Evaluation Of Deep Effective Reservoirs Of Palaeogene In Dongying Depression

Based on the comprehensive application of core, well logging, testing, and assaying data, the reservoir characteristics, reservoir pressure and compartment characteristics, lower limit of petrophysical parameters of effective reservoirs, controlling factors and evaluation of effective reservoirs of the deep buried stratum of the fourth member of the Shahejie Formation(Es4)and Kongdian Formation(Ek) of Palaeogene in Dongying Depression were systematically studied. The sand bodies of nearshore subaqueous fan, sublacustrine fan and flood-overlake were developed in Es4 and Ek. The diagenetic stage of the deep reservoirs is divided into middle diagenetic substage A1 and A2, middle diagenetic stage B and late diagenetic stage. The deep reservoirs mainly developed compaction, cementation, metasomasis and dissolution. The mixed pores and secondary pores and fractures are the main reservoir spaces of the deep reservoirs. Several overpressure zones exist in Es4 and Ek, and the pressure coefficient gradually diminishes from the center to margin of the Depression. Three pressure compartments may be divided in Es4 and Ek, that is, the compartment of the upper part of Es4, the compartment of the lower part of Es4 and the compartment of Ek, and there are three types of compartments that are normal pressure, overpressure and complex pressure compartment. Five compartment-combination types were developed vertically in Es4, which are the type of simple overpressure, overpressure-overpressure, overpressure-complex pressure, complex pressure-normal pressure and complex pressure-complex pressure, and in plane several compartments exist side by side. The lower limit of petrophysical parameters of effective reservoirs is mainly controlled by temperature and pressure, and is closely relative to buried depth. Sedimentation is the most important controlling factor to form deep high quality effective reservoirs, and overpressure is more effective than diagenesis in controlling the formation of effective reservoirs. There are many favorable factors for developing high quality effective reservoirs, that is, lithology is thick sandstones and pebbled sandstones, adjacent rocks are blue melanic mudstone, sedimentary facies are the braided channel of nearshore subaqueous fan and sublacustrine fan, diagenetic stage is anadiagenesis A1 substage, and reservoir pressure is overpressure. According to the analysis of main controlling factor of deep effective reservoirs, combining the analysis of effective porposity and permeability and production,the deep reservoirs are classified into 8 categories, of which,â… andâ…¡1 is the high quality effective reservoirs,â…¡2 andâ…¢1 is middle effective reservoirs,â…¡3 is the low effective reservoirs, andâ…¢2,â…¢3 andâ…£is noneffective reservoirs.