Research On Diagenesis Of Yanchang Series Of Upper Triassic, Jiyuan District Of Ordos Basin

Jiyuan area located in the west of Ordos basin, the key oil-bearing series are Chang8andChang9reservoir sets of Yanchang group. It is the typital lithologic reservoir, the distributionof oil reservoir mainly controlled by deposition and diagenesis. In this paper, the authormakes a comprehensive use of theoretical basis of sedimentology, reservoir geology, by coreobservation and description and multiple assays (casting thin sections identification, scanningelectron microscopy, cathode luminescence, X-ray diffraction, mercury intrusion analysis andpermeability test). On the basis of sedimentary background research, the reservoir petrologiccharacteristics, reservoir pore characteristics, diagenesis types, diagenetic stages anddiagenetic facies are studied.The favorable reservoirs of Chang8and Chang9reservoir sets of Jiyuan area areunderwater distributary channel sands and channel-mouth bar sands of delta front anddistributary channel sands of delta plainThe main interstitial material of Chang91reservoir sets are Illite, illite/smectiteformation, laumontite, calcite, quartz and kaolinite, et al. The main interstitial material ofChang82and Chang81reservoir sets are chlorite, kaolinite and ferrocalcite. Chang8andChang9reservoir sets have entered in the middle diagenetic stage A to the ealier diageneticstage B. Among the main cement, the appearance of siliceous and carbonate make thereservoir worse, and the porosity is in positive correlation with the content of chlorite films,when the content of chlorite films is less than5%, it is in positive correlation withpermeability, and when the content is more than5%, it is in negative correlation withpermeability. The influence of increase of hydromica content to porosity is not obvious, but itmakes the permeability reduce obviously. The content of laumontite is in positive correlationwith physical properties.According to the relationship of different diagenetic minerals and pore types, thediagenetic facies of Chang8and Chang9reservoir sets of Jiyuan area can be divided into sixdiagenetic facies: chlorite films-intergranular pore face, kaolinite cementation-dissolved poreface, chlorite films-dissolved pore face and laumontite cementation-dissolved pore face areconstructive diagenetic facies, siliceous cementation and carbonate cementation aredestructive diagenetic facies. The development of diagenetic facies can effectively control thereservoir physical properties, the I,II class reservoirs mainly developed in chlorite films-intergranular pore face, laumontite cementation-dissolved pore face, kaolinite cementation-dissolved pore face and chlorite films-dissolved pore face; the III class reservoirs mainlydeveloped in siliceous cementation and carbonate cementation.