The Characteristics Research On Chang8 Reservoirs Of Yanchang Formation Of Zhang Cunyi In Zhiluo Oilfield

Zhiluo oilfield of Zhang Cunyi is located in Fuxian,this area about 1000 square kilometers. Its tectonic location is in the southeast of Shanbei slope, Ordos Basin. The main oil-bearing being developed is Chang 2, and the degree of its exploration and utilization are both very high. In recent years, it constantly make a major breakthrough on petroleum exploration in Chang8, a lot of industrial oil output have been obtained from many oil wells. It illustrates that the lower Yanchang formation has wide exploration potential. Therefore, the lower Yanchang formation will be important substitution in proven reserves growing and curde oil production increasing in the future. It is significant for the sustainable development of Zhiluo oilfield in this study.In this paper, the theories of petroleum geology, sedimentary geology and reservoir geology were based on as the instruction, experimental testing technologies were relied on and the data of field outcrops, drilling, logging and production were all used synthetically. We make the study of sedimentary facies and distribution of sand bodies for the first step. Then the petrologic features, physical properties, pore structure characteristics and diagenesis were studied and analyzed. The understanding and results achieved are in the following.According to the field outcrop observation, core observation, sedimentary tectonics and logging facies analysis, it shows that the main sedimentary microfacies developed in Chang8 period is underwater distributary channel, channel flank and distributary bay, it belongs to delta front subfacies sedimentary. Through core description and rock slice identification, it shows that the main rock types of Chang8 reservoir is minute-minuteness granular feldspathic lithic sandstone and feldspathic sandstone. The major clastic constituents are quartz, feldspar, rock debris and a little of interstitial material including chlorite, illite, carbonate minerals, siliceous, feldspathic cement and so on. Both compositional and textural maturities of the sandstones are low.On the basis of regular physical data, the results of the analysis is that Chang8 reservoirs which are low porosity and low permeability. The secondary is Chang8 reservoir, the average porosity is 8.12% and the average permeability is 0.25×10-3μm2.Based on the data analysis of rock slice, casting slice, scanning electron microscope and so on, the result shows that it mainly develops inter-grain poer, feldspar dissolved pore, lithic dissolved poer, interstitial material dissolved pore and microfracture in Chang8 reservoir. According to the data of mercury injection capillary pressure testing, the sorted behaviour of Chang8 reservoir is worse and the mainly types of throat are fine throat and micro throat.It indicates that the diagenesis types in this study area are mainly mechanical compaction, cementation, metasomatism, dissolution and rupturing by the analysis testing technologies including casting slice observation of rock, scanning electron microscopy and X-ray diffraction and so on. Based on the synthetic judgment on vitrinite reflectance, the mature of organics,the S% of I/S, quartz increased level,the type of particle contact and the type of pore, the results show that Chang8 reservoir is at B period of mesogenetic stage.According to the standard of reservoir classification, the reservoirs of Chang8 are divided into four classes in this paper. The ClassⅠreservoir is high quality reservoir, the reservoir quality of ClassⅡ is better and of Class Ⅲ is relatively poor, and the Class Ⅳ is tight reservoir, the comparison and evaluation of Chang8 reservoir is carried out from more than one angle.