济阳坳陷花沟—高青气田CO2气成因与成藏机制——兼对莺歌海盆地CO2气成因的质疑

ORIGIN AND ACCUMULATION OF CO2 GAS IN HUAGOU-GAOQING GAS FIELD, JIYANG DEPRESSION

花沟-高青气田是济阳坳陷唯一的纯气田, 存在着多种类型的天然气藏, 以CO2气藏为主.气藏围绕青城凸起分布, 天然气组成呈东西分区特点(烃类气藏分布于东部-北部, 西部以CO2气藏为主), 这与凸起东邻博兴生烃洼陷以及西部火山活动强烈有关.西部气藏中CO2含量高达70%以上, δ13CCO2值范围为-3.4‰～-4.5‰, He气含量大于1%, 3 He/*$4 He比值为3.55×10-6～4.49×10-6, 为岩浆-幔源成因; 花501井馆陶组气藏CO2含量大于30%, 而N2含量大于50%, 系幔源成因为主的CO2-N2气藏.有利于形成CO2气藏的大地构造环境是地幔隆起和超壳断裂-岩浆活动带.花沟-高青气田CO2气藏正处于上新世-中新世玄武岩分布区内, 每一期岩浆的侵入和喷出就是一次成气期和可能的成藏期.上新世是本区最主要的非烃类气体的成藏期.在岩浆活动以前形成并与气源断裂直接连通的构造为CO2气聚集的有利圈闭.与此相比, 莺歌海盆地CO2气不大可能是含钙砂泥岩的热解产物,其形成很可能与中新世岩浆热液活动有关.

Huagou_Gaoqing field is the only pure gasfield in Jiyang Depression, where there are multiple types of gas reservoir dominated by CO 2. These gas reservoirs surround Qingcheng Arch and can be divided into two groups in terms of gas composition(with the northeast group dominated by hydrocarbon gas and the west group by CO 2), which may result from adjacent hydrocarbon_generation Boxing Sag east of the Arch and the western intense volcanism. For the west group reservoirs, CO 2 may be over 70%,δ 13 C CO 2 may range from-3.4‰ to-4.5‰, and He is over 1%. The He gas has 3He/? 4He ratios from 3.55×10 -6 to 4.49×10 -6 , indicating its magma_mantle origin. In Hua_501 well, Guantao Formation is a CO 2?N 2 reservoir with a mantle_dominated origin due to its CO 2 over 30% and N 2 over 50%. The tectonic environments favorable to CO 2 accumulation are mantle bulges and crustal faulting_magmatic activities. The CO 2 reservoirs in Huagou_Gaoqing field occur just in a Miocene_Pliocene basalt area, where each magmatic intrusion and eruption may become a phase of gas generation and accumulation. The structures that formed prior to magmatic activities and are connected with gas_source faults may be traps favorable to CO 2 accumulation. As compared with this, the CO 2 in Yinggehai Basin is unlikely to be pyrolysis product of calcareous sandstone and mudstone, and its origin is possibly related to Miocene magmatic hydrothermal activities.