The principles of helium exploration

Commercial helium systems have been found to date as a serendipitous by-product of petroleum exploration. There are nevertheless significant differences in the source and migration properties of helium compared with petroleum. An understanding of these differences enables prospects for helium gas accumulations to be identified in regions where petroleum exploration would not be tenable. Here we show how the basic petroleum exploration playbook (source, primary migration from the source rock, secondary longer distance migration, trapping) can be modified to identify helium plays. Plays are the areas occupied by a prospective reservoir and overlying seal associated with a mature helium source. This is the first step in identifying the detail of helium prospects (discrete pools of trapped helium). We show how these principles, adapted for helium, can be applied using the Rukwa Basin in the Tanzanian section of the East African Rift as a case study. Thermal hiatus caused by rifting of the continental basement has resulted in a surface expression of deep crustal gas release in the form of high-nitrogen gas seeps containing up to 10% 4He. We calculate the total likely regional source rock helium generative capacity, identify the role of the Rungwe volcanic province in releasing the accumulated crustal helium, and show the spatial control of helium concentration dilution by the associated volcanic CO2. Nitrogen, both dissolved and as a free gas phase, plays a key role in the primary and secondary migration of crustal helium and its accumulation into what might become a commercially viable gas pool. This too is examined. We identify and discuss evidence that structures and seals suitable for trapping hydrocarbon and CO2 gases will likely also be efficient for helium accumulation on the timescale of the Rukwa basin activity.The Rukwa Basin prospective recoverable P50 resources of helium have been independently estimated to be about 138 billion standard cubic feet (2.78 x 109 m3 at STP). If this volume is confirmed it would represent about 25% of the current global helium reserve. Two exploration wells Tai 1 and Tai 2 completed by August 2021 have proved the presence of seal and reservoir horizons with the reservoirs containing significant helium shows.This article is part of the Energy Geoscience Series available at https://www.lyellcollection.org/cc/energy-geoscience-series

Geochemical characteristics and origins of biodegraded oils in the Bongor Basin (Chad) and their implications for petroleum exploration

The Bongor Basin is a typical lacustrine passive-rifted basin situated in the West and Central African Rift System (WCARS). It has experienced two phases of tectonic inversion and features a complex process of petroleum generation and accumulation. A total of 41 crude oil samples from the basin were geochemically analyzed to investigate their compositions of molecular markers. The results show that the oils have similar origins and are likely to belong to the same oil population. However, there are significant differences in geochemical characteristics and physical properties, caused by the secondary alteration. The relative contents and distribution patterns of normal alkanes and acyclic isoprenoids indicate that some of the oils have suffered biodegradation to varying degrees. The samples can be divided into three categories according to their relative degrees of degradation: normal oil, slightly biodegraded oil (PM 1–3), and severely biodegraded oil (PM 5–7). The burial depth of oil reservoirs in this area is the predominant factor impacting on the level of biodegradation. Crude oils in reservoirs with burial depths of less than 800 m are all severely biodegraded, while oils in reservoirs with burial depths greater than 1300 m have experienced no evident biodegradation. In reservoirs with burial depths between 800 m and 1300 m, the biodegradation degrees vary from normal to severely biodegraded. Oil reservoirs with burial depths less than 1300 m and adjacent to major faults are readily subject to biodegradation, while reservoirs with similar burial depths, but a certain distance away from major faults, have suffered no evident biodegradation. Moreover, if primary reservoirs have been modified by tectonic activity after accumulation, the crude oils are more likely to be biodegraded. Faulted anticline traps may create more favorable geological conditions for preservation of crude oil than reverse extrusion anticline reservoirs. This study may provide practical guidance for the assessment and prediction of oil quality in future oil exploration.

Evaluating the Implications of Lineaments on Petroleum Fields: South Sumatra, Indonesia

Declining oil prices has led to a reduction of petroleum exploration as oil production as no longer a lucrative area of investment as in the previous years. Current exploration activities are supported by field work which are intensive considering the resources required. There is need to develop low cost methods to delineate areas of potential hydrocarbon resources. This research uses Land Satellite (Landsat) 8 Operational Land Imager (OLI) for alteration extraction, Shutter Radar Topography Mission (SRTM) for lineament extraction, Geological maps to develop a low cost method of petroleum exploration. The results indicate high OH bearing alterations on the Gumai and Kasai formation, a seal rock. Extensional tectonics is responsible for the migration of petroleum from the subsurface. It is suggested that future exploration be concentrated on the Gumai and Kasai formation based on evidence of micro seepage.

Dinoflagellate biostratigraphy of Eastern Indonesia stratigraphy: key of petroleum exploration success

Several major discoveries in the eastern part of Indonesia (e.g. Tangguh and Abadi) have increased more petroleum exploration interest in the area. These sizeable discoveries encountered gas in the Jurassic sandstone, which is a key reservoir target in the Northwest Shelf of Australia. The Mesozoic sandstone provenance is located in the Australian Continental Plate or also known as the Sahul Shelf. Thousands of wells were drilled in the Sahul Shelf and the stratigraphy in this area is well understood. The extension of the Mesozoic sandstone towards Indonesian territory, with much less well information, is one of the keys of success for petroleum exploration. Refinement of the stratigraphy of the eastern part of Indonesia is crucial to understand the extension.To refine the stratigraphy of Eastern Indonesia, especially for the Mesozoic interval, dinoflagellates play a significant role. Several types of this marine biota have been used by Australian stratigraphers as markers. In the case where stratigraphic tie to Northwest Shelf Australia discoveries, key wells or standard chronostratigraphy, dinoflagellate understanding is critical.Dinoflagellate markers are used to mark several subdivisions of Plover Sandstone. Norvick (2001) used W. indotata and D. caddaensis Maximum Flooding Surfaces to subdivide the reservoir target into upper, middle and lower Plover Formation. These surfaces are named after dinoflagellates. More markers were identified to mark the source rock and seal in the petroleum system. To have a detail correlation from Indonesia to the NW Shelf, understanding of dinoflagellates is crucial.

Optimization of Exploration Prospects Based on Ant Colony Algorithm and XGBoost Combined Optimization Model

Traditional exploration prospect optimization is uncertain due to human factor, the primary reason of that problem is the complex nonlinear relationship between trap quality and related geological factors. Some researchers proposed use artificial neural network (ANN) to solve the problem of the comprehensive geological evaluation of traps, because ANN can describe the nonlinear relationship of multiple geological factors. Considering ANN has some drawbacks, such as it is need lots of parameters for training, and the learning process can not be observed. In this paper we proposed a combined optimization model to accomplish optimization of exploration prospects, and express the affinity order between the prospects and its related geological factors, also can provide the data support for exploration. Based on trap data of an oilfield in Africa, there are 12 geological factors related to trap quality, including trap coefficient, trap depth, trap scale, trap area, Reservoir coefficient, Preservation coefficient, hydrocarbon source coefficient, resources etc.. The ant colony algorithm is used for feature selection, and irrelevant and redundant features are eliminated through multiple iterations, making it suitable for model processing and improving training speed. Based on ant colony algorithm, we get the key parameters for XGBoost model training, namely trap area, reservoir coefficient, preservation coefficient, resource, and the key features are used in XGBoost model for training and prediction. Finally, we compared our prediction results with expert prediction, the error is 0. In this paper, we proposed a combined optimization model based on ant colony algorithm and XGBoost for exploration prospect optimization. We recognized the key geological factors and different characteristic rules for exploration prospect optimization, in the process of optimization, ant colony discards the bad features that interfere with classification and recognition, and retains the features that contribute greatly to classification. In comprehensive geological evaluate of trap, the proposed combined optimization model is suitable for complicated nonlinear geological relationship, and express the affinity order between the prospects, the proposed method can work as an auxiliary way in petroleum exploration, also the proposed method can provide decision support for exploration prospect optimization, and finally can fulfill cost decreasing and benefit increasing.

Stratigraphic and tectonic framework of Late Cretaceous and Paleogene strata of southern Aotea Basin, northwest New Zealand

<p>Seismic reflection data reveal thick sediment sequences of Late Cretaceous to Paleogene age in the region northwest of Taranaki Basin. A new stratigraphic framework for latest Cretaceous and Paleogene strata is created based on stacking patterns and stratal termination relationships of seismic reflectors. Sequence-bounding reflectors are tied to petroleum exploration wells, including recently-drilled Romney-1, to assign age and paleoenvironment interpretation. I identify the following sequences: (1) a late Haumurian to Teurian (68 – 56 Ma) aggradational shelf sequence, with at least two regressional events linked to eustatic sea-level falls; (2) a diachronous deepening of the basin that progressed from north to south during the late Waipawan to Heretaungan (53 – 46 Ma); (3) small-scale volcanism at the southern boundary with Taranaki Basin is contemporaneous with this deepening; (4) a prograding delta on Challenger Plateau during the Porangan to Runangan (46 – 35 Ma) that is evidence for tectonic uplift of the basin margins; and (5) an onlapping sequence from latest Runangan to present (35 – 0 Ma) that indicates Challenger Plateau subsided 1,300 m. A revised set of paleogeography maps and generalised stratigraphic chart summarise these observations. The Eocene phase (52-46 Ma) of tectonic subsidence and diffuse volcanism is one of the earliest signs of tectonic activity associated with development of the Cenozoic plate boundary through New Zealand. Petroleum system analysis reveals that southern Aotea Basin is prospective for petroleum exploration, with 3 plays identified in the Late Haumurian to Teurian (79 – 56 Ma) strata, in spite of Romney-1 proving unsuccessful.</p>

Stratigraphic and tectonic framework of Late Cretaceous and Paleogene strata of southern Aotea Basin, northwest New Zealand

<p>Seismic reflection data reveal thick sediment sequences of Late Cretaceous to Paleogene age in the region northwest of Taranaki Basin. A new stratigraphic framework for latest Cretaceous and Paleogene strata is created based on stacking patterns and stratal termination relationships of seismic reflectors. Sequence-bounding reflectors are tied to petroleum exploration wells, including recently-drilled Romney-1, to assign age and paleoenvironment interpretation. I identify the following sequences: (1) a late Haumurian to Teurian (68 – 56 Ma) aggradational shelf sequence, with at least two regressional events linked to eustatic sea-level falls; (2) a diachronous deepening of the basin that progressed from north to south during the late Waipawan to Heretaungan (53 – 46 Ma); (3) small-scale volcanism at the southern boundary with Taranaki Basin is contemporaneous with this deepening; (4) a prograding delta on Challenger Plateau during the Porangan to Runangan (46 – 35 Ma) that is evidence for tectonic uplift of the basin margins; and (5) an onlapping sequence from latest Runangan to present (35 – 0 Ma) that indicates Challenger Plateau subsided 1,300 m. A revised set of paleogeography maps and generalised stratigraphic chart summarise these observations. The Eocene phase (52-46 Ma) of tectonic subsidence and diffuse volcanism is one of the earliest signs of tectonic activity associated with development of the Cenozoic plate boundary through New Zealand. Petroleum system analysis reveals that southern Aotea Basin is prospective for petroleum exploration, with 3 plays identified in the Late Haumurian to Teurian (79 – 56 Ma) strata, in spite of Romney-1 proving unsuccessful.</p>