Characteristics Of Jiange Palaeohigh And Its Controlling On Oil&Gas In The Northwestern Sichuan Basin

Sichuan Basin lies in the mid-west of China, where is the earliest development and utilization of gas. Until now, hundreds of large and medium size oil and gas fields have been found, therefore, it is an enormous exploration potential basin. This basin has foregone six periods’tectonic movements, which are Jinning Movement, Caledonian Movement, Hercynian Movement, Indo-China Movement, Yanshan Movement and Himalayan Movement, respectively. These movements formed many palaeohighs, and Jiange pelaeohigh is one of them which have developed in Indo-Chinese epoch.Based on the fine interpretations of seismic profiles, combining the basic concepts of sequence stratigraphy, structural geology, basin analysis and so forth, this paper dissects the Jiange palaeohigh.The formation of Jiange palaeohigh owes to the uplift of Indo-Chinese epoch’s strata, and this palaeohigh developed two unconformities, which contained the bottom of Xujiahe formation and Jurassic System, and they represent the products of Early and Late Indo-China Movement, respectively. The palaeohigh is bounded by the pinchout boundary of Xu 4 member in map, generally distributes along the belt of Wangcang-Guangyuan-Jiange-Jiangyou, and constringes nearby Jiangyou area, which its area is about 5640km2.In the chronographic chart, the Y-coordinate represents time, and the X-coordinate represents space. Then the time-space domain can indicate the units of sedimentary facies in the internal system tracts, whereas others can represent the positions and durations of non-sedimentary trap, absent area, passing area and denudation area. Through mapping the chronographic chart, it is concluded that the denudation time of Xu 4 member is 2Ma, and Xu 3 member is 6Ma.Many methods are used to calculate the thickness of strata denudation at home and abroad nowadays, however, each method has its own limitation. According to the regional geology, combining the documents in hand, this paper selects the strata trend method to estimate denudation. The results of research display that the denudation thickness of Xu 4 member is 0-150m, and Xu 3 member is 0-280m. Based on the geometries of section and the characteristics of basin tectonic evolution, the structural evolution of Jiange palaeohigh can be divided three stages, which are the uplift denudation stage of Indo-Chinese epoch, the stratigraphic deposition stage of Yanshan epoch and the destroying remodeling stage of Himalayan epoch.Finally, from the discussion of the controlling on oil and gas of Jiange palaeohigh, it is concluded that the palaehigh can form the reservoirs of truncation unconformity and reservoirs of unconformity of lap along the top and bottom of unconformities. Moreover, from analysis of seismic profiles, it is predicted that the belt behind the mountain of north segment of Longmenshan Mountain has no exploration prospect, whereas the frontiers of the segment especially nearby the ramp region of Zitong depression are the most important exploration region.