油气藏上方吸附丝指标异常模式及成因分析——以塔里木盆地英南2井侏罗系气藏为例

ANOMALY PATTERN ORIGINS OF THE WIRE-ADSORBED HYDROCARBON INDICATORS——OVER THE JURASSIC GAS RESERVOIR OF WELL YINGNAN 2 IN THE TARIM BASIN

分析了塔里木盆地英吉苏凹陷英南2井侏罗系气藏特殊的封闭成藏特征及其不同的油气微渗漏方式,并对测区吸附丝轻烃指标(C2-8)、重烃指标(C15-19)地球化学场特征进行了研究,发现该气藏上方二指标的地球化学场特征、异常模式等均存在显著差异。研究认为:该气藏致密砂岩的水锁效应、气藏烃物质微渗漏方式(扩散、渗透)等因素是引起上述差异的根源;气体游离扩散相重烃物质扩散散失是气藏区上方C15-19指标异常的成因,重烃物质局部扩散系数从构造顶部高值区到构造翼部低值区的变化趋势是气藏区上方C15-19指标曲线倒"V"状特征的形成原因;未发生水锁效应气藏边缘区轻烃物质的渗透散失强于发生水锁效应气藏区轻烃物质的扩散散失,是研究区C2-8指标剖面曲线"驼峰"状特征的成因。应用该气藏上方吸附丝二指标的异常模式及组合关系对孔雀1井的钻前预测得到了后期勘探成果的有效验证,其对孔雀河古斜坡区、英吉苏致密砂岩区的油气勘探也具有借鉴意义。

A research on the causes of the anomaly patterns of the wire-adsorbed geochemical indicators over the Jurassic gas reservoir of Well Yingnan 2 in the Yingjishu Sag of the Tarim Basin has been conducted. The knowledge was gained that the water lock effect provides the favorable trapping and accumulation conditions for this gas reservoir, and the hydrocarbon gases within the reservoir can migrate upward through different ways （such as diffusion and permeation）. The Jurassic gas reservoir of Well Yingnan 2 was chosen to conduct the research of the geochemical field characteristics and the anomaly patterns of the light wire-adsorbed hydrocarbon （G2-8） and the heavy wire-adsorbed hydrocarbon （C15-19） indicators. It is found that both the characteristics of the geochemical field and the anomaly patterns of the 2 kinds of indicators differ obviously from each other. The analysis results indicate that the water lock effect of the tight sandstones and the microseepage and diffusion ways of the hydrocarbons are the root causes of these differences; and the diffusion rate of the light hydrocarbons within the water-locked sandstone area in the gas reservoir is less than that within the area without water lock effect in the edge of the gas reservoir, which causes the high anomaly values of the light wire-adsorbed hydrocarbons （C2-8） in the edge of the gas reservoir and the sub-high anomaly values of these hydrocarbons in the gas reservoir area. The study also indicates that the low-content of heavy hydrocarbons in the gas reservoir and the local diffusion coefficient of the reservoir hydrocarbon gases are the geological causes of the high value anomaly of the heavy wire-adsorbed hydrocarbon indicators （ C15-19 ） over the top of the this gas reservoir.