Exploration methods for late Quaternary shallow biogenic gas reservoirs in the Hangzhou Bay area, eastern China

Abstract

Commercial accumulations of shallow biogenic gas have been widely found in the world. The successful development and exploitation of shallow gas is dependent on using suitable technology to effectively prospect for this kind of resource. Shallow biogenic gas reservoirs, buried less than 120 m (393.7 ft), have been discovered and successfully exploited in the Hangzhou Bay area, northern Zhejiang Province, eastern China. In this study, we describe the methods used for the exploration of shallow gas, including cone penetration test (CPT), shallow shear-wave seismic data, soil-gas radon analysis, microbiological prospecting, and electromagnetic surveying. The CPT is effective in helping to determine stratigraphic divisions and correlations, especially reservoir identification. Dense CPTs are useful for both the preliminary exploration and enlarging a known gas field. Shallow shear-wave seismic profiles identify the top surface of a gas-bearing sand bed, which shows a strong reflecting boundary. The reflection will sharply decline where the gas-bearing sand body pinches out. Thus, a gas-bearing sand body can be outlined. The area of gas reservoirs can further be determined by high soil-gas radon content over the boundary of the gas accumulation. Methane-consuming bacteria can act as an indicator for the presence of methane within the gas-bearing area. Electromagnetic methods can aid in determining whether there is gas in the sand bodies and in determining the thickness of the gas layer.