Kathy R. Bruner

Paleokarst and reservoir porosity in the Ordovician Beekmantown Dolomite of the central Appalachian basin

A karst-unconformity play at the top of the Ordovician Beekmantown Dolomite is judged to have great petroleum potential in Ohio and adjacent states; wells have high ultimate reserves and large areas remain untested. To better understand the origin, development, and distribution of Beekmantown porosity, we conducted a petrologic-stratigraphic study of cores and thin sections from 15 oil and gas wells. The massive dolomite, characterized by a hypidiotopic-idiotopic texture, formed by the replacement of stacked peritidal carbonate cycles. Secondary porosity occurs at two scales: (1) mesoscopic—breccia porosity, solution-enlarged fractures, large vugs, and caverns, and (2) microscopic—intercrystalline, intracrystalline, molds, small vugs, and microfractures. Mesoscopic pores (providing the major storage capacity in this reservoir) were produced by intrastratal solution and collapse of carbonate layers, whereas microscopic pores (connecting the larger pores) generally formed by the leaching of individual carbonate grains and crystals. Most pore types developed during periods of subaerial exposure across the carbonate bank, tied to either the numerous, though brief falls of relative sea level during Beekmantown deposition or more importantly the prolonged Knox unconformity at the close of sedimentation. The distribution of reservoir-quality porosity is quite heterogeneous, being confined vertically to a zone immediately below the unconformity and best developed laterally beneath buried hills and noses of this erosion surface. The inferred, shallow flow of ground water in the Beckmantown karst, primarily below topographic highs and above a diagenetic base level close to the water table, led to this irregular distribution of porosity.

Stratigraphic-Tectonic Relations in Spain's Cantabrian Mountains: Fan Delta Meets Carbonate Shelf

ABSTRACT Stratigraphic patterns indicate that the Hercynian orogenic belt of northwestern Spain underwent an important reorganization in the latest Carboniferous Period. The passive margin of the Cantabrian foreland basin, initially far removed from southwestern mountains, was the early site of a major carbonate platform. This distant margin, however, experienced a late phase of deformation directed from the north. Limestones of the passive platform then became the thrust-faulted source area for three successive fan deltas, which prograded across the remaining carbonate shelf. The fan deltas are comprised of conglomerates and coarse sandstones of several areally restricted Upper Carboniferous formations. Their distribution identifies a local subbasin in the Picos de Europa Province, and paleocurrent data confirm a new northern source of sediment. These coarse-grained deposits are interpreted to have formed in direct response to tectonic uplift along a nearby thrust-fault system. The stratigraphic succession spans a 7 Ma interval from latest Moscovian to Late Kasimovian time and defines three separate tectonic episodes: late Myachkovskian (304 Ma), early Chamovnicheskian (300 Ma), and early Dorogomilovskian (298 Ma). Rather than advancing basinward, though, the fan deltas shifted laterally during this period. They become younger in an eastward direction, that is, parallel to the structural grain. The underlying subregional unconformity, likewise related to thrust faulting, also becomes younger to the east. The thrust-fault system apparently propagated laterally by means of three consecutive tectonic episodes, which led in turn to the sideward displacement of sediment source area and fan-delta depocenter.

The Cyborg Astrobiologist: matching of prior textures by image compression for geological mapping and novelty detection

We describe an image-comparison technique of Heidemann and Ritter (2008a, b), which uses image compression, and is capable of: (i) detecting novel textures in a series of images, as well as of: (ii) alerting the user to the similarity of a new image to a previously observed texture. This image-comparison technique has been implemented and tested using our Astrobiology Phone-cam system, which employs Bluetooth communication to send images to a local laptop server in the field for the image-compression analysis. We tested the system in a field site displaying a heterogeneous suite of sandstones, limestones, mudstones and coal beds. Some of the rocks are partly covered with lichen. The image-matching procedure of this system performed very well with data obtained through our field test, grouping all images of yellow lichens together and grouping all images of a coal bed together, and giving 91% accuracy for similarity detection. Such similarity detection could be employed to make maps of different geological units. The novelty-detection performance of our system was also rather good (64% accuracy). Such novelty detection may become valuable in searching for new geological units, which could be of astrobiological interest. The current system is not directly intended for mapping and novelty detection of a second field site based on image-compression analysis of an image database from a first field site, although our current system could be further developed towards this end. Furthermore, the image-comparison technique is an unsupervised technique that is not capable of directly classifying an image as containing a particular geological feature; labelling of such geological features is done post facto by human geologists associated with this study, for the purpose of analysing the systems performance. By providing more advanced capabilities for similarity detection and novelty detection, this image-compression technique could be useful in giving more scientific autonomy to robotic planetary rovers, and in assisting human astronauts in their geological exploration and assessment.

Resource Assessment of the Marcellus Shale

Estimates of gas in place (GIP) for the Marcellus Shale can be calculated from analysis of the organic-rich rock by programmed pyrolysis. The GIP is a function of several factors, including the original hydrocarbon-generation potential of immature shale (S2o) as measured by programmed pyrolysis; a conversion factor (C) to determine the gas-volume equivalent generated by cracking of kerogen, bitumen, and oil; the thickness (t) of organic-rich shale; organic richness (O) compared with a standard sample; the transformation ratio (TR) of kerogen to hydrocarbon; and percent retention (R) of gas after primary migration. In particular, Technically recoverable reserves are computed to be 20% of the GIP. By way of example, our calculated GIP for Steuben County, New York, is 39 bcfg/mi2, and that for Broome County, New York, is 217 bcfg/mi2, a fivefold increase within 100 mi (161 km). Because geologic controls over GIP vary so greatly across the Appalachian Basin, gas resources and reserves should properly be calculated from local geochemical data.