Lacustrine basin hydrocarbon exploration – current thoughts

Although much of the world's petroleum resource-base is associated with marine systems, regionally lacustrine petroleum systems are important. Individual accumulations may exceed several billion barrels. In each of these cases the oil is derived from a lacustrine source rock and may be produced from either nonmarine or marine reservoir rocks. The purpose of this paper is to describe the factors that control lacustrine source rock development and the nature of lacustrine reservoirs. Lacustrine oils display different physical and chemical characteristics than their marine counterparts. These differences can be related to the nature of their precursor material. Although the nature of the products are different, the geochemical threshold criteria for defining source rocks in both settings are the same because of common expulsion requirements. Commercially significant lacustrine systems require the presence of large, long-lived lakes. Such lake settings are tectonic in origin and restricted to climatic settings where precipitation exceeds evaporation. Within these large lake systems three primary factors determine source rock potential and quality. These factors are primary productivity level, organic preservation potential, and matrix sedimentation rate, which controls the dilution of preserved organic matter. Source rock potential is maximized where both productivity and preservation potential are maximized and sedimentation rate is minimized. To some degree these factors can compensate for each other. Hydrocarbon reservoir potential within lacustrine basins is partially impacted by overall tectonic setting. Within extensional settings, transport distances tend to be limited, with much of the sediment being transported away from the basin. The sediments delivered to the lake are poorly sorted and sedimentologically immature, commonly resulting in poor reservoirs due to both primary properties and their susceptibility to diagenesis. Within rifts better reservoirs tend to develop along platform or flexural margins. Stacking of reservoirs is important in lacustrine systems but baffles and barriers are often present between individual sand units. These barriers form as a result of lake level fluctuations. In compressional settings transport distances tend to be longer, resulting in more mature, better sorted sediments leading to higher quality reservoirs. These reservoirs typically develop in fluvial-deltaic and wave-dominated shoreline settings. Lacustrine carbonate reservoirs are locally important. These carbonates tend to develop during lake level lowstands and are dependent on diagenesis (dissolution and karstification) for porosity and permeability development. Lacustrine reservoirs are often stratigraphically and areally limited and display low individual well production rates. Within pure lacustrine systems exploration opportunities appear to be often restricted by either reservoir presence or quality (i.e., production rates). The best exploration opportunities in lacustrine basins appear to be associated with hybrid systems where a lacustrine source and marine reservoir exist.     

Parameterization of Ozone Photolysis Frequency in the Lower Troposphere Using Data from Photodiode Array Detector Spectrometers

Spectroradiometers using photodiode array detectors (PDAs) are increasingly applied for airborne and ground-based atmospheric measurements of spectral actinic flux densities due to their high time resolution (less than one second). However they have limited sensitivity of ultraviolet (UV) radiation for wavelengths less than about 305 nm. This results in uncertainties of ozone photolysis frequencies derived from spectral actinic flux density measurements using PDA spectrometers. To overcome this limitation a parameterization method is introduced which extrapolates the data towards the wavelength range of limited sensitivity of the PDA spectrometers (less than about 305 nm). The parameterization is based on radiative transfer simulations and is valid for measurements in the lower troposphere. The components of the suggested parameterization are the lower threshold wavelength of the PDA spectrometer, the slant ozone column (ratio of the total ozone column and the cosine of the solar zenith angle), and the ambient temperature. Tests of the parameterization with simulated actinic flux density spectra have revealed an uncertainty of the derived ozone photolysis frequency of ±5%. Field comparisons of the parameterization results with independent measurements of the ozone photolysis frequency were within ±10% for solar zenith angles less than 70^∘. Finally the parameterization was applied to airborne measurements to emphasize the advantage of high time resolution of PDA spectrometers to study ozone photolysis frequency fields in inhomogeneous cloud condtitions.     

Low‐temperature thermochronology of francolite: Insights into timing of Dead Sea Transform motion

Cambrian siliciclastic sequences along the Dead Sea Transform (DST) margin in southern Israel and southern Jordan host both detrital fluorapatite [D‐apatite] and U‐rich authigenic carbonate‐fluorapatite (francolite) [A‐apatite]. D‐apatite and underlying Neoproterozoic basement apatite yield fission‐track (FT) data reflecting Palaeozoic–Mesozoic sedimentary cycles and epeirogenic events, and dispersed (U–Th–Sm)/He (AHe) ages. A‐apatite, which may partially or completely replace D‐apatite, yields an early Miocene FT age suggesting formation by fracturing, hydrothermal fluid ascent and intra‐strata recrystallisation, linked to early DST motion. The DST, separating the African and Arabian plates, records ~105 km of sinistral strike‐slip displacement, but became more transtensional post‐5 Ma. Helium diffusion measurements on A‐apatite are consistent with thermally activated volume diffusion, indicating Tc ~52 to 56 ± 10°C (cooling rate 10°C/Ma). A‐apatite AHe data record Pliocene cooling (~35 to 40°C) during the transtensional phase of movement. This suggests that timing of important milestones in DST motion can be discerned using A‐apatite low‐temperature thermochronology data alone.     

The Ultimate CCD for Laser Guide Star Wavefront Sensing on Extremely Large Telescopes

All of the extremely large telescopes (ELTs) will utilize sodium laser guide star (LGS) adaptive optics (AO) systems. Most of these telescopes plan to use the Shack-Hartmann approach for wavefront sensing. In these AO systems, the laser spots in subapertures at the edge of the pupil will suffer from spot elongation due to the 10 km extent of the sodium layer and the large separation from the projection laser. This spot elongation will severely degrade the performance of standard geometry wavefront sensing systems. In this paper, we present a CCD with custom pixel morphology that aligns the pixels of each subaperture with the radial extension of the LGS spot. This CCD design will give better performance than a standard geometry CCDs for continuous wave lasers. In addition, this CCD design is optimal for a pulsed sodium laser. The pixel geometry enables each subaperture to follow a laser pulse traversing the sodium layer, providing optimal sampling of a limited number of detected photons. In addition to novel pixel layout, this CCD will also incorporate experimental JFET sense amplifiers and use CMOS design approaches to simplify the routing of biases, clocks and video output. This CCD will attain photon-noise limited performance at high frame rates, and is being incorporated in the plans for the Thirty Meter Telescope (TMT).     

Alaska as a site for high duty-cycle solar observations

The day/night cycle at a single observatory prevents definitive observations of many aspects of solar activity, convection, and oscillations with timescales near 1 day. Solutions to this problem include multi-site networks, spacecraft observatories, and observations from high-latitude sites during their summer season. We report here on our experience in using Alaska as a high-latitude site for observations of solar oscillations.     

The what?

Environmental Geology -     

Isotopic study of alluvial groundwaters,south-west lockyer valley,queensland, australia

The isotopic chemistry of alluvial groundwaters from two adjacent valleys are described and hydrological processes within related aquifers are identified as evidenced by oxygen-¹⁸, deuterium, tritium and chloride data. A plot of δ¹⁸O against δD values reveals isotopic enrichment of the groundwater by the recycling of spray irrigation water. A plot of tritium versus chloride concentrations displays separate linear correlations for alluvial groundwaters within the two valleys. The salinity has a common source, therefore the separate correlations are interpreted as the past transfer of low salinity groundwater from the alluvial aquifers in one valley to the underlying sandstone aquifers.     

Earthquake prediction: a new physical basis

Summary. Subcritical crack growth in the laboratory occurs slowly but progressively in solids subjected to low stresses at low strain rates. The cracks tend to grow parallel to the maximum compressive stress so that, when this stress is aligned over a large enough region, the cracks will also be aligned and possess effective seismic anisotropy. It is suggested that such subcritical crack growth produces extensive-dilatancy anisotropy (EDA) throughout earth-quake preparation zones. This process is a possible driving mechanism for earthquake precursors observed at substantial distances from impending focal zones, and provides, in the shear-wave splitting which has been observed in several seismic regions, a possible technique for monitoring the build-up of stress before earthquakes.     

Accuracy of tretyakov precipitation gauge: Result of wmo intercomparison

The Tretyakov non-recording precipitation gauge has been used historically as the official precipitation measurement instrument in the Russian (formerly the USSR) climatic and hydrological station network and in a number of other European countries. From 1986 to 1993, the accuracy and performance of this gauge were evaluated during the WMO Solid Precipitation Measurement Intercomparison at 11 stations in Canada, the USA, Russia, Germany, Finland, Romania and Croatia. The double fence intercomparison reference (DFIR) was the reference standard used at all the Intercomparison stations in the Intercomparison. The Intercomparison data collected at the different sites are compatible with respect to the catch ratio (measured/DFIR) for the same gauge, when compared using mean wind speed at the height of the gauge orifice during the observation period. The Intercomparison data for the Tretyakov gauge were compiled from measurements made at these WMO intercomparison sites. These data represent a variety of climates, terrains and exposures. The effects of environmental factors, such as wind speed, wind direction, type of precipitation and temperature, on gauge catch ratios were investigated. Wind speed was found to be the most important factor determining the gauge catch and air temperature had a secondary effect when precipitation was classified into snow, mixed and rain. The results of the analysis of gauge catch ratio versus wind speed and temperature on a daily time step are presented for various types of precipitation. Independent checks of the correction equations against the DFIR have been conducted at those Intercomparison stations and a good agreement (difference less than 10%) has been obtained. The use of such adjustment procedures should significantly improve the accuracy and homogeneity of gauge-measured precipitation data over large regions of the former USSR and central Europe.     

The observed intermediate-degreef-mode eigenfrequency spectrum of the sun and tests of the mode classification proficiency

Power spectra of the 1979 solar differential observations (Bos, 1982) have been analyzed for evidence of intermediate-degreef-modes. A set of 19 intermediate-degreef-mode multiplets has been identified and classified based on more than 300 classified modes of oscillation. The angular degree of the multiplets ranges from 18 to 36. Them=0 eigenfrequency spectrum, measured with an accuracy of typically 0.01–0.02 Hz, was found to be on the average 10 Hz greater than that predicted by the standard solar model of Saio (1982). Rotational splitting effects up to fifth order inm were obtained. The multiplet fine structure that is linear inm was found to be consistent with the internal rotation curve obtained by Hillet al. (1986a). The multiplet fine structure that is described by terms that are cubic and fifth order inm were found to be consistent with the differential rotation curve of Hillet al. (1986b). The probability that this set of 19 Zeeman-like frequency patterns were obtained from a set of peaks randomly distributed in frequency was estimated to be 10^–9. The effectiveness of the mode detection and classification program in this work has been established in part by observing the horizontal spatial properties of thef-mode eigenfunctions. One consequence obtained from the study of the horizontal spatial properties of the modes is the estimate, obtained observationally, of the number of correct mode identifications: these results indicate that 73±6% of the 374 modes are correctly classified.SCLERA is an acronym for Santa Catalina Laboratory for Experimental Relativity by Astrometry, a facility operated by the University of Arizona.