Buried Diagenesis, Structurally Controlled ThermalFluid Process and Their Effect on Ordovician Carbonate Reservoirs in Tahe, Tarim Basin

Key words: 
• burial diagenesis

Abstract: The understanding for layered weathering crust model once sustained oil and gas exploration of the Lower Paleozoic deepburied carbonate in the Tarim Basin. However, strong heterogeneous characteristics of the carbonate reservoir types increases exploration risk in the study area. As a case study, The MiddleLower Ordovician carbonate reservoirs of Tahe area, Tarim basin, are studied in this paper, with focuses on superposition effect of burial diagenesis and structurally controlled thermalfluid, on reservoir formation. Finally, combined with other elements including epigenetic karst process and so on, a comprehensive explanation on reservoir distribution is given in this research. The main recognition includes: ① Normal deepburied diagenesis of Ordovician carbonates mainly resulted in precipitation rather than dissolution, and constructive modification primarily related to the epigenetic karstification (paleokarst) or structurally controlled thermalfluid flow and led to strong heterogeneity of carbonate reservoirs. ② From the Lower Ordovician to Upper Ordovician, thermal fluid flow evidence in the lower carbonate strata is stronger than that of the upper carbonate strata. ③ The constructive modification of structuralthermal fluid flow in Ordovician carbonate mainly occurred in structural intersection of superimposed faults developed during MiddleLate Devonian and Permian, respectively, and the strong preexisted epigenetic karstification area formed at MiddleLate Ordovician and preCarboniferous periods. The most efficient carbonate reservoirs have limited genetic relation with highenergy depositional facies in the study area. This paper puts forward a conceptual model about structuralgeofluid processes and related reservoir formation for the Ordovician carbonates in Tahe area, which provides a new clue for further understanding formation and distribution of the studied reservoirs. 