地表砂岩样品含油气显示与确认——以青藏高原措勤、比如、昌都、可可西里盆地为例

OIL-BEARING CHARACTERISTICS IDENTIFICATION IN SURFACE SANDSTONES —TAKING CUOQIN, KEKEXILI, BIRU AND CHANGDU BASINS IN TIBET FOR EXAMPLE

地面岩石油气显示对于新区油气勘探具有极重要的意义。岩石热解、薄片分析、氯仿"A"抽提、电子探针等技术可用于地面砂岩样品含油显示的确认。青藏高原地区地面砂岩含油显示判定标准是,薄片鉴定发荧光,裂隙充填物电子探针分析C原子>70%,O/C原子比<0.5为有含油显示。热解含烃量换算的原始含油饱和度>45%,氯仿"A"含量>120×10-6,原始含油级别为含油—饱含油;原始含油饱和度20%～45%,氯仿"A"含量(60～120)×10-6,原始含油级别为油浸—油斑;原始含油饱和度<20%,氯仿"A"含量<60×10-6,原始含油级别为油迹-荧光。研究确定措勤盆地3个砂岩样品、比如盆地3个细砂岩样品为含油气显示,可可西里盆地4个砂岩、昌都盆地4个砂岩样品为含油显示。其中含油显示级别最高的是措勤盆地郎山组C163号深灰色细砂岩,氯仿抽提物123×10-6,恢复后岩石中含烃量28.36mg/g,估算原始含油饱和度51.16%,原始储油层性质评价为油层。最后指出,措勤盆地、可可西里盆地具有良好的石油勘探远景,而昌都盆地、比如盆地应以找气为目标。

It is very important to find oil shows in surface samples for a new oil and gas exploration area. Rock-Eval, chloroform extract, fluorescence observation, and element analysis of filling matter in pores can be used to determine whether surface sandstone is oil-bearing .If the fluorescence exist and carbon content is >75% and O/C atom ratio is <0.5 in pore filling matter, the surface oil-bearing sandstone will be characterized qualitatively in Tibet area. Meanwhile, pyrolysis hydrocarbon content can be used to calculate original oil-bearing saturation. In Tibet area oil-bearing level originally was from oil saturated to oil-showing if original oil-bearing saturated is >45% and chloroform extract is >120 ×10^(-6). It was oil immersed to oil spot while oil-bearing saturation is 20%-45% and extracts is(60-120)×10^(-6).It was only oil trace if they respectively are <20% and<60 ×10^(-6). Surface oil-bearing sandstones have been found in 4 basins of Tibet, that is, 3 in Cuoqin, 4 in Kekexili, 3 in Biru, and 4 in Changdu basins. Among them the best is C163 sandstone in Cuoqin basin. The pyrolysis hydrocarbon is 28.36mg/g and saturation is 51.8% and chloroform extracts is 123 ×10^(-6). Finally, Cuoqin and Kekexili basins are considered as oil-bearing basins, and Biru and Changdu basin natural gas-bearing ones.