Developmental Characteristics And Controlling Factor Of Secondary Pore Of Paleogene Sandstone Reservoir In Xihu Sag

The genesis and evolution of secondary pore development zone is important basis for the high-quality reservoir evaluation and the deployment of oil and gas exploration in mid-deep formation.Generally,several secondary pore development zones are developed in a petroliferous basin.At present,it is considered that feldspar and carbonate cements dissolved by organic acids is the cause of the first secondary pore development zone corresponding to organic matter maturity in shallow formation.While,there are two views on the causes of deep secondary pore development zones.One is that deep secondary pore development zones were formed in deep formation;Another is that deep secondary pore development zones were the secondary pore development zones forming in the shallow formation and preserved to the deep formation.If the genesis and evolution of secondary pore development zones can't be determined,the success rate of hydrocarbon exploration will be affected a lot.So the research on the genetic mechanism and evolution model of secondary pore development zones has great leading significance in theory for oil and gas exploration in mid-deep formation.This dissertation focused on the case study of the sand-conglomerate body of the middle part of Es3z~Es4 of Paleogene in Dongying depression.Based on a conjunction of core observation,thin section identification,image analysis,SEM observation,fluid-inclusion analysis,core X-ray analysis,testing of vitrinite reflectance and core properties analysis and other methods,and the research achievements as the tectonic evolution history,thermal evolution of organic matters,and the history of hydrocarbon accumulation,the genetic mechanism and evolution model of secondary pore development zones in mid-deep formation were systematically studied.(1)By analyzing a lot of the results of flake identification,particle size analysis and measured physical properties,it is concluded that the quartz content of the sandstone of the Huagang Formation and Pinghu Formation in Xihu sag is the highest,and there are some feldspar and cuttings,which provide the material basis for the formation of secondary pores.The rock types of the blocks are mainly composed of feldspar lithic sandstone and lithic feldspar sandstone,and the rock granularity is mainly composed of fine sand and very fine sand,sorted behavior is mainly composed of medium-well,matrix content is low.Compared to the Pinghu Formation sandstone,Huagang Formation sandstone is more clean.(2)The pore type of Huahang Formation and Pinghu Formation reservoir in Xihu sag are mainly secondary pores,accounting for 77.5% and 75.6% of the total porosity respectively,and the secondary pores are mainly dissolution pores.The proportion of the secondary pore in the Pingbei,Xiciao and south central of central inversion tectonic belt is higher,which proportion of the total porosity is over 80%.The Secondary pore rate in Pingbei of Pinghu Formation is the highest,and The proportion of secondary porosity to the total face rate is the highest in the Xiciao.(3)The matching pattern of reservoir diagenetic sequence and reservoir pore evolution process of Huagang Formation and Pinghu Formation in Xihu Sag was established.The initial porosity of the rock is reduced by the compaction in the subsurface formation,and the dissolution of the soluble minerals in the reservoirs by early hydrocarbon and atmospheric fresh water dissolution.The diagenesis stage,compaction,calcite cementation and clay mineral cementation lead to the pores are reduced;the organic matter releases a large amount of organic acid and the reservoir enters the acid diagenetic environment,and the secondary dissolution pore increases.(4)Oil and gas fill to Huagang Formation and Pinghu Formation reservoir in the depth of 3000 ~ 5000 m position,when Ro between 0.5%-1.3%,and the reservoir hydrocarbon filling began to active.This maturity range and depth are the important reservoir development stages of secondary pore of Huagang Formation and Pinghu Formation.(5)Sedimentation,abnormal high pressure,oil and gas filling,tectonic evolution and diagenesis control the secondary porosity development and evolution of the reservoirs of the Paleogene Huagang Formation and Pinghu Formation in Xihu Sag,which can be summarized as "two Period formation,acid-soluble,high-pressure-hydrocarbon protection ".