Characteristics Of Sequence, Sedimentary Facies And Reservoir Of Changxing Formation In Southeast Area Of Sichuan Basin

This paper is based on the theory of sequence stratigraphy, sedimentology,petrography, paleontology and geophysics. In order to explore sequence andsedimentary facies of Changxing Formation in southeast area of Sichuan Basin, stepsare taken as following: first sum up predecessors’ research, measuring and observingthe field cut plane of studying area. Then combine the data of well drilling and welllogging with distribution of seismic facies, and finally come to the conclusions that:The studying area develops two tertiary sequences, six quarternary sequences.The two tertiary sequences are bottom tertiary sequence SQ1and upper tertiarysequence SQ2. There are no lowstand systems tract but transgressive systems tractand highstand systems tract in the area.This area deposits carbonatite plateau facies, characterized by reef flat of openplatform subfacies. It can be divided into four microfacies: interbank limestone，lowpowered oolitic beach/bioclastic beach，high powered oolitic beach/bioclastic beachand platform basin/platform downslope.Through establishing quarternary sequences framework and comparingsedimentary facies, we got the idea that beneficial reservoir mainly develops inhighstand systems tract, while in transgressive systems tract the scale is small. On thebasis of sedimentary facies comparison, sum up the depositional model of this area.Nearing normal wave base deposits heavy bedded high powered ooliticbeach/bioclastic beach.While, the area deposits low powered oolitic beach/bioclastic beach betweennormal wave base and storm wave base. Its platform downslope is in the southwesternarea and high powered beach and organic reef are in the northeastern area. In turndevelops downslope and basin.The seismic facies of Changxing Formation can be divided into four kinds ofreflection:1) weak amplitude and continuously parallel sheet reflection,2)low-frequency weak-strong amplitude, continuously-precontinuously obliquecrossing prograde seismic facies,3) hummocky seismic facies, the roof developslow-frequency，weak amplitude reflection, overlying strata presents overlap and blankor disconnected reflection inside,4) imbricated prograde seismic facies, it developsmedium axis partly, represents weak-moderate amplitude, partly high amplitude. Development of Changxing Formation reservoir is mainly influenced bydeposition and diagenesis. Deposition is the precondition of reservoir formation.Diagenesis includes compaction, pressolution, cementation, dolomitization,denudation, cataclasis, silicatization and recrystallization. Combining sedimentaryfacies, seismic facies with the study and forecast of reservoir, ultimately, we think thatbeneficial exploring area of Changxing Formation are center and northern part,exploring potential of southern part is not very good.