Formation And Evolution Of Normal Fault Propagation Folds And Their Significance In Petroleum Geology

This paper takes the Beier sag in the Hailar Basin as the target area,and systematically analyzes the formation and evolution of normal fault propagation folds and its petroleum geological significance.Based on the study of the main fault style in flat and section,combined with its related fold geometric pattern,this paper analyzes the matching relationship between the fault and its related fold,and it is considered that the monoclinic structure developed near the normal fault from the Nantun Formation to the Damaguaihe Formation is a normal fault propagation fold.The normal fault propagation fold is divided into two types: unbroken through folds and broken through folds.Unbroken through folds are mainly distributed on the early extension faults in the sub-sag.Broken through folds are mainly distributed on the hanging wall of the long-term active large fault.There are two main causes of normal fault propagation folds: one is the change of tectonic stress field at the end of the Nantun Formation,which leads to the weakening of the activity intensity of the faults;the second is the sand and mudstone interlayer in the Nantun Formation and its ability to compete with the Damaguaihe Formation are propitious to the formation of normal fault propagation fold.Based on the concepts of continuous distance and discontinuous distance,the corresponding fault throw-distance and depth-throw curves are drawn to quantitatively identify the formation of propagation folds and break-through periods,and it is considered that the normal fault propagation fold formation period is mainly during the deposition period of the Nantun Formation and the lower part of Damoguaihe Formation,the faulting period is mainly the deposition period of the upper part of Damoguaihe Formation.From the two perspectives of inversion and forward modeling,the equilibrium profile and trishear numerical simulation technology are used to verify the evolution process of normal fault propagation folds,which is in accordance with the results of fault kinematic analysis.The formation and evolution process of normal fault propagation folds has a good spatial-temporal matching relationship with petroleum accumulation conditions in Beier depression.Based on the plane structural map,seismic profile map and reservoir section,it is believed that normal fault propagation folds have a good effect on trap types and distribution matching relationship: in the unbroken propagation folds,the footwall and the end of the fault will form structural traps,and above the folds will form stratigraphic traps;in the broken propagation folds,the hanging wall syncline and faults constitute the structural traps adjacent to the fault.,and away from the fault to form stratigraphic trap.This has guiding significance for the subsequent exploration and development of mature exploration areas.