Diagenesis and Diagenetic Facies of Submarine Fan in Zhujiang Formation, Pearl River Mouth Basin

Key words: 
• submarine fan /
• sandstone reservoir /
• diagenesis /
• diagenetic facies /
• Zhujiang Formation /
• Baiyun sag /
• Pearl River Mouth Basin

Abstract: The Liwan area is located in the east edge of the deep waters of the Baiyun sag，belonging to the most development block of the Zhujiang Formation submarine fan sedimentary system in Pearl River Mouth Basin, which has very superior petroleum geological conditions. The research of diagenesis and diagenetic phase is one of the most important basic researches about the reservoir of the submarine fan and accumulation characteristics. But there is no systematic research about the relationship of diagenesis and high quality sandstone reservoir development in submarine fan. According to the results of analysis  from thinsection, scanning electron microscope and stable carbon and oxygen isotopic composition. This paper comprehensively analyzes  the diagenesis and evolutionary sequences in Zhujiang Formation of submarine fan in Pearl River Mouth Basin, sum up the diagenetic phase characteristics  to play the role of predicting and evaluating the high quality of sandstone reservoir in deepwater fan.
 Firstly, based on the materials of the drilling cores, outcrop, rock slice identification and grain size analysis, etc, the author has made a study on the pearl river groups about the type of sandstone, the maturity of composition and the pore types.Then, the author concludes that the sandstone in pearl river groups consists of detrital feldspathic sandstone primarily and feldspathic litharenite secondly, and in which the sandstone is mainly dominated by primary intergranular pores and the intergranular pores after compaction and cementation, with few solution pores and organism cavity pores.
 Secondly, according to the core description, scanning electron microscope and casting thin sections, the author concludes that the diagenesis of deepwater fan sandstone reservoirs in Pearl River group is relatively weak, of which the compaction, cementation, filling of authigenic mineral and metasomatism is not conducive to formation and evolution of reservoir space, but the compression effect comes from early silica cementation and later dissolution are beneficial to the formation and evolution of the reservoir space.
 In addition, based on the analysis of the Xray diffraction, vitrinite reflectance, the illitemontmorillonite mixedlayer, smectite content, the author divides the diagenesis of pearl river group into three evolutionary stages and five substages in accordance with the national standard of diagenetic stage. The three evolutionary stages are penecontemporaneous stage, early diagentic stage,  and middle diagenetic stage. The diagenesis of Pearl River group were mainly in middle diagenetic stage A, and some of them in burial part entered the middle diagenetic stage B.
 Finally, on the basis of analysis of diagenesis and diagenetic series and according to the rule of combination and distribution for the diagenesis of deepwater fan sedimentary system in Pearl River group, the author concludes that the lithofacies assemblages may be divided into four phases : weak compactionweakly cementedstrong dissolution diagenetic phase, medium compactionweakly cementedmedium dissolution phase, weak compactionweak solutionstrong carbonate cementation diagenetic phase and compactioncementation diagenetic phase. Especially, the sandbody physical property in the middle weak compactionweakly cementedstrong dissolution phase is the best, and the sandbody of deepwater fan channel in Pearl River group is dominated by this kind.