| Zhenjing area is located in the southwest margin of Ordos Basin.Chang8 oil layer of Yanchang Formation is the main producing layer.At the early stage of exploration and exploitation,the production of several horizontal wells reached more than 100t per day,but the research area has complex geological conditions.The 3D seismic dataset reveals that faults are developed extensively in this are,and the source direction and sedimentary facies are also still controversial.The formation of petroleum accumulations is complex.Some of the horizontal wells produced petroleum less than 3t one day,and the water content was higher than 95%.So it's urgent to study the controlling factors to improve the drilling rate and avoid the low oil production area.In this paper,the three generation coherence technique and the ant body technique are used to predict the fracture of the 3-D seismic zone.Through core observation,sampling and analysis of core,seismic data,logging data and the results of previous studies,the characteristics and distribution of sand reservoir,source direction,sedimentary facies and distribution of hydrocarbon source rock are identified.The study found that the thickness of source rock is between 10m?15m.The quantity of hydrocarbon generation and expulsion is limited,which is not enough to fill the C8 sandstone bodies.The petroleum accumulations is controlled by numerous factors in the study area including thickness and distribution of hydrocarbon source rocks,the distribution of the mudstone interlayer in the top of C8 and sand body reservoir.The C7 and C8 sandstones mainly come from the southwest Longxi ancient land followed by the south Qinling Mountain provenance.C81 is a transitional deposit from fluvial facies to semi deep lake.The reservoir of C8 is feldspathic sandstone in Zhenyuan area,and lithic sandstone in Jingchuan area.The pores are mainly intergranular pores,intergranular pores and dissolved pores.In addition,the secondary quartz was found in the pores.The porosity is 3%-17%,permeability between(0.1?0.5)×10-3 ?m2,pore radius between 0.04?0.56?m.According to the low permeability reservoir classification by Zhao Jingzhou in Ordos basin,the study area belongs to the small fine pore type and super low permeability layer.The oil was mainly vertical migration under the abnormal pressure of shale at the bottom of the C7 in the area.There were 5?10m thick silty mudstone interlayer at the top of C8,and abnormal pressure was not strong enough to break the blockade of the mudstone.The strike-slip faults can be divided into 3 classes,the class ? strike-slip faults cut the strata from the Ordovician to the Cretaceous,which developed two sets of the upright shear faults in the NW-SE and the NE-SW directions.The Class ? disconnected the strata from the internal Triassic to the Cretaceous extending in the NE direction.The Class? cut through the strata from the Ordovician to the internal Pernian extending in the NEE direction.Among them,type ? and type ? faults connect with C7 and C8,which can be used as oil migration channels,and type ? faults are invalid faults for oil accumulation.When the sand body is thick and even in large scale,crude oil cannot fully filled sandstone reservoir.Oil gathered in high positions of local structures controlled by the capillary pressure.The drilling also confirmed that around the fault development zone,or the sand reservoir in direct contact with the source rock,or the high positions of the large-scale sand reservoir,it is easy to be drilling in the high yield well(production is more than 12t one day). |
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