银额盆地YHC1井白垩系气藏形成的地质环境及其远景意义

Geological environment and prospective significance of Cretaceous gas reservoir in Well YHC1 of Yin'e Basin

作为国内为数不多的未进行系统油气勘探、开发的大型古—中生代多旋回叠合沉积盆地,YHC1井气藏的突破势必将引领银额盆地进一步的勘探投入,促进银额盆地新区块、新层系油气的新发现,从而使其成为未来的勘探重点。通过地质与地球物理方法相结合,钻测井、地震、古生物、地球化学等资料"四位一体",首次对银额盆地YHC1井白垩系气藏形成的地质环境进行了深入的研究,尤其是在地层展布、构造发育、烃源岩特征、沉积储层分析、成藏模式及远景意义等方面取得了如下重要成果和新认识:1研究区发育2套主要目的层系——中生界白垩系K、上古生界C—P,其中白垩系整体分布广、厚度大,哈日凹陷、拐子湖凹陷是它的主要发育地区,YHC1井位于沉积中心,保证了YHC1白垩系气藏地层体系的完整性。2研究区内呈现"凹凸相间"的构造格局,断裂均为正断层,多集中在各凹陷的中央,控凹边界断裂控制着研究区的构造格局和沉积体系发育,形成北北东走向的单断箕状凹陷,促进了YHC1井白垩系气藏储集空间的形成。3白垩系沉积时期YHC1井一直处于良好的有效烃源岩富集区,烃源岩成熟度好,生烃潜力大,其巴音戈壁组发育的大套深灰色—黑色含灰泥岩成为该气藏形成最重要的基石。4白垩系发育的沉积体系为水下扇、扇三角洲、辫状河、辫状河三角洲、湖泊和火成岩相,YHC1井优势体系多为半深湖—深湖沉积体系,决定了有机物的转化、保存以及储层发育的环境。5钻井揭示白垩系沉积时期,YHC1井偶见Ⅲ类和Ⅳ类储层,多以Ⅴ类(非)储层出现。6YHC1井巴音戈壁组出气层段可能为裂缝贯通及溶蚀孔洞的含碳酸盐质泥岩气藏体系,推断属源内成藏的特殊岩性油气藏。

As the few large Paleozoic and Mesozoic superimposed sedimentary basin with multiple cycles and non-systematic exploration and exploitation,the breakthrough of Well YHC1 must lead a further exploration input to Yin＇e Basin and promoted the new oil-gas discovery of new region and formation in Yin＇e Basin which will become the future exploration aim.Combined with geology and geophysics,using quaternity of drilling and well logging,seismic data,palaeobiologies and geochemistry,it was the first time to do the research on geological environment of Cretaceous gas reservoir in Well YHC1 of Yin＇e Basin.And especially we got the following important achievements and new understandings in stratigraphic distribution,tectonic development,source rocks feature,deposition and reservoir analysis,reservoir model and prospective significance：（1）There are two main targets formations,K of Cretaceous in Mesozoic and C-P of Upper Paleozoic.Cretaceous covers widely in this region and has big thickness.Hari and Guaizihu Depressions are the main development areas of it.Well YHC1 locates in the depositional center,which ensures the integrity of stratigraphic units in Cretaceous gas reservoir.（2）The tectonic framework shows alternate concave and convex feature.The faults are all normal and mostly centralized in the center of each depression.Fault-margin controls the whole tectonic framework and depositional systems of the research area and forms the NNE-strike half graben-like basin.The tectonic activity promotes the formation of reservoir space in fractured-cavernous mudstone of YHC1 Cretaceous gas reservoir.（3）In Cretaceous,Well YHC1 was always in a rich effective source rock region with good maturity and great hydrocarbon potential.And a large set of dark grey-black limy mudstone in Bayingebi Formation becomes an important foundation of this gas reservoir.（4）The Cretaceous depositional systems contain subaqueous fan,fan delta,braided river,braided river delta,lake and igneous faces.The preponderant depositional systems of Well YHC1 are semi-deep and deep lacustrine depositional systems which decide the transformation and preservation of organic materials and developmental environment of reservoir.（5）The exploratory data shows that during the period of Cretaceous,III and IV class reservoirs were occasional and V class（non）reservoir was the main type of Well YHC1.In view of this,we promptly change the exploration idea,expand the exploration object and bring limy or lime mudstone of Well YHC1 into exploration range.Through this bold attempt to fractured-cavernous special reservoir,we finally get the historical breakthrough.（6）The gas property of Bayingebi Formation in Well YHC1 is probably a system of carbonate mudstone with through cracks and dissolved vugs,belonging to special lithologic reservoir within source accumulation by inference.