| Block D,located in the northwest of Fuxian County,Shaanxi Province,is the main exploration block of Fuxian Oilfield.According to the existing drilling,logging,logging,analysis and production test data of Yanchang Formation in Block D,in-depth research is carried out on the formation,structure,sedimentation,reservoir and reservoir formation of the main oil-bearing formations of Chang8,Chang6 and Chang2,and the favorable oil-bearing blocks are predicted on the basis of comprehensive analysis of the oil and gas enrichment law and main control factors of reservoir formation of Yanchang Formation,It provides scientific basis for the next oil and gas exploration and development deployment in Block D.The research results show that the Yanchang Formation in Block D develops small nose uplift locally under the background of west-dipping monocline,and its sedimentary microfacies change and sand body distribution are very complex.The delta front subfacies are mainly developed in the Chang8,Chang6 and Chang2 phases,and the underwater distributary channel is the most important oil and gas reservoir.The reservoir rock type of the main study layer is relatively single,mainly feldspathic lithic sandstone and feldspathic sandstone,with fine grain size and medium-good sorting.The pore type is mainly residual intergranular pore,and the pore structure is mainly small pore and micro-throat type.The reservoir has strong heterogeneity and poor physical properties.Generally,it is dominated by low,ultra-low porosity-ultra-low permeability and ultra-low permeability reservoirs,with a small amount of medium-porosity and ultra-low permeability reservoirs.The types of diagenesis mainly include compaction and pressure solution,cementation,dissolution and metasomatism.The Yanchang Formation in Block D develops multiple sets of source rocks,such as the top of Chang 9,the middle of Chang 8,Chang 7,Chang 6,Chang 4+5,and multiple sets of caprocks,such as Chang 7,the middle of Chang 8,Chang 4+5,and Chang 1,which provide good sealing conditions for Chang 8,Chang 6,and Chang 2 reservoirs.The lower source-reservoir-cap combination is characterized by the upper source-reservoir type.Longitudinally,Chang 8 and Chang 2 oil reservoirs are the most developed.On the plane,the oil reservoirs are mainly distributed in the areas with good physical properties in the center of underwater distributary channels.The oil reservoirs are all lithologic oil reservoirs.The enrichment of oil and gas is mainly controlled by such factors as oil source conditions,sedimentary microfacies,sand body distribution characteristics,reservoir physical properties,shielding and cap rock conditions. |
