The Analysis Of The Unconformity In The Upper Cambrian To The Lower Ordovician Of The Tarim Basin

Research on deep carbonate reservoirs in Tarim is the focus of current work, and studies suggest that research of unconformity has a certain significance on the exploration of oil and gas.We analysis the unconformity in the Upper Cambrian to the Lower Ordovician of the Tarim basin by reseach outcrops in Bachu-Kalpin Area, wells mainly in Tahe, and seismic data. The outcrops include the Shuinichang in Kalpin area, Penglai, Yongan and Yingshanbeipo and so on.We study the unconformity in the wild by the observation of the weathering crust,lithology,colour and the change of stratigraphic stacking patterns and on-site measurement of f major element and GR value;In Tahe Area, wells drilled down to Yingshan formation include TS1, TS2, Ts4, S88,and AD11 etc. Among them TS1, TS2, S88 were drilled through Yingshan formation. Those wells are the focus of our study. We study the unconformity in the wells through the observation and measurement of core,the analysis of the thin section and the conventional loggingy; The study make full use of seismic data in Tarim area mainly include Tahe and Tazhong.I concluded that the T₈¹ and T₈⁰ interface are second order unconformity interface, T₇⁸、T₇⁶and T₇⁵ are tertiary unconformity interface, These interface show up as parallel unconformity and micro- angular unconformity. Lithologic contact relationship above and below the interface mainly include limestone- limestone, limestone- dolomite, dolomite- dolomite. In most cases, the colour above the interface is different with that below the interface.The elements persis show up some characteristics at the interface,For example,Al, Fe, Ti and other inert elements enrich at the interface, Elements such as Sr, Ba, K show up a oupling relationship with the interface.We identify three transitional surfaces.of diferent parasequence set intraYingshan formation, The Yingshan formation is divided into 4 four order sequences by the three transitional surface. We find Comparable characteristics of those 4 four order sequences in GR curve.We consider interface in Tarim intra- Yingshan formation andT₈⁰、T₇⁸、T₇⁵ are mainly controlled by the change of sea level. T₈⁰、T₇⁸and nterface intra- Yingshan formation are exposure unconformity caused by the drop of sea level. T₇⁵ interface in the wild and the Tahe region are both controlled by sea-level change, at Shuinichang in Kalpin the T₇⁵ interface is drowned unconformity caused by the rise of sea leave relatively abrupt, In Tahe Area,the T₇⁵ interface is exposure unconformity caused by the drop of sea level.The I level and II leve unconformites is the critical factor of the development of carbonate karst reservoirs in the Tarim Basin, III level and IV leve unconformites developed karst cave system in many times by causing eriodic exposure of the carbonate rocks.