Deposision Characteristics Of Changxing Formation In Yuanba Area，Northeast Sichuan

In recent years, the situation of exploration in the northeastern Sichuan showsthat this region has great potential for gas exploration. Puguang, Longgang, and otherlarge gas fields have been discovered, Yuanba become the focus of attention of oilcompanies and researchers, and has been achieved an important breakthrough. Thestudy revealed Yuanba area major producing reservoir was a dolomite reservoir whichwas located in the top of the Changxing Formation. the reservoir at the top of reefshowed a strong reflection on the seismic profiles, like a lid on the nearly blankreflection reef, so called reef cover. Predecessors has done a lot of work for reef coverreservoir in Yuanba, and achieved a certain degree of knowledge and results.But innew situation, there are many questions such as division of sedimentary facies is notaccurate and has great differences.On the basis of previous research, this paper use of sequence stratigraphystandardized technology roadmap, establish sequence stratigraphic framework ofChangxing Formation in Yuanba area. And, respectively, use of seismic line drawing、wells-seismic contrast and seismic scanning technology to study stacking patterns offormation、facies on well-connecting profile and seismic facies of lowstand systemstract in the top of Changxing. Finally, through the combination of litho-facies andseismic facies, this paper research on the sedimentary facies and reservior predictionof the top of the lowstand systems tract. Ultimately, to achieve the following progressand understanding：(1) From deposition trend analysis of single well to establishment of thesequence stratigraphic framework in Changxing Formation, five systems tracts areidentified through the application of sequence stratigraphy standardizedtheoretical.From the bottom of these systems tracts respectively is LST、TST、HST、FSST and LST which is bounded by mfs1、mfs2、mfs3、CC**. In the transverse, thesefive systems tracts contrast good.(2) It is obtained that stacking patterns of reef and bank are mainly verticalaggradation and Lateral aggradation, on the basis of using layer flattening method torestore original shape of sedimentary basin,through applying seismic line drawing toanalyze stacking patterns of the lowstand systems tract at the top of ChangxingFormation. Ultimately, in the terms of stacking patterns, it is knew that carbonatewhich is mainly to chemical depositie is different from clastic that mainly to depositethrough transporting of river.(3) Through litho-facies and seismic facies contrast each other, repeatedlydemonstrate and modify,it is obtained that the sedimentary facies of lowstand systemstract at the top of Changxing Formation is composed of basin、slope、platform margin and open platform. Sedimentary facies diagram of lowstand systems tract at the top ofChangxing Formation show that reef and bank during this period are well developed,reef grow mainly on platform margin and distribute from the North West to SouthEast, bank develop mainly on open platform and distribute to different direction.(4) Through palaeogeomorphology of the period which in the early of lowstandsystems tract at the top of Changxing Formation contrast with Sedimentary faciesdiagram of lowstand systems tract at the top of Changxing Formation, it is found thatthe reef which in the lowstand systems tract at the top of Changxing Formation ismainly developed in height of the ancient geomorphological, this prove thatpalaeogeomorphology is an important factor in leading reef development of lowstandsystems tract at the top of the Changxing Formation.(5) On the basis of above studies, the reef cover reservoir that in the lowstandsystems tract at the top of Changxing Formation is delineated10main distributionzone. And according to the seismic amplitude strength,4most favorable zone is thedirection of further exploration and development for Yuanba area.