Analysis Of Sequence Stratigraphy And Key Uncomformity In Ordovician In Tazhong Area, Tarim Basin

Tazhong area belongs to Trim basin. The researched formation is the Ordovician. Based onthe theory of P.R.Vail's seismic stratigraphy sequence, the features of the stratigraphy sequence inthis region were studied with the seismic and well-logs data. We selected 10 seismic profiles asframework lines, and analyzed 4 seismic profiles elaborately on seismic configuration. Ordovicianis marked off 4 sequence by well-logs: S5, S6, S7 and S8. On the basis of the isochronous stratigraphy framework, and through the study ofdepositional facies and depositional system of Ordovician,the author summarize the majortypes,the sequence,the longitudinal evolvement features of Ordovician depostional facies,and thecombination relationships in the surface as well as the distribution rules of each sequence, andpoints out the features and distribution of depostional systems are strict controlled by the sea levelchange, palaeostructure and palaeogeography. We identify the precipitation facies : the evaporatedplatform, the restricted platform, the open platform , the margin of platform and the shelf facies.Ordovican is generally an inundation phase. Through the longitudinal evolvement process, theevaporated platform, the restricted platform, and the open platform ,are developed in Ordovicianof Tazhong area from bottom to top,and evolved into the margin of platform and the shelf faciesgradually. According to the spread of stratigraphy distribution and depostion is affected bypaleogeography and palaeostructure, through identifying and tracing the truncation and diastemsurface of depostion from seism and togethering with the analyse of well-log, we study the portraitserial distribute and summarize the characters of the key uncomformity (viz.T_7⁴) in Ordovician. Through identifying and tracing the reflection characters from the seism, we summarize thecharacter of the key uncomformity;Together with analysing and demarcating of seism andwell-log, we identify the geological attribute about the uncomformity and outline the distributearea of isochronous or lithology or isochronous-lithology uncomformity; In virtue of the reflecttrend of the seism , the constructible character of the seism, the relations of the lithologycombination and depositing thickness, and so on ,we take the emphasis research about thephenomenon of onlap and truncation from the seism and qualitative and quantitative analyse theerosive degree about the key uncomformity. Combined with the configuration among generating rock, reservoir and cap and with thegenerating conditions of oil-gas reservoir , the paper evaluates the reef-bank reservoir ofOrdovician in Tazhong area, and designates two prospecting oil-gas zones: burial hill zone andaroud area in Tazhong, the margin slope zone of platform in Ordovician.