Late Mesozoic Multi-stage Strata Denudation And Its Effect On Hydrocarbon Accumulation In The Northern Ordos Basin

In recent years,Dong Sheng gas field is found in the north of Ordos Basin.With the development of exploration,tectonic activities in the late Mesozoic had a great restraining effect on the late Paleozoic reservoir forming factors and the migration of natural gas.In this paper,through the investigation of the principle and method of formation denudation recovery,48 Wells and two seismic profiles have been used to determine the existence of 4-stage unconformity in the late Mesozoic in the study area from the perspective of acoustic time difference and formation correlation,and the formation denudation thickness has been restored.By late Mesozoic fault activities and stratigraphic erosion thickness trend research,combined with inclusions homogenization temperature test,illite dating,single-well simulation methods,analysis of gas accumulation process and tectonic activities in the study area for gas accumulation,the influence of the conclusions are as follows:(1)Late Mesozoic in the north of ordos basin development 4 unconformity surface.(2)Denudation trend and intensity were similar between Zhi Luo group and Yan An group.The denudation thickness decreased from west to east,respectively 650-150 m and 800-200 m.In the west of Well Jin127-Jin108-Jin95,the denudation thickness is over 500 m.The west and southwest of the study area are in the state of uplift and denudation.The denudation thickness of the north plate of The Boer Jianghaizi fault is relatively small(300m)and the denudation intensity is relatively weak.This characteristic is related to the stretching activity of The Boer Jianghaizi fault at the same period.(3)During the An Ding group,the denudation thickness in the study area decreased from NW to SE,about 900-200 m.The denudation thickness is greater than 500 m to the west of Jin101 well area and to the north of The Boer Jianghaizi fault.The denudation thickness to the north of The Boer Jianghaizi fault reaches about 900 m.In the northern part of the study area,the fault is strongly reversed,mainly by thrusting structure.(4)During the Zhi Dan Period,the denudation thickness to the north of The Boer Jianghaizi fault increased from 300 m to700m.The denudation thickness in other areas was less than 300 m.(5)Thermal evolution of source rocks in the study area controlled by late Mesozoic tectonic activities;The fault activity can improve the reservoir physical property positively.At the same time,the difference of tectonic activity controls the trap formation,trap type and gas migration direction.There are first-phase gas accumulation events(176-172Ma)in the southern area of Hangjinqi Fault zone,and two-phase gas accumulation events(166-154 Ma and 128-115Ma)in the northern area.