Gas Trap's Feature And Research On Reservoir Mechanism From Quantou Formation To Nenjiang Formation In South Songliao Basin

The Songliao basin locate at the northeast continent of China , is the large compound deposit basin which has the taphrogenic and sag double structure Mesozoic and Cenozoic in China. Songliao basin Clip in huabei, Siberian and Pacific plate, zhe basin pile up thick more ten thousand meters sinks the river and lake accumulate to composition large sedimentary band assume NE. The southern songliao basin is thirteen dot three thousand kilometers square(according to Nenjiang,the frist Songhuajiang and Lalinhe), includes the southeast upheave area, the south of central-cols area, the south of west-pitch area and the north of southwest upheave area four stair tectonic units. the southeast upheave area, the south of central-cols area divide into 13 second-class structure units. The southern songliao basin's mostly aggraded stratum include Jurassic, Cretacic, Tertiary and Quaternary.Based on the outcrop of field, lithology, results of previous work, and log data, we recognized five facies, alluvial fans facies, fluvial facies, fan delta facies, delta facies and lake facies. Furthermore, we confirmed the characteristics of sedimentary evolution in different periods. The fluvial facies and delta facies are the main facies in the third and fourth Section of the Quantou Formation. The lake facies is developed in Qingshankou Formation and Yaojia Formation. During Nenjiang Formation, the area of the lake is diminished and the delta facies is developed.According to the statistics analysis of primary geochemistry data, we achieved that hydrocarbon Source Rocks of the deep seated coal type gas are Shahezi Formation, Yingcheng Formation and the first section of Quantou Formation in Dongnan lift. The evaluating results of content of organic carbon on Shahezi Formation and Yingchengzi Formation are"good"and"the best". The kerogen types of Shahezi Formation, Yingcheng Formation and Denglouku Formation areâ…¢, which does favor in transforming from hydrocarbon to gas. The thermal evolution of kerogen is high maturity in Denglouku Formation, maturity or high maturity in Yingcheng Formation, high maturity or over maturity in Shahezi Formation.Based on the statistics analysis of porosity, permeability and sandstone pore-throat radius of reservoir rocks, we gained that Daan biogas reservoir has good characteristics of reservoir and porosity, from Sifangtai Formation to fourth and fifth section of Nenjiang Formation; The main reservoirs of oil type gas are sandstone reservoirs of fan delta in Yingtai and Honggang, delta in middle and bottom of Qianan and Changling sag. The reservoirs of coal type gas are sand body of belt-river channel, belt-nature bank, boom crevasse fan and so on. The porosity of sandstone reservoir of coal type gas in Quantou Formation is better than other Formations in low cretaceous.For the characteristics of caprock, we took the porosity, breakthrough pressure, clay minerals in to consider, and get that the direct caprock of biogas and regional caprock are delta front subfacies, mudstone of lake facies and plain mire, which has a super sealing ability. The caprock of middle bed oil type gas is made of mudstone of Qingshakou Formation and Nenjiang Formation, which has a higher potential capacity of hydrocarbon generation, characteristics of sealing in the physical property, the hydrocarbon concentration and pressure.According to the generation of different gas reservoir and the main control factors of gas reservoir we divided them into three types structure conglomerate gas reservoir, none structure conglomerate gas reservoir and composite gas reservoir. We also classify them into subtypes anticline gas reservoir, fault occlusion gas reservoir, lithology gas reservoir, strata gas reservoir lithology-structural gas reservoir, structural-litho- logy gas reservoir and 13 subclasses. We also take some examples to illustrate the formation mechanism and control factors.There is summarized that the gas trap's orderliness in the Southe Songliao basin. The whole's directions of variety is that the reservoir from simplex type lithology gas reservoir and anticline gas reservoir to composite gas reservoir and to fault occlusion gas reservoir from the west to east and south. the south of central-cols area mainly is lithology gas reservoir, secondly there is having anticline gas reservoir, there is a little fault occlusion gas reservoir in parts, there is appearance that a little composite gas reservoir in verge of central-cols area. The southeast upheave area mainly is composite gas reservoir, secondly there is having fault occlusion gas reservoir and a little strata gas reservoir.It have relation between gas trap's form and gas type, Coal type gas easiness cumulated in composite gas reservoir and fault occlusion gas reservoir, biogas and oil type gas mainly cumulated in lithology gas reservoir and anticline gas reservoir, carbon dioxide gas mainly cumulated in fault occlusion gas reservoir, there is that a little cumulate in lava at Yingcheng Formation in Changling.According hydrocarbon Source Rocks, constitution evolution and migration accumulate to analysis, associative liquid inclusion's research to analyze reservoir mechanism. oil type gas occur one time migration bring forepart- afternoon in Nenjiang Formation,in nenjiang formation time,the region's basement promontory,and go with fault brought,hydrocarbon migration along moded fault accumulate to be reservoir; Coal type gas have two times to be reservoir,the first time is the forepart- afternoon in Qingshankou Formation, the gas upwards migration along fault which shaping at the aulacogen period; the second time is the forepart- afternoon in Nenjiang Formation, the time is Coal type gas's mainly to be reservoir'time, it is inverse structural period, the gas migration along moded fault accumulate to be reservoir.