Geosciences

Rising heat As explorers, we focus on sedimentary basins and don't often look beyond their limits for the causes of their formation.

Victor Schmidt • Houston

Rising heat

As explorers, we focus on sedimentary basins and don't often look beyond their limits for the causes of their formation. Plate tectonics govern our thinking of how the continents move and warp to form sedimentary basins, but the driver of the process is still under debate.

Many researchers theorize that mantle plumes drive the process. A recent article in Science reported progress in our understanding of the Earth's inner dynamics. Raffaella Montelli of Princeton University and five co-authors used finite frequency processing to generate wave front travel paths of earthquake signals rather than the traditional ray path approach. This gave a better image of smaller interior Earth structures from which the team identified 32 mantle plumes.

What is even more interesting is that the plumes begin at varying depths within the Earth. The plumes begin as shallow as 660 km, but a few come from the core at 2,900 km. A more complete understanding of the Earth's interior processes will help unravel the history of tectonic movement and basin formation around the world.

Fluid integration

The oil industry continues to squeeze costs and increase productivity with the goal of creating a seamless flow of goods and services, while generating a profit from its operations. The equipment, data, and people flows are maximized when the constituent parts are available at commodity prices, just like the industry's hydrocarbon products.

Consider the term fluid in its widest context:

  • Equipment use is a flow of goods that are ultimately connected
  • Data is a stream of packeted information that is aggregated for a purpose
  • Ideas or theories integrate to explain the world in a consistent way.

Great strides have been made in getting oilfield equipment from different manufacturers to integrate smoothly. Hardware standards rule strength and connectedness. Plumbing specs make up a large part of the rules for confinement and storage of oil and gas. Oilfield hardware is a commodity, and the integration work, while specialized, is a global commodity.

Data integration is complex and ephemeral. Data types and standards vary widely depending on the "data fluid" needed for a task. For many uses, commodity data is available (including 3D seismic). But to be useful, data must be in the right format and be presented in a common space so that the interpreter/manager can extract meaning from differing data types. Visualization systems are the preferred integration tool. The flow of data is both expanding and becoming cheaper on a unit basis. Data is a global commodity.

Likewise, the integrated flow of ideas forms the basis for the oil professions. The ideas do not require a specific standard (except the human brain), but they must fit into a wider intellectual construct to solve a problem, e.g., geoscience for understanding the Earth, its physical systems, and their interactions.

Every generation or so, a major paradigm shift occurs in our intellectual constructs, which creates significant change and adds greater value to the profession. While ideas are infinite in number and costless – a commodity – specific ideas that alter the intellectual construct and create great value are unique and therefore priceless.

One recent example is from offshore West Africa. The operator and partner drilled several wells based on traditional structural concepts and encountered only non-commercial hydrocarbons. The partner sold his interest, leaving the operator to carry on. A rethinking of the regional sedimentation led to a new play concept for the area – stratigraphic trapping in buried submarine canyons. The first well drilled on this concept was successful, and the operator has identified eight more canyons to test.

The business of business is to lower cost and increase value. The business of petroleum geoscientists is to create ideas for finding oil and gas. Unique ideas are the only place that a geoscientist can rise above commodity pricing and add value for the company.

Shelf-margin deltas

The challenge of developing a sophisticated understanding of sediment deposition from the continental shelf into the deeper basin inspired "Shelf margin deltas and linked down slope petroleum systems – Global significance and future exploration potential," the 23rd Gulf Coast Section of the Society of Economic Paleontologists and Mineralogists Conference held recently in Houston. Organized annually by the GCSSEPM, this meeting focused on questions of immediate concern to petroleum explorers. The conference examined deltaic depositional systems from around the world, but most talks dealt with exploration studies of northern Gulf of Mexico producing trends.

The dynamics of marine deposition still hold many mysteries because the processes are immediately responsive to changes in sea level and sediment flux. Understanding the sediment pathways and the dynamics of sand transport and deposition are key to finding new clastic reservoirs for oil and gas.

Several themes were considered throughout the three-day event:

  • Sediment supply – Studies show that climate change has only a minor effect on sediment yield. Yield is tied to the tectonic system and topographic/bathymetric relief
  • Sediment transport – Two models were proposed: "vacuum cleaner" and "conveyor belt" movement of material. The difference is best seen at lowstand sea levels
  • Sequence boundaries – The location of a sequence boundary significantly alters the expectation of sediment supply for a given shelf margin delta. Lowstand systems are thought to hold more sand
  • Sediment loading – In basins with active salt, the interaction between ponded and perched sediment helps the interpreter understand sediment-loading effects versus space accommodation (salt or fault movement) in complex terrains.

The focus of exploration is shifting, moving down the continental slope and onto the abyssal plain. It is also moving into deeper and older sediments where the rock systems are less well known. New reservoirs can be found, by closely examining younger shelf-margin delta systems, sedimentation, and its interaction with other forces.

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