Due to the mineral composition complexity, mixed tight sedimentation develop complicated pore structures and varies reservoir properties. The mixed tight dolomite-analcite sedimentation has tight oil resource potential in Dujiatai pay set in the fourth Member of Shahejie Formation in Leijia district, western Liaohe depression. The mixed tight reservoir were divided as dolomicrite, fine grained diamictite and analcimolith based on X-ray powder diffraction(XRD)analysis. Casting thin sections and high resolution FIB/SEM image analysis are used to study the reservoir space types. It showed that these tight reservoirs have meso-micron, micro-micron and nano pore-throat system. Meso-micron pore throat(with pore throat radii above 10 μm)include intergranular dissolved pore, intergranular pore, and dolomite/analcime intracrystal dissolved pores. Micro-micron pore throat(with pore throat radii between 1 μm to 10 μm)include dolomite intercrystal pore, detrital minerals intergranular pore and some dissolved micro-pores. While most dolomite intracrystal solution pores and intergranular pores of clay minerals are nanopores, with radius below 1 μm. Mercury Injection Capillary Pressure was used to find pore size distribution of the three kinds of reservoirs. It showed the pore throat radius have duplex peak. The pore throat radius of dolomicrite is found to be around 10 nm within a nanopore range and around 4 μm within a micro-micron pore range. The proportion of the nanopore and micro-micron pore is 63.1% and 25.1% respectively. While the proportion of the nanopore and micro-micron pore is 79.1% and 20.9% in fine grained diamictite. The proportion of the nanopore and micro-micron pore is 79.1% and 20.9% respectively in analcimolith. The pore type and size of mixed tight reservoir are mainly controlled by mineral components. The pores complexities controlled by different mineral components are the main reason for duplex peak pore throat radius. The dolomite intergranular pores have good connectivity. Analcite usually filled the solution pores and fractures. Clay minerals mainly develop nano intergranular pores. Combining these factors, the porosity of mixed tight sedimentation is negatively correlated with the content of analcite, and positively correlated with the content of feldspar-quartz debris. Due to the common developed fractures in these reservoirs, the correlation between mineral composition and permeability is poor.
. Reservoir property and pore-throat characteristics of mixed tight sedimentation: A case study of Dujiatai pay set in Leijia district, western Liaohe depression[J]. Chinese Journal of Geology, 2016, 51(2): 448-459.