A Study On The Heterogeneity And Characteristics Of Chang 6 Reservoir Of Yanchang Formation In Ansai Hezhuang Oil Field, Ordos Basin

The Chang 6 reservoir of Yanchang Formation is the main producing pay of Ansai Hezhuang oil field, which has been entered a period of stabilized production. Researching on the Heterogeneity and characteristic is very important for waterflooding development scientifically and regulating of the producing position for the oil field reasonably.Guided by multidisciplinary theories of reservoir sedimentology, logging geology, petroleum geology and reservoir development geology, based on analysis of a great deal of data of drilling, logging and laboratory experiments results of more than 800 development wells, combined with litho facies and logging facies, a series of studies of Chang 6 reservoir of Hezhuang oil field have been carried, including stratigraphic division and correlation, sedimentary microfacies, the basic characteristics and heterogeneity of the reservoir. During the course of the study, many research methods have been taken, such as thin section analysis, SEMP, mercury injection and grain grade analysis.Chang 6 reservoir of the study area is belonged to delta front sub-facies, and the dominant sedimentary microfacies are underwater distributary channel and mouth bar. The rock type is fine feldspar sandstone. Cementing materials include self-generation chlorite, laumontite, calcite and authigenic quartz. Pore types of the reservoir include intergranular dissolved pore, intragranular dissolved pore and residual primary pore. The intergranular dissolved pore mainly refers to laumontite dissolved pore, which is the mainly accumulate space of the hydrocarbon. The result of the mercury penetration experiment suggest that the reservoir has a characteristic of moderate initial expulsion pressure, high median expulsion pressure and minimal median radius of pore throat. With a compact lithology, the communication of pore space is on the low side and belongs to meso pore with minimal pore throat type. The reservoir has strong heterogeneity in both of innerlayer and interlayer with obvious permeability aeolotropism. The plane heterogeneity of the sandbodies in the main underwater distributary channel is relative weaker than those in the minor distributary channel, the side channel and the mouth bar. The heterogeneous degrees of the reservoir is controlled by its depositional microfacies, and affected by the later diagenesis.The distribution of the hydrocarbon in the area is extremely malconformation both in the vertical and plane direction. From the lower to upper strata, the hydrocarbon concentrate area has a tendency of moving towards north and east. The lithologic characteristic, migration distance and local structure has great effect to the distribution of the hydrocarbon in the study area, however, the mainly controller factor is the sedimentary microfacies of the oil bearing sand body. The primary sedimentary microfacies of the oilibearing sandbody are underwater distributary channel and the combination of the channel and the mouth bar. Application of "weight method" for reservoir comprehensive evaluation, the result shows that the Chang 6^2-2 layer reservoir is the most enrichment pay bed of the Chang 6 reservoir.