微生物油气勘探技术在岩性气藏勘探中的应用——以柴达木盆地三湖坳陷为例

Application of microbial oil surveying to exploration of lithologic gas reservoirs:A case from the Sanhu Depression,Qaidam Basin,NW China

为了有效识别柴达木盆地三湖坳陷岩性生物气藏,以台南—台东地区为研究区,开展微生物勘探技术试验研究。东西向长24 km的采样测线横穿工区,在各采样点(间隔150 m)采集20 cm深度处的土壤200 g,样品共156个,由美国GMT公司完成甲烷氧化菌分析。结果显示,研究区20 cm深度处土壤湿度可维持甲烷氧化菌的生长;pH值平均为8.20,不抑制甲烷氧化菌生长;大量样品全盐盐度大于20%,高盐度降低了甲烷氧化菌的浓度,但气藏区与非气藏区微生物浓度差别显著,气藏上方盐度高达50%以上仍发育微生物异常;而且探井试气产量与其上方微生物浓度呈显著正相关,表明微生物勘探技术适用于三湖坳陷。利用微生物异常判断,在台南9井东侧1 km处、台南气田西侧边界以外可能存在含气丰度高于台南9井的岩性气藏,是较为有利的勘探目标区。

To effectively detect lithologic biogas reservoirs in the Sanhu Depression,an experimental investigation of Microbial Oil Surveying Technique（MOST）was conducted in the Tainan-Taidong area.Samples were from 156 sampling stations located 150 m apart in a near straight line of 24 km and extending from the west to the east of the investigated area,200 g of soil from each sample site was taken at depth of 20 cm,and GMT Inc.of U.S.A.completed the analysis of soil methanotrophs.The result shows that moisture of soil at depth of 20 cm can maintain the growth of methanotrophs;The average of soil pH is 8.20,which does not inhibit the growth of methanotrophs;The salinity of many samples are more than 20%,the high salinity decreases methanotrophs concentrations,but the difference of methanotrophs concentrations between gas reservoirs and background areas is obvious,and the samples above gas reservoirs whose salinity are more than 50% still have microbial anomaly;Gas well testing production shows a significant positive correlation with methanotrophs concentrations of soil above the well,indicating the MOST is applicable to the Sanhu Depression.According to the microbial anomaly,two favorable exploration targets were identified in the eastern side of Well Tainan 9 and the western side near the limits of the Tainan gas field,their gas bearing abundance is better than the Well Tainan 9.