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Gas Migration (gas + migration)

Distribution by Scientific Domains

Earth and Environmental Science	100%

Selected Abstracts

Geothermometry and geobarometry of overpressured environments in Qiongdongnan Basin, South China Sea,

GEOFLUIDS (ELECTRONIC), Issue 3 2003
Honghan Chen
Abstract We demonstrate the use of PVT fluid inclusion modelling in the calculation of palaeofluid formation pressures, using samples from the YC21-1-1 and YC21-1-4 wells in the YC21-1 structural closure, Qiongdongnan Basin, South China Sea. Homogenisation temperatures and gas/liquid ratios were measured in aqueous fluid inclusions, and associated light hydrocarbon/CO2 -bearing inclusions, and their compositions were determined using a crushing technique. The vtflinc software was used to construct P,T phase diagrams that enabled derivation of the minimum trapping pressure for each order of fluid inclusion. Through the projection of average homogenisation temperatures (155, 185.5 and 204.5°C) for three orders of fluid inclusion on the thermal-burial history diagram of the Oligocene Yacheng and Lingshui formations, their trapping times were constrained at 4.3, 2.1 and 1.8 Ma, respectively. The formation pressure coefficient, the ratio of fluid pressure/hydrostatic pressure established by PVT modelling coupled with DST data, demonstrates that one and a half cycles of pressure increase,discharge developed in the Yacheng and Lingshui formations for about 4.3 Ma. In comparison, the residual formation pressure determined by 2D numerical modelling in the centre of LeDong depression shows two and a half pressure increase,discharge cycles for about 28 Ma. The two different methods suggest that a high fluid potential in the Oligocene reservoir of the YC21-1 structure developed at two critical stages for regional oil and natural gas migration and accumulation (5.8 and 2.0 Ma, respectively). Natural gas exploration in this area is therefore not advisable. [source]

HYDROCARBON SEEPAGE AND CARBONATE MOUND FORMATION: A BASIN MODELLING STUDY FROM THE PORCUPINE BASIN (OFFSHORE IRELAND)

JOURNAL OF PETROLEUM GEOLOGY, Issue 2 2005
J. Naeth
This study assesses whether the growth of deep water carbonate mounds on the continental slope of the north Atlantic may be associated with active hydrocarbon leakage. The carbonate mounds studied occur in two distinct areas of the Porcupine Basin, 200 km offshore Ireland, known as the Hovland-Magellan and the Belgica areas. To evaluate the possible link between hydrocarbon leakage and mound growth, we used two dimensional cross-section and map-based basin modelling. Geological information was derived from interpretation of five seismic lines across the province as well as the Connemara oilfield. Calibration data was available from the northern part of the study area and included vitrinite reflectance, temperature and apatite fission track data. Modelling results indicate that the main Jurassic source rocks are mature to overmature for hydrocarbon generation throughout the basin. Hydrocarbon generation and migration started in the Late Cretaceous. Based on our stratigraphic and lithologic model definitions, hydrocarbon migration is modelled to be mainly vertical, with only Aptian and Tertiary deltaic strata directing hydrocarbon flow laterally out of the basin. Gas chimneys observed in the Connemara field were reproduced using flow modelling and are related to leakage at the apices of rotated Jurassic fault blocks. The model predicts significant focussing of gas migration towards the Belgica mounds, where Cretaceous and Tertiary carrier layers pinch out. In the Hovland-Magellan area, no obvious focus of hydrocarbon flow was modelled from the 2D section, but drainage area analysis of Tertiary maps indicates a link between mound position and shallow Tertiary closures which may focus hydrocarbon flow towards the mounds. [source]

Structural and stratigraphic relationships of the Palaeocene mounds of the Utsira High

BASIN RESEARCH, Issue 4 2010
John Wild
ABSTRACT The Balder and Ringhorne Tertiary oilfields of the Utsira High are a cluster of prominent Palaeocene mounds, whose presence has confounded geologists since they were first observed on 2D seismic data back in the 1960s and 1970s. Until recently, the Balder Field geologic model consisted of distal, deep-water Heimdal, Hermod and Balder Formation sandy-debrite and turbidite sands, compensationally stacked along the flanks of the Utsira palaeo-high, with intervening layers of hemipelagic shale. Remobilization of the sands by large-scale fluidization accentuated the high-relief mounds and sand injections linked reservoirs that were originally isolated. Reprocessed seismic data show strong primary reflectors that cannot be reconciled with this model; continuous sand bodies are observed to cross-cut normal, biostratigraphically constrained sequence-stratigraphic reflectors. The implication is that many, if not most, of the Hermod and Balder sands are not depositional, but were emplaced by injection. Furthermore, most of the Palaeocene mounds are associated with major ,tears' in the normally smooth Top Cretaceous chalk seismic reflector, and overlying chalk ,rafts'. The chalk rafts were formerly thought to be detached glide-blocks, shed from distant scarps to the east, but the improved data show that they are always positioned above matching depressions in the main Chalk, implying a local origin. Some of the rafts are immense, exceeding half a kilometre in width and millions of tonnes in mass. We believe the association of the chalk features with the mounds is more than a coincidence and suggest that they are genetically related. A number of driving mechanisms have been proposed for the formation of the Palaeocene mounds of the Utsira High, including normal post-depositional compaction, fluidization by earthquakes, overpressuring due to gas migration and gravity-sliding back into the Viking Graben. Our observations are, however, more consistent with the mounds resulting from episodic supra-lithostatic pressure escape from beneath the Chalk. [source]

Origin and Accumulation of Natural Gases in the Upper Paleozoic Strata of the Ordos Basin in Central China

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 1 2009
Yangming ZHU
Abstract: The natural gases in the Upper Paleozoic strata of the Ordos basin are characterized by relatively heavy C isotope of gaseous alkanes with ,13C1 and ,13C2 values ranging mainly from ,35, to ,30, and ,27, to ,22,, respectively, high ,13C excursions (round 10) between ethane and methane and predominant methane in hydrocarbon gases with most C1/(C1 -C5) ratios in excess of 0.95, suggesting an origin of coal-derived gas. The gases exhibit different carbon isotopic profiles for C1 -C4 alkanes with those of the natural gases found in the Lower Paleozoic of this basin, and believed to be originated from Carboniferous-Permian coal measures. The occurrence of regionally pervasive gas accumulation is distinct in the gently southward-dipping Shanbei slope of the central basin. It is noted that molecular and isotopic composition changes of the gases in various gas reservoirs are associated with the thermal maturities of gas source rocks. The abundances and ,13C values of methane generally decline northwards and from the basin center to its margins, and the effects of hydrocarbon migration on compositional modification seem insignificant. However, C isotopes of autogenetic calcites in the vertical and lateral section of reservoirs show a regular variation, and are as a whole depleted upwards and towards basin margins. Combination with gas maturity gradient, the analysis could be considered to be a useful tool for gas migration. [source]

Structural Analysis of the Multi-layer Detachment Folding in Eastern Sichuan Province

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2010
Zongxiu WANG
Abstract: A serial of "comb-like and trough-like" folds developed in eastern Sichuan, controlled by the multi-layer detachment folding, is different from the classical Jura-type structure in their development. The key factor resulting in the development of these structures is the occurrence of detachment layers in different parts of Neoprotozoic to Mesozoic stratigraphy of study area, which, from the bottom to the top, are the lower part of Banxi Group, Lower Cambrian (Niutitang Formation), Lower Silurian (Longmaxi Formation and Luoreping Formation), Upper Permian (Wujiaping Formation) and Lower Triassic (Daye Formation). On the basis of field survey combined with sand-box modeling, this study argued that the detachment layer of the lower part of Banxi Group controlled the development of the "comb-like" folds, and the lower part of Cambrian detachment layer controlled the development of "trough-like" folds. Because of several detachment layers occurring in the study area, the development of duplex structures different scales is an important deformation mechanism, and the duplexes are the important structures distinguished from the typical detachment folding structures. Due to these duplexes, the surface structures and structural highs may not be the structural highs in the depth. Meanwhile, the detachment layers are good channels for oil/gas migration benefiting the understanding of accumulation and migration of oil and gas. [source]