Research on the Forming Stages of Deep Natural Gas Reservoirs in Baimiao Area of Dongpu Depression

Key words: 
• Dongpu depression

Abstract: As the dynamics of oilgas exploration is bigger, many large gas fields has been found in the basin in recently. Biaomiao area is in the eastern of Dongpu depression, which is the exploration degree high oilgas area in Dongpu depression, there are mainly gas in the Baimiao area,some industrial oilgas wells has been found now, the producing gas condition is very superior,it has discovered Es3下,Es31,Es32,Es334 four sets of main oilgas formation. The gas area is smaller in the upper and part bigger in the lower part. The gas in Baimiao are at  the top of gas reservoirs with oil hoop. Oil and gas distribution is gas in the upper and oil in the lower part.  For oil and gas relation is complicated in Baimiao area,the research on the regulation of oil and gas is very poor and no systematic analysis up to now. It influences the step of gas exploration.
 The analysis on the formation time of oilgas reservoirs is hot problem, the determination of it helps to recognize the formation regulation of oilgas reservoirs. In recent, there are important progresses in the aspect of the chronology of formation time of hydrocarbon reservoirs.There are many methods, such as illite dating method, homogenization temperatures of fluid inclusion, the formation history of traps, hydrocarbon generated and hydrocarbon expulsed process,and so on.The different method is of different sense. On the basis of illite dating method and homogenization temperatures of fluid inclusion，it is found that the formation time of hydrocarbon reserviors exist mainly two stages in Baimiao area of Dongpu depression. One is about 31.4～20.4 Ma, which is corresponding to sedimentary period of Dongying FormationEarly period of Guantao Formation.The other is from 2 Ma to now, corresponding to Quaternary to now. In the first stage, a great majority of the formation age of natural gas reserviors distribute in the denudation period from 27 Ma to 17 Ma,which is the main formation time. The decreasing of  pressure in the denuded period help to formation of oil and gas reserviors. In the second stage,from 2 Ma to now, the Baimiao area is in the deficient compensation state since sedimentary period of Guantao formation, the area having not second process of generating gas. on the one hand, Qianliyuan depression and Gegangji depression continue producing gases, which migrate to the Baimiao area; on the other hand, the gas reserviors formed in the first stage is adjusted again. Gas in this stage comes mainly from the second time gas of Qianliyuan depression and Gegangji depression. The faults are important to control the formation time of oilgas reservoirs, the formation time in different area is very different. The Biaomiao area is divided into two forming oilgas reservoirs by Duzhai fault. The formation time of oilgas reservoirs is earlier in West area and later in East area. In vertical order,the formation time of oilgas reservoirs is earlier in old position and later in new position. In general, the characteristics of the formation time of the natural gas reserviors in Baimiao area is earlier in the west area and later in the east area, earlier in the north area and later in  the south area. The results are important for the deep exploration in Dongpu depression.