| Based on the theory of sedimentary petrology, mineralogy, reservoir geology, well logging, development geology, petroleum geology, and reservoir engineering, in combination with outcrops, drilling, logging, cores, and test anslysis data, this research aim to systematically discuss the reservoir characteristics and delicate descrip the reservoir of Chang 2 member and Chang 6 member of Yanchang formation in Zichang oilfield, eastern Shanbei slope. Study of stratigraphic correlation and sedimentary facies determined that Chang 2 member belongs to the braided river facies, which develop many sets of the superimposed and continuous lenticular sand bodies with channels were strongly stacked, while Chang 6 member is the delta deposits, in which sand bodies distribution with mudstones superimposed each other.Based on thin sections, stain thin sections, scanning electron microscope, cathodoluminescence, X-ray analysis, physical properties and mercury penetration data, this paper study the reservoir characteristics. It shows that reservoir of Chang 2 and Chang 6 member are composed mainly of fine-grained arkose sandstone, but there are more debris in Chang 6 member than in Chang 2 member. Cement composition were different, which calcites are the main compents and chlorite takes the second place in Chang 2, while laumontite cement are the main compents and chlorite takes the second place in Chang 6. The reservoirs of the study area mainly developed dissolved pores, which are dissolved carbonate cements in Chang 2 member related to fresh water leaching, and laumontite dissolved pores in Chang 6 member in concention with organic acid, respectively. The Chang 6 member is more heterogeneous than Chang 2 because of different genesis of sand body, sedimentary micro-facies, particle size, mineral composition, diagenesis, and fracturing. Porosity and permeability of Chang 2 is higher than Chang 6. Chang 2 is low porosity-low permeability and low porosity-extra low permeability reservoir, while Chang 6 is low porosity-extra low permeability or extra low porosity-ultra low permeability.Both the low penetrability reservoir of Chang 2 member and the ultra-low penetrability reservoir of Chang 6 member are structurally west dipping monoclines. The high structure relief amplitude, nosie background and small micro tectonics were developed in Chang 2 member, which controlled the reservoirs types and residual oil distribution, and formed lithologic reservoir, lithologic-tectonic reservoir, and secondary diagenesis-lithologic reservoir, while lithologic reservoirs and secondary diagenesis-lithologic reservoir were developed in Chang 6 member.Hydrocarbon reservoir model of the study area belongs to proximal accumulation model with main migration pathways The situation that Chang 2 reservoirs mainly distributed in the southwest and Chang 6 reservoirs mainly existed in the northeast of the study area and coexist in the middle area with Chang 2 and Chang 6 reservoirs which formed during the migration process from southwest to northeast and to vertical in study area.Through quantitative calculation of reservoir numerical simulation and geology analysis, macroscopic residual oil distribution of Chang 2 reservoir is mainly affected by micro-structure, lithology, physical properties and the correspondence relationship of injection-production. Horizontally residual oil mainly distributes in the structural high area and sand body edge area and imperfect injection-production well area, and vertically it uniformly distributes in sand body. Chang6 reservoir macroscopic residual oil distribution is mainly affected by lithology, physical properties and the correspondence relationship of injection-production, which are mainly distributed in sand bodies of edge area, lithology or physical properties change area and imperfect injection-production well area and distributed in the upper sand body in vertical. According to the actual situation of block adjustment scheme are presented. |
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