Pore formation mechanism and prediction is one of the difficult scientific problems for study of lacustrine tight carbonate reservoirs.This paper aims to study the thermal evolution of pores during burial through hydrous pyrolysis experiments

in which the samples were collected from the lower part of the 3

rd

Member of Shahejie Formation in the Shulu sag

Bohai Bay Basin.The geochemical analysis

focus ion bean milling Scanning Electronic Microscope(FIB-SEM)and lower temperature nitrogen adsorption were performed to examine the impacts of organic matter occurrence and thermal maturation on pore development and to reveal thermal evolution mechanism of organic pores in the tight reservoirs.The experimental result shows that the organic matter mainly occurs as combination of organic matter-argillaceous or marl matrix in the lacustrine carbonates

and the maturation has significant impact on the organic pore formation and evolution.With thermal maturity increasing from 0.5% to 1.5%(R

o

)

the total organic carbon(TOC)lowers more than half from 2.07% down to 0.85%

and porous volume and total specific surface area increase by 3 to 4 times.The organic pores is poor developed during the low thermal maturity-oil window(R

o

=0.5%-1.0%)

but increases dramatically during high thermal maturity-gas window stage(R

o

≥1.5%)due to the development of pores and fractures.The decomposition of organic matter should be the primary explanation for the increase of pore volume and specific surface area.The newly generated pores are dominated by organic pores

with the micro-and meso-organic pores being most sensitive to maturity.The pores with diameter less than 5nm make the biggest contribution to the additional total pore volume and specific surface area.The increase of total pore volume and specific surface area mainly comes from the formation of new pores instead of the enlargement of the existing pores.