Overpressure

About: Overpressure is a research topic. Over the lifetime, 3236 publications have been published within this topic receiving 34648 citations.

Evolution of Geopressure Field in Niuzhuang Sag in Dongying Depression and Its Effect on Petroleum Accumulation

Abstract: The present geopressure field in Niuzhuang sag in Dongying depression can be divided into dissimilar zones vertically and different areas horizontally. Overpressure is closely related to both the upper part of the fourth member and the lower part of the third member of Shahejie Formation whose source rocks matured. Large-scale faults surrounding Niuzhuang sag limit the horizontal overpressure distribution. Inside the sag it is strongly overpressured while outside it is much less overpressured. The forward modeling indicates that the overpressure evolution in the sag is divided into three stages: original-forming, meta-declining and latest-raising stages. And the main mechanism for generating overpressures evolved from undercompaction into combination of both undercompaction and hydrocarbon generation. Meanwhile, both lateral seal by large-scale faults surrounding Niuzhuang sag and vertical seal by the thick and shale-enriched bottom layer of the middle part of the third member of Shahejie Formation determined the special distribution of overpressure. The overpressure in Niuzhuang sag provided the petroleum migration with original forces in those two important accumulation periods. Coupling of overpressure evolution and tectonic activities played an active role in petroleum accumulation in the bordering faulted zone near Niuzhuang sag.

Seal failure assessment of a major gas field via integration of seal properties and leakage phenomena

Abstract: We present a seismic- and well-based interpretation of a large leakage zone above the Scarborough gas field, Exmouth plateau, North West shelf of Australia. This leakage zone, well imaged on three-dimensional seismic data, extends over a region of 100 km2 (39 mi2), encompassing both the crest and flanks of the anticlinal trap, and is termed here as distributed crestal leakage. The present-day gas–water contact is 85 m (278 ft), and the spillpoint is 110 m (328 ft) below the crest, implying that the trap is underfilled at present. The leakage zone comprises more than 500 pockmarks at the present-day seabed with no crosscutting or cannibalization, suggesting that they formed in a short interval of time. These are underlain by sediment remobilization features and amplitude anomalies, consistent with a relatively high flux leakage of gas from the underlying Cretaceous deep-water sand-rich reservoir. By analyzing the geometrical relationship between the leakage zone, the top-seal properties, and the gas–water contact, we conclude that the mode of leakage in this specific setting is not the result of gradual addition of gas charge but is instead consistent with a sudden increase of aquifer overpressure. We suggest two alternative models for seal failure in this case study: a conservative model consistent with a modest but rapid increase in aquifer overpressure leading to membrane seal failure and a model dominated by high aquifer overpressure leading to leakage through hydraulically dilated faults and fractures.