塔中地区北坡中—下奥陶统早成岩岩溶作用及储层形成模式

Eogenetic karstification and reservoir formation model of the Middle-Lower Ordovician in the northeast slope of Tazhong uplift,Tarim Basin

高频层序界面下发育的多种类型早成岩岩溶与埋藏阶段沿着断裂带发育的深成岩溶叠加作用,成为深层—超深层碳酸盐岩储层发育的关键要素。在梳理岩溶作用概念的基础上,通过对塔中地区北坡顺南地区深层—超深层中—下奥陶统岩心、薄片岩石学和阴极发光观察以及流体包裹体和稳定氧、碳同位素分析,结合3D地震均方根振幅和古地貌恢复,不仅从微观上识别出了高位体系域上部同生岩溶和层间岩溶作用类型,并从宏观上建立了这种早成岩岩溶储层"准层状"发育模式,认为受控于古地貌和断裂的早成岩岩溶型储层因后续碳酸盐胶结物充填严重,平均残留孔隙度仅约2.0%,但叠加深成岩溶改造了的储层的最高平均孔隙度可达约19%。因此,早成岩岩溶叠加深成岩溶型储层将成为研究区深层—超深层下古生界斜坡带勘探的重要目标。

Superimposition of multiple types of eogenetic karsts developing under high-frequency sequence boundary and hypogenic karsts developing along fault belts during burial diagenesis becomes a key factor of deep-ultradeep carbonate reservoir development.Based on an outline of karstification concept,deep-ultradeep Middle-Lower Ordovician strata in Shunnan area in the northern slope of Tazhong uplift,Tarim Basin were studied by means of core observation,thin-section petrological observation,cathodoluminescene imaging,fluid inclusion measurement,stable oxygen and carbon isotope analyses,as well as RMS amplitude computation for 3D seismic data and paleotopography restoration;not only syngenetic karst and interstratal karst types in the upper highstand system tract were microscopically identified,but also a＂quasi-layered＂development model for such eogenetic karst reservoir was established macroscopically.It is believed that,being seriously filled with subsequent carbonate cement,the eogenetic karst-type reservoir controlled by paleotopography and paleofault had a mean residual porosity of just about 2.0%,whereas the reservoir transformed by hypogenic karst superimposition had a maximum mean porosity up to about 19%.Therefore,reservoirs with eogenetic karsts superimposed by hypogenic karsts will become important targets of exploration in deep-ultradeep Lower Paleozoic ramp zone in the study area.