Integrated geophysical studies on the distribution of Quaternary biogenic gases in the Qaidam Basin, NW China

Abstract

Quaternary biogenic gas fields in the Sanhu area of the Qaidam Basin are characterized by gentle structures, shallow burial, weak compaction, high porosity and great bulk thickness, which determine their unique geophysical anomalies, such as the locally low gravity, micro-magnetic high frequency anomaly, seismic event push-down and attribute anomaly. An integrated geophysical processing and interpretation scheme is put forward for shallow biogenic gas prediction in this area. Amplitude preservation is performed for 1:100000 gravity data and the processing results are correlated with known gas distributions and aeromagnetic results, remote sensing and seismic hydrocarbon detection. This study shows that the residual gravity low anomaly has a good correlation with the gas field and, as an important feature of the biogenic gas field, the amplitude of residual gravity low anomaly is directly proportional to the measure of gas reservoir. Based on the residual gravity low anomaly and other exploration data, the distribution of gas reservoirs in the Sanhu area is characterized by vertical overlapping, lateral zoning and local enrichment. Residual gravity anomaly, in combination with regional geologic data, reveals three favorable zones, one fairly favorable zone (low gas production zone), five possibly favorable zones and four favorable targets. Key words: Qaidam Basin, Sanhu area, Quaternary, biogenic gas, gravity, magnetic, seismic, geophysical integration, exploration direction