percent in massive sulfide layers.
On review of the critical functional requirements for the Nautilus Minerals 2010 SMS drilling, Seafloor Geoservices (Houston) determined the attributes and capabilities of the Rovdrill 3 system were close to meeting the Nautilus requirements. In 2010, Nautilus selected Seafloor Geoservices to provide the Rovdrill 3. Forum Energy Technologies, the parent company of both Seafloor Geoservices and Perry Slingsby Systems, sponsored the development and manufacturing of the project’s equipment.
Rovdrill 3 Development
In 2008 and 2009, Perry Slingsby and Seafloor Geoservices developed the Rovdrill 3 in Houston, Texas. The impetus for this development was mainly to build upon the previously field-proven rigs, Rovdrill 1 and 2, but with considerable redesign and enhanced capabilities to address much broader subsea geotechnical investigation applications and markets other than SMS exploration.
Unlike the first-generation Rovdrill 1 and 2, the Rovdrill 3 was not designed and built in response to a specific project requirement but rather as a result of market requirements and a survey of client groups, including potential mineral exploration clients and offshore oil and gas geotechnical investigation clients. To meet Nautilus Minerals’ drilling requirements, the Rovdrill 3 required additional upgrades and modifications, principally to the subsea drill module assembly to address and overcome the limitations experienced with the previous Rovdrill systems.
Due to the extreme environmental conditions prevalent at the target drill sites (e.g., steep gradients, loose unconsolidated formations and dense clusters of hydrothermal chimneys), the primary obstacle was to ensure that the drilling module could be landed and stabilized safely and sufficiently on or as close as possible to the 50-some initial target drill sites identified by Nautilus Minerals geologists. Using previously surveyed bathymetry data, computer-based landing simulation scenarios were developed to help establish if it was possible for the drilling module to access the target drill sites, and if not, how close the module could be deployed. This was done by importing the bathymetry data into Forum Energy Technologies’ VMAX Project Simulator software in the native one-meter pixel data set in .DXF source format. The data were then converted into 3D Studio MAX (now Autodesk 3ds Max), which allowed the development team to run accurate interactive landing simulation scenarios.
This process helped produce a concept design for the drill module landing foundation geometry and dimensions. The resulting four-legged, jack-up-type foundation module assembly interfaced to the base of the drill module and deployed as a complete subsea package.
Having successfully engineered a landing foundation solution for the drilling module, the next task was to stabilize the hole collar in the upper unconsolidated zones to ensure the borings could progress into the firmer underlying mineralized zones. This was achieved using wireline drilling and sampling and deploying multiple hole casing strings in the hole’s upper zone. By utilizing wireline drilling and sampling, the risk of hole collapse was reduced significantly because the outer drill string remained in the hole during inner sampling tube deployment and recovery. To continue this article please click here.
Allan Spencer is a professional engineer at Forum Energy Technologies who has 12 years of experience in the design, project management and offshore operation of subsea remote intervention technologies. He specializes in ROV-based geotechnologies and has held a variety of senior managerial positions in the U.K. and U.S.
Allen Ramsey is a professional engineer at Forum Energy Technologies 10 years of experience in project management and the operation of specialized remotely operated and manned subsea vehicles and equipment. He has held senior positions in the U.K. as project engineer and senior project manager, and in the U.S. as operations manager.
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