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The Evolutionary History And Distributional Regularities Of Huanghua Depression Buried Hills In Bohai Bay Basin

Posted on:2014-12-01Degree:DoctorType:Dissertation
Country:ChinaCandidate:G C LuFull Text:PDF
GTID:1260330425975286Subject:Energy Geological Engineering
Abstract/Summary:PDF Full Text Request
Huanghua depression is located in the central of Bohai Bay basin, it is a complex depression dating from Cenozoi., After large-scale extrusion tectonic movement of the Pre-tertiary and tension destruction of the Tertiary, the original structural features of Huanghua depression buried hills were completely destroyed. The tectonic evolution process is clearly recorded by many thrust, strike-slip and inversion tectonic deformation styles in the depression, under the guidance of dynamic sedimentary basins and the tectonic stratigraphic analysis theory and method, this paper make a systematic research on the evolution history and distribution regularities of Huanghua depression buried hills basing on using the mega-sized seismic data of the latest merged-processing. Firstly we track and identify many important stratigraphic interfaces, such as J, Mz and C, then Summarize the distribution regularities of many different genetic types buried hills, and research the relationship between formation and accumulation of buried hills, and make the distribution of better buried hills clearly, at last we put forward the overall deployment plan. This research is good to deepening the understanding of the buried hills’ evolution history in Bohai Bay basin, and also is good to the buried hills oil-gas exploration of Dagang oilfield. The primary understanding and the conclusion is as follows:1、We Tease the key horizons of Huanghua depression buried hills systematically, and sum up the synthetical geological characteristics, including seismic, well logging, Sedimentology and so on, then we identify the key interface—Indosinian structural surface with the key tracking and identification technology.1) the improvement of the sismic recognition and interpretation technologyThey have the different lithological association and seismic response characteristics in different stratas, we do the identification and interpretation in unconformity surface according to the geological and seismic characteristics of the key exploration stratum. It can be divided into the following steps:①horizon correlation.we confirm the seismic characteristics of the unconformity surface by the synthetic seismogram of some wells, then gradually expand to the whole study area;②angular unconformity identification. We should find the more obvious and large angular unconformity by carefully analysising the seismic data because of lacking the enough drilling data.③interface determination. They have the different seismic responses in different tectonic movements, we can interpret the key horizons and the more obvious interface, then broad our horizon interpretation and study to the upper and lower horizon. It may save you a little time.2) the identification of the key horizons of buried hillsThe previous study on buried hills is mainly based on the structural modeling which is built by the interface of inner buried hill, so it is lack of synthetical understanding on the key interface which control the evolution and accumulation of buried hills. This paper confirm that the Indosinian structural surface is a large angular unconformity in Huanghua depression basing on the research on the tertiary tectonic movement, it is shown as truncation and onlaping obviously in the seismic section, it is easy to track by comparing to the upper and lower horizons and the horizon correlation. the pre-tertiary strata above the Indosinian surface mainly include J1+2and J3-K1, the former is the stable coal bed, thick sand bed and mudstone which is formed in the transitional face depositing interactively, it is shown as middle-weak amplitude including two to four middle-strong amplitude, continuous phase, and also is easer to track. It is the important exploration strata of pre-tertiary. The latter is shown as middle-strong amplitude, discontinuous reflection. the pre-tertiary buried hills targets strata below the Indosinian surface mainly include PZ1-∈,O, PZ2-C. the Cambrian is formed by carbonate and mudstone, it is shown as strong and continuous phase obviously, and is easy to identify and track. It is abundant in carbonate in the Ordovician with distributional stability, it is shown as blank or weak, continuous seismic reflection. the main sedimentary formation is coal bed in the carboniferous, it is shown as three to four strong amplitude, continuous reflection, and is easy to identify and track. The Permian belong to continental sedimentation, it is shown as weak, continuous seismic reflection in P1x, it is shown as two continuous phases in P2s and P2sh because of the high shale content. There are mostly blank reflections without continuous reflection in Triassic, it is interbed of sand and shale belonging to continental sedimentation. The interpretation of Indosinian surface is important to deepen the study on reservoir distribution, reconstruction and accumulation. So the study on the Indosinian surface not only improve the evolution series of an basin., but also make it systematic to the buried hills exploration, it wll be an entry path to the buried hills exploration of the Palaeozoic and the Mesozoic.2、In this article we clarified the characteristics of the buried hill structure in Huanghua depression, and summarized the favorable areas for buried hill development,take Qikou Sag for example.The distribution of buried hill structure in Qikou Sag is mainly controlled by Mesozoic and Cenozoic structures, it’s characteristics are revealed as the superposition of structures and it doesn’t coincide fully with the secondary structural belt. On a macro level the distribution of buried hill structure is influenced by bedrock slope, which extends from the uplift of basin inside and basin edge to the sag. Generally it can be divided into four tectonic regions:the southwest of Qikou Sag, southern margin of Qikou Sag, Tanggu-Xingang structure zone and Jian south-Dashentang structure area. The Kongdian high in southwest margin is the watershed, which segments Qikou Sag and Cang east-Nanpi sag. It is also a development zone of the basement buried hill structure. The fault terrace zone in southern margin also is a favorable area of buried hills development, including the buried hill structural belts in Chenghai and Cheng North. The buried hill structure in the north of Qikou Sag, namely Jian south-Dashentang buried hill structure distribution area, is mainly influenced by the basal uplift of county Cang and the extension basal uplift of Jian south.To sum up, the buried hills mainly developed in the southwest margin and south of Qikou Sag. And the regularities presented by the changes from sag centers to the basin edge are the formations are newer, the residual palaeozoic is increasing, and the inside structures gradually tend to simplification. The buried hills in basin edge are mainly the block mountains in Mesozoic and the inside buried hills in Palaeozoic, and the buried hills in the sag center are the composite of Indosinian monadnocks and fault blocks.3、We based on the study on the ups and downs of paleostructure, using the ancient layer flattening technic and block recovery technology, combined with the ancient geological map and residual stratum thickness figure to study the buried hill development.The main purpose of buried hill analysis is to explore the process of the basement tectonic deformation and its influences on the insider configuration and reservoir development. Usually, the evolution research of buried hill structural mainly uses the methods of balance analysis of geological section and the thickness analysis, and on the basis of palaeostructure recovery to study on the evolution. By the analysis of tectonic evolution, combining with the ancient geological map in pre-Jurassic and pre-Cenozoic of Qikou Sag, you can see that the formation and evolution of buried hills in Qikou Sag have a direct relationship with the three tectonic movements in Mesozoic and Cenozoic, they are the Indosinian movement, Yanshan Movement and early Himalayan movement.1) tectonic deformation in Indosinian movement has an important influence on the formation of Qikou buried hills.The tectonic deformation characteristics are bright in Qikou Sag in Indosinian, inside and surroundings, which embody the characteristics of orogeny and thrust fold in early of the north China craton cracking. According to the recovered ancient tectonic frame, Qikou Sag is characterized by the giant uplift in northern uplift zone before Jurassic. Ancient uplift of Qikou Sag includes the current subsidence centre and the north parts of county Cang uplift, which is contrasted brightly with the southern syncline structure. Around the ancient uplift,"two slow, one steep" slope structure developed.2) fracture development in Yanshanian influences on the formation of Qikou buried hills.Yanshanian tectonic deformation of Qikou Sag is mainly starting from late Jurassic. In the early and mid Jurassic small coal bearing basin distribute along the ancient uplift in indosinian, especially in the southwest edge area, forming long axis of the ancient landform basin groups. After the late Jurassic, faulting of Qikou Sag is more strong, large strike-slip faults and grabens appeared in the north and south of ancient uplift in Palaeohigh.3) in Himalayan, the differential settlement influences the buried hill formation.In late Eocene to Oligocene, Qikou Sag is in the stage of fault depression period. The warped fault blocks of Qikou Sag is becoming with the shovel-like faults activity at the edge of Cang east, Zhao north-Yangerzhuang and Chadian. Be controlled by the secondary faults in the basin, the basement evolution of periclinal area in Qikou Sag is differential settlement, forming multiple warped tilting fault block structures, becoming the main factors of the forming of half horst buried hills. In this phase, the large basement deformation already covers the early buried hills. At present, the implementation of the buried hill structural belt is mainly the product of Himalayan fault depression stage. As a result of the action of Himalayan fault depression, buried hill structure of Qikou Sag is in final.4、Considering the formation mechanism, the inside structure and the accumulation condition of buried hills, and following the causes of formation, the buried hills of QiKou Depression are classified into three categories and twelve tectonic types.The first category is called erosion remnant buried hill. It was the direct result of regional unconformity and differential weathering-leaching. According to the formation constitutions and inside architectural features, this category is further divided into two types which are crust weathered-remaining buried hill and inside remnant buried hill. The former type has simple inside structure and the latter has complex thrust fault inside, such as QianMiqiao buried hill.The second category is named strike-slip extension fault block-buried hill. Because of Indosinian movement, this kind of buried hill mainly distributes at the slope or depression. On top of Paleozoic erathem (Pz), differential weathering buried hill was not formed at the unconformity. And the layers of Mesozoic erathem (Mz) deposited stably relatively above the formations of Pz. The buried hills mainly formed due to the differential rise and down which were caused by strike-slip extension fault of Mz and Cenozoic erathem (Kz). According to the location where buried hills lied, the formations which buried hills consisted and the patterns of the fault blocks, this category is further divided into two formations and six types. The buried hills of Pz include tilted fault block-buried hill (e.g. GangXi buried hill, YangSanmu and KouCun buried hill), horst fault block-buried hill (e.g. D Area of ZhaoDong), extension strike-slip fault block-buried hill (e.g. ChengHai and ChangLu), and low bench fault block-buried hill (e.g. the north of TaoXing and XinGang). In the formation of Mz, there developed two types of buried hills which were nosing fault block-buried hills controlled by antithetic faults and second bench fault block-buried hill located at the margin of the basin. These buried hills are typical tectonic buried hills, represented by the buried of ChengHaidong.The third category is thrust-type buried hill and fold-type buried hill. This category is further divided into four subclasses in accordance with the features inside buried hills and the sequence of formations. The four subclasses are as follows:(1) Large bending fold buried hill. This type is represented by the buried hill at the deep tectonic belt of KongDian. It located in the upper wall of CangDong fault and was controlled by the fold which was related to the faults of Paleogene. At the top of the buried hill, garben-horst structures can be seen everywhere.(2) Buckle fold buried hill. It was the result of lateral extrusion, and this type of buried hill is relatively infrequent in QiKou Depression and its surrounding areas. One of the example is the buried hill of DongGuan at the south of KongDian.(3) Anticlinal buried hill remolded by tensile stress. Take the buried hill of WangGuantun as an example. In early stage, it was squeezed anticline, and the movement of tilted fault block turned it into the buried hill now.(4) Thrust fold buried hill. It was buried in deep formations and the typical example is the buried hill of WuMaying.5、Researches of buried hills reservoir-forming controls help our understanding of the difference between the reservoir-forming, affirm the potential reservoir there and guild the further prospecting.(1) Regularity of oil and gas distribution in buried hillsFrom the formations of prospecting in buried hills, the resources discovered in Ordovician are mainly gas, but in Permian and Mz are mainly oil. From the sequence of buried hills, in shallow buried hills, the resources of oil are found mainly in Jurassic and Permian. And in deep buried hill, the resources of gas are mainly found in Permian and Ordovician. From the scale of deposit, the large-scale traps in Ordovician are rich in gas. In comparison the traps in Permian are very poor, and the reserves of each buried hill is less than500,000tons. In the buried hills of Mz, multi-oil measures presented with great thickness, so the production per well is high. Therefore, the buried hills in QiKou Depression occupy the important position in the prospect in this area.From the geological background of buried hills, there is a certain regularity. In QiKou Depression, the resources in the buried hill of Ordovician mainly located at palaeohigh and its two flanks. After that, as a result of the series reform of listric fault at the margin of basin and second-grade fault in the basin, these buried hills now mainly locate at the slope and fault-step zone. And the resources in the clastic rocks of Permian and Mz mainly distributed at the intersection belt of bedrock fracture. So in the shallow carbonate buried hills, no resources were found, but the oil and gas were produced in grievances at almost the same depth. (2) The key conditions for reservoir-forming in buried hillsThe reservoirs of buried hills in QiKou Depression formed depending on the generating and reserving conditions, but the capping rocks played less roll in reservoir-forming. In this thesis, four characters of reservoir-forming are summarized as follows. First of all, two kinds of sources could form two kinds of reservoirs. For one kind of them, the hydrocarbons generated in new formations and reserved in old formations. And for the other kind, the hydrocarbons generated in old formations and reserved there. For example, in southern part of QiKou, there developed much source rocks in Carboniferous and Permian, and also developed much oil shale in Kong-2members. Therefore, all of them constitute the basic conditions for the formation of primary hydrocarbon. Secondly, the depth inversion of old and new formations could also provide conditions for hydrocarbon accumulations. This is the character of unique evolution, and it made the deep buried hill have intensive fractures, undergo weathering-leaching, and develop better reservoir-capping conditions than the shallow buried hills. Thirdly, the formations of Neogene buried deep, which created favorable conditions for capping hydrocarbons in the buried hills. Because in QiKou Depression the majority of traps in buried hills were buried in the basin at that time. Finally, the radial distribution of fractures in bedrocks established good connection between the buried hills in the slope and the major source rocks in QiKou Depression.In conclusion, there are two key factors in reservoir-forming of buried hills in QiKou Depression. One is the abundant sources for hydrocarbons. The important preconditions for the scale of oil and gas reservoirs are the window that fractures provide hydrocarbons and fracture system inside the buried hills. The other is the reserving conditions. In the buried hills of Ordovician, the carbonate rocks required more strict conditions for the types and properties of the reservoirs. The palaeohigh caused by Indosinian movement inversed the thrust faults, and that’s why the properties of the middle and deep buried hills are very good.
Keywords/Search Tags:Huanghua depression, Buried hills, Tentonic characteristics, TectonicEvolution, Hydrocarbon reservoir
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