Study On Oil And Gas Geological Characteristics Of Changxing Formation-Feixianguan Formation Of Heimenten Formation In Eastern Sichuan Basin

According to the investigation on the field section outcrop and the observation of drilling cores in the northeast of Sichuan, stratum features of the Permian and Trias was cleared. Basing on that, this paper aiming to the Feixianguan Formation and Changxing Formation studied the identification characteristics of petrology and sedimentology in detail. On the one hand, it was turned out that the lithologies of Changxing Formation mainly were dolomite on the middle-upper part, especially were reef dolomite and bioclastic dolomite, and the lower part are limestone. On the other hand, the Feixianguan Formation are formed by micrite, only the No.4 section of Feixianguan has a small quantity of oosparite.The research about sedimentary environment considered that the argillaceous limestone and mud-stone of Changxing Formation's lower part were products of open-platform or slightly restricted-platform; and the middle-upper part was restricted-platform where there were reefs and shoals that be dolomitized deeply making them beneficial to become reservoirs; whereas the top of Changxing Formation was restricted-platform too which also be dolomitized well, but because of the grain's little size this part was not so good for reservoir transformation. As to Feixianguan Formation, its No.1 to No.3 section were products from deeper slope while No.4 section was from tidal flat environment.The research on the reservoir characteristics of Changxin--Feixianguan formation showed that the reservoir type of Changxin formation included grain dolomite and bioclastic dolomite, and the main reservoir space were intergranular pores, intergranular dissolution pores, and the plaster mold holes and fractures. The top of Changxin formation's reservoir was low porosity and low permeability reservoir. And in the middle of the reservoir, the porosity and the effective fractures were well developed, which belonged to middle porosity and low permeability reservoir. However, Feixianguan formation's reservoir was thick, and its reservoir rock type was mainly grain gray dolomite, which belonged to low porosity and low permeability reservoir. In general, the reservoir quality of Changxin-Feixianguan formation was poor in this study area, because the high quality reservoir in the platform edge reef and shoal facies was not met.In addition, studies combined with the latest 3D data and previous 2D data turned out that Heiloumen structure existed only one highest point named Maigaoshan which was east-west oriented, and its trap area from shallow to deep gradually became smaller until the bottom of the Cambrian.And the comprehensive evaluation of the reservoir forming condition thought that, the major source rock of Changxin--Feixianguan formation's gas reservoir in Heiloumen structure was the Longtan formation, the major reservoir rock were Changxin formation and Feixianguan formation's No.1 to No.3 section, the major cap rock was Jialinjiang formation. On the whole, there were good combinations between source, reservoir and cap. That is to say, its hydrocarbon source condition was superior, the cap's sealing property was good too, only the reservoir quality was a little poor.