PORE CHARACTERISTICS AND CONTROLLING FACTORS OF SALIFEROUS SHALE IN DONGPU DEPRESSION, BOHAI BAY BASIN，CHINA

Mesozoic-Cenozoic Salt Lake basins are widely developed in China, and saliferous shale strata rich in organic matter is abundant. The study area Dongpu depression in Bohai bay basin is a typical terrestrial saline lacustrine depression in China. Previous exploration practice showed the important controlling effect of saliferous shale on the source rock distribution and characteristics (compared with general shale strata, saliferous shale strata is characterized by higher organic matter abundance and oil-prone organic matter). However, studies on the pore characteristics and controlling factors under the participation of evaporite minerals in saliferous shale strata are still lacking.

In the study, 9 samples with different contents of evaporate minerals were selected from Es₃ member in Dongpu depression. Geochemical experiments and pore structures were investigated using argon milling FE-SEM observations and N₂ adsorption analysis. The results show that TOC contents of saliferous shale range from 0.10 % to 7.78 % and their Ro values are between 0.41% and 2.67%. All the samples are clay rich, ranging from 24%-64.9%, quartz, feldspar and carbonate are well developed, evaporate minerals including halite, gypsum and anhydrite can also be found in the samples, ranging from 0.6% to 7.2%, 2.52 % in average. Interparticle, intraparticle and OM pores are well developed with pore sizes ranging from several to several hundred nanometers, and micron meter microfractures can also be found.

The specific surface area (SSA) varies from 4.035 m²/g to 28.598 m²/g, and pore volume (PV) is from 0.05 cm³/g to 0.062 cm³/g. TOC, carbonate and brittle mineral content is negatively correlated with SSA, while R_O and clay mineral content is positively correlated with SSA. TOC and carbonate mineral content have a positive relationship with PV, while a negative correlation exists between R_O, brittle mineral contents, clay mineral contents and PV. When content of evaporite is less than 3%, evaporite has a good positive correlation with SSA and PV. However, when the content of evaporate is larger than 3%, it may constrain the development of pores. More work needs to be done when sample capacity gets larger and quantitative correlation should be studied.

Key words: Dongpu depression; Saliferous shale；Pore characteristics; Controlling factors