GOM Operations Enter New Era

President Dave Rensink, speaking at the recent AAPG International Conference and Exhibition in Calgary. About 2,300 people registered. Watch the November EXPLORER for a full report.
President Dave Rensink, speaking at the recent AAPG International Conference and Exhibition in Calgary. About 2,300 people registered. Watch the November EXPLORER for a full report.

BP’s Macondo well has been plugged using top-kill techniques, and the oil on the surface of the Gulf of Mexico is dissipating faster than many had predicted. The oil flow has stopped and the well has been sealed. This is very good news.

You probably have heard all that you want to hear about this tragedy, but the collateral effects of the blowout are not over by any means.

BP has retrieved the blowout preventer stack (BOP) and, we can all hope, has determined why the last line of defense did not work.

The surface analysis of the BOP failure may prompt design changes in the BOP system, but it almost certainly will lead to new regulations on testing, maintenance and composition of the blowout preventer stacks in both deep and shallow water. We can expect to see any proposed changes for the Gulf of Mexico ultimately implemented worldwide.

I hope this catastrophe will be as close to a worst-case scenario as we will ever see.

As unfortunate as this has been, it has created a laboratory from which we will be able to answer two questions we were only able to speculate about previously:

  • What are the long-term effects of such a catastrophe?
  • How quickly will the ecosystem recover?

The answers to these questions will have great impact on future environmental assessment requirements for leasing.

The catastrophe also has raised questions regarding our ability to respond quickly and effectively to the pollution caused by a major oil blowout in the Gulf of Mexico. It probably is more correct to say that it has exposed our inability to effectively respond to a spill of this magnitude.

Chevron, ConocoPhillips, ExxonMobil and Shell should be commended on their plans to deploy a rapid response system to contain oil from any future blowout.

The moratorium on GOM deepwater drilling made sense immediately after the Macondo blowout while safety inspections were conducted. It makes less sense to carry it through to its November termination, since any safety deficiencies discovered have been corrected (see Washington Watch). The administration has stated the moratorium will not last a day longer than it deems necessary.

Even in November, there is no guarantee that the moratorium will not be extended; nor is there any certainty that new drilling permits will be issued in a reasonable time frame after the moratorium expires for drilling to resume quickly.

Based on the observations that very few deepwater rigs have left the Gulf of Mexico for international assignments and the changes in international rig counts have been minor, the GOM deepwater moratorium seems to have had a global impact. That likely is an over simplification. Most GOM operators and drilling companies have taken a wait and see attitude, and the decision to deploy their resources to international deepwater basins may not be made until later this year.

The issuance of few drilling permits for new locations on the GOM shelf since the blowout has essentially created a de facto drilling moratorium in the entire Gulf of Mexico. Operators report the only drilling permits currently being issued are those that involve sidetracking existing well bores.

This premise of a de facto moratorium is re-enforced by the cancellation of the western GOM lease sale originally scheduled for August.

In addition, there no longer is any support for leasing in the eastern GOM, off the Atlantic coast or off the California coast.

The spill is history and so is easy access to public lands – at least in the near term. Many of you would argue that we have never had “easy access” to public lands. That may be true, but whatever level of access existed in the past has gotten more difficult.

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President's Column - David G. Rensink

David G. Rensink, AAPG President (2010-11), is a consultant out of Houston. He retired from Apache Corp in 2009.

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Alternative Resources, Structure, Geochemistry and Basin Modeling, Sedimentology and Stratigraphy, Geophysics, Business and Economics, Engineering, Petrophysics and Well Logs, Environmental, Geomechanics and Fracture Analysis, Compressional Systems, Salt Tectonics, Tectonics (General), Extensional Systems, Fold and Thrust Belts, Structural Analysis (Other), Basin Modeling, Source Rock, Migration, Petroleum Systems, Thermal History, Oil Seeps, Oil and Gas Analysis, Maturation, Sequence Stratigraphy, Clastics, Carbonates, Evaporites, Seismic, Gravity, Magnetic, Direct Hydrocarbon Indicators, Resource Estimates, Reserve Estimation, Risk Analysis, Economics, Reservoir Characterization, Development and Operations, Production, Structural Traps, Oil Sands, Oil Shale, Shale Gas, Coalbed Methane, Deep Basin Gas, Diagenetic Traps, Fractured Carbonate Reservoirs, Stratigraphic Traps, Subsalt Traps, Tight Gas Sands, Gas Hydrates, Coal, Uranium (Nuclear), Geothermal, Renewable Energy, Eolian Sandstones, Sheet Sand Deposits, Estuarine Deposits, Fluvial Deltaic Systems, Deep Sea / Deepwater, Lacustrine Deposits, Marine, Regressive Deposits, Transgressive Deposits, Shelf Sand Deposits, Slope, High Stand Deposits, Incised Valley Deposits, Low Stand Deposits, Conventional Sandstones, Deepwater Turbidites, Dolostones, Carbonate Reefs, (Carbonate) Shelf Sand Deposits, Carbonate Platforms, Sebkha, Lacustrine Deposits, Salt, Conventional Drilling, Directional Drilling, Infill Drilling, Coring, Hydraulic Fracturing, Primary Recovery, Secondary Recovery, Water Flooding, Gas Injection, Tertiary Recovery, Chemical Flooding Processes, Thermal Recovery Processes, Miscible Recovery, Microbial Recovery, Drive Mechanisms, Depletion Drive, Water Drive, Ground Water, Hydrology, Reclamation, Remediation, Remote Sensing, Water Resources, Monitoring, Pollution, Natural Resources, Wind Energy, Solar Energy, Hydroelectric Energy, Bioenergy, Hydrogen Energy
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See Also: Bulletin Article

This article addresses the controls exerted by sedimentologic and diagenetic factors on the preservation and modification of pore-network characteristics (porosity, pore types, sizes, shapes, and distribution) of carbonates belonging to the Bolognano Formation. This formation, exposed at the Majella Mountain, Italy, is composed of Oligocene–Miocene carbonates deposited in middle- to outer-ramp settings. The carbonates consist of (1) grainstones predominantly composed of either larger benthic foraminifera, especially Lepidocyclina, or bryozoans; (2) grainstones to packstones with abundant echinoid plates and spines; and (3) marly wackestones to mudstones with planktonic foraminifera.

The results of this field- and laboratory-based study are consistent with skeletal grain assemblages, grain sizes, sorting, and shapes, all representing the sedimentologic factors responsible for high values of connected primary macroporosity in grainstones deposited on the high-energy, middle to proximal outer ramp. Cementation, responsible for porosity reduction and overall macropore shape and distribution in grainstones to packstones deposited on the intermediate outer ramp, was mainly dependent on the following factors: (1) amount of echinoid plates and spines, (2) grain size, (3) grain sorting and shapes, and (4) clay amount. Differently, in the wackestones to mudstones, laid down on the low-energy, distal outer ramp, matrix is the key sedimentologic factor responsible for low values of scattered macroporosity and dominance of microporosity. The aforementioned results may be useful to improve the prediction of reservoir quality by means of mapping, simulating, and assessing individual carbonate facies with peculiar pore-network characteristics.

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Thus far, the subject of deep-marine sands emplaced by baroclinic currents associated with internal waves and internal tides as potential reservoirs has remained an alien topic in petroleum exploration. Internal waves are gravity waves that oscillate along oceanic pycnoclines. Internal tides are internal waves with a tidal frequency. Internal solitary waves (i.e., solitons), the most common type, are commonly generated near the shelf edge (100–200 m [328–656 ft] in bathymetry) and in the deep ocean over areas of sea-floor irregularities, such as mid-ocean ridges, seamounts, and guyots. Empirical data from 51 locations in the Atlantic, Pacific, Indian, Arctic, and Antarctic oceans reveal that internal solitary waves travel in packets. Internal waves commonly exhibit (1) higher wave amplitudes (5–50 m [16–164 ft]) than surface waves (lt2 m [6.56 ft]), (2) longer wavelengths (0.5–15 km [0.31–9 mi]) than surface waves (100 m [328 ft]), (3) longer wave periods (5–50 min) than surface waves (9–10 s), and (4) higher wave speeds (0.5–2 m s–1 [1.64–6.56 ft s–1]) than surface waves (25 cm s–1 [10 in. s–1]). Maximum speeds of 48 cm s–1 (19 in. s–1) for baroclinic currents were measured on guyots. However, core-based sedimentologic studies of modern sediments emplaced by baroclinic currents on continental slopes, in submarine canyons, and on submarine guyots are lacking. No cogent sedimentologic or seismic criteria exist for distinguishing ancient counterparts. Outcrop-based facies models of these deposits are untenable. Therefore, potential exists for misinterpreting deep-marine baroclinic sands as turbidites, contourites, basin-floor fans, and others. Economic risks associated with such misinterpretations could be real.
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See Also: DL Abstract

In his classic 1965 GSA Bulletin paper “Origin of ‘Reverse Drag’ on the Downthrown Side of Normal Faults” Hamblin presented a conceptual model linking the formation of reverse drag (the down-warping of hanging wall strata toward a normal fault) to slip on faults with listric (curved, concave up) cross-sectional profiles. Although this model has been widely accepted, some authors have noted that reverse drag may also form in response to slip on planar faults that terminate at depth. A universal explanation for the origin of reverse drag, a common element of extensional terranes, thus remains elusive almost 50 years after Hamblin’s seminal paper on the subject.

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