AAPG’s Publishing Legacy Adds New Chapters

AAPG is a science publisher. It’s a tradition that dates back to our founding. And our flagship journal, the BULLETIN, and our special publications are usually a core part of a petroleum geoscientist’s professional library.

Last month was a big one for AAPG science publishing.

AAPG’s associate editors were invited by Elected Editor Steve Laubach to gather in Houston on Feb. 4 to discuss improvements to the BULLETIN’s editorial process, select publication awards and talk about developing a short course for aspiring young authors.

That evening the attendees were inducted into the Charles Taylor Fellowship. The fellowship, named after the BULLETIN’s first editor, Charles H. Taylor, was established by AAPG’s Executive Committee to recognize the vital contributions that all current and former associate editors have made to ensuring that AAPG maintains high standards of published science.

Then on Feb. 7, at a meeting convened by AAPG President Ted Beaumont and SEG President David Monk, my SEG counterpart Steven Davis and I signed a memorandum of understanding for AAPG to join as a partner in the new journal Interpretation.

Interpretation, launched by SEG late last year, is a peer-reviewed quarterly designed to publish papers on the science and practice of interpreting data to better understand Earth’s subsurface, particularly as it relates to the exploration and extraction of resources and for environmental and engineering applications.

This journal fills an important space in science publishing and our participation is the outgrowth of an enhanced and evolving partnership with SEG.

Finally, last month marked the launch of a new BULLETIN feature.

Editor Laubach has been working closely with Beverly Molyneaux, AAPG’s managing editor of technical publications, and Geoscience Director Jim Blankenship to ensure that BULLETIN authors’ manuscripts are published as quickly as possible.

The result is a new website for the BULLETIN and a new feature called Ahead of Print . There you will find manuscripts that have been peer-reviewed and accepted for publication, but have not yet gone through the lay-out and production process.

Ahead of Print gives our members and subscribers the ability to access AAPG science as soon as it’s accepted. This benefits users and is an important step in attracting authors to publish in the BULLETIN.

Ensuring that AAPG remains a relevant and successful science publisher is vital to our long-term objectives. Last month’s activities build upon a strong foundation and position us for the future.

And there are further improvements to come.

I’d like to leave you with one more thought:

Most of us are consumers of the science information published by AAPG. We sift through the online BULLETIN archives and Search and Discovery for papers or presentations that will help us better understand an exploration concept or the geology of a particular region.

That’s great! That’s what these resources are meant to do – to help you do your job better.

But those papers and presentations are only there because someone took the time – usually personal time – to put words on paper, to draft figures and to edit and revise. They probably didn’t do it for fame and fortune (although I wouldn’t dismiss the possibility). Instead they likely saw this contribution as a way to improve their own understanding, to enhance their professional standing and to step into the role of teacher, contributing to the scientific discourse.

They decided to become active participants in advancing our science.

What paper or presentation is locked inside you?

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Director's Corner

Director's Corner - David Curtiss

David Curtiss is an AAPG member and was named AAPG Executive Director in August 2011. He was previously Director of the AAPG GEO-DC Office in Washington D.C.

The Director's Corner covers Association news and industry events from the worldview perspective of the AAPG Executive Director.

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The influence of moisture, temperature, coal rank, and differential enthalpy on the methane (CH4) and carbon dioxide (CO2) sorption capacity of coals of different rank has been investigated by using high-pressure sorption isotherms at 303, 318, and 333 K (CH4) and 318, 333, and 348 K (CO2), respectively. The variation of sorption capacity was studied as a function of burial depth of coal seams using the corresponding Langmuir parameters in combination with a geothermal gradient of 0.03 K/m and a normal hydrostatic pressure gradient. Taking the gas content corresponding to 100% gas saturation at maximum burial depth as a reference value, the theoretical CH4 saturation after the uplift of the coal seam was computed as a function of depth. According to these calculations, the change in sorption capacity caused by changing pressure, temperature conditions during uplift will lead consistently to high saturation values. Therefore, the commonly observed undersaturation of coal seams is most likely related to dismigration (losses into adjacent formations and atmosphere). Finally, we attempt to identify sweet spots for CO2-enhanced coalbed methane (CO2-ECBM) production. The CO2-ECBM is expected to become less effective with increasing depth because the CO2-to-CH4 sorption capacity ratio decreases with increasing temperature and pressure. Furthermore, CO2-ECBM efficiency will decrease with increasing maturity because of the highest sorption capacity ratio and affinity difference between CO2 and CH4 for low mature coals.

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In prospective basins affected by exhumation, uncertainty commonly exists regarding the maximum burial depths of source, reservoir, and seal horizons. One such basin is the Otway Basin, an important gas province in southeastern Australia, which has witnessed several exhumation events. Here, we present estimates of net exhumation magnitudes for 110 onshore and offshore petroleum wells based on the sonic transit time analyses of Lower Cretaceous fluvial shales. Our results show significant post-Albian net exhumation in the eastern onshore Otway Basin (gt1500 m [sim4920 ft]) and a generally minor net exhumation (lt200 m [sim655 ft]) elsewhere in the Otway Basin, consistent with estimates based on thermal history data. The distribution of net exhumation magnitudes in relation to mid-Cretaceous and Neogene compressional structures indicates that exhumation was dominantly controlled by short-wavelength basin inversion driven by plate-boundary forces.

Deeper burial coupled with high geothermal gradients in the onshore eastern Otway Basin and along the northern basin margin during the early Cretaceous have rendered Lower Cretaceous source rocks mostly overmature, with any remaining hydrocarbons from the initial charge likely to be trapped in tightly compacted reservoirs and/or secondary (fracture-related) porosity. However, the embrittlement of these reservoirs during their deeper burial may present opportunities for the development of low-permeability plays through hydraulic fracturing where smectite clay minerals are illitized. Source rocks at near-maximum burial at present day are at temperatures suitable for gas generation, with key controls on prospectivity in these areas including the sealing potential of faulted traps and the relationship between charge and trap development.

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Anomalously high porosities and permeabilities are commonly found in the fluvial channel sandstone facies of the Triassic Skagerrak Formation in the central North Sea at burial depths greater than 3200 m (10,499 ft), from which hydrocarbons are currently being produced. The aim of our study was to improve understanding of sandstone diagenesis in the Skagerrak Formation to help predict whether the facies with high porosity may be found at even greater depths. The Skagerrak sandstones comprise fine to medium-grained arkosic to lithic-arkosic arenites. We have used scanning electron microscopy, petrographic analysis, pressure history modeling, and core analysis to assess the timing of growth and origin of mineral cements, with generation, and the impact of high fluid pressure on reservoir quality. Our interpretation is that the anomalously high porosities in the Skagerrak sandstones were maintained by a history of overpressure generation and maintenance from the Late Triassic onward, in combination with early microquartz cementation and subsequent precipitation of robust chlorite grain coats. Increasing salinity of pore fluids during burial diagenesis led to pore-filling halite cements in sustained phreatic conditions. The halite pore-filling cements removed most of the remaining porosity and limited the precipitation of other diagenetic phases. Fluid flow associated with the migration of hydrocarbons during the Neogene is inferred to have dissolved the halite locally. Dissolution of halite cements in the channel sands has given rise to megapores and porosities of as much as 35% at current production depths.
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The presence of hydrocarbon-bearing sandstones within the Eocene of the Forties area was first documented in 1985, when a Forties field (Paleocene) development well discovered the Brimmond field. Further hydrocarbons in the Eocene were discovered in the adjacent Maule field in 2009. Reservoir geometry derived from three-dimensional seismic data has provided evidence for both a depositional and a sand injectite origin for the Eocene sandstones. The Brimmond field is located in a deep-water channel complex that extends to the southeast, whereas the Maule field sandstones have the geometry of an injection sheet on the updip margin of the Brimmond channel system with a cone-shape feature emanating from the top of the Forties Sandstone Member (Paleocene). The geometry of the Eocene sandstones in the Maule field indicates that they are intrusive and originated by the fluidization and injection of sand during burial. From seismic and borehole data, it is unclear whether the sand that was injected to form the Maule reservoir was derived from depositional Eocene sandstones or from the underlying Forties Sandstone Member. These two alternatives are tested by comparing the heavy mineral and garnet geochemical characteristics of the injectite sandstones in the Maule field with the depositional sandstones of the Brimmond field and the Forties sandstones of the Forties field.

The study revealed significant differences between the sandstones in the Forties field and those of the Maule and Brimmond fields), both in terms of heavy mineral and garnet geochemical data. The Brimmond-Maule and Forties sandstones therefore have different provenances and are genetically unrelated, indicating that the sandstones in the Maule field did not originate by the fluidization of Forties sandstones. By contrast, the provenance characteristics of the depositional Brimmond sandstones are closely comparable with sandstone intrusions in the Maule field. We conclude that the injectites in the Maule field formed by the fluidization of depositional Brimmond sandstones but do not exclude the important function of water from the huge underlying Forties Sandstone Member aquifer as the agent for developing the fluid supply and elevating pore pressure to fluidize and inject the Eocene sand. The study has demonstrated that heavy mineral provenance studies are an effective method of tracing the origin of injected sandstones, which are increasingly being recognized as an important hydrocarbon play.

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We present a method of using fault displacement-distance profiles to distinguish fault-bend, shear fault-bend, and fault-propagation folds, and use these insights to guide balanced and retrodeformable interpretations of these structures. We first describe the displacement profiles associated with different end-member fault-related folding models, then provide examples of structures that are consistent with these model-based predictions. Natural examples are imaged in high-resolution two- and three dimensional seismic reflection data sets from the Niger Delta, Sichuan Basin, Sierras Pampeanas, and Cascadia to record variations in displacement with distance updip along faults (termed displacement-distance profiles). Fault-bend folds exhibit constant displacement along fault segments and changes in displacement associated with bends in faults, shear fault-bend folds demonstrate an increase in displacement through the shearing interval, and fault-propagation folds exhibit decreasing displacement toward the fault tip. More complex structures are then investigated using this method, demonstrating that displacement-distance profiles can be used to provide insight into structures that involve multiple fault-related folding processes or have changed kinematic behavior over time. These interpretations are supported by comparison with the kinematics inferred from the geometry of growth strata overlying these structures. Collectively, these analyses illustrate that the displacement-distance approach can provide valuable insights into the styles of fault-related folding.

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