| Fangzheng faulted depression is located at eastern ragion of Songhua river, Heilongjiang province. E 128°15′～129°15′,N 45°30′～46°50′, include most ragions of Tonghe, Fangzheng, Yanshou county, area of about 2500km2. Fangzheng faulted depression is a negative tectonic unit in the north of Yishu graben, and also is a Mesozoic and Cenozoic double faulted rift, which is controled by two deep fractures, with a NE 40°～50°orientation distribution in overall.In order to study the structural characteristics and hydrocarbon accumulation law of Fangzheng faulted depression, and find the favorable oil and gas traps, we use sedimentology, oil & gas fields of geology and petroleum geology theories andmethods, and based on explore research-based practice and geological research, study the tectonic evolution history, to analyze types of sedimentary facies and their distribution characteristics, to discuss the characteristics and the Composition of source bed, reservoir, and cap, and the oil and gas trap, to carry out the prediction of a favorable area for exploration.Tectonic environmental instructions of magmatite, tectonic styles of the cover, fracture characteristics of field observations and filling accumulation characteristics show that, tectonic evolution of Yishu graben can be divided into four stages, which are the stage of formation of boundary faults (early Yanshan period); the stage of regional uplift (late Yanshan period); the stage of strongly rifting (E2～E3); the stage of tectonic inversion(N).From the perspective of Rift formation and evolution, the tectonic sequence of Fangzheng faulted depression can be divided into Pre-rift sequence, which is composed of pre- Paleozoic and Paleozoic basement structure layer; rift sequence, which is composed of Paleogene Dalianhe Group (D) and Xinancun Group (X); post-rift sequence, Which is composed of Neogene Daotaiqiao Group (Nd) and loose Quaternary.From the perspective of Sedimentary evolution, the formation and evolution of Fangzheng faulted depression can be divided into three stages. First, late Jurassic to Early Cretaceous period of the Mesozoic basin formation; Second, late Paleocene to Oligocene period of rift formation; Third, Neogene period of tectonic inversion.Fangzheng faulted depression developes stratum of Cretaceous, Paleogene, Neogene and Quaternary from bottom to top. The target zone of this paper is Paleogene Dlianhe Group, Thickness of more than 2000m, mainly of mudstone, siltstone and gravel.Two different tectonic style decide Sedimentary filling of different ways in Fangzheng faulted depression. Da 1 Section and Da 2 Section shows east off and west over in north, fan-delta deposits in the eastern, shallow lake deposits in the western; Da 3 Section and Da 4 Section deposits just the opposite in eastern and western edge, double-break type deposits in the southern, east and west sides are all developing fan-delta facies.Hydrocarbon source rocks develop in the strongly defaulted period of water in– water back in the Paleogene, and the stable strongly defaulted period of water in. Studies show that dark mudstone is mostly developed in Da 1 Section and Da 2 Section, average organic carbon content is moer than 0.5% in 4 wells, chloroform bitumen "A" and the total hydrocarbon source rocks all reached classⅢ; the main type of organic matter is transitional type, a few areⅢkerogen; Dalianhe Group has entered a mature stage in most parts. Comprehensive analysis that Da 1 Section is the most favourable Hydrocarbon source rocks, then Da 2 Section.The reservoir developes well, characteristic is medium– well, especially in Da 3 Section and Da 4 Section(average porosity > 20% penetration rate > 100×10-3μm2), then Da 1 Section, again Da 2 Section, the worst is Cretaceous.As the result of strongly fractured segmentation, sedimentary environment is unstable and distribution is restricted, and sedimentary center migrates several times, caused the lateral cover is no comparable, therefore, there is no basin-wide cap, only exist some Regional caps and Local covers. Dark mudstone developes well in Da 1 Section and Da 2 Section in central and northern rift, can be used as a good local cap rocks.Combination of sandstone-mudstone configuration relations in exploration wells, Hydrocarbon potential and show of oil and gas, we can analyze that there are five sets of reservoir-cap combination. The most important is the former three, which are Apical style, self-generating & self-accumulating & upper-cover-style, self-generating & self-accumulating & self-cover type. The main trap type are fault block and faulted anticline, which is mainly controlled by faults, especially fracture of the control basin, controlled concave, and most caused by the Himalayan movement.The above study suggests that Demoli structure in North slope, Xiaolantun structure in central uplift and depression zone in north slope is the most favorable oil and gas exploration area.
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