The latest AAPG Geoscience Technology Workshop, “Mixed Systems on Continental Margins,” focused on turbidite, contourite and mass-transport deposits and was held in Lisbon, Portugal in June. More than 75 participants from six continents from the energy industry, academic institutions and government agencies discussed the recent achievements and uncertainties of global deepwater sedimentary systems. Highlights included a geological field trip, deep technical contributions by the presenters, a networking dinner at the local legend Trindade and a geohistory tour of the Alfama, Baixa, Chiado and Mouraria districts of downtown Lisbon.
The conference began with a geological field trip to localities north of Lisbon featuring Late Jurassic outcrops in the Lusitanian Basin that record active rifting. Abrupt, short-distance, lateral changes from conglomeratic submarine fans to low-density turbidity current deposits, with localized reefs developed near the basin margin, were explored during this one-day field trip.
“The crown jewel was the Santa Cruz beach outcrop with its stunning conglomeratic channel-fill cutting down into the marly low-density turbidity current deposits,” added field trip leaders Gil Machado of Chronosurveys and Ricardo Pereira of Nova University, Lisbon.
The technical program consisted of 30 oral presentations, 21 posters and five keynote speakers. Presenters and attendees were treated to an engaging two days of superb learning in the areas of energy geosciences, the greater energy industry, outcrop and subsurface case studies and regional analysis. A wide range of topics were discussed, and each participant gained a greater appreciation for the scale, scope, relevance and potential for mixed deepwater systems. Common themes and keywords that emerged from the technical program included exploration, discovery, integration across disciplines, global collaboration, teamwork, dogma-busting, CCUS, resource valuation and the future of deepwater.
Several themes emerged over the two days of presentations in the technical program. The presentations and discussions demonstrated that contourites and mixed systems are important deepwater sedimentary systems – even at a basin scale.
“These systems are not underrepresented but under-recognized! They are commonly controlled by plate tectonic evolution of inter-oceanic gateways and environmental changes through time. They could have high economic resource value, and in our low-carbon future as deepwater dominates exploration and development, these systems will become increasingly important,” said F. Javier Hernández-Molina, leader of the Drifters Research Group Joint Industry Project No. 2 and general chair of the conference.
New Understanding of Deepwater Processes
There is a new paradigm concerning deepwater. No longer are gravity flows considered to be dominant in every system. In fact, the total energy of vast oceanic bottom currents and associated oceanographic processes (deep tides, internal waves, eddies) is greater than even the largest shorter-term gravity-flow events.
“While a large turbidity current might weigh in at 1,015 kilojoules, a single water mass in the ocean might be four or five orders of magnitude larger. Even the best-known historical example of a large turbidity current, the Grand Banks event of 1929, was affected by the synchronous Western Boundary Undercurrent, which removed most of the silt and mud that made up the original upper slope failure,” observed Ben Kneller, professor from University of Aberdeen and the first keynote speaker of the technical program.
The interactions of deepwater processes are much better understood now than they were a decade ago, but still are poorly resolved due to insufficient data in modern and ancient systems. Several presenters emphasized the need for more spatial and temporal evidence of these mixed systems and their internal and external controlling factors, with better calibration and more accurate measurements.
“New research presented this week in Lisbon shows that mixed systems are not only impacted by oceanographic processes and climatic-eustatic changes, but also by sediment supply variations and tectonics,” said Sara Rodrigues, post-doctoral researcher at Royal Holloway.
“Most oceanographic processes and climatic changes affect the sedimentary processes responsible for their formation directly, whereas tectonics may impact the seafloor morphology, ocean circulation patterns or the nature of the sediment,” added Debora Duarte, post-doctoral researcher at Heriot-Watt University.
By the end of the conference, it became apparent that the energy industry, scientific drilling and monitoring programs, and many other agencies need to combine forces to better understand these processes, their deposits and their increasing importance to the total energy mix. A decade ago, there were relatively few “mixed system” play types, but today, it’s more the rule than the exception in many basins around the world.
“Mixed systems are found now on all continental margins. We need to understand the role of bottom currents and their implications for petroleum systems. It could lead to additional alternatives for the definition of exploration targets and prospect risk assessment,” said François Raisson, exploration adviser for sedimentary systems at TotalEnergies.
Deepwater will be important to watch over the next several decades.
“Multiple sources indicate that deepwater petroleum production will increase an estimated 33 percent over the next decade, suggesting the scenario that deepwater will see the highest growth of any oil and gas asset class in the world,” noted Adriano Viana from Petrobras in his keynote presentation. “The prolific deepwater basins typically recover huge volumes of oil and gas from each well, with strong economic returns and low CO2 emissions intensities relative to most other oil and gas resource theaters. Such characteristics of deepwater plays pave the path for a decarbonization of the energy matrix but imply continuing investment in new upstream oil and gas over the next 30 years.”
Carbon Storage in Deepwater Systems
CCUS was a key theme emerging from the conference.
Presenters Hugo Matias of net4CO2 and Estefanía Llave of IGME elaborated on this topic.
“Contourite and mixed sedimentary systems are typically deposited at depths that place them in a privileged situation for CO2 storage. Moreover, they are comprised of stacks of reservoirs and seals which, if properly combined in a trap, can provide a perfect storage system and play a highly relevant role in the decarbonization process,” said Matias.
“An example about the interest on this topic is the ALGEMAR Spanish project (2023-26), which represents a multidisciplinary project and boasts a close collaboration between the academia and industry, constituting an opportunity to continue the advances in the knowledge of these systems as energy storages and CO2 capture,” said Llave.
These mixed deepwater systems are by no means small. In fact, they can comprise the fill of entire continental margins and contain supergiant oil and gas fields.
Chris Elders from Curtin University emphasized that, “Bottom current activity has affected large parts of the Northwest Shelf of Australia for a period of approximately 100 million years ago from the middle of the Cretaceous to the Oligocene, creating deposits that significantly shape the velocity structure of the overburden and require different drilling approaches when targeting deeper prospects.”
Christophe Serié of AkerBP stated, “Regional and super-regional context is of an essence when trying to understand the interaction between turbidity and bottom currents, as well as the use of regional 3-D seismic data allowing the observation of fine details through spectral decomposition techniques.”
And while “deep” is becoming fashionable in energy exploration, these processes can operate in ultradeep conditions specifically in gaps connecting abyssal plains.
Royal Holloway, University of London doctoral student Tatiana Glazkova observed, “Current intensification through topographic constrictions may lead to sedimentary archives of bottom water exchange between abyssal plains. These archives greatly contribute to our understanding of the regional setting for large areas of the ocean situated at great depth.”
Better Data, Methods for Better Understanding
How will we learn more about these systems in the field? Outcrop and field analogs are critical to understand emerging deepwater mixed system plays. The latest of these plays includes SNE and FAN, Greater Tortue and Ahmeyim, Coral and Mamba, Graaf and several others. Many of these new discoveries are considered giant fields, or greater than 500 million barrels of oil-equivalent recoverable. Promising outcrops that are being studied to learn more about the 3-D architecture of total petroleum systems in mixed deepwater sedimentary systems include those in Cyprus, Morocco, Malaysia, California and Angola.
“The Kwanza Basin from Barra do Dande to Cabo de São Braz, expose excellent outcrops showing mixed systems (contourites and turbidite) processes, analogues to the offshore reservoir architecture,” noted Cirilo Cauxeiro, vice president for scientific affairs and graduate studies at ISPTEC
Nursyazwani Abdul Jalil, geologist at Eliis, presented an insightful outcrop characterization of the Oligo-Miocene Kudat Formation, Malaysia.
“Hybrid bed research is essential to help understand the sedimentological processes and their preservation in the geological record. Additionally, such research aids in the identification of potential new play types, as deepwater exploration gains prominence in Southeast Asia, especially Malaysia,” she said.
Higher resolution regional data are beginning to answer specific questions about the role of mixed systems in the total petroleum system. Andreas Laake, adviser at SLB, who gave two talks in the technical program, introduced a novel method for processing and interpreting seismic data using color processing.
“This method generates realistic images of sedimentary environments in the subsurface with colors that resemble satellite images of the earth surface,” he said.
A team of researchers at the Laboratory on Basin Analysis at Federal University of Paraná are making some of these key advances in seismic interpretation.
“The various seismic studies presented showed us the potential of this approach to understand the geometry and other particular characteristics of each type of deposit in deepwater systems, as well as the temporal and spatial relationship among deepwater deposits, including their interaction and the influence of other geological processes on their formation, such as salt tectonics,” said post-doctoral researcher Mérolyn Camila Naves de Lima Rodrigues. “We saw how integration with data from different scales, such as field data, can help to further illustrate the relationship between the various processes, including the formation of important stratigraphic traps, as demonstrated by Thammy Mottin and collaborators in a study on MTD and turbidite complexes.”
Doctoral student Vanessa Assis noted, “Exceptional quality 3-D seismic data from the Northern Santos Basin (offshore Brazil) has been used to identify different types of deepwater systems over geological time in a relatively small area, providing an opportunity for several studies focusing on specific deposits.”
Graduate student Giovana Rebelo Diório observed, “This conference was an intensive course to open our minds to everything that can be found in deepwater settings, how multiple interactions can happen and how we can identify and address implications of these complex evolutions.”
Higher resolution also extends to sub-bed-scale, which can, in turn, affect reservoir deliverability. Post-doctoral researcher Javier Dorador and Professor F. Rodríguez-Tovar, both at University of Granada in Spain, are pioneers in cutting-edge technology used to evaluate the petrophysical properties of burrowed sedimentary intervals.
“Multi-technique approaches reveal that trace fossils can affect some petrophysical properties either in a positive or negative way, but also can exhibit dual behavior as different parts of the same trace fossil can enhance or degrade reservoir quality,” said Rodriguez-Tovar.
Evolution of Mixed Systems
Capturing change through time was also highlighted by several talks that showed the evolution of mixed system development in discrete stages. Process-modeling experiments, such as those shown in a presentation by Joris Eggenhuisen, professor at University of Utrecht and scientific director of Eurotank Flume Laboratory, have been among the first in the world to test hypotheses in how mixed systems evolve. Eggenhuisen stated,
“Many researchers like myself have previously treated submarine fans with a complete focus on gravity-driven processes. In fact, ocean dynamics and deposits related to bottom currents play an important role in many systems. Now that we have broadened our view, we recognize the need for new, different models to treat mixed systems. Process-modeling can play an important role by supplying and testing these new models, as it has for submarine fans in the past,” he said.
Presenters showed how the scientific and industry communities are exploring deepwater systems in frontier areas with limited seismic and core data to understand new discoveries.
Specific examples illustrated the difficulty of differentiating between extra-basinal gravity flows and intra-basinal bottom-current deposits and suggested that carbonate stable isotope data can be critical in this regard.
“For example, the gradual opening of the Atlantic has promoted increasingly active bottom-current exchange between the polar and equatorial water masses, under the influence of tides, storms and geostrophic ocean currents,” added John Cater of PetroStrat.
Presenters stressed the need for even more tech increases in the areas of acoustic imaging.
“The power of high-resolution 3-D seismic is necessary to visualize the detailed complexity of mixed systems and fluid-flow systems that develop in them, as demonstrated by the pockmarks fields controlled by sediment waves located offshore southwest Portugal. The three-dimensional capacity is critical to understand the migration of seep-controlling seafloor bedforms through time, especially when affected by a mix of deepwater processes,” observed Davide Gamboa, professor at the University of Aveiro.
A Geologic History of Lisbon
The conference concluded with a geological-historical tour of Lisbon led by Gil Machado to understand how its geology has shaped the city, influenced its history, and in two millennia of civilization sculpted Lisbon into what it is today. The tour started downtown, in the “new” part of the city, rebuilt after the 1755 earthquake and built according to newly developed, anti-seismic engineering rules that still apply today.
“We explored the Roman and Moorish heritage in and out of the original city walls that also reflect the building stone available during each historical period. The Portuguese medieval and Renaissance eras were explored in several landmark buildings of the old town, in the heart of this vibrant and evolving city,” said Machado.
Conference delegates enjoyed the program and gained additional insight, knowledge and enthusiasm for exploring deepwater basins over the next 10, 20, even 100 years.
“The AAPG GTW was exceptional. The presentations from basins around the world will have a significant impact on both academic and industry initiatives over the next few decades. There are substantial new findings regarding deepwater mixed systems that defined paradigm changes in deep-marine sedimentation. Deep-marine mixed systems are not only important for economic potential in hydrocarbon exploration, but also necessary for the energy transition,” noted Cahyagempita Putri, geologist with PT Pertamina Hulu Energi. Reagan Africa.
“It was incredible to see how contourites and mixed depositional systems along the South African margin compared to the global examples presented at the conference,” said Anthony Fielies of the Petroleum Agency of South Africa. “The opportunity to interact and converse with geoscientists at the forefront within their respective fields provided crucial insights into hydrocarbon potential and implications for the energy transition. The conference filled us with immense excitement for the future of deepwater exploration and the impact it will have on our home country of South Africa and the African continent as a whole.”