MINERALOGY AND PORE STRUCTURES OF THE ORDOVICIAN UTICA SHALE IN QUEBEC, CANADA

The Ordovician Utica marine shale developed on the St. Lawrence Platform of Quebec, Canada is a set of deposits with great potential of shale oil and shale gas. Based on outcrop and drilling core samples, field emission scanning electron microscope, TIMA integrated mineral analysis system and organic geochemical analysis are used to systematically study the mineral composition and organic matters of the shale, so as to reveal pore characteristics and their influencing factors. The results show that the organic matters in the Utica shale are relatively rich and have undergone a thermal evolution process from mature or high-mature stage to over-mature stage as the depth increases. The shale mainly consists of calcite, quartz, feldspar and clay minerals, with a small amount of dolomite and pyrite. With the increase in thermal evolution degree, calcite decreases, feldspar and quartz increase gradually, while the content of clay minerals remains little changed. Pores can be classified into types of matrix pores (intergranular pore and intragranular pore), organic matter (OM) pores and fractures. Average porosity shows a decreasing trend with the increase in burial depth. Further analysis shows that the impact of buried thermal evolution and diagenesis are obvious on porosity evolution. In mature or high-mature stage, organic matter pores dominate. Carbonate cementation may significantly reduce porosity, but clay minerals have well developed internal pores and contribute to certain extent to the total. In contrast, shale pore spaces are greatly diminished by compaction, and thus the over-mature stage is mostly predominated by matrix pores.