Application of laser in-situ U-Pb dating to reconstruct the reservoir porosity evolution in the Cambrian Xiaoerbulake Formation, Tarim Basin 激光铀铅同位素定年技术在塔里木盆地肖尔布拉克组储层孔隙演化研究中的应用

The Laser Ablation (LA)Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS) technique, co-developed by the CNPC Key Laboratory of Carbonate Reservoir and School of Earth and Environmental Sciences, The University of Queensland, has huge potential to overcome the difficulty in sampling and dating ultra-low concentration U-Pb minerals in ancient marine carbonates that are relatively smaller in diameter in diagenetic fabric, which was untenable by the conventional isotope dilution (ID) methods. The in-situ analysis by LA combined with MC-ICP-MS has been applied to the study on the diagenesis and porosity evolution of the Cambrian Xiaoerbulake reservoir, Tarim Basin.By dating of dolomitic and calcitic cements from filled vugs, matrix pores and fractures in different stages, we suggested that the burial diagenetic history of dolomite reservoir in the Cambrian Xiaoerblake Formation mainly features the filling of primary pores and vugs generated under karstification. The filling of vugs mainly occurred during the early Caledonian, while the filling of matrix pores mainly occurred in the middle Caledonian and Indosinian. Fractures activated during the Caledonian and Indosinian served as the channels for hydrothermal migration, providing the materials to cement the vugs and pores; while the residual vugs, pores and fractures with no filling of dolomite, calcite and siliceous cements were the main reservoir space. The diagenesis and porosity evolution history of dolomite reservoir in the Cambrian Xiaoerbulake Formation, Tarim Basin, was hence established. The understandings mentioned above are highly consistent with the tectonic-burial history and basin thermal history in the study area, which may be effective tools to date the ancient marine carbonate reservoir cements, to reconstruct diagenesis and porosity evolution history, and to evaluate effective pores before hydrocarbon migration in the ancient marine carbonates.