Formation And Evolution For The Main Fault Systems And Their Implication To Petroleum Geology In Qikou Depression

By collecting related geological,geophysical and well logging data and applying advanced fault activity quantity research technology and balanced crossed-section technology to our study area,This paper has analyzed the detailed formation and evolution process through depicting the geometry characteristics of the main fault systems in Qikou depression. This research shows great significance in dividing ancient tectonic framework,the genetic mechanism of the fault systems,the control effect of uplift and depression situation. What is more, this work has practical application value in petroleum control by faults in Qikou depression.1. This paper has pointed out the division of tectonic units, sketched out the boundary of the central uplift zone, and described the basic framework character of Qikou depression.—From north to south, along the North-Dagang buried hill to the Baidong tectonic zone, there is a prominent uplift zone. The Banqiao sub-depression (locates in the north of the uplift zone) and the Qibei sub-depression (locates in the south of the uplift zone) is the distinct subsidence depressed zone, in both of which the sedimentary thickness of paleogene strata. The slope zone, based on the Chengning uplift, locates in the south and southeast of the Qikou depression.2. This paper has depicted meticulously the planar and section distribution characters and the assemble pattern of the main first order and second order faults, and pointed out the spatial variation law of these geometric styles. Based on the formation mechanism, the faults of the Qikou depression can be divided into five fault systems, as follows, Xingang-Haihe fault zone, North Dagang-Binhail fault zone, Qizhong-Qidong fault zone, South Dagang fault zone and Chengbei step-fault zone. The tectonic styles cf faults between the western side and eastern side of basin are completely different - (1) the fault zone locates in the western side, such as North Dagang fault zone and South Dagang fault zone, mostly trend NE, while the eastern fault zones, such as Haihe-Xingang fault zone, Qizhong fault zone and Zhangdong fault zone, mostly trend nearly EW; (2) the terrestrial faults which mainly act as large-scale shovel-like faults and cut the basement, is the basin-controlling faults. And the sediment thickness is lager in the footwall. While the fault zones locate in the offshore. 3.The kinematics characteristics of CangDong Fault and the other 4 fault systems has been analyzed emphasized.(1)The segmentation activity characteristics of single fault has been educed in Qikou depression. The activity transference regulations and the growth,connection and enlarge regulations ,which are summarized by applying the distance-length method and ancient throw method ,are as follows: CangDong Fault which is the boundary fault of the basin has evident segmentation activity; What is more, its main activity term is in Es1 period. The fault systems in the Western activated intensely in Es, continually activated in Ed and barely activated in Neogene. The fault systems in offshore in the Eastern began to activate in Es1 period, intensely in Ed and continually in Neogene. In one word, the fault systems transferred from land to offshore.(2) The article has found and summarized 4 fault growths and enlarges patterns-simplelateral propagation, unidirectional lateral propagation, amalgamation of two faults and the complex growth pattern.4. On the basis of fault quantity analyzed, the control effect of fault activity to uplift and depression situation was studied by tectonic evolution history analysis and subsidence history analysis and paleo-tectonic framework maps, put forward:(1) The backbone faults activities have distinct stages.During the period of Es2-Es3, the Nandagang fault,Gangxi fault and Gangdong fault showed strong activities, which made the tectonic situation of " two uplifts and three depressions". During the Es1 period, the Cangdong Fault in the western boundary and Haihe-Xingang faults in the North boundary had successive activity. Along with the continual activity of boundary faults, the NE direction and EW direction fault began to develop, forming two different kinds of tectonic style. All the structural styles changed from Es1 period. It is the key transformation period in this area. At the end of Ed period, fault activities transferred toward Eastern continually, which made a lot of new faults developed. So the intrinsic structures were made complex by them. The rift depression show little activities and the characteristics of stronger activities in the north and weaker in the south. During the period of Neogene, the basin entered into the period of thermal subsidence stage. The evolution process of Qikou depression shows the character of transformation from south to north and from west to east. In other words, the structure in the southern-west was developed earlier than in the NE.(2)The fault activity in different periods evidently controlled the transference regularity of subsidence center and the change of uplift and depression situation.The rate of subsidence quicken from west to east , subsidence center locates in Qibei depression controlling by Gangxi and Gangdong faults and Qinan depression controlling by Nandagang fault in Es2+3 stage. The total rate of subsidence in Es1 stage even is more than in the Es2+3 stage, the fault which controlled depression continues activities, the subsidence center locates in every depression and migrates to the east. the rate of subsidence is comparatively low in Ed stage, the amplitude of subsidence is relatively small, the strong fault activity area turns around the eastern, the subsidence center locates in Qikou main depression. Tectonic subsidence rate show the character of the rapid subsidence which is leaded by the activity fault in Paleogene. In Neocene, the subsidence of basin is slow in Nm period, the subsidence of whole area quicken up , which show the character of the rapid subsidence.A detailed analysis on activity of the main fault system controlling the Patterns of uplift and depression combining the thickness maps in Paleogene, The following regularity are: the basin patterns of uplift and depression is significantly in Es3 stage. The shape of Banqiao hypo-depression, Qibei hypo-depression ,Qinan hypo-depression and Qikou main depression is clear, the resistance of segmentation is strong , Qikou main depression and Beitang depression is a unified lake Basin, the spreading direction of subsidence center presents NE. the amplitude of the basin uplift and depth of subsidence weakens obvious, the whole basin is quiet period in Es2 stage. The Structure of uplift and depression is quite clearly , the range of lake Basin develops the most extensive in Ed stage, the spreading direction of three notable most and sub subsidence center presents NE or NEE; Haihe uplift comparts northern Beitang depression and southern Qikou depression . the amplitude of the bas(?)n uplift weakens obvious, Haihe fault comparts northern Beitang depression and southern deep Qikou depression, the spreading direction of subsidence center presents EW.5. Dividing the tectonic evolution stages and recovers the paleo tectonic framework of the basin. Determines that the Es1 stage is an important rifting stage turning point and its bottom boundary divides Paleocene into two episodes, one is Es₂₊₃ stage that mainly extend in NE, the other is Es₁,Ed stages that mainly extend in NS.6. Summarizing the formation and evolution for the main fault systems and their implication to petroleum geology in Qikou depression, distinguishing five types of structural-related trap: drape anticline trap, reverse drag anticline trap, syndeposit-slip fault anticline trap, fault block trap and fault-lithology trap. This paper also advancing the composite hydrocarbon migration and accumulation model in Beidagang-Binghail fault zone and the bedding step hydrocarbon migration and accumulation model in Chenbei step-fault zone.