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Description
The Mishrif Formation in the Hafaya Oilfield is mainly characterized by porous carbonate reservoir with large marine biology, different sediments and complex diagenesis. Reservoir in this area has diverse pore types, poor correlation between porosity and permeability, poor well logging response and reservoir evaluation is difficult. The diagenetic patterns of different microfacies have been established based on core, cast thin film, mercury intrusion data and scanning electron microscopy, and the diagenesis mechanism of pore carbonate rocks and the reformation of reservoirs have been clarified. Microfacies in the Mishrif Formation control the types of biomask particles, and the biological shells have different ability in resistance dissolution. Selective dissolution leads to various moldic pore. The environment determines the type of diagenesis. In briny environment, the main types are mud crystallization, biogenicagency and rim cementation. The nemorphism and selective dissolution are the main types of diagenesis in freshwater environment. Hypergene zone is dominated by weather erosion and non-selective dissolution, In burial environment, the main diagenesis are coarse-grained cemented and dolomitization.The type of diagenesis determines the tendency of reservoir reformation, in which the compaction, the pressolution and the cementation reduce the porosity and the dissolution increases the porosity and provides the cementing material.The dolomitization has two sides, if the calcite is replaced, porosity increases and if the pore is filled, porosity decreases. The diagenetic stage controls the pros and cons of reservoir reformation. The early cementation and late dissolution is favorable for pores protection. The late dissolution and early cementation is the most unfavorable.The results show that reservoir reformation is the comprehensive superimposition of sedimentary materials, diagenetic stages, environments and types. Sedimentation provides the material and environment determines the diagenesis type and sequence. The type and period of diagenesis determine the reformation tendency of reservoir in the Mishrif Formation. It is of great significance to clarify the mechanism of diagenesis for the reservoir evaluation and the potential analysis of reserves.
References
[1] Jiang S, Cai D, Zhu X, et al. Diagenesis of Liaozhong sag in Liaohe depression and pore evolutionin its middle-deep strata[J]. Oil & Gas Geology, 2007, 28(3):362-369.
[2] Ren D Z, Sun W, Tian H, et al. Research on the characteristic of diagenesis and porosity evolution of Chang 6 Reservoir in Jiyuan Oilfield,Ordos Basin[J]. Journal of Northwest University, 2016.
[3] Jiao X, Wang X, Feng P, et al. Microstructure Evolution and Pore Formation Mechanism of Porous TiAl 3, Intermetallics via Reactive Sintering[J]. Acta Metallurgica Sinica, 2017:1-9.
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