Characterization Of Normal Fault Damage Zones In The Subsurface Of Wangxuzhuang Oilfield,China

The fault damage zone may have a significant impact on the fault behavior,e.g.,migration of fluid and the development of unconventional resources.Most of the studies of fault damage zones are based on the direct observations of the field outcrops.Due to the complexities of the fault zone and the lack of data,damage zones in subsurface remain enigmatic.The characterization of the subsurface normal fault system can help to infer the details of its damage zone,serving well placement near the fault zone and reservoir characterization to maximize the oil production.The purpose of this thesis is to characterize the damage zones in the subsurface of Wangxuzhuang Oilfield,by using seismic attributes of variance,reflection intensity,and dip-azimuth.We focus on Es1x member with Shahejie formation in Huanghua Depression,the Bohai Bay Basin.Based on integration of the core analysis,well logging,and the literature,we found that the study area is mainly composed of bio-limestone with abundant biological pores and holes,and dense brittle vertical-fractures.The seismic attributes show potential for the characterization of fault damage zones in the study area,in which the variance attribute is more efficient in fault damage zones.The variance present a big number of faults developed mainly in the east-west direction,and fractionally in the north-south direction.Intensive deformations are found in the northeast part of the 1st fault block,the south part of the 2nd fault block and the northeastern part of the 3rd fault block.Furthermore,damage zones are developed at the linkage of different fault segments to different extents.In order to analyze the damage zones more properly,we measured the damage intensity around four small isolated normal faults with relatively small offsets and two fault systems by seismic variance attribute.We estimate the thickness of the damage zone for each fault and present the decaying relationship between variance value and the fault distance.The variance value is highest within the fault core and as the distance increases away from the core to a level of low values as background.The seismic distortion,e.g.,high variance zone is interpreted as fault damage zones.The implication of the damage zones in this study could help characterize the bio-limestone reservoir and petroleum migration.