长岭断陷深层天然气成藏期研究

利用榆深1井营城组未熟样品的热模拟实验、碳同位素分馏实验以及长深1等井的流体包裹体测试结果,在热史恢复的基础上,根据化学动力学和碳同位素分馏动力学理论,从烃源岩生烃史、甲烷碳同位素分馏效应以及包裹体均一温度等方面,对长岭断陷天然气成藏期加以判断。长岭断陷甲烷碳同位素均值为-33.11‰,碳同位素分馏效应显示天然气为116 Ma以来累积聚集成藏;生烃史表明营城组源岩在100～67.7 Ma大量生气,沙河子组在125～74 Ma达到生气高峰;同时包裹体证据表明查干花次洼的烃类气主要在110～78 Ma聚集成藏,伏龙泉次洼主要在110～1 Ma成藏。成藏期的判断结果说明:长岭断陷沙河子组早期生成的天然气未聚集成藏,仅116 Ma以后生成的天然气才具有成藏贡献,损失约14%左右;而营城组烃源岩生烃较晚,有利于成藏,包裹体证据也印证这一观点。

Accumulation Periods of Deep Gas Reservoirs in Changling Fault Depression

Using thermal simulation experiment and carbon isotope fractionation experiment of immature samples of the Yingcheng Formation in Yushen 1 well,as well as the fluid inclusion test results of the Changshen 1 well and other informations,the thermal history of the area was reconstructed.The gas accumulation periods of the Changling fault depression are further analyzed based on chemical kinetics and dynamics of carbon isotope fractionation,hydrocarbon generation histories,fractionation effect of methane carbon isotope and inclusion homogenization temperature.The main methane carbon isotope of the Changling fault depression is averaged at-33.11 ‰ and the carbon isotopic fractionation effect shows that the natural gas in the depression was formed since 116 Ma;hydrocarbon generation history indicates that the peak hydrocarbon-generating stage of the Yingcheng Formation is 100-67.7 Ma while the Shahezi Formation reached its gas generation peak around 125-74 Ma;Furthermore,the evidence from the fluid inclusion studies indicate that the hydrocarbon gas in Chaganhua sub-depression were mainly formed at 110-78 Ma and the hydrocarbon gas in the Fulongquan sub-depression were mainly formed during 110-1 Ma.Our result on the gas accumulation periods indicate that the gas generated at early stage in the Shahezi Formation was not accumulated.Only those gas generated after 116 Ma were accumulated,thus lost about 14% of the total gas generated.However,the natural gas generated later were mostly accumulated.The conclusion is also supported by the fluid inclusion evidence.