断陷盆地顺向断阶带油气充注期次与成藏模式——以渤海湾盆地歧口凹陷埕北断阶带为例

Hydrocarbon charging stage and accumulation mode of forward fault step zone in fault basin:taking the Chengbei fault step zone in Qikou Sag,Bohai Bay Basin as an example

我国东部断陷湖盆多发育断阶带构造,其中顺向断阶带比例较高,其时空配置关系和油气成藏期次、成藏条件对区域油气勘探地质评价起着关键性作用,但研究难度大。渤海湾盆地歧口凹陷埕北断阶带是具有典型意义的顺向断阶带,为了进一步明确其油气成藏模式和充注期次,以古近系东营组和沙河街组为主要目的层,选取歧东3-1井、张10井和埕海16井分别代表断阶区的低、中、高断阶,通过储层显微岩相观察、流体包裹体鉴定、盐水包裹体均一温度和盐度测试、GOI统计分析等技术,对埕北各区不同充注期的油气性质和分布规律进行了研究;应用激光拉曼测试对张10井和歧东3-1井单个包裹体的气体成分进行有效识别,结合歧东3-1井单井埋藏史、古地温史图和自生伊利石K-Ar同位素测年技术,确定出埕北断阶区的具体油气成藏时间,并在调研和样品实验的基础上总结了埕北区的烃源岩、储集层、保存和运聚4个成藏要素条件。研究区储层存在2期充注:第一期油气具体成藏时间在东营末期—馆陶初期,约16 Ma左右;第二期成藏时间在明化镇初期,从6 Ma左右开始延续至今。研究区具有多套生储盖层,发育的断阶构造对源储的沟通和油气的封堵、保存和运聚成藏起到控制作用;区域成藏条件较为成熟,在油气成藏过程中体现出双源供烃、多期成藏的横向运聚模式和断砂耦合、接力爬坡的纵向运聚模式。

Fault step zones are well developed in faulted lake basins in the eastern part of China,among which,forward fault step zones account for a large proportion,and their spatiotemporal configuration relationship,oil and gas accumulation periods and accumulation conditions,which play a key role in the geological evaluation of regional oil and gas exploration,are difficult to study.In order to further clarify its hydrocarbon accumulation mode and filling period,the authors,by taking the Paleogene Dongying and Shahejie formations in the study area as the main target layers,and selecting wells Qidong 3⁃1,Zhang 10 and Chenghai 16 to represent the low,medium and high fault levels of the fault area,respectively,conducted in⁃depth research on the oil and gas properties and distribution laws of different charging stages in various districts of Chengbei through reservoir microlithography observation,fluid inclusion identification,salt water inclusion homogenization temperature and salinity test,GOI statistical analysis and other technologies;applied laser Raman test to effectively identify the gas composition of single inclusions in wells Zhang⁃10 and Qidong 3⁃1,determined the specific oil and gas accumulation time in Chengbei fault step zone in combination with the single well burial history,paleogeothermal history and autoclastic illite K⁃Ar isotopic dating technology of well Qidong 3⁃1,and summarized the four accumulation elements of source rocks,reservoirs,preservation and transportation in Chengbei area.There are two charging stages in the reservoir,the specific accumulation time of the first stage is from the end of Dongying to the early stage of Guantao,about 16 Ma±,while that of the second stage is in the early stage of Minghua Town,starting from 6 Ma±and continuing to the present.Multiple sets of reservoir layers are developed in the study area,and the special fault step structure plays a controlling role in channeling the source rocks and reservoirs,the sealing and preservation of oil and gas,and the transportation and accumulation of reservoirs.The regional accumulation conditions are relatively mature,and the lateral migration-accumulation mode of dual⁃source hydrocarbon supply and multi⁃stage accumulation and the longitudinal migration-accumulation mode of fault-sand coupling and relay climbing are reflected in the process of oil and gas accumulation.