松辽盆地大庆长垣南部浅层气富集规律及潜力评价

Shallow gas accumulation pattern and potential evaluation in southern Daqing placanticline,Songliao Basin

浅层气作为我国非常规油气勘探与开发的新领域,具有极大的资源潜力。利用岩心、测井、三维地震和室内分析化验等资料,对松辽盆地大庆长垣南部黑帝庙油层浅层气气藏类型、分布特征、成因机制及富集主控因素进行研究,结果表明:受背斜构造背景与多方位断层分割,气藏圈闭主要有背斜、断背斜、断块和断鼻4种类型;气藏平面上受正向构造影响,主要分布在背斜和鼻状构造高点,垂向上受储盖组合特征影响,主要分布在中、下部H5Ⅰ—H1Ⅱ小层;葡萄花构造天然气成因为生物气,主要来自嫩江组一段、二段,葡西鼻状构造天然气成因为生物气、油型气和无机成因气组成的混合气,分别来自嫩江组一段、二段、青山口组和深部。进而总结出黑帝庙油层浅层气富集主控因素:1多套优质烃源岩构成了浅层气富集基础;2气源断层与有效盖层匹配控制浅层气富集层位;3河控三角洲前缘亚相砂体构成了浅层气富集优质储层;4断层侧向封闭性决定浅层气富集规模。最终建立了浅层气成藏模式:明水组沉积末期构造反转定型,断层密集带边界断层复活开启,下伏烃源岩生成的天然气沿着气源断层上运,然后进入与气源断层沟通的水下分流河道、河口坝和远砂坝优质储层砂体短距离侧向运移,最终在背斜、断背斜、断块和断鼻圈闭中聚集成藏。在气测解释基础上采用容积法计算浅层气累计地质储量86.8×108m3,并刻画出7个浅层气富集区块。

As a new field of unconventional oil and gas exploration and development in China,shallow gas is large in resource potential. Various data including core,well logging,3D seismic and laboratory test data were integrated to study the shallow gas reservoir types,distribution characteristics,genetic mechanism and main controlling factors of shallow gas enrichment. The following results were obtained. The gas traps are controlled by anticline structure background and segmentation of multiple faults and there are mainly 4 types of gas reservoir traps,including anticline,faulted-anticline,faultblock and fault-nose. And the areal distribution of gas reservoirs is controlled by the positive structures and they mainly occur at the high positions of anticline and nose structures. Vertically,the single layer HⅠ^5—HⅡ^1,which is in the middle and lower parts of formation,is the main gas bearing interval affected by reservoir-cap assemblages. Gas in the Putaohua structure is mainly of biological genesis and is sourced from the first and second members of the Nenjiang Formation. In contrast,gas in the Puxi nosing structure is generated from the first and second members of the Nenjiang Formation,Qingshankou Formation and deeper formations,and is a mixture of biological gas,oil-type gas and abiogenetic gas. On this basis,the main controlling factors of shallow gas enrichment in Heidimiao reservoirs are summarized as follows： 1multiple sets of good hydrocarbon source rocks offer a material basis for shallow gas; 2reasonable timing of gas source faults and effective cap rock controls the horizons of shallow gas accumulation; 3sandbodies of fluvial-dominated delta front act as high quality reservoirs; 4lateral sealing capacity of fault ddetermines enrichment scale of shallow gas. Finally,the shallow gas accumulation pattern is established and showed as follows： tectonic reverse happened at the end of the Mingshui For-mation stage,and the boundary faults in the areas with densely distributed faults were activated and opened,so that gas generated by the underlying source rocks migrated upward along the source rock-rooted faults into the high quality reservoirs connected well with the source rock-rooted faults,such as under water distributary channel,mouth bars and distal bars. After a short distance lateral migration in the high quality reservoirs,the shallow gas accumulated in anticlinal traps,fault-anticline,fault-block and fault-nose traps. The cumulative geological reserve of shallow gas was calculated to be 8. 68 BCM by using volumetric methods on the basis of gas logging interpretation and 7 potential target areas were identified.