A Case Study On Characteristic Of Reservoir Related To Sedimentology Of Chang 4+5 Oil Layers Of The Yanchang Formation In Shanzhuang District, Erdos Basin

This thesis is guided by multi-subject theory, and it is also based on the observation of cores and thin sections, combined with a great deal of previous data, as well as referred to testing results from lab, the characteristics of provenance, sedimentation, reservoir and genetic types of reservoir body of Chang 4+5 oil layers of the Yanchang Formation in Shanzhuang district of Erdos Basin is comprehensively discussed. The analyzing results show that the study area is mainly controlled by the provenances of north-east and south-west, based on which, the controlling factors of the development of this reservoir has been studied out.Also based on previous data and observation of field outcrop sections and cores, together with logging data, the main depositional facies of Chang 4+5 oil layers are lacustrine and lacustrine-delta, and the subfacies are deltafront, pro-delta, shoreshallow lacustrine and semi-deep- deep lake. The Chang 4+5 oil layers has mainly experienced two depositional stages of Chang 4+51 and Chang 4+52, during them, the Chang 4+51 stage has developed favorable sand bodies while the sand of the Chang 4+52 stage became worse obviously.On the basis of thin sections observation and SEM analysis, the reservoir lithology and diagenesis are studied, the results show that the study area develops a set of grey-green fine sandstone, the lithology are mainly lithic feldspathic sandstone and feldspathic sandstone. According to casting thin sections analysis, the pore of the Chang 4+5 oil layers in Shanzhuang area is mainly intergranular pore, and then feldspathic dissolved pore and lithic dissolved pore, with a small amount of intercsystalline pores and micro-fractures. The average porosity and permeability of the study area is 11.94% and 0.51×10-3μm2, respectively, and the reservoir is defined as moderate porosity and low permeability reservoir, however, the reservoir has fluctuate physical properties during different depositional stages..Another conclusion obtained from cores, thin sections observation and SEM analysis is the diagenesis of the Chang 4+5 oil layers, which are mainly compaction, cementation, metasomatism and dissolution. Combined with relative data, the study area can be defined as four diagenetic zones which are chlorite intergranular pore zone, carbonate cementation zone, illite-silicate cementation zone and mudstone compaction zone.Comprehensively analysing the characteristics of provenance, sedimentation, reservoir characteristics and diagenesis, it is concluded that the sedimentation is the foundation of the reservoir development, as it influenced physical properties of the reservoir in some extent and it also controlled the size, roundness and sorting of the deposits, in which, the porosity would be better conserved among well sorted particles. On the other hand, reservoir diagenesis are the key factors influencing physical properties, compaction and cementation makes reservoir porosities decreased, while dissolution is one of the key factor which improves the physical properties of the reservoir in some extent. Finally, the influence on physical properties of the reservoir brought by different diagenesis is analyzed quantitatively, and the porosity changing of every diagenetic stages in Chang 4+5 oil layers in the study area is also evaluated quantitatively for the first time.