Field Acquisition Services
Seabed Geochemical Surveys
Surface Geochemical Exploration (SGE)
Download the Surface Geochemical Exploration flyer HERE
Surface Geochemical Exploration is a petroleum prospecting tool based on the premise that traces of upward migrated petroleum from deep source rocks and reservoirs can be detected in selected seabed sediments and used to evaluate exploration potential. Deep seismic and multibeam surveys are used to select piston coring locations based on surface expression of deep faults and other features related to conduits for upward migration of hydrocarbons. The science and art of this seep hunting involves (1) proper selection of core sites from the seismic records, (2) safe and skillful acquisition of seabed cores at these exact sites, (3) analytically distinguishing promising samples from samples with varying levels of natural background concentrations, and (4) properly interpreting the geochemical results in a geologic context.
TDI-Brooks uses a sequence of specific procedures that we developed and improved over several decades. Our method consistently yields highly accurate identification and a quantitative evaluation of potential sites with migrated oil. Our interpretation of survey results is made even more robust by comparison with our world-wide database of SGE survey results from 100,000+ samples we have collected, analyzed, and interpreted over the years. We add our knowledge of historical background levels of the analytes for an area, environmental factors, and any unique characteristics of the region being sampled. The process consists of the following sequential steps: Core Site Selection, Core Acquisition, Laboratory Analysis, and Interpretation.
Heavily oil stained piston core sample, out gassing due to presence of gas hydrates
Multibeam Core Site Selection
- High cost and operational complexity of acquisition;
- Limited areal coverage of the area of interest; and
- Low resolution
In the past decade there has been an increased use of multibeam bathymetric survey data (bathymetry, backscatter and water column plume) as a cost effective alternative / complimentary tool for the identification of seepage targets for SGE core sampling. Compared to 2D or 3D seismic, multibeam surveys have a number of advantages including:
- Lower cost and operational complexity of acquisition
- 100% areal coverage of the area of interest;
- Very high resolution;
- Low probability of negative impact on marine mammals, environmental permitting issues reduced;
- Rapid turnaround time of data processing and interp / seep target selection;
- Can be used independently or in conjunction with 2D or 3D seismic data for seep target selection ; and
- Seeps can have a bathymetric or backscatter signature on the seafloor, or both.
TDI-Brooks and our partners have been involved in the design and execution of numerous ‘seep hunting’ MBES programs. TDI-Brooks operates two vessels with Kongsberg MBES systems, the RV Gyre and RV GeoExplorer, and has chartered third party vessels equipped with similar MBES systems suitable for seep hunting missions.
Multibeam echo sounders, like other sonar systems, emit sound waves in the shape of a fan from directly beneath a ship’s hull. These systems measure and record the time it takes for the acoustic signal to travel from the transmitter (transducer) to the seafloor (or object) and back to the receiver. In this way, multibeam sonars produce a “swath” of soundings (i.e., depths) for broad coverage of a survey area. Survey speed is typically higher than seismic operations (up to 10 kts).
|MBES operation and example of processed bathymetry data from EM710 on RV GeoExplorer|
The area of coverage on the seafloor (swath) per ping depends on the depth of the water, seafloor composition, and the operating frequency of the multibeam sonar. Echosounders that transmit low frequency sound can travel a longer distance in the water (increased range and coverage) but have a lower resolution and are less precise. Sound from high-frequency echosounders cannot travel long distances in water but achieve a higher resolution and are more precise.
Most mid to deep water MBES systems are capable of meeting the resolution / data quality requirements for seep hunting missions. In general, lower frequency MBES systems will allow for increased coverage and reduce survey time, but this may be offset by higher vessel costs, as these system typically require a larger vessel to mount the transducer arrays than higher frequency systems (which use smaller transducer arrays).
Hydrocarbon Seep Identification with MBES data
The typical multibeam dataset for seep identification will consist of:
- Bathymetric surface grid (5 – 20m resolution)
- Quantitative backscatter grid (3 – 5m resolution)
- Water column plume data
Hydrocarbon seeps occur as point sources or clusters of point sources due to the vertical migration of hydrocarbons focusing into vertical chimneys. Hydrocarbons will follow a path of least resistance while migrating and therefore tend to form relatively small pathways compared to the overall volume of rock and sediments. As a result, surface expressions of seepage occur as discrete features, often with bathymetric character, such as a mud volcano or pockmark.
Backscatter is defined as the amount of acoustic energy being received by the sonar after interaction with the seafloor. This data can be used to characterize bottom type, because different bottom types “scatter” sound energy differently. For example, a softer bottom such as mud will return a weaker signal than a harder bottom, like rock.
While some surface seeps have an easily identifiable surface expression, there are many more occurrences with either very subdued or absent bathymetric response. Hydrocarbon seepage provides nutrients to chemosynthetic fauna, and also leads to precipitates such as authigenic carbonate, and, in appropriate temperature and pressure conditions, seafloor or near-seafloor gas hydrate. All of these conditions have an impact on the acoustic properties of the seafloor or the shallow sub-surface and can be identified by an elevated backscatter response. This backscatter response is the reason seep hunting works so well in the marine environment.
In addition to recording the bottom return data (in the form of bathymetry and backscatter), many current generation MBES systems can record the returns throughout the entire water column. This data can be used to detect bubbles or gas plumes above the seafloor which could be indicative of hydrocarbon seepage. This plume data can be digitized and georeferenced to correlate with bathymetry and backscatter data.
When combined, MBES bathymetry, backscatter and water column data give trained interpreters a powerful and cost effective tool for identifying potential hydrocarbon seep sites.
Piston Core Acquisition
Our vessels deployed to sample the core targets typically collect additional acoustic data with a hull-mounted sub-bottom profiler prior to core acquisition. These real-time on-site surveys are used to correlate the seabed or sub-bottom feature to be cored with the corresponding seismic record used originally to high-grade the site. This process can refine the best core target location, and provides sub-bottom structure, bottom hardness, and features associated with migrated petroleum on the seabed (e.g. faults, mud mounds, fractures, upwelling features) within 1 to 2 meters.
We use USBL navigated piston coring to collect the precisely located sediment core samples. Piston coring offers several advantages over gravity coring: greater penetration depths, better core recovery, and higher quality samples.
Using piston coring to sample depths up to 6 meters significantly reduces intracore variability due to bioturbation, loss by diffusion of gases, and mixing of natural hydrocarbon seepage or pollution in the top meter of sea floor sediments with deeper sections of the core. In particular, the quality of information gained from measurement of sediment gases increases dramatically in sections collected deeper than about 2.5 meters. Sediment gas concentrations can change several orders of magnitude through the 2 to 5 meter depth range in marine sediments, greatly enhancing the type and quality of measurements that can be made on the samples.
A clean shipboard laboratory area is used to process collected geochemistry cores in a hydrocarbon-free environment. Sections of the core are sampled based on a systematic sampling scheme dependent on core length. Geochemical, interstitial gas analysis and archive samples are collected from the bottom portion of each core and stored in a -20°C freezer until analysis in our Texas laboratory.
The determination of interstitial light hydrocarbon gases (including methane, ethene, ethane, propene, propane, iso-butane, n-butane, neo-pentane, iso-pentane, and n-pentane) from canned sediment samples is useful because low molecular weight hydrocarbon gases are the most mobile phase of petroleum and, if present in the core section, are easily detected, quantified, and distinguished from local background.
Samples that contain elevated concentrations of migrated petroleum based on the TSF, C15+GC, and/or gas screening data can be further analyzed for saturate and aromatic biological markers and stable carbon isotopes. These more detailed analyses can usually confirm the presence of migrated petroleum and are often used to match hydrocarbons in the sediment extract with a specific produced oil and/or source rock.
Gas hydrates were recovered from eight sites on the Louisiana slope of the Gulf of Mexico. The gas hydrate discoveries ranged in water depths from 530 to 2400 m occurring as small to medium sized (0.5–50 mm) nodules, interspersed layers (1–10 mm thick) or as solid masses (> 150 mm thick). The hydrates have gas:fluid ratios as high as 170:1 at STP, C1/(C2 + C3) ratios ranging from 1.9 to > 1000 and δ13C ratios from −43 to −71‰. Thermogenic gas hydrates are associated with oil-stained cores containing up to 7% extractable oil exhibiting moderate to severe biodegradation. Biogenic gas hydrates are also associated with elevated bitumen levels (10–700 ppm). All gas hydrate associated cores contain high percentages (up to 65%) of authigenic, isotopically light carbonate. The hydrate-containing cores are associated with seismic “wipeout” zones indicative of gassy sediments. Collapsed structures, diapiric crests, or deep faults on the flanks of diapirs appear to be the sites of the shallow hydrates.
Concentrations of the C1-C3 hydrocarbons and stable carbon isotope compositions of methane in recent sediments and seep gases of the Texas-Louisiana shelf-slope region were determined. These gases have been produced by both microbial and themocatalytic processes. Microbially-produced gases consist almost exclusively of methane, having C1/(C2+C3) hydrocarbon ratios greater than 1000 and δ13CPDB values of methane more negative than -60‰. Petroleum-related hydrocarbon gases generally have C1/(C2+C3) ratios smaller than 50 and isotopic ratios more positive than -50‰. A geochemical model based on these two parameters is used to show that natural gas compositions can be altered due to mixing of gases from the two sources as well as by microbial action and migration through sediments.
Light hydrocarbons in the upper few meters of Gulf of Mexico sediments are almost entirely of…
Interstitial methane profiles from six sediment cores taken on the slope and abyssal plain of the Gulf of Mexico can be explained by simple kinetic modeling. Methane is apparently produced at a constant rate and microbially consumed in the sulfate-reducing zone. Rates of production and consumption are estimated from best-fit solutions to a steady-state diagenetic equation. Production and consumption balance to form uniform concentrations of 5 to 10 µll-1 in the first few meters of slope and abyssal sediments. Effects of upward diffusion from large accumulations of methane in sulfate-free zones deeper than about 10m are not detectable.
Seabed Geotechnical Surveys
Geotechnical Field Services
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TDI-Brooks International, Inc. offers a comprehensive suite of offshore geotechnical field services, including piston coring, jumbo piston coring, box coring, and the deployment of multiple CPT tools. Our vessels can also be used to accommodate some third party geotechnical equipment packages. Geotechnical analytical services are offered to complement our field services.
The CPT-Stinger is installed in a JPC core-head, deployed and triggered with the well-proven TDI-Brooks JPC process, and allowed to free-fall ballistically to insert itself into the sediment like a JPC. Once fully embedded in the seafloor with the necessary resulting reaction force now available, the CPT-Stinger is programmed to extend a rod from inside the barrel deeper into the formation (like a stinger) at the standard ASTM (static) cone push rate.
The standard Long barrel CPT Stinger can be ballistically inserted to about 62 ft BML (while gathering dynamic CPT data), and then used to push a cone penetrometer to about 115 ft BML while gathering static CPT data. The Extended Long CPT Stinger can be inserted to about 72 ft BML (while gathering dynamic CPT data), and then used to push a cone penetrometer to about 135 ft BML while gathering static CPT data. Because the extended rod is essentially as long as its barrel, in-situ CPT data can be acquired to sediment depths double of that of the barrel length of the tool (or of a corresponding JPC).
The CPT Stinger has its own engineered barrel assembly, internal rod set, control module, and PCPT cone with data logger. The rig is deployed in the same manner as if acquiring a JPC. After trigger less than 1 m above the seabed, the dynamic cone data are acquired at a high rate during ballistic penetration into the formation. After penetration to full embedment, the cone data acquisition continues while the cone is slowly pushed deeper into the formation at a constant rate. During this push phase, the probe advances at a controlled ASTM rate of 2.0 cm/sec ± 0.5 cm/sec. Data from the probe are logged as the push progresses. Once complete, the system is retrieved to the vessel and data are downloaded from the probe for evaluation and analysis. The tool is then readied for the next deployment, typically in less than 20 minutes, making 3 to 5 deepwater deployments per 12-hour day routine. The tested minimum water depth for the CPT-Stinger is currently 350 m, though a shallower water capability may be possible.
Jumbo Piston Coring
The main winch, main-line rope, and the stern A-Frame are used for deploying and retrieving the JPC rig. In addition to the deployed hardware, several assemblies are mounted to the vessel working deck to manage the deployment and retrieval of the coring rig. These assemblies include the main sheave from the stern A-Frame and the deployment, retrieval and trigger tugger winches with their hydraulic power pack.
The main winch, main-line coring rope, and the starboard A-Frame are used for deploying and retrieving the 3-in. piston core rig. In addition to the deployed hardware, several assemblies are mounted to the vessel working deck to manage the deployment and retrieval of the coring rig. These assemblies include the main sheave from the starboard A-Frame and the core-head and trigger tugger winches with their hydraulic power pack.
A piston corer uses a free fall of the coring rig to achieve the desired initial force on impact, and a sliding piston inside the core barrel to reduce inside wall friction with the sediment and to assist in the rapid evacuation of displaced water from the top of the corer. These elements act in concert to maximize core recovery.
Our box coring system is designed to be a safe, simple, effective mechanism for acquiring large-volume undisturbed shallow sediment samples from the seabed. Such samples are essential for the accurate determination of geotechnical characteristics of marine sediments and the assessment of the benthic ecology (infauna) as required in environmental impact assessments.
The sample box of the core rig is fabricated from stainless steel and is clean and smooth to minimize frictional resistance between the box and the sediment. The corers have a variable weight capability so that the weight stack can be adjusted to suit different seabed conditions that may be encountered.
Geotechnical Laboratory Analysis and Interpretation
We have a comprehensive geotechnical laboratory to supplement our acquisition services. The lab is headed by Nick Clark.
Seabed Heatflow Surveys
Heat Flow Exploration
Download the Heat Flow Exploration flyer HERE
Heat flow measurements serve critical purposes in oil exploration and production. The measured background or equilibrium heat flow, and measured sediment thermal conductivity provide strict constraints to geochemical models that determine regional scale maturation of basins with respect to oil and gas. In addition, area-wide heat flow surveys provide significant geological information on fluid flow from faults, lineaments, and around structures. Heat flow measurements in conjunction with seismic and sea floor geochemical studies provide a mechanism to assess fault and structural seals and contribute to a better understanding of regional hydrodynamics and hydrocarbon occurrence.
TDI-Brooks International has performed heat flow studies across the world. The map to the left shows the many locations we’ve collected heatflow measurements. TDI-Brooks International’s heat flow probe performs heat flow surveys in water depths up to 6000 m. In addition to measuring the sediment temperatures, the probe measures in situ thermal conductivity and water temperature profiles. The probe is capable of multiple measurements during a single 12-24 hour deployment. This one ton instrument is deployable from sea going vessels or platforms with a suitable winch and deployment system.
The heat flow in a region is due to heat moving upward from the mantle, together with thermal input from the radioactive decay of long-lived, naturally occurring isotopes in the earth’s crust. This conductive thermal regime is easily perturbed by the movement of fluids, which is the most effective form of heat transport. Thus, heat flow anomalies are indicative of recent or ongoing fluid flow in a sedimentary basin. Heat flow variations may also provide insight into basin stretching, sedimentation rates, and the presence of salt. Salt has a high thermal conductivity and thus enhances heat flow and perturbs maturation patterns and hydrodynamics around salt structures. In addition, the geotechnical stability of the ocean floor can be addressed as measured temperatures can determine the stability of gas hydrates in shallow sediments.
Environmental Baseline Surveys
Environmental Baseline Study (EBS)
Download the Environmental Baseline Study (EBS) flyer HERE
Since inception of the EBS concept in the early 1970’s, TDI-Brooks International’s scientists have been performing EBSs for clients in the most rigorous regulatory environments. Decades of experience in refining techniques, working with regulatory agencies, and developing a functional network of specialists/associates provides our clients with an effective and defensible approach to resolving environmental impact issues in the marine environment.
We have completed seven EBS projects with Bureau of Ocean Energy Management (BOEM) over the past 20 years:
- Deepwater Program: Exploration and Research of Northern Gulf of Mexico Deepwater Natural and Artificial Hard Bottom Habitats with Emphasis on Coral Communities: Reefs, Rigs and Wreck – Lophelia II
- Investigations of Chemosynthetic Communities on the Lower Continental Slope of the Gulf of Mexico- CHEMO III
- NOAA Status and Trends Mussel Watch -over 20 years
- West African EBS Programs
- 3 years as the first USEPA Environmental Monitoring Assessment Program, Near Coastal (EMAP-NC)
- National Estuary Programs in Galveston and Casco Bays
- 4 years in Russian Arctic on ONR’s Arctic Nuclear Waste Assessment Program
Environmental Baseline Studies are often required in offshore prospects as a defense against potential litigation, to satisfy leasing stipulations, and as good faith measures in responsible environmental stewardship. When performed in conjunction with TDI-Brooks’ SGE surveys, TDI-BI is able to leverage our experience, logistical support, and presence to provide cost effective EBSs conducted under the stringent HSE standards that industry demands, thereby providing our client with timely solutions to environmental concerns backed with the highest scientific and technical credibility.
Our scientists have held key roles in the most high profile, prestigious Environmental Impact Assessment projects both in the US and internationally. Our client history includes USEPA, BOEM (formerly Minerals Management Service), National Oceanic and Atmospheric Administration, Office of Naval Research, and US Fish and Wildlife Service.
Hydrographic Marine Services
Hydrographic Marine Services
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TDI-Brooks International, Inc. provides full arrays of hull-mounted and towed sensor acquisition systems to perform hydrographic and marine geophysical surveys around the world safely, effectively, and economically. We have the global experience, knowledge and resources needed for any marine site survey investigation.
We employ an experienced team that includes hydrographers, geophysicists, geologists, oceanographers, mariners, cartographers, and GIS and CADD specialists working with our own vessels and equipment, producing surveys and deliverables of the highest quality.geochemical and heat flow programs, environmental assessments, metocean, site surveys and seabed surveys.
Areas of Expertise include the following:
• 2DHR Seismic multi channel & site surveys
• Shallow & Deepwater Multibeam (MBES) surveys
• Marine analog & hazard surveys
• Hydrographic mapping
• Hazard surveys
• Rig & Platform siting feasibility studies
• Tow route clearances
• Platform and pipeline damage assessments and inspection
• Pipeline / cable route surveys
• Burial assessments
• Underwater infrastructure inspection
• Fisheries habitat
• Offshore Wind Farm assessments
• LNG and FPSO offloading facilities
• Bureau of Ocean Energy Management (BOEM) surveys
• Academic research
Hydrographic Marine Surveys are critical to any site investigation and/or seabed mapping project. Hydrographic survey is the science of measurement and description of features which affect maritime navigation, marine construction, dredging, offshore oil exploration/offshore oil drilling and related activities. Strong emphasis is placed on soundings, shorelines, tides, currents, seabed and submerged obstructions that relate to the previously mentioned activities.
Each TDI-Brooks vessel uses its multibeam echo sounder to conduct hydrographic surveys. Multibeam sonar measures the depth of the sea floor by analyzing the time it takes for sound waves to travel from a boat to the sea floor and back. In addition to our onboard services, we offer portable tool kits which can be shipped to any vessel of opportunity.
Marine Analog and Digital Site and Hazard Survey Services
A geophysical survey involves a number of data requirements including water depths, seabed topography, seabed and sub-seabed obstructions, seabed soils, shallow geology and ground conditions and identification of any man-made and naturally occurring hazards that may adversely impact the objective of the site investigation (geohazards).
The basic survey package on our vessels consist of:
- Klein System 3000 Dual Frequency Side Scan Sonar (two on board)
- Conducting cable winch and slip rings with 2,200-m of cable
- Geometrics G-882 Marine Magnetometer (two on board)
- Benthos Chirp II Sub-Bottom Profiler w/ 16 hull mounted transducers
- Kongsberg HiPAP 350 USBL systems
- C-Nav DPGS System and Winfrog navigation package
- Kongsberg EA400 Single-Beam Echo Sounder
- Seabird SBE19 Plus CTD
- VSS DMS05 Vertical Reference Unit (VRU)
- Kongsberg EM1002 Multi-Beam Echo Sounder
- Hydrographic Workstation w/ SIS acquisition software
- Seapath 200 Motion Sensor
- AVS Sound Velocity and Temperature Measurement Sensor
- AVS SVPlus Sound Velocity Profiler
- Kongsberg EM701 MkII Multi-Beam Echo Sounder
- upgraded in 2015 to MkII configuration (40 – 100kHz frequency range)
- water column logging
- Hydrographic Workstation w/ SIS acquisition software
- Seapath 200 Motion Sensor
- AVS Sound Velocity and Temperature Measurement Sensor
- AVS SVPlus Sound Velocity Profiler
Surveys Using Our Portable Tool Kits
TDI-Brooks International keeps a complete set of portable field equipment on hand.
We have the capability to quickly mobilize for offshore coring and field sampling operations on virtually any suitable vessel. For further information, please contact us.
GeoEel & Air Gun Array
The GeoEel system is a lightweight fully digital marine seismic streamer system designed for application to a wide range of surveys, including oil and gas exploration, gas hydrates surveys and a variety of special engineering surveys. In addition to towed streamer seismic applications, the GeoEel is also suitable for use as a bay cable in shallow water transition zone regions.
The GeoEel streamer and on-board data acquisition system is very portable and easy to mobilize for installation on small shallow draft survey vessels for operation in shallow water less than 10 meters, or on larger reel equipped deep water vessels. The acquisition system can be configured for use with almost any type of marine impulsive source. We also have the Sodera Mini GI Air Gun (60 cu in), and an Alpha Seismic ASC100D 100 SCFM compressor. Both single source and multi-source arrays can be deployed for a variety of seismic data requirements.
- Footprint: 10’1″ x9′
- Weight : 3,000lbs’
- Modular I Beam construction
- Workplatform: 10″ off deck on grating.
- A-Frame arms: 14′ 2″ high
- Safe working load: 2,000lb SWL with a full outboard n stops pullout load rating of 8,000lbf line pull
Shallow Water, Intertidal, & land Surveys
TDI-Brooks International extends its full suite of deep water acquisition services to shallow water, the transition zone and onshore. Such services include geotechnical, geochemical, environmental and general surveys with comprehensive reporting. Our expertise lies in acquiring the highest quality, cost effective data from the most challenging areas around the world.
TDI-Brooks has over twenty years involvement in shallow water and transition zone geochemical and environmental assessments as well as numerous environmental baseline studies, especially in remote areas of West Africa. Decades of experience have refined techniques, and from working closely with regulatory agencies, and by developing a functional network of specialists/associates, we provide our clients with an effective and defensible approach to resolving Environmental Impact issues in the marine environment.
Geotechnical acquisition services in conjunction with well-equipped local or US based partners will be supported by TDI-Brooks existing Geotechnical laboratory and GIS services. Furthermore all levels of reporting can be provided with the assistance of our engineering partner network.
Buttressing advanced surveys are the basic surveys and data reporting which we provide. Such basic surveys include hydrographic, topographic, cadastral and boundary surveys. As well as; dredging, constructability and hazard surveys, pipeline and flowline corridor, construction, and post lay including depth-of-cover, and as-built surveys.
Our personnel, processes and equipment follow established guidelines and industry best practices to perform work within environmentally sensitive wetlands, intertidal areas, surf zones, coastal waters, and rivers.