Abstract: The formation process of metamorphic buried-hill reservoirs in Bohai Oilfield was complicated, which was affected by tectonic movement, weathering and leaching, paleogeomorphology and other geological factors, resulting in the diversified reservoir space and extremely strong non-homogeneity. However, the existing reservoir physical properties evaluation methods had problems such as low quality of collected data, strong multi-solutions and poor real-time accuracy. For this reason, the metamorphic buried-hill reservoir in Bohai Oilfield was taken as a target area, the field outcrop sampling was carried out, interval transit time and microdrill drilling experiments were carried out to obtain the interval transit time and mechanical specific energy values of rocks with different physical characteristics, and a mathematical model of physical property index and reservoir porosity were established. The study shows that the interval transit time of the outcrops of the Archaeozoic metamorphic rocks of the Bohai Oilfield ranges from 371.75 to 617.29 μs/m, and the mechanical specific energy value ranges from 297.43 to 1207.47 MPa. The value of the mechanical specific energy shows an exponential function to decrease with the increase of the interval transit time, and the porosity shows a logarithmic function to decrease with the increase of the physical property index. The method has been popularized and applied in the metamorphic buried-hill reservoir of Bohai Oilfield, and the compliance rate with the logging interpretation results has reached more than 85%. This study provide reference and basis for the identification of metamorphic buried-hill reservoirs.

Key words: metamorphic rock, buried-hill reservoir, while drilling, mud logging engineering parameters, porosity, Bohai Oilfield