Stratigraphic Sequence, Evolutionary History, And Petroleum Perspective Of Sunwu-Jiayin Basin

With the decreasing of oil & gas available reserve in Songliao Basin, sedimentary basins outer Daqing prospect-area became the major superseded area. Sunwu-Jiayin Basin extends 22810km2, and this acreage makes it the third one in those outer Daqing prospect area basins. The field geological works have approved the basin successions are Cretaceous strata, and Taoqihe formation, Yongancun Formation, and Taipinglinchang Formation yield dark mudstone, the total thickness reaches 616m. The organic types are mainly II-type, and have achieved low-mature phase. The oil contained sandstones had been found, and with OGT (oil and gas traces) occurrence. The resource extent is counted as 0.888~2.986×108t by volume-density method. This result indicates a considerable oil produce potential, and the basin has been confirmed the tactic basin. However, the basin research level still quite low, most of the study are all based on outcrop observation, section measurement, and geophysical compendium perambulation. Cross-researches also lack between those methods, thus, current dissertation's purpose is to fill up this vacancy. Integrated studies including stratigraphy, tectonics, sedimentary and oil & gas reserving perspective, which is based on outcrop stratigraphic data and geophysical acquired gravity-magnetism-electricity, seismic and borehole data, can not only provide valuable information on understanding the formation and evolution of Mesozoic and Cenozoic rift basin systems, but also is the need of tactic exploration and preferring.Sunwu-Jiayin Basin has a typical dualistic structure, they are pre-Mesozoic basement and Mesozoic-Cenozoic cap formation. The basin fill successions from bottom up are Early Cretaceous Ningyuancun Formation and Taoqihe Formation, Late Cretaceous Yongancun Formation, Taipinglinchang Formation, Yuliangzi Formation and Furao Formation, Paleocene Wuyun Formation, Miocene-Pliocene Sunwu Formation, and Quaternary. A synthetical strata sequence and geochronologic framework has been established by the studies of lithostratigraphy, biostratigraphy, and chronology. The age of Ningyuancun Formation is early Early Cretaceous, about Valanginian-Hauterivian, the age of the lower member of Taoqihe Formation is Hauterivian–Barremian, the age of the upper member of Taoqihe Formation is late Early Cretaceous Aptian–Albian, the age of Yongancun Formation is Late Cretaceous Cenomanian–Turonian, the age of Taipinglinchang Formation is Santonian–Campanian, the age of Yuliangzi Formation is late Late Cretaceous, about Campanian–early-middle Maastrichtian, and the age of Furao Formation is latest Late Cretaceous, about late Maastrichtian. Identify signs are established to make analyses of seismic and borehole data, and to upbuild sequence stratigraphic framework. Sections clearly showed the Xunke-Zhanhe and Jiayin are all fault subsidence and sag superimposed Basins. Sonic data from two bore-holes have been used to make seismic synthetical records. Five seismic reflecting boundaries (T1-1, T2, T3, T4, and T5) are demarcated, and they are also the unconformity boundaries of the sequences. T3 is the boundary separated the fault-subsidence phase and the sag phase in both Zhanhe and Jiayin fault-subsidence. Correspondingly, 4 seismic sequences could be confirmed:1) T5-T4 seismic sequenceThis sequence is composed of volcano-sedimentary successions Ningyuancun Formation, whose litho is buildup with gray-variedness rhyolite tuff lava, gray mud siltstone. These strata distributed all around the basin. Two secondary sequences could be identified in fault-subsidence, and they correspond to the lower and upper members of Ningyuancun Formation.2) T4-T3 seismic sequenceThis sequence is equivalent to the deposits of Taoqihe Formation, and two secondary sequences correspond to lower and upper member of Taoqihe Formation could be subdivided in both Zhanhe and Jiayin fault-subsidence, and the Taoqihe Formation could be subdivided into lower and upper member. The lower part of this formation is composed of coarseclastic sediments conglomerate, and gradually changed to gray-green sandstone, siltstone, and mudstone.3) T3-T2 seismic sequenceThis sequence is composed of Late Cretaceous Yongancun , Taipinglinchang and Yuliangzi Formation which is widely distributed in most of the current area, and absent in the uplift areas along the sides of Jiayin uplift and subsidence. The strata are composed of gray mudstone, mud siltstone, and silt feldspar sandstone.4) T2-T1 seismic sequenceThis sequence is composed of Paleocene Wuyun Formation and Miocene-Pliocene Sunwu Formation, and distributed in the most area of Zhanhe fault-subsidence and the Wulaga sag in Jiayin fault-subsidence. The strata are mainly composed of gray mudstone, green-gray mud siltstone, siltstone corresbedding.Gravity-magnetism and seismic data are combined to provide new views on the location of subsidence control faults and tectonic divisions, and the Sunwu-Jiayin Basin is subdivided four fault-subsidence and three uplift, from west to east are Sunwu fault-subsidence, Maolanhe uplift, Xunke-Zhanhe fault-subsidence, Furao uplift, Wuyun fault subsidence, Wuyunhe uplift, and Jiayin fault-subsidence. The main subsidence control and boundary faults are Maolanhe, Zhanhe, Kuerbinghe , Pingyanhe , Wulagahe and Shuanghezhen Fault.Faults distributions are newly reflected by the seismic reflecting characters. Most of them are NE, NNE trend basement fault, and small fault are few. 15 faults are recognized in each two fault-subsidences (Jianyin and Zhanhe), and the extended main faults are in domain, pressed contrary faults and press-wring strike slip fault. Those faults show disciplinarian characters. Syn-rift faults are NNE trend in domain. In Ximalaya Period, pressures from northeast made the faults active again, and turned to be strike-slip faults and contrary thrust slip faults, the trends are mainly NW trend and EW trend. Therefore, faults in the basin have the multi-phases active characters, especially the deep faults and regional faults, and with volcanism activity in different periods.Based on the study in the fault-subsidence, accompanied with different tectonics movement form, 4 structural mode, spread fault block, twist tectonic assemble, cover surge, and suppress fault block are developed in two fault-subsidences. Spread fault block mode is the main extension represent, and also one of the main tectonic visages.The basin evolution comes through a history of two steges, Early Cretaceous rift (Ningyuancun and Taoqihe) and Late Cretaceous sag (Yongancun and Taipinglinchang).Based on the field observation and recognition of single bore-hole face and seismic faces, the sedimentary faces in the basin have been studied, and six kinds of sedimentary systems including alluvial, delta, braid river, meander delta, lake, lake bottom fan. volcanic rocks in Ningyuancun Formation could be divided into 3 types: crater-flooding, flooding- erupt, and volcano-sedimentary faces. Based on the vertical sequences of the two bore-hole data and complanate distribution of each sequences faces, we suggest: During the sedimentary period of early Cretaceous Ningyuncun Formation, the fault-subsidence extensively extended, and deposited alluvial-fan delta-volcanic deposits, this sequence could be correlated with the Huoshiling and Shahezi Formation in Songliao Basin. During the sedimentary period of early Cretaceous Taoqihe Formation, the fault-subsidence subsidized quickly, and deposited fan delta-braid river-lake faces, this sequence could be correlated with the Yingcheng Formation in Songliao Basin. During the sedimentary period of late Cretaceous Yongancun,Taipinglinchang and Yuliangzi Formation, the basin subsidized steadily. Yongancun Formation, which is composed of river delta-lake faces, could be correlated with Yaojia Formation in Songliao Basin. Taipinglinchang Formation, which is fan delta- shore shallow lake faces, could be correlated with Nenjiang Formation in Songliao Basin. Late Cretaceous Yuliangzi Formation could be correlated with the Sifangtai-Mingshui Formation, but during this period, most area of NE China is in a environment of press, uplift, and shrink distortion geodynamic progress, only a small part of this period sediments exposed in the east of basin. Paleocene Wuyun Formation is partly exist in the basin, and is composed of braid river-braid river delta-lake faces. Oligocene to Pliocene Sunwu Formation are not showed in the seismic section, but the litho is alluvial-fan delta-lake faces. The ends of Wuyun Formation and Sunwu Formation sedimentary period the basin come through the strong tectonic movement, the faults contrary trusted, and stratum were widely eroded.Resulted from the faces study, the basin has two oil generating stratum, three reservoirs, and three covers. The first oil generating strata is Taoqihe Formation, and the second one is Yongancun Formation in Jiayin fault-subsidence. The first good coarse clastics reservoirs are in the top of Ningyuancun Formation and the bottom of Taoqihe Formation, the second one is in the top of Taoqihe Formation and the bottom of Yongancun Formation, and the third one is in the top of Yongancun Formation and the bottom of Taipinglinchang Formation. The three covers are middle-upper part of Taoqihe Formation, middle-lower part of Yongancun Formation, and Taipinglinchang Formation.Based on those above research conclusion and the petroleum generating conditions, we consider the organism abundance is high in Sunwu-Jiayin Basin, mixed organic well developed (II type in domain), and they are in low mature to mature phase, so the basin has a good petroleum generating condition, and the reservoirs and cover layers also well matched. The perspected resource extent is counted as 2.1×108t by volume-density method, this means a big resource extent. Yaotun fault concave in Sunwu fault subsidence, Zhanhe syncline in Zhanhe fault subsidence, and Wulaga sag have the big acreage and deep burying, with rich organic matter deposited, have the conditions to form the oil & gas, and they are favorable exploration perspective areas. Encirclements are fault-lithologic, lithologic two types in domain.