Research On Sediment Microfacies In The Lower Fomation Zhujiang Group Carbonate, Huizhou Area Dongsha-Uplift Pearl River Mouth Basin

Lower Miocene Zhujiang Group carbonate rocks are the latest marine sedimentary record which is preserved in Pearl River Mouth Basin in South China Sea. Abundant geological information, such as climate fluctuation, biological evolution, eustatic and tectonic subsidence is implicated by them. Because the relatively abundant drilling data and a large number of cores originate in the upper carbonate rock,so carbonate mineralogy and petrology sediment microfacies research mainly concentrated on Lufeng, Liuhua and Baiyun-Sag area. The lower fomation of carbonate rocks relatively lack of physical data,so that few research which restricts the scientific understanding evolution of Zhujiang Group sedimentary environment.So based on “Carbonate Reservoir identification and evaluation in deep water of the Northern South China Sea”,the subproject of the nationl “Twelfth Five-Year Plan”Major project—Key technologies of oil and gas exploration on offshore deepwater,the author collect cores cuttings,logging data as first-hand information of Huizhou28-1-1 well and other four wells of Dongsha Uplift which come from CNOOC branch Shenzhen and apply basic principles,theories and methods,such as sedimentary geology,stratigraphy,paleontology,geophysical logging,lithofacies-paleogeography to research mineralogy,petrology,paleontology,sedimentary microfacies and logging response characteristics of lower fomation Zhujiang Group,the conclusions are as follows:1. Based on Mineralogy、 Petrology and Paleontology studies,author identify9 kinds of sedimentary microfacies in Zhujiang Group Huizhou region Dongsha Uplift: silty mudstone,foraminiferal packstones,foraminifera debris packstones,algal clastic debris bioclastic packstones Zcontaining bio-debris wackston, bio-debris wackstone,containing sand debris algae debris packstones algae,algal limestones and algal bonding rocks,according to these sedimentary microfacies about environmental instructions,lower Zhujiang Group carbonate which preserved in Huizhou,derived from mixed continental shelf、ramp、platform margin and shallow shelf sedimentary environment.2. Author apply research results which about the lower fomation Zhujiang Group carbonate of micro-facies and sedimentary facies to preliminary analyze sedimentary environment of Zhujiang Group carbonate.The sediments environmentevolution can be divided in to 4 stages: the first stage,as sea level rise,terrigenous clastic injections reduc, throughout the Dongsha Platform is mixed shelf environment,mixed sediments are mainly concentrated in the East of the study area,And the Huizhou region for Fine-grained limestone deposit of carbonate shelf; the second stage: due to sea levels fall,previously mixed shelf evolved into carbonate ramp, and Huizhou region in high-energy facies of carbonate ramp, the sediment is mainly mud stone which containing coralline algae debris and dolomite algae foraminifera debris mud stone,the third stage:Miocene in the medium-term,Dongsha Uplift carbonate ramp evolved into carbonate platform,previous high-energy facies carbonate ramp evolve into the facies of platform margin which reef and shoal,the sediment is mainly foraminiferal debris algae debris packstones,coralline algae debris packstones and coral gal debris foraminiferal packstones the fouth stage: as the relative sea level continued to rise,carbonate platform edge scale expanded further,carbonate sediment were banded distribution in eastern Huizhou.