Pearl River Mouth Basin Carbonate Reservoir Diagenesis And Second Porosity Formation Mechanism Of Liuhua11-1Oilfield

The study area of Liuhua11-1Oilfield is located on Dongsha uplift of Pearl River Mouth Basin in South China Sea. The study object deals mainly with the carbonate reservoirs of Zhujiang Formation in Liuhua11-1Oilfield. Based on systematically reading and summarizing relevant literature the author has taken a detailed microscopic observation of thinsections of carbonate reservoir rocks in Liuhua11-1Oilfield. In the light of synthesizing theories of multi-disciplines the diagenetic features and porosity formation of Liuhua11-1Oilfield have been systematically studied, and the controlling factors of formation of high and low porosity intervals and the influence of diagenesis on physical property of reservoir rocks have been clarified.The study is based on observation of drilling cores from relevant wells and microscopic identification of thinsections in a large amount. Following the classification scheme of carbonate rocks raised by Dunham (1962), according to the grains/micrite ratio, the microfacies in thinsections are divided into mudstone, wackestone, packstone and grainstone, the boundstones of the study area are divided into bafflestone, bindstone and framestone, and the rock with crystalline structure is divided into crystalline rock. Rock microfacies in different sedimentary facies belts have been named according to this naming scheme. In order to facilitate the study of reservoir unites, cell division scheme (A-F), raised by predecessors, is applied, where A, C and E belong to the low-porosity units, and B, D, F belong to the high porosity units. Rock character and its sedimentary characteristics of every unit are described in detail.Combined with the study of sedimentary facies of the study area by predecessors, sedimentary microfacies with different biological assemblages are differentiated, which are categorized into two kinds of reef microfacies (coral reef microfacies and coral-coralline-algae microfacies), and three kinds of shoal microfacies (foram shoal microfacies, coralline-algae-clasts-foram-shoal microfacies, and bioclastic shoal microfacies).Based on the observation of a large number of thinsections, the author has acquired a systematic understanding of diagenesis of Liuhua11-1Oilfield. In accordance with burial stages of rocks the diagenetic stages of the study area are divided into near surface burial stage and meso-deep burial stage, and their diagenetic characteristics are separately described. The thesis focuses mainly on several diageneses, which affect greatly reservoir properties of reservoir rocks, such as: dissolution, cementation, chalkification and dolomitization. On the basis of the study of diagenesis, the evolution sequence of diagenetic events of Liuhua11-1Oilfield is set out, and the chronological diagenetic order is subdivided.Pore size distribution of Liuhua11-1Oilfield is obviously affected by diagenesis, reservoir heterogeneity is significant, and there has developed a large number of porous horizons and dense horizons. In combination with thinsection analysis and istopic data interpretation the thesis has discussed how the meteoric water in early diagenetic stage and acitic fluid in the later stage transformed and influenced the reservoir carbonates in Liuhua11-1Oilfield.