柴达木盆地第四系生物气分布综合地球物理研究

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

柴达木盆地三湖地区第四系生物气藏构造平缓、地层压实作用小、孔隙度大、埋藏浅、累计厚度大,具有独特的地球物理异常:局部重力低、航磁高频微磁异常、地震同相轴下拉以及地震属性异常等,据此提出了针对该地区浅层生物气预测的综合地球物理处理解释方案。对1︰100 000重力资料进行了保幅处理,并将处理结果与已知气田及航磁、遥感、地震烃类检测结果进行了对比分析,发现局部重力低与生物气藏有着较好的对应关系,指出局部剩余重力低是浅层生物气藏的重要地球物理特征,且剩余重力异常的幅值与浅层气藏的规模成正比。根据剩余重力异常及其他资料,提出三湖地区气藏具有纵向叠合、横向成带、局部富集的分布特征;以区域面积性的剩余重力异常为主,综合各种资料预测了3个有利区带、1个较有利区带(低产气区带)、5个可能的有利区及4个有利目标区。

Quaternary biogenic gas fields in the Sanhu area of the Qaidam Basin are characterized by gentle structure,shallow burial,weak compaction,high porosity and large bulk thickness,which determine their unique geophysical anomalies,such as locally low gravity,micro-magnetic high frequency anomaly,seismic event push-down and attribute anomaly,etc.An integrated geophysical processing and interpretation scheme is put forward for shallow biogenic gas prediction in this area.Amplitude preserving is performed for 1：100000 gravity data and the processing results are correlated with the known gas distributions and the results of aeromagnetics,remote sensing and seismic hydrocarbon detection.Study shows that the residual gravity low anomaly has a good correlation with the gas field and is 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 3 favorable zones,1 fairly favorable zone（low gas production zone）,5 possibly favorable zones and 4 favorable targets.