The Structure Pattern Research And The Evaluation Of The Favorable Region With Oil And Gas Of Basin-ridge Coupling And Basin-mountain Coupling In The Front Of Longmen Mountain

Longmen mountain front zone, which located between An county- Guan county’s fault and Guangyuan-Dayi(concealed deposit)’s fault, can be referred to the long and narrow regions which spreading in north-eastwards. The length of which is about five hundred kilometers and the width of which is about five to ten kilometers. Since the 1930 s, lots of geologists have done scientific research on Longmen mountains’ orogenic belts and so far the geological research in this area has been nearly a century’s history. In recent years, with the growing tension of the oil and gas resources, Chinese National Sino Petroleum Corp and Chinese National Petroleum Corp have spent lots of exploration and research work on the front of Longmen mountain, and have got a series of exploration achievements in terms of the oil and gas exploration in this area, for instance some gas fields and oil-gas construction such as Zhongba、Dayi、Linhuashan、Pingluoba have been successively found. All these research work can be used to demonstrate that there are good oil and gas exploration prospects in the front of Longmen Mountains.The basin-mountain coupling and basin-ridge coupling are key points of structural geology research in recent years. On the one hand The research of the basin-ridge coupling is based on the dynamic evolution of ridge、plateaus and sedimentary basin, on the other hand the research of the basin-mountain coupling is based on the dynamic evolution of long and narrow orogenic belts and sedimentary basin. This paper chooses Longmen mountain tectonic belts, which located in Yangtze plate’s north-rim and Sichuan plateau, which is adjacent with this tectonic belts as research objects, takes the plate tectonics as the key link, takes the activity theory and continental dynamics as the guiding thought, starts from the angle of the basin-mountain coupling and the basin-ridge coupling, comprehensively utilizes basin dynamics、tectonic geology and sedimentary geology, is based on field geological reconnaissance, combines the means of drilling、 logging、earthquake、physical simulation and so on and uses the research method that combines geology and geophysical exploration to research the elements of the southern and northern parts of the front of Longmen mountain’s tectonic geometry、kinematics and dynamics and so on. In the lecture the author discusses the distribution characteristics and control factors of detachment faults and the combination of tectonic style in this area, and made out the tectonic deformation characteristics of the front of Longmen Mountain. Furthermore, combining with the two geological sections, which include the southern part and the northern part, the author discusses the geometry characteristics’ differences in the southern and northern parts of the front of Longmen Mountain. By such researching which includes the coupling process and tectonic dynamic evolution of Sichuan plateau、Longmen mountain’s orogenic belts and Songpan ganzi plateau, the author has analyzed some typical oil and gas constructions in detail,for instance Kuangshanliang 、 Tianjingshan and Gaojiachang. Besides, combining with the production、storage、entrapment and ancient tectonic research achievements in the research, the author finally put forward advantageous of oil and gas exploration in the area of the southern and northern parts of Longmen mountain.1、Through field geological survey and combining with the analysis of drilling and seismic data, the author deems that there vertically exists two sets of shallow and deep regional detachment faults series in the northern part of Longmen mountain: Deep detachment faults can reach to the lower part of sinian system or reach into the former sinian system strata in the piedmont zones and westwards. The lower part of detachment faults of piedmont zones is mainly the Lower Cambrian series of the Yangtze river channel formation; The shallow detachment faults series of the piedmont zones should be the shale period of the upper part of the Feixianguan formation. There vertically exist two sets of regional detachment faults series in the southern part of the front of Longmen Mountain: one is gypsum in Jialingjiang Formation and Leikoupo Formation and the other is mudstones in Jurassic period.2、By the researching of tectonic style in the southern and northern parts of the front of Longmen mountain, the author claims that in the northern part of the front of Longmen mountain the mainly tectonic style can be divided into two parts: one is compressive tectonic style and the other is gliding napped tectonic style; On the other hand in the south part of the piedmont zones the mainly tectonic style also can be divided into two parts: one is compressive tectonic style and the other is pressure torsion tectonic style.3、By the restoring work between the fault and fold deformation in the southern part of the front of Longmen mountain, we may find that from north to south, which from Gaojiachang,Sanhechang to Zhangjiaping,Linhuashan, the tectonic fault activities become more and more intense obviously,moreover the horizontal displacement which caused by fault has gradually increased. The principal part of tectonic fold deformation shortening ratio is comparatively large, but the terminal part of tectonic fold deformation shortening ratio is small.4、By the researching of deformation characteristics of the front of Longmen mountain, we may consider that the deformation of Longmen mountain’s orogenic belts has experienced multiphase tectonic deformation for instance the Indo-chinese epoch、Yanshanian and Himalayan. Tectonic deformation has such characteristics that it’s early in north but late in south,the north is strong but the south is weak in the Indo-chinese epoch and the south is strong but the north is weak in the Himalayan. The northern part of the front of Longmen Mountain takes concentric fold and thrust imbricated structure as typical characteristics, and the tectonic level is relatively deep. The middle and southern parts mainly develop imbricated thrust system whose brittleness is strong and its level is shallow, meanwhile, the piedmont zones of the middle and southern parts develop kilppe, but relatively rare in the northern part. In the front of Longmen Mountains, the deformation of the northern part’s shallow layer is relatively simple and is mainly monocline; the southern part’s deformation is relatively complicated, and the strata above Leikoupo Formation are involved in fault fold deformation to varying degrees.5、By analyzing the tectonic evolution history of Longmen mountain, we may consider that during T3-J2, Longmen mountain’s tectonic belts manifested as basin ridge coupling and mainly featured the basin ridge structure formed by continental apron and extension. With the epeirogenic uplift due to the differences, there formed a transitional large slope belt(being equivalent to current Longmen mountain region) between the ridge of Songpan ganzi and Sichuan plateau. Because there had existed many sets of detachment faults under the influence of gravity, it had formed a series of gravity gliding nappe(belonging to thin-skinned structure) and manifest as appearing a series of overturned or recumbent fold and so on in front of slope. Since J3, due to the collage of Lhasa block(the late Jurassic Bangong Co-Nujiang suture zone) and the collision of Indian plate(the Late cretaceous of India-Brahmaputra suture zone), the background of Tectonic dynamics has gradually transformed into extrusion from tension and has formed the thick-skinned structure that basement was involved into deformation. In the early stage, the normal fault has flipped and formed lots of high-angle thrust faults. Finally, it presents the current Longmen mountain that is distributed in long strip north-eastwards- the basin mountain coupling’s tectonic framework formed by Sichuan plateau.6、Based on establishing the geological models which constructed by actual geological conditions, by vertical uplift tilted tectonic physical simulated experiment it truly reappeared that during T3-J2.Due to differences uplift and combined effects between detachment faults and gravity gliding napes, the front of slope which located in the Longmen mountain’s slope belts area, between Songpan-ganzi plateau and Sichuan basin, had formed fold thrust structure, furthermore during this period the fold mainly manifested as the overturned or recumbent fold and the thin-skinned structure that the basement was not involved into.7、Combining with the achievements of forefathers’ oil and gas researching, more over by doing anatomical research for multiple oil and gas constructions in this area for instance Tianjingshan, Kuangshanliang、Gaojiachang and Linhuashan, the thesis put forward the next oil and gas exploration direction and the reasonable oil and gas exploration area of the front of Longmen mountain in the method of structure geology. We may believe that the imbricate structure and the pop-up structure developed under the detachments(Feixianguan Formation) on the northern part of the front of Longmen mountain are the favorable area of oil and gas exploration, and the floweriness structure and pop-up structure developed under the Leikoupo formation detachments on the southern part of the front of Longmen mountain are the favorable area of oil and gas exploration.