The Study On The Sequence, The Sedimentary Facies And The Development And Distribution Principles Of The Reservoir Of Changxing Formation In The Northeast Of The Sichuan Basin

With the carbonate rock of Permian Changxing formation in Northeast ofSichuan Basin as the object of the study, the development and distribution principlesof the reservoirs are known from the study on the sequence, the sedimentary faciesand the relations among the development and distribution of the reservoirs, thesequence and the sedimentary facies by integrating analysis on field outcrops, indoorthin sections, seismic sections and well logging curve under the guidance of carbonatesequence stratigraphy, seismic stratigraphy, sedimentology and reservoir sedimentolo-gy.Well logging and seismic data are combined to build the frameworks of the3rd-order sequence and the high-frequency sequence of Changxing Formation whichcan be divided into two3rd-order sequences, eight4th-order sequences and eighteen5th-order sequences. Third-order sequence may realize comparison in the whole area.There is high comparability on platform area while it is difficult to compare betweenthe platform area and the slope-shelf area for high-frequency sequence.By integrating the analyzing results of lithology and sedimentary facies of wellsand seismic facies, reef and shoal facies interpretation can be effectively carried outon seismic sections. The3rd-order sequence system tract is taken as unit to describethe distribution of sedimentary facies and reef and shoal of Changxing Formation, andreveal the spatio-temporal distribution and evolution of sedimentary facies and reefand shoal in isochronous and dynamic mode. In southwest area, the lower ChangxingFormation carbonate rocks sedimentation follows the slope mode. The lower3rd-ordersequence completes the change from slope to initial platform while the upper3rd-order sequence completes the change from initial platform to mature rimmed platform. Innortheast area, the carbonate rocks deposit in isolated platform sedimentary mode inearlier stage where only open platform facies can be distinguished. In later stage ofthe lower3rd-order sequence, platform margin facies come into being with thedevelopment of reef and shoal at platform margin, and then the whole isolatedplatform formed. In southwest area, on the lower3rd-order sequence stage, bioclasticbeach develops in most of zones and reef develops in some zones. On upper3rd-ordersequence of Changxing Formation stage, reef develops in platform margin whilebioclastic beach develops inside the platform. In transgression system tract, the reefand shoal develops in small scale while in high-stand system tract, the reef and shoaldevelops in large scale. Reef and shoal grow in aggradation and overlapping type. Innortheast area, the reef and shoal at platform margin mainly develop in high-standsystem tract in later stage while no reef and shoal develop in platform inside.Based on the analysis on cores, thin sections and well-logging data, it is knownthat reservoirs develop in platform margin and platform inside, including dolomite(limestone) reef-facies reservoir, dolomite (limestone) shoal-facies reservoir anddolomite tidal-flat-facies reservoir which are related to shallow sediments, while fewreservoirs develop in slope-shelf facies. High-quality reservoirs are mainly dolomiteshoal-facies reservoir and dolomite reef-facies reservoir. Reservoirs may grow insuccession lengthways, especially thick on later stage of high-stand system tract.Reservoirs mainly develop in high-stand system tract and also develop intransgression system tract or even maximal flooding surface. As to high-frequencysequence, reservoirs mainly develop on the middle and upper5th-order sequence.By analyzing the development and distribution principles of the reservoirs inChangxing Formation, it is concluded that the reef and shoal facies in platform margincan be divided as Type I reservoir development zone and the reef and shoal facies inplatform inside can be divided as Type II reservoir development zone; other zones inplatform inside can be divided as Type III reservoir development zone.