Abstract:

The weathering crust of deep metamorphic rocks is relatively dense, and the development of fractures is key to reservoir quality.The formation mechanism of high-quality buried-hill reservoir of deep Archaean metamorphic rocks in the BZ 19-6 structure was analyzed through core description, casting thin section observation, microscopic fluorescent analysis of thin section, scanning electron microscopy and conventional physical property measurements.The results show that the Archaean rocks in the BZ 19-6 structure are dominated by gneiss, metamorphic granite and migmatite, in which the high content of felsic minerals with great brittleness is prone to fracture development.Thus, they tend to develop high-quality reservoirs.The fragmentation under continuous deformation and stress makes large-scale fracture zones and stress fragmenting zones developed inside the buried hill, which is the key to the formation of high-quality reservoirs in metamorphic rocks.The weathering resulted in a large number of secondary dissolution pores and dissolution enlarged pores along fractures on top of the buried hill.However, the weathering crust became relatively dense under deep burial.Under the guidance of controlling factors mentioned above, a reservoir distribution pattern of "vertical connectivity, and lateral continuity" is revealed for large-scale deep metamorphic reservoirs of high quality.

Key words: metamorphic rock, high-quality reservoir, buried hill, Archaean, BZ 19-6 structure, Bozhong Depression, Bohai Sea area