Sedimentary Characteristics And Distribution Of The Reefs In The Changxing Formation Of The Permian In The Guang'an-Fengdu Area

The indistinct knowledge of intraplatfonn reefs type and distribution of changxing Formation in guangyuan-fengdu area,also it is necessary to deepen the understanding of the accurate distribution and internal details of the reef belt,all of these have an important effect on research result.Therefore,this study is of great significance to the exploitation of Reef Gas Reservoirs in Sichuan basin.Changxing Formation in guangyuan-fengdu area is a set of carbonate sedimentary formation,and based on micrite,bioclastic limestone,bioherm limestone.In changxing group from top to bottom is divided into three parts.Formation is complete,and have a obvious boundary.in the group from northeast to southwest terrain rendering high-low-high pattern,This study combines the ancient landform features,core,seismic facies characteristics,according to the topography from high to low in turn to open subtidal sub facies,depressed basin of platform subfacies,slope in the platform subfacies.In the slop environment can be developed with reefs of platform,reefs of platform can be further identified with reef core,reef base,reef cap.The study of modern biological reef results show that the reefs only growth in clean,warm,high-energy tropical and subtropical oceans,reef building organism mainly include frame building organism,barrier-bonded products,accessory reef organism.The study on the basis of drilling data,the vertical profile is rich,according to the lithology and the growth and development regularity of reefs,reefs of platform can be identified with reef core micro facies,reef base microfacies,reef cap microfacies.In guangyuan—fengdu area the intraplatform reefs of changing group main developmental barrier-bonded products is given priority to,framestone is less.The core of the reef is lower in GR curve,the curve is straight,the fluctuation is small,but interval transit time difference is generally less than 50?s/ft,and higher resistivity.Reef and reef cap reservoirs show a typical"three low and high"(low resistivity,low gamma,low density,high neutron,high time difference)features.In the study area,the reef reflection in the study area is a mound like clutter reflection.When the reef size is large,there will be a slight drop phenomenon in the bottom of the reef.Sndeposit tensional fracture movement in directions of NW and EW in late Permian,and dominate the differentiation of sedimentary framework,and reform the stretch ocean trough and depressed basin of platform.the intraplatfonn reef flat development zone distribution in the platform margin and platform inner is controlled.intraplatform reefs distribution of changxing Formation in guangyuan-fengdu area is mainly controlled by synsedimentary fault zone and sea-level change,the distribution characteristics of intraplatform reefs distribution overall conforms to the "dominated by NW,decorated by NE" charged with basement crackin reef model.