Fractal Dimension Identification Method of Fractures in Igneous Buried Hill Based on Mechanical Layer Division

Igneous buried⁃hill oil and gas reservoir has become a new field for increasing reserves and production, which has broad exploration and development prospects. The burial⁃hill gas reservoir in Qiongdongnan Basin is affected by multi⁃stage magma intrusion, the rock structure is complex and varied, the reservoir space distribution is highly heterogeneous, and it is difficult to identify fractures by logging curves.In view of the difficult problem of identifying fractures in igneous rock buried hill logging, the fracture characteristics and logging response rules are analyzed by using the data of core, thin section, imaging logging and conventional logging. The classical rock elastic parameter calculation model is used to establish the rock mechanics section, and the rock mechanics layer is divided according to the difference of the longitudinal mechanical properties of the well section. The rock mechanics evaluation model reflecting rock stability is introduced, and the fractal dimension principle of curve fluctuation is adopted to identify the fractures in buried hills of igneous rocks by the constraint of mechanical layer division to eliminate the interference of lithology change. The results show that the development of fractures in buriedhill has obvious lithology selection bias, and the fractures developed in monzonitic granite have the largest opening degree and retain more open fractures. The change of rock properties is easy to cause the difference of fracture distribution, which leads to the change of density and wave velocity. The cross analysis of the ratio of P⁃wave to S⁃wave time difference and photoelectric absorption cross section can distinguish most of the more developed cracks and most of the more developed fractures to the greatest extent. On the basis of mechanical interval division, segmented identification of natural fractures can improve the identification effect of buried hill fractures, and the identification coincidence rate is 85% with that of dissolution fractures + high conductivity fractures in imaging logging, which can meet the research needs and provide guidance for the effective development of buried hill gas reservoirs.