Genetic Analysis Of Calcite Cementation In The Tight Sandstone Reservoirs Of Sangonghe Formation On Blocks ? And ? Areas In Central Junggar Basin

Unconventional oil and gas resources are important targets of the national energy strategy in the new era.The reservoir of Jurassic Sangonghe Formation in the central Junggar Basin is a set of tight sandstone reservoirs with abundant resource of oil-gas and great exploration potential.Carbonate cementation of tight sandstone reservoir is developed,which has great influence and control on reservoir densification and hydrocarbon accumulation.Based on the observation of core and slice,sem analysis,fluid inclusion and carbon-oxygen isotope analysis,combined with diagenesis study,the formation temperature and time of calcite cementation were determined,the genetic mechanism of calcite cement is discussed and the spatial distribution of different genetic calcite cement is revealed.The results show that the tight sandstone reservoirs of Sangonghe Formation on the Blocks I and III areas are mainly developed in the underwater distributary channel and estuary dam in the sub-facies of delta front.The main reservoir rock types are medium coarse and medium fine feldspar lithic sandstone and lithic sandstone with medium-low porosity and ultra-low porosity.The homogenization temperature of fluid inclusion in calcite cement and the oxygen isotope thermometer of calcite suggested that the calcites were formed at 44.8??125.8?during 110Ma to 20Ma.This study also indicates that there are four geneses of calcite cement,they are inorganic genesis,BSR genesis,TSR genesis,and organic acid decarboxylation genesis.The?¹³C _PDBof inorganic calcite is mainly distributed in-4.0‰?4.0‰and formation temperature is under 100?,it is formed before and during hydrocarbon accumulation.The?¹³C _PDBof BSR calcite is mainly distributed between-25.0‰and-10.0‰;and the temperature is generally less than 90?,which is formed during the process of reservoir destruction.The?¹³C _PDBof TSR calcite is mainly distributed between-25.0‰and-10.0‰,its formation temperature is between 100?and 140?,which is formed during hydrocarbon accumulation.The?¹³C _PDBof acid decarboxylation is mainly distributed between-10.0‰and-5.0‰,its formation temperature is usually less than100?,which is formed during hydrocarbon accumulation.The calcite of different origin has a regular spatial distribution.On Block I,from Shawodi to Moxizhuang,and Zhensha village,the calcite cementation evolved from BSR,organic acid decarboxylation and inorganic genesis,to organic acid decarboxylation and inorganic genesis,and then to inorganic genesis,respectively;TSR calcite mainly distributed on the Block?.