乌石凹陷西洼烃源条件及勘探潜力分析

Hydrocarbon source conditions and exploration prospect in the west sag of Wushi Depression

为了解决北部湾盆地乌石凹陷西洼烃源条件认识不清、下一步勘探方向不明等勘探难题,以乌石西洼烃源岩和有利勘探目标为研究对象,采用地震资料类比、沉积相和有机相类比、周边井分析等研究方法,类比分析了乌石西洼烃源分布层系、烃源品质和生烃潜力,指出了西洼的烃源岩特征及下一步重点勘探方向。研究结果表明:(1)乌石凹陷西洼发育始新统流沙港组二段、流沙港组一段、渐新统涠洲组二段3套烃源岩,沉积相和有机相类比预测乌石西洼流二段、涠二段烃源岩主要为C型有机相,烃源品质优,流一段主要为A型有机相,烃源品质较好;(2)流二段、流一段、涠二段3套主力烃源岩均已成熟,生烃量达到10×10^(8)t,西洼潜在资源量为1×10^(8)t;(3)研究区发育多套有利的储盖组合,其中涠洲组、新近系埋深浅、储层物性好,是当前有利的勘探层系。结论认为:(1)乌石凹陷西洼流二段、流一段、涠二段3套烃源岩品质优、分布范围广,生烃潜力大;(2)乌石凹陷西洼发育乌石A、B等多个断背斜、断块圈闭,油气成藏条件优越,勘探潜力大,是下一步油气勘探的重点评价目标。

To make clear both hydrocarbon source conditions and next exploration directions in the west sag of Wushi Depression, the source rocks and favorable targets in this sag were taken as objectives to perform some analog analysis on the distribution, quality and hydrocarbon-generating potential of the source rocks by means of the analog of seismic data, and sedimentary and organic facies as well as certain analysis on periphery wells.Moreover, source-rock characteristics and the next key exploration directions were summarized and pointed out.Results show that(1) there exist three sets of source rocks in the west sag, namely Eocene Liushagang 1 and Liushagang 2 Members together with Oligocene Weizhou 2 Member. An analog prediction on both sedimentary and organic facies indicates that the source rocks of both Liushagang 2 Member and Weizhou 2 Member are mainly of high quality with type C organic facies while that of Liushagang 1 Member is better with type A;(2)these three sets of principal source rocks are all mature with hydrocarbon-generating capacity up to 10×10^(8)t,and the quantity of potential resources is 1×10^(8)t in the west sag;and(3) there are multiple favorable reservoircaprock assemblages, among which, not only Weizhou Formation but the Neogene may currently serve as beneficial sequences with shallower burial depth and better physical properties. In conclusion, these source rocks in the west sag of Wushi Depression(including Liushagang 1 and Liushagang 2 Members as well as Weizhou 2Member) are characterized by excellent quality, wide distribution and great hydrocarbon-generating potential.What’s more, a few faulted-anticline and faulted-block traps containing Wushi A and Wushi B are extended,boasting favorable reservoir-forming conditions and vast exploration prospect, which can be conducted as critical evaluation targets in the subsequent exploration.