Comparing the results of lineament analysis with isotope geochemistry data

This article presents the results of a geochemical survey carried out in the southwestern part of the Siberian platform, within the Sayan-Yenisei (Angara) syneclise (a superorder Riphean-Middle Paleozoic structure). The object of research was hydrocarbon gases contained in the subsoil rocks (clays). The subsoil samples were taken from the bottom of boreholes (40 mm in diameter) made with an electric drill. The sampling depth was 0.6–1 m. Further laboratory studies included chromatographic and isotope analysis. Lineament analysis of the digital elevation model was carried out as a complementary study. One of the lineament analysis results was a lineament density map, which reflects the permeability (macro-fracture density) of the sedimentary cover. This allowed a comparison of the macro-fracture density with the gas content and isotopic composition. The study revealed that gases with a high content of heavy isotopes tend to gather in the low permeability areas. This can be explained by the fact that the gases disperse quickly within fractured zones, and deep gases should be expected only in the areas with strong cap rocks, i.e. in the areas with low macrofracture density where stable hydrocarbon deposits have already formed. Keywords: hydrocarbons; geochemical survey; isotope geochemistry; lineament analysis.

Results of reinterpretation of marine geochemical survey on the Sakhalin shelf

Geochemical survey of hydrocarbons (HC) all over the world is a reliable tool of the complex of geological exploration, which allows to localize hydrocarbon saturation in structures exposed by seismic exploration, as well as to identify non-structural deposits. In 2011, a marine geochemical survey of the sorbed gases of bottom sediments was carried out on the shelf section of the northwest of Sakhalin Island. Based on the results of geochemical studies, 12 maps of the distribution of hydrocarbon and non-hydrocarbon gases in the work area and 7 maps of the distribution of metals in bottom sediments were constructed. Promising areas were distinguished by anomalies with the maximum content of parameters. The research area is characterized by a complex structure, located within the Baikal synclinal zone of the North Sakhalin oil and gas basin, which is part of the rift system of the Cenozoic sedimentary basins the Sea of Okhotsk. In 2019, the authors began to re-process and reinterpret the data in order to clarify the results. The work was based on modern theoretical foundations and methodological approaches of oil and gas prospecting geochemistry. The interpretation of the results was carried out on the basis of the model of interpretation of geochemical anomalies developed by the authors. Maps of anomalies were constructed according to 11 geochemical criteria and two geological and geochemical sections. The complex interpretation of geological and geochemical data was carried out taking into account the results of seismic exploration and drilling in a single project. According to the results of the complex interpretation, 6 promising sites were identified, which are ranked according to the degree of prospects.

Microseepage through Evaporite Sequences – a Gulf of Suez Example

Salt is one of the most effective agents for trapping oil and gas. As a ductile material it can move and deform surrounding sediments and create traps. However, effective sealing of reservoirs for movement of hydrocarbons along breaching faults or fracture swarms (i.e. macroseepage) is a completely different mechanism than the molecular movement of hydrocarbons through grain boundaries and microfractures as found in microseepage. Forum Exploration chose to evaluate the applicability of passive surface geochemistry for mapping hydrocarbons in their onshore West Gebel El Zeit lease due to difficulties in seismic imaging through salt and anhydrites sequences. Two economic producing wells had been drilled in the lease, but due to compartmentalization and complexity in the area, three dry wells had also been drilled. Target formations included the Kareem Formation at ∼2,700 m and the Rudeis Formation at ∼3,000 m.The geochemical survey encompassed 100 passive geochemical modules. Passive samplers were also deployed around two producing wells and one dry well. Calibration data generated positive thermogenic signatures around the two producing wells in contrast to the background or baseline signature developed around the dry well. The Rudeis Formation calibration signature ranged from ∼nC5 - ∼nC9 while the Kareem Formation calibration signature ranged from ∼nC6 – nC12. This suggested the Rudeis calibration signature was lighter than the Kareem. This correlated with independent API gravity testing on produced oil samples (41o API gravity oil for the Rudeis, 35o API gravity oil for the Kareem).A post-survey well, Fh85-8, was drilled based on combined geochemical and seismic data results. The well was an oil discovery, with initial production of 800 BOPD. The evidence presented in this Gulf of Suez example shows that microseepage can occur through salt sequences. As such, ultrasensitive passive surface geochemical surveys provide a powerful tool for derisking salt plays.

One’s soil is another one’s regolith – let’s combine our efforts in investigating the critical zone

<p>Earth observation is invaluable for the agricultural sector as well as the critical metals sector, providing cost-effective, spatially comprehensive information about Earth’s surface composition from the regional to paddock/mine-scale. A wide range of remote sensing instruments are used to monitor soils, to give information on properties such as moisture and mineralogy. At the same time, remote sensing data facilitate the discovery and mining of mineral deposits, including iron ore, copper and other metals critical for the transition of the fossil fuel-based energy sector to a sustainable, renewable energy future. One common factor of these two sectors is that all Earth observation systems require calibration sites that help to ensure the data being collected is of high accuracy. Another common factor is that both sectors require ground validation of the remotely sensed data, producing a plethora of publicly available Earth surface data distributed across numerous web portals and platforms. Both sectors aim, ultimately, towards characterising the composition of the subsurface - which starts in both sectors at Earth’s surface and reaches to 10s or even 100s of metres below. This can be achieved by developing conceptual models that describe the weathering of bedrock in the soil/regolith. In mineral resource exploration, specific weathering-resistant minerals (e.g. talc) can be traced at Earth’s surface by means of Earth observation to characterise the type of bedrock through cover (i.e. beneath the soil/regolith). Another example is the mapping of differences in kaolin crystallinity at Earth’s surface and in the subsurface (e.g. drilling, trenches) to infer the distribution of in-situ versus transported regolith, which is of key importance for raw materials exploration. Remote sensing is also commonly used for collecting baseline environmental data prior to mining and for monitoring its impact on the environment during and after the process. In soil science, infrared spectral measurements have been conducted on soil samples in laboratories for estimation of soil properties, such as soil carbon, pH, EC. These estimations require a training library as well as standardised preparation of the samples and measurement technique. The ultimate goal is the accurate measurement of these soil properties using remote sensing, where complex variance of the nature of the materials and illumination conditions exists.  </p><p>This paper discusses opportunities for sharing facilities, data, workflows and methods for collecting, processing and interpreting remote and proximal multi- and hyperspectral sensing technologies. For this, publicly available mineralogical and geochemical data sets collected from the critical zone, such as in the frame of the National Geochemical Survey of Australia (NGSA; https://www.ga.gov.au/about/projects/resources/national-geochemical-survey) project and AuScope’s National Virtual Core Library Infrastructure Program (NVCL; https://www.auscope.org.au/nvcl), as well as publicly available Earth observation products, such as the Australian ASTER Geoscience Products, will be used to demonstrate the multidisciplinary applications of multi- and hyperspectral remote and proximal sensing data. For the benefit of meeting the United Nations’ Sustainable Development Goals, agriculture, resources and environment sectors should overcome unnecessary competition and work hand in hand.</p>