| Zhiluo oilfield is located in Fuxian,this area is3450kilometers. Its tectonic location is in the southeast of Shanbei slope, Ordos Basin. The main oil-bearing being developed is Chang2before2000, 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 Chang6, Chang7and 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, diagenesis and macroscopic heterogeneity 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 Chang6and Chang8periods are underwater distributary channel, channel flank and distributary bay, it belongs to delta front subfacies sedimentary. In Chang7period the main sedimentary microfacies are deep lake argillaceous and turbidite facies, it belongs to the deep lake subfacies sedimentary.Through core description and rock slice identification, it shows that the main rock types of Chang6-Chang8reservoir are medium-fine 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 Chang6-Chang8reservoirs which are low porosity and low permeability. The physical property of Chang6is the best, the average porosity is8.39%and the average permeability is0.33mD. The secondaryis Chang8reservoir, the average porosity is8.12%and the average permeability is0.25mD.The physical property is of Chang7is the worst, the average porosity is7.67%and theaverage permeability is0.21mD.Based on the data analysis of rock slice, casting slice, scanning electron microscope andso on, the result shows that it mainly develops inter-grain poer, feldspar dissolved pore, lithicdissolved poer, interstitial material dissolved pore and microfracture in Chang6-Chang8reservoir. According to the data of mercury injection capillary pressure testing, the results ofthe analysis is the pore structure of Chang6reservoir is better than Chang8and Chang7. Thesorted behaviour of Chang6reservoir is better and the mainly type of throat is fine throat,medium throat can be found in part. But the sorted behaviour of Chang8and Chang7reservoirs are 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 technologiesincluding casting slice observation of rock, scanning electron microscopy and X-raydiffraction and so on. Based on the synthetic judgment on vitrinite reflectance, the mature oforganics，the S%of I/S, quartz increased level，the type of particle contact and the type of pore,the results show that Chang6reservoir belongs to A-B period of mesogenetic stage, andChang7and Chang8reservoirs are both at B period of mesogenetic stage.In the research of reservoir macroscopic heterogeneity, it finds out that the degree ofin-layer heterogeneity in Chang6reservoir is weak, Chang8is medium and Chang7is severe.The degree of interlayer heterogeneity in Chang7is the strongest, the secondary are Chang81and Chang61, but the degree of interlayer heterogeneity in Chang82，Chang62and Chang63arerelatively weak. The plane heterogeneity of Chang6, Chang7and Chang8are all severe.According to the standard of reservoir classification, the reservoirs of Chang6-Chang8are divided into four classes in this paper. The ClassⅠ reservoir is high quality reservoir, thereservoir quality of Class Ⅱ is better and of Class Ⅲ is relatively poor, and the ClassⅣ istight reservoir, the comparison and evaluation of Chang6-Chang8reservoirs are carried outfrom more than one angle. |
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