High-resolution Sequences Stratigraphy And Main Sandstones Extend Of Bashijiqike Formations Of The Cretaceous In The Kuqa Depression, Tarim Basin, XinJiang

Through the comprehensive analysis of outcrops , rock cores ,well logs, and under the guidance of the theory and technology of the high-resolution sequences stratigraphy founded by T.A.Cross, two middle-term cycles were divided, namely, four hemicycles in the Bashijiqike Formation of the Cretaceous in the Kuqa Depression, Tarim Basin,XinJiang. On the basis of these four hemicyles,the high-resolution sequences stratigraphy framework constructed.The ralationship between the base-level cycles and the characters of reservoir such as porality and permeability is intimate. When deposited in lower accommodation and lower mid-term base-level, these characters of reservoir are favorable.when accommodation and mid-term base-level were all high, these characters of reservoir are unfavorable. According to these relationships, the reservoir type of Bashijiqike Formation has been forecasted. The second and the third hemicycles are the best hemicycles.Accordingly,their sandstones were more beneficial sandstones.Bashijiqike Formation of this area has three different provenances which located in kelasu zone, Dina-Yaha zone, Dabei-Tubei zone.Therefore,it formed three deltas.It's main sedimentary facies are alluvial facies , delta facies , lacustrine facies .The granularity were normaly graded from Notrth to South.The sedimentary facies has close relationship with the characters of reservoir such as porality and permeability too. Sedimentary environment affects primary porisity, and the dissolution of calcite cement formed secondary porisity.With comparision of different subfacies,such conclusion can be drawn. Braided delta front subfacies and the curve area of lacustrine facies are the most favorable subfacies. The best location consisted in the middle west of Keyi tectonic zone and in the east of Qiulitage tectonic zone,especially Kela201 well, Kela203 well, Kela2 well, Kela3 well and Dongqiu5 well, Dongqiu8 well.On the basis of the above studies,the favorable sandbodies were the Braided delta front sandstones and Eolian sandstones which lied in the the second and the third hemicyles in the middle west of Keyi tectonic zone and in the east of Qiulitage tectonic zone. The most favorable sandstones are the sandbodies from Kela201 well Kela203 well, Kela2 well, Kela3 well and Dongqiu5 well, Dongqiu8 well.