天然气混合比例研究新方法及其应用

NEW METHOD OF INVESTIGATING THE MIXING PROPORTION OF NATURAL GAS AND ITS APPLICATION

松辽盆地深层存在多套有效气源岩,导致多源天然气混合成藏的现象非常普遍.由于无法直接获得单源气,混合天然气比例的确定是始终没有能解决的难题,这在一定程度上制约了松辽盆地深层天然气的勘探.为此,研制了密闭撞击式岩石吸附气制备仪.针对松辽盆地深层大量高成熟-过成熟源岩样品的实验结果证明,制备的源岩吸附气可以近似地作为单一来源的天然气.用C5～C7重烃化合物组成的指标和甲烷碳同位素值,建立了混合气藏中各种来源气所占比例的计算方法.用该方法对松辽盆地北部徐家围子断陷昌德气田3口井天然气的混合比例进行探索性研究,获得了基本可信的定量结果:该井区65%～75%的天然气来源于沙河子组和火石岭组气源岩,其余部分来自登娄库组、营城组和盆地基底石炭-二叠系地层.

There exist multiple series effective gas source rocks in Songliao Basin, thus causing multiplr-source gas reservoir formation in the basin. Owing to the fact that the single-source gas samples couldn’t be collected, it was difficult to determine the mixing proportion of natural gas, by which the deep gas exploration in the basin was restricted to a certain extent. For this reason, a closed impact rock-adsorbed gas preparation device was developed by the authors. In light of the experimental results of a large number of the high maturity-postmaturity source rock samples collected from the deep strata in the basin, it was proved that the prepared source rock-adsorbed gas may be regarded as the single-source natural gas. A new method of calculating the mixing proportion of multiple-source gases in the reservoir was established by use of the indexes composed by C_5—C_7 heavy hydrocarbons and methane carbon isotopic ratios. Through calculating the mixing proportions of gas samples from the three wells in Changde gas field in Xujiaweizi fault depression of Songliao Basin by applying the method, the authors achieved a credible conclusion that 65—75% of the natural gases in this area might be generated in Shahezi Formation and Huoshiling Formation and the others came from the Denglouku Formation and Yingcheng Formation as well as the basement of Carboniferous-Permian.