Sealing mechanism for cap beds of shallow-biogenic gas reservoirs in the Qiantang River incised valley, China

Characteristics and accumulation model of the late Quaternary shallow biogenic gas in the modern Changjiang delta area, eastern China

“…The permeabilities of 16 samples were measured by falling-head permeability test apparatus (cf. Zhang et al 2013). The total organic carbon (TOC) and chloroform bitumen contents of 41 samples were analyzed following the method of Stax and Stein (1993).…”

“…Lin et al 2004;Zhang et al 2013). H/C and O/C ratios of kerogen vary in a range of 0.89-1.25 and 0.27-0.38, respectively, and plot in the type III kerogen area (gas prone; cf.…”

“…Incised valleys generally have high preservation potential for their fill deposits (Dalrymple et al 1994) and provide a fundamental and important background for the formation of the shallow biogenic-gas reservoirs therein, i.e., gas-source beds, cap beds, and sand reservoirs can occur together in close geographic and stratigraphic proximity (Xu et al 2009;Lin et al 2004;Zhang et al 2014). Considerable biogenic-gas accumulations with depth \120 m have been discovered and well documented in the late Quaternary Qiantang River incised valley with a predicted total gas amount of 244.5 9 10 9 m 3 (Lin et al 2004Zhang et al 2013). Also, the produced gas was used as gas supply for local villages and factories .…”

“…Recently, researchers have drawn considerable attention to the shallow biogenic gas in the near-surface marine and coastal sediments such as bay or estuarine deposits and late Quaternary incised-valley fills (García-García et al 2007;Xu et al 2009;Lin et al 2010;Zhang et al 2013;Jones et al 2014;Okay and Aydemir 2016), in terms of the shallow-burial depth ranging from several tens of meters to hundreds of meters and easy exploitation with low investment and high benefit. Commercial reservoirs of shallow biogenic gas have been widely found in the world, including the North Sea (Heggland 1997; Vielstädte et al 2015), Ria de Vigo incised valley, Spain (Garcia-Gil et al 2002), western Gulf of Maine, USA (Rogers et al 2006), and Lawrence Estuary, Canada (Pinet et al 2008).…”

“…Shallow biogenic-gas reservoirs are principally distributed along the eastern and southern coasts of China, especially the Jiangsu-Zhejiang coastal plain area, where the postglacial Changjiang and Qiantang River incised valleys are located (Wang 1982;Zheng 1998;Lin et al 2004;Liu et al 2008;Li et al 2010a;Zhang et al 2013Zhang et al , 2014. Incised valleys generally have high preservation potential for their fill deposits (Dalrymple et al 1994) and provide a fundamental and important background for the formation of the shallow biogenic-gas reservoirs therein, i.e., gas-source beds, cap beds, and sand reservoirs can occur together in close geographic and stratigraphic proximity (Xu et al 2009;Lin et al 2004;Zhang et al 2014).…”