Heat flow derived from BSR and its implications for gas hydrate stability zone in Shenhu Area of northern South China Se
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ORIGINAL RESEARCH PAPER
Heat flow derived from BSR and its implications for gas hydrate stability zone in Shenhu Area of northern South China Sea Lun Li • Xinhua Lei • Xin Zhang • Guangxue Zhang
Received: 24 July 2011 / Accepted: 31 January 2012 / Published online: 14 February 2012 Ó Springer Science+Business Media B.V. 2012
Abstract Bottom simulating reflectors (BSRs), known as the base of gas hydrate stability zone, have been recognized and mapped using good quality three-dimensional (3D) pre-stack migration seismic data in Shenhu Area of northern South China Sea. Additionally, seismic attribute technique has been applied to better constrain on the distribution of gas hydrate. The results demonstrate that gas hydrate is characterized by ‘‘blank’’ zone (low amplitude) in instantaneous amplitude attribute. The thickness of gas hydrate stability zone inferred from BSR ranges from 125 to 355 m with an average of 240 m at sea water depth from 950 to 1,600 m in this new gas hydrate province. The volume of gas in-place bound in hydrate is estimated from 1.7 9 109 to 4.8 9 109 m3, with the most likely value of around 3.3 9 109 m3, using Monte Carlo simulation. Furthermore, geothermal gradient and heat flow are derived from the depths of BSRs using a conductive heat transfer model. The geothermal gradient varies from 35 to 95°C km-1 with an average of 54°C km-1. Corresponding heat flow values range from 43 to 105 mW m-2 with an average of 64 mW m-2. By comparison with geological characteristics, we suggest that the distribution of gas hydrate and heat flow are largely associated with gas chimneys and faults, which are extensively distributed in Shenhu Area, providing easy pathways for fluids migrating
L. Li (&) University of Houston, Houston, TX 77004, USA e-mail: [email protected] L. Li X. Lei X. Zhang China University of Geosciences, Beijing 100083, China G. Zhang Guangzhou Marine Geological Survey, MLR, Guangzhou 510760, China
into the gas hydrate stability zone for the formation of gas hydrate. This study can place useful constraints for modeling gas hydrate stability zone from measured heat flow data and understanding the mechanism of gas hydrate formation in Shenhu Area. Keywords Gas hydrate stability zone (GHSZ) Heat flow Bottom simulating reflector (BSR) Gas reserve, South China Sea Shenhu Area
Introduction Gas hydrate is a kind of solid compounds composed of water molecules and gas molecules (Kvenvolden 1998). It is widely distributed in continental shelves and permafrost regions (Kvenvolden 1998). Milkov (2004) estimated that the global hydrocarbon trapped in gas hydrate was 1–5 9 1015 m3. In addition, some authors (e.g. Kennett et al. 2003) argued that gas hydrate might have a large effect on global climate change. Therefore, there has been considerable interest recently in evaluating the role of gas hydrate on climate change and as a kind of alternative energy. Shenhu Area of northern South China Sea (SCS) has been regarded as a promising area for the presence of gas hydrate (Yang et al. 2008;
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