Mineralogical Mapping with Accurately Corrected Shortwave Infrared Hyperspectral Data Acquired Obliquely from UAVs

While uncrewed aerial vehicles are routinely used as platforms for hyperspectral sensors, their application is mostly confined to nadir imaging orientations. Oblique hyperspectral imaging has been impeded by the absence of robust registration and correction protocols, which are essential to extract accurate information. These corrections are especially important for detecting the typically small spectral features produced by minerals, and for infrared data acquired using pushbroom sensors. The complex movements of unstable platforms (such as UAVs) require rigorous geometric and radiometric corrections, especially in the rugged terrain often encountered for geological applications. In this contribution we propose a novel correction methodology, and associated toolbox, dedicated to the accurate production of hyperspectral data acquired by UAVs, without any restriction concerning view angles or target geometry. We make these codes freely available to the community, and thus hope to trigger an increasing usage of hyperspectral data in Earth sciences, and demonstrate them with the production of, to our knowledge, the first fully corrected oblique SWIR drone-survey. This covers a vertical cliff in the Dolomites (Italy), and allowed us to distinguish distinct calcitic and dolomitic carbonate units, map the qualitative abundance of clay/mica minerals, and thus characterise seismic scale facies architecture.

Seismic-Scale Evidence of Thrust-Perpendicular Normal Faulting in the Western Outer Carpathians, Poland

Based on the interpretation of 2D seismic profiles integrated with surface geological investigations, a mechanism responsible for the formation of a large scale normal fault zone has been proposed. The fault, here referred to as the Rycerka Fault, has a predominantly normal dip-slip component with the detachment surface located at the base of Carpathian units. The fault developed due to the formation of an anticlinal stack within the Dukla Unit overlain by the Magura Units. Stacking of a relatively narrow duplex led to the growth of a dome-like culmination in the lower unit, i.e., the Dukla Unit, and, as a consequence of differential uplift of the unit above and outside the duplex, the upper unit (the Magura Unit) was subjected to stretching. This process invoked normal faulting along the lateral culmination wall and was facilitated by the regional, syn-thrusting arc–parallel extension. Horizontal movement along the fault plane is a result of tear faulting accommodating a varied rate of advancement of Carpathian units. The time of the fault formation is not well constrained; however, based on superposition criterion, the syn -thrusting origin is anticipated.

Active faulting controls bedform development on a deep-water fan

Tectonically controlled topography influences deep-water sedimentary systems. Using 3-D seismic reflection data from the Levant Basin, eastern Mediterranean Sea, we investigate the spatial and temporal evolution of bedforms on a deep-water fan cut by an active normal fault. In the footwall, the fan comprises cyclic steps and antidunes along its axial and external portions, respectively, which we interpret to result from the spatial variation in flow velocity due to the loss of confinement at the canyon mouth. Conversely, in the hanging wall, the seafloor is nearly featureless at seismic scale. Numerical modeling of turbidity currents shows that the fault triggers a hydraulic jump that suppresses the flow velocity downstream, which thus explains the lack of visible bedforms basinward. This study shows that the topography generated by active normal faulting controls the downslope evolution of turbidity currents and the associated bedforms and that seafloor geomorphology can be used to evince syn-tectonic deposition.

Interpreter's Corner

Basaltic reservoirs have produced hydrocarbon from Yurihara Field in Japan, Quiko Depression in China, and Padra Field of Cambay Basin and Western Offshore Basin in India. The availability of fractured, altered, and vesicular basalts contributes to reservoir development in this stratigraphic unit. This study is conducted in the Kutch-Saurashtra Basin, located at the western continental margin of the Indian subcontinent wherein, the Deccan basalt, with a thickness range of 200–2500 m, overlies Mesozoic sediments. The Jurassic and Cretaceous sediments constitute the main source rock in the area. Several wells have been drilled through the entire basalt section, and some are hydrocarbon bearing in basalt. The entire basalt section in the study area has been classified into four major units using gamma-ray logs. These units have been further subdivided into individual flows and correlated all over the basin. Analysis shows that the base of an individual basalt flow is massive, and the top is differentially altered. Crossplot analysis of P-impedance and VP/VS ratio carried out on logs delineates a zone of moderately weathered/altered basalt, which is due to spheroidal weathering and calibrated with sidewall cores. These moderately altered zones between two successive flows of basalt are the probable reservoir facies for hydrocarbon accumulation, provided that there is an overlying seal in the form of massive or completely altered basalt. Three-dimensional seismic data in the area show an alternating reflection pattern in the basalt section due to the alternation of massive and weathered basalt. The seismic signature of basalt in the area is similar to that of a sedimentary sequence in any given area. Continuity of the identified individual flows in seismic scale has been propagated over the entire seismic, and subsequent inversion has facilitated the deciphering of the probable hydrocarbon-bearing locales within basalt.

Channel, dune and sand sheet architectures of strait-adjacent deltas

Sea strait geographies amplify tidal currents, which can result in the formation of tidal strait deposits with a symmetrical facies arrangement. It can be problematic to distinguish such confined tidal strait deposits from strait systems that developed in less constricted settings. To push a more robust differentiation between the confined tidal strait model and a model for less constricted tidal deposits, this study presents an example of a strait-adjacent delta and compares it to the existing model of confined tidal straits. The strait-adjacent delta interpretations are based on an exposed succession in Northern Morocco, that formed in the Miocene Rifian Corridor. The multi-km, seismic-scale exposures at the Ben Allou locality, formed in a region with a largely unconstrained coastline. Clayey and silty portions dominate the distal offshore and prodelta facies, while the proximal delta front and delta plain are comprised of carbonate-rich sandstones. These sandstones exhibit complex architectures of stacked channels and dunes in the delta front, and mud drape-bearing sand sheets on the delta plain. It is shown that the strait-adjacent delta model that is presented herein, is different from a confined tidal strait deposit as it has an asymmetric facies arrangement, and a basinward reduction in depositional energy.

Dolomitization geometry and reservoir quality from supervised Bayesian classification and probabilistic neural networks: Midland Basin Leonardian Wichita and Clear Fork Formations

Extensive dolomitization is prevalent in the platform and periplatform carbonates in the Lower-Middle Permian strata in the Midland and greater Permian Basin. Early workers have found that the platform and shelf-top carbonates were dolomitized, whereas slope and basinal carbonates remained calcitic, proposing a reflux dolomitization model as the possible diagenetic mechanism. More importantly, they underline that this dolomitization pattern controls the porosity and forms an updip seal. These studies are predominately conducted using well logs, cores, and outcrop analogs, and although exhibiting high resolution vertically, such determinations are laterally sparse. We have used supervised Bayesian classification and probabilistic neural networks (PNN) on a 3D seismic volume to create an estimation of the most probable distribution of dolomite and limestone within a subsurface 3D volume petrophysically constrained. Combining this lithologic information with porosity, we then illuminate the diagenetic effects on a seismic scale. We started our workflow by deriving lithology classifications from well-log crossplots of neutron porosity and acoustic impedance to determine the a priori proportions of the lithology and the probability density functions calculation for each lithology type. Then, we applied these probability distributions and a priori proportions to 3D seismic volumes of the acoustic impedance and predicted neutron porosity volume to create a lithology volume and probability volumes for each lithology type. The acoustic impedance volume was obtained by model-based poststack inversion, and the neutron porosity volume was obtained by the PNN. Our results best supported a regional reflux dolomitization model, in which the porosity is increasing from shelf to slope while the dolomitization is decreasing, but with sea-level forcing. With this study, we determined that diagenesis and the corresponding reservoir quality in these platforms and periplatform strata can be directly imaged and mapped on a seismic scale by quantitative seismic interpretation and supervised classification methods.

Integration of Well Logs and Seismic Attribute Analysis in Reservoir Identification on PGS Field Onshore Niger Delta, Nigeria

Integrated well dataset and seismics delineated the PGS field onshore Niger Delta for reservoir identification. Gamma ray, resistivity, Neutron and density Logs identified four lithologies: sandstone, shaly sandstone, shaly sand and shale. They consist of sand-shale intercalation with the traces of shale sometimes found within the sand Formation. Petrophysical parameters of the reservoirs showed varying degree of lower density, low gamma ray, high porosity and resistivity response with prolific hydrocarbon reservoir G due to its shale volume and the clean sand mapped as a probable hydrocarbon reservoir. 3D seismic data located both seismic scale and sub-seismic scale structural and stratigraphic elements. Risk reduction in dry hole drilling due fault missing in conventional seismic attribute analysis and interpretation, have to be integrated into the Oil companies standard practice.