The Neogene seismic stratigraphy and uplift history of the Otago Shelf, New Zealand

<p>The Otago continental shelf is a prospective petroleum area on the east side of the South Island New Zealand. During the Neogene it evolved from a post-rift to passive margin as giant progrades extended eastward across the shelf, fed by tectonic uplift and erosion of the Southern Alps to the west. Seismic reflection profiles reveal an uplifted limestone horizon near the Dunedin Volcano. This may be caused by a buoyant load under the lithosphere and can be spatially and temporally linked to the Dunedin Volcano and geophysical anomalies in the area. This thesis utilises 2D and 3D seismic data to map Neogene sequence boundaries over the Otago Shelf. Seven such sequence boundaries have been mapped based on distinctive seismic characteristics above and below these surfaces. These surfaces have been tied to nearby petroleum and Integrated Ocean Drilling Project wells using biostratigraphic data and then used to generate a series of isopach and depth maps that document the Neogene evolution of this margin. The maps depict the deposition of Neogene sediment and provide age constraints to structural events in the basin such as the uplift near Dunedin and fault movement on the Endeavour High. The maps are then used to develop a lithospheric flexure model where uplift is interpreted to have been caused by asthenospheric upwelling beneath Dunedin. The model provides insight into the conditions that led to the flexure of the lithosphere, specifically the elastic thickness of the plate and the magnitude and depth distribution of buoyant intrusive material that fed the Dunedin Volcano. Asthenospheric upwelling explains elevated heat flow around Dunedin and would result in enhanced petroleum maturity. This highlights the potential for petroleum generation in source rocks immediately offshore from Dunedin.</p>

The Neogene seismic stratigraphy and uplift history of the Otago Shelf, New Zealand

<p>The Otago continental shelf is a prospective petroleum area on the east side of the South Island New Zealand. During the Neogene it evolved from a post-rift to passive margin as giant progrades extended eastward across the shelf, fed by tectonic uplift and erosion of the Southern Alps to the west. Seismic reflection profiles reveal an uplifted limestone horizon near the Dunedin Volcano. This may be caused by a buoyant load under the lithosphere and can be spatially and temporally linked to the Dunedin Volcano and geophysical anomalies in the area. This thesis utilises 2D and 3D seismic data to map Neogene sequence boundaries over the Otago Shelf. Seven such sequence boundaries have been mapped based on distinctive seismic characteristics above and below these surfaces. These surfaces have been tied to nearby petroleum and Integrated Ocean Drilling Project wells using biostratigraphic data and then used to generate a series of isopach and depth maps that document the Neogene evolution of this margin. The maps depict the deposition of Neogene sediment and provide age constraints to structural events in the basin such as the uplift near Dunedin and fault movement on the Endeavour High. The maps are then used to develop a lithospheric flexure model where uplift is interpreted to have been caused by asthenospheric upwelling beneath Dunedin. The model provides insight into the conditions that led to the flexure of the lithosphere, specifically the elastic thickness of the plate and the magnitude and depth distribution of buoyant intrusive material that fed the Dunedin Volcano. Asthenospheric upwelling explains elevated heat flow around Dunedin and would result in enhanced petroleum maturity. This highlights the potential for petroleum generation in source rocks immediately offshore from Dunedin.</p>

Inventory of onshore petroleum seeps and stains in Greenland: a web-based GIS model

A new inventory on onshore petroleum seeps and stains in Greenland has been released by the Geological Survey of Denmark and Greenland as a web-based GIS model on the Greenland Mineral Resources Portal: Petroleum Seeps and Stains in Greenland. Knowledge on oil and gas seeps, oil stains and solid bitumen occurrences provides key information on mineral and petroleum systems, especially in frontier basins. As the understanding of recent and previous migrations of fluids and gases is important for both mineral and petroleum explorations in Greenland, this new inventory has been developed to facilitate exploration and new activities. The classification includes the following types of occurrences: (1) oil seeps, (2) gas seeps, (3) mud diapirs, pingos and gas-rich springs, (4) oil stains in volcanics, carbonates and sandstones, (5) solid macroscopic bitumen and (6) fluid inclusions and other evidence of micro-seepage. The inventory comprises detailed information on localities, coordinates and sample numbers. It also includes descriptions of features and geology, references to data, reports and publications. All information is summarised in either a mineral or petroleum systems context. Petroleum seeps and stains have been reported from most Palaeozoic, Mesozoic and Cenozoic basins in Greenland where they add important information on petroleum systems, especially distribution and facies variation of source rocks, petroleum generation and later migration, accumulation, remigration, uplift and degradation. The inventory is designed to be updated with additional localities and descriptions and new organic geochemical data. This paper provides a general overview of classification, nomenclature, organisation and content of the inventory. We introduce the regional distribution of petroleum seeps and stains in Greenland and general interpretations in the context of mineral and petroleum systems.

Java Volcanic Arc, what lies beneath?

Java Island is an active volcanic arc that resides in the southwestern - southern boundary of Sundaland edges. The volcanic arc consists of several volcanism episodes, with a relatively younging trend northward (Late Oligocene to Pleistocene), following the Indo-Australian plates inward migration. In contrast to the prolific neighboring Northwest and Northeast Java Basins in the Northern edges of Java Island; the basin reconstruction and development in the East-West trending depression in median ranges of Java (from Bogor to Kendeng Troughs) are overlooked and lays bare the challenge to the seismic imaging due to the structural complexity of the overthrusted Neogene unit as well as immense Quaternary volcanic eruption covers. On the other hand, oil and gas seepages around the northern and central parts of the Island confirmed the active petroleum generation. Five focused window areas are selected for this study. A total of 1,893 Km sections, 584 rock samples, 1569 gravity, and magnetic data, and 29 geochemical samples (rocks, oil, and gas samples) were acquired during the study. Geological fieldwork was focused on the stratigraphic unit composition and the observable features of deformation products from the outcrops. Due to the scarcity of the Paleogene deposit exposure in the Central-East Java area, the rock samples were also collected from the mud volcano ejected materials in the Sangiran Dome. Both Bogor and Kendeng Troughs are active petroleum systems that generate type II /III Kerogen typical to the reduction organic material derived from transition to the shallow marine environment. The result suggests that these basins are secular from the neighboring basins, The Northwest and Northeast Java Basins, characterized by oxidized terrigenous type III Kerogen. The contrasting subsurface configuration between Bogor and Kendeng Troughs mainly concerns the fold-thrust belt basement involvement and the tectonic shortening effect on the formerly rift basin.

Alginite-Rich Layers in the Bazhenov Deposits of Western Siberia

In this study, we identified the luminescent layers containing a significant amount of alginite in the Upper Jurassic–Lower Cretaceous Bazhenov Formation named “the alginite-rich layers”. Lithological and geochemical methods were used to determine distinctive features of these layers and to evaluate their impact on the total petroleum generation potential of the Bazhenov Formation. We have shown that the composition of the alginite-rich layers differs significantly from the organic-rich siliceous Bazhenov rocks. Rock-Eval pyrolysis, bulk kinetics of thermal decomposition, elemental analysis, and the composition of pyrolysis products indicate type I kerogen to be the predominant component of the organic matter (OM). Isotope composition of carbon, nitrogen, and sulfur was used to provide insights into their origin and formation pathways. The luminescent alginite-rich layers proved to be good regional stratigraphic markers of the Bazhenov Formation due to widespread distribution over the central part of Western Siberia. They can also be applied for maturity evaluation of the deposits from immature to middle of the oil window, since the luminescence of the layers changes the color and intensity during maturation.

Key factors controlling shale oil enrichment in saline lacustrine rift basin: implications from two shale oil wells in Dongpu Depression, Bohai Bay Basin

Comparative analyses of petroleum generation potential, reservoir volume, frackability, and oil mobility were conducted on 102 shale cores from the Dongpu Depression. Results show the shale has high organic matter contents composed of oil-prone type I and type II kerogens within the oil window. Various types of pores and fractures exist in the shale, with a porosity of up to 14.9%. The shale has high brittle mineral contents, extensive fractures, and high potential for oil mobility due to high seepage capacity and overpressure. Although the petroleum generation potential of the shale at Well PS18-8 is relatively greater than that at Well PS18-1, oil content of the latter is greater due to the greater TOC. The porosity and fracture density observed in Well PS18-1 are greater and more conducive to shale oil enrichment. Although the shales in Wells PS18-1 and PS18-8 have similar brittle mineral contents, the former is more favorable for anthropogenic fracturing due to a higher preexisting fracture density. Besides, the shale at Well PS18-1 has a higher seepage capacity and overpressure and therefore a higher oil mobility. The fracture density and overpressure play key roles in shale oil enrichment.

Comparative Assessment of Hydrocarbon Generation Potential of Organic Matter from Shale Sediments along Isugwuato – Okigwe Axis, Anambra Basin, SE Nigeria

TRACT: The Cretaceous sediments in the Anambra Basin (SE Nigeria) consist of a cyclic succession of coals, carbonaceous shales, silty shales and siltstones interpreted as deltaic deposits. The objective of this study is to compare the hydrocarbon generation potential of organic matter from shale sediments along Isugwuato-Okigwe axis in the Anambra Basin, Nigeria. Data obtained indicates the presence of Type III kerogen with Tmax values are between 424 and 441ºC indicating that the shales are thermally immature to marginally mature with respect to petroleum generation. Hydrogen Index (HI) values range from 14 to 388.9mgHC/gTOC while S1 + S2 yields values ranging from 0.2 to 1.0mgHC/g rock, suggesting that the shale have gas generating potential. The TOC values rangesfrom 1.3 to 3.0%, an indication of a good source rock of terrestrially derived organic matter. The high oxygen index (OI) (16.3 mgCO2g-1TOC), TS (1.35) and TOC/TS (1.5) suggest deposition in a shallow marine environment. Based on the kerogen type, shales from the studied area will equally generate oil and gas if its organic matter attained sufficient thermal temperature. Keywords: Shale, kerogen type, maturity, oil generation.