Abstract:

The state and content of oil and gas in shale are closely related to the shale reservoir pores, and the complex size of
the reservoir pore network in shale is between the nanometer and micrometer levels, which is jointly influenced by multiple factors such as hydrocarbon evolution, hydrocarbon forming organism types, and the combination of mineral and organic matter characteristics. In this paper, we take the combined shale of multi-algal-type symbiotic muddy texture-microcrystalline gray texture in the Fengye 1-1HF well of the Minfeng Depression of the Dongying Depression and the combined shale of cyanobacterial algal mat muddy texture-microcrystalline gray texture in the Niuzhuang Depression Niuye 2HF well of the Niuzhuang Depression as the objects of our study. Thermal simulation experiments, pyrolysis, organic carbon mass fraction, specular plasma reflectivity, whole-rock X-ray diffraction, scanning electron microscopy,nuclear magnetic resonance cryoporomety and other analytical tests were utilized to reveal the evolutionary characteristics of reservoir pores during hydrocarbon production in shales of different lithological types. The results show that there are differences in the hydrocarbon generation process and pore development and evolution characteristics of shales in different lithologies. The oil generation window of the sample from the Fengye 1-1HF well is wide, and a large number of organic matter cavities and clay mineral intergranular pores are developed in the mud grain layer of the multi-algal symbiosis, and microcrystalline intergranular pores are developed in the gray grain layer. There are two peaks of hydrocarbon production in the samples from the Niuye 2HF well, the clay mineral intergranular pores are mainly developed in the cyanobacterial algal mat muddy texture layer, and the gray texture layer of gravelly algal gravel is tightly stacked, with poorly developed pores. The transformation of clay minerals during hydrocarbon production and the dissolution and reprecipitation of alkaline minerals have important effects on the pore modification of shale reservoirs. 

Key words: Dongying Depression, Shahejie Formation, shale reservoir, thermal simulation experiment, pore evolution