碳酸盐岩变形带特征及其与油气关系——以塔里木盆地下古生界为例

Characteristics of Carbonate Deformation Band and its Significance for Hydrocarbon Exploration——An Example from the Lower Paleozoic in the Tarim Basin

深入了解变形带的差异性对碳酸盐岩储层渗流作用与油气勘探开发研究具有重要意义。通过野外露头、井下岩心的宏观与微观特征分析,发现塔里木盆地下古生界碳酸盐岩变形带发育,存在压实变形带、剪切变形带和膨胀变形带等3类成因变形带。根据变形带的发育演化特征可以进一步划分为8种类型:压实变形带又可分为解聚压实变形带、碎裂压实变形带和压溶压实变形带3种类型;解聚剪切变形带、碎裂剪切变形带和胶结剪切变形带则是3种常见的剪切变形带;膨胀变形带包括碎裂膨胀变形带和胶结膨胀变形带。不同类型变形带特征各异,以解聚压实变形带与碎裂剪切变形带最发育,各类变形带呈现从解聚型向剪切型和胶结型演变的趋势。不同于碎屑岩变形带渗透性急剧降低,塔里木盆地碳酸盐岩变形带的物性与围岩差别较小,不同次级类型变形带渗流特征不同,局部孔隙发育,并影响油气储层非均质性。受控于溶蚀、破裂与白云石化等三种后期改造作用,塔里木盆地下古生界碳酸盐岩发育高渗透变形带,可能形成有效渗流通道。

The insight of the differentiation between sandstone and carbonate deformation bands is significant to seepage effect and production dynamic monitoring in hydrocarbon reservoirs. Based on the macroscopic and microscopic analysis of the lower Paleozoic carbonate rocks from the outcrops and wells in the Tarim basin, we found that deformation bands can be divided into 3 types by mechanism and 8 subtypes by kinematics. The compaction band can be subdivided into disaggregation, cataclastic and pressolution compaction band. There are various shear bands including disaggregation shear band, cataclastic shear band and cementation shear band. Cataclastic and cementation bands of subtypes can be found in dilation bands. Except for different features in subtype deformation bands and well-developed disaggregated compactional bands and cataclastic shear bands, the evolution characteristics of them indicated that they all evolved from a disaggregation subtype to a cataclastic subtype, then to a dissolution and cementation subtype. In contrast with their strongly lowering permeability of sandstones, the deformation bands did not cause significant petrophysical property changes of the lower Paleozoic carbonate in the Tarim basin. Although the permeability reduced in the early deformation stage, there is not much difference of permeability between deformation bands and host rocks by long-term diagenesis and polytype permeability increase effects. There are local high porous zones developed in shear deformation bands as well as some other kind deformation bands, which influence the reservoir heterogeneity to some extent. In spite of the permeability reduction in most deformation bands with different effect on fluid flow, it is demonstrated that there are some high permeability deformation bands in the lower Paleozoic carbonate in the Tarim basin. The structural diagenesis of dissolution, fracturing and dolomization resulted in the effective reservoirs and efficient seepage channels of some local deformation bands, the cataclastic shear bands in particular, which is obvious different from that in the Meso-Cenozoic reservoirs.