| The sedimentary sequence of Qingshuihe Formation in Hong003well area presents a positive cycle characterized by upper--groase and lower--fine. Qingshuihe Formation has a angular unconformable contact with the underlying strata which is Qigu formation and has a conformable contact with the overlying strata which is Cretaceous Hutubihe formation. According to the features of cycles, lithologic combinations and electrical property, Qingshuihe Formation can be divided into for members which are K1q11、K1q12、K1q13、 KIq14Rocks in Qingshuihe Formation are mainly composed of Conglomerates, pebbled sandstone and sandstones with minor gompholite, shaly sandstone and mudstone, and it seldom contains calcareous mudstone. The sandstone are mainly consists of lithic sandstone with medium sorting and low texture and compositional maturity. The color of the sandstones and conglomerates in Qingshuihe Formation are mainly gray and dust color, and it will turn to brown and deep brown after being immersed by oil. The color of the mudstones and muddy siltstone in Qingshuihe Formation are brownish red which indicates the oxidizing environment on land.Statistics show that the size of basal conglomerates deposited in Qingshuihe Period turns small from northwest to south and southeast, and the content of quartz which is stable component becomes higher from north to south, while that of feldspar which is unstable component becomes lower on the contrary. The ZTR index in each member of Qingshuihe Formation becomes higher from northwest to southeast or from north to south, which indicates that the Zhayier Montain is the provenance and the paleocurrent flowed from north.Based on the analysis results of well core and logging, the sedimentary types of the first member of Qingshuihe Formation in well Hong003area are retrogradational alluvial fan caused by flood and gravity flow accompanied by few sediments brought by temporary current. There are three subfacies which are root fan, middle fan and fan edge of alluvial fan and seven microfacies which are main channel, overland flow, braided streamline(sandstone), braided streamline(conglomerate), braided stream sandy bar, wetland in fan edge and stream flow channel. The alluvial fan deposition in the first member of Qingshuihe Formation in well Hong003area are caused by alternate flood period and dry period. During the flood period, with strong hydrodynamic force, sediments are mainly conglomerate and sandy conglomerate and covered large area. During the dry period, with weak hydrodynamic force, sediments are mainly sandstone and covered small area near the river channel. On the section, the sedimentary facies change from braided streamline (sandstone), braided streamline (conglomerate) to overland flow and fan edge wetland upward. In the plane, sedimentary facies from northwest to southeast are root fan, middle fan and fan edge of alluvial fan. From K1q14to K1q11, coarse clastics become little and litter and the size of alluvial fan also become small. Alluvial fan is fully-developed in K1q14、K1q13, the microfacies contains braided streamline (sandstone),braided streamline (conglomerate), and overland flow. In K1q12、 K1q11, the development of alluvial fan decline. In K1q12overland flow was the main microfacies. In the late K1q11alluvial fan development near the end, only developed fan edge wetland and stream flow channel. Research on the relationship between micro sedimentary facies and lithology, sediments property and oil bearing properties shows that braided streamline (sandstone) is the most favorable facies for exploitation. Braided streamline (conglomerate) is the second favorable facies for exploitation. Fan edge wetland consists mainly mudstone and the reservoir and oil-bearing properties in overland flow microfaciece is bad, so both of them are unfavorable facies... |
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