Late Quaternary shallow biogenic gas reservoirs have been discovered and exploited in the Qiantang River (QR) estuary area, eastern China. The fall of global sea level during the Last Glacial Maximum resulted in the formation of the QR incised valley. From bottom to top, the incised valley successions can be grouped into four sedimentary facies: river channel facies, floodplain–estuarine facies, estuarine-shallow marine facies, and estuarine sand bar facies.All commercial biogenic gas pools occur in floodplain–estuarine sand bodies of the QR incised valley and its branches. The deeply incised valleys provided favorable conditions for the generation and accumulation of shallow biogenic gas.The clay beds that serve as the direct cap beds of the gas pools are mostly restricted within the QR incised valley, with burial depths ranging from 30 to 80 m, remnant thicknesses of 10–30 m, and porosities of 42.2–62.6%. In contrast, the mud beds cover the whole incised valley and occur as indirect cap beds, with burial depths varying from 5 to 35 m, thicknesses of 10–20 m, and porosities of 50.6–53.9%. The pore-water pressures of clay and mud beds are higher than that of sand bodies, and the difference can be as much as 0.48 MPa. The pore-water pressures of clay or mud beds can exceed the total pore-water pressure and gas pressure of underlying sand reservoirs. Shallow biogenic gas can be completely sealed by the clay and mud beds, which have higher pore-water pressure. The direct cap beds have better sealing ability than the indirect cap beds.Generally, the pore-water pressure dissipation time of clay and mud beds is conspicuously longer than that of sand beds. This indicates that the clay and mud beds have worse permeability and better sealing ability than the sand beds. However, once the gas enters the sand lenses, the pore-water pressure cannot release efficiently. 相似文献
Water supply and sanitation are examined with the objective of describing the evaluation of alternative technologies for providing these services within urban areas of developing countries. First, an overview is given of the Pace of urbanization and the magnitude of the water and sanitation problem. A brief review of various water-supply and sanitation technologies follows, with a discussion of some basic principles involved in their comparison. An empirical study of the situation in Cali, Colombia is then provided as an example, with particular attention given to economic costing and some of its difficulties. The concluding part discusses the role of such analyses in urban planning and policy making, providing specific examples in the areas of low-cost housing, appropriate technology, water conservation, and urban expansion.
A recent decision to allow higher levels of urban development in central Oahu, Hawaii, has heightened the concern about possible loss of agricultural land and further drops in aquifer levels. This paper examines such potential impacts and offers a procedure for incorporating them into land use planning. First, a water-balance simulation model computes the change in groundwater recharge under changes in land use and irrigation technology. The resulting changes, together with estimated water demands for the agricultural, commercial and residential sectors, are then included in a multiobjective programming model that identifies optimal patterns of land use conversion under different objective trade-offs. Objectives treated are the minimization of agricultural land loss and of water demand, and the maximumization of recharge over withdrawal. The second objective pertains to water management during drought, while the third refers to sustainable groundwater management. Results show that, depending on the relative importance given each of these two objectives, land moving out of sugar cane will differ significantly in amount and by type of irrigation presently used. The relative importance of these objectives thus needs to be determined if water is to play a coherent and guiding role in land use planning. 相似文献