| The paper takes an example of condensed gas feild in Qianmiqiao buried-hills. Based on the research of formation and development of the buried-hills, three important subjects in the research are discussed with the application of advanced technical and methods (namely, balanced cross sections, analysis of carbon isotope , mensuration of reservoir fluid inclusion): (1) the development of karstification and characters of reservoir in Ordovician ; (2) lower Tertiary (Es3) source in the depression nearby ; (3) the hydrocarbon generation history , migration phase and reservoir formation history. Results obtained in the research are:l.By the virtue of palaeostructure analysis and method of balanced cross sections, we have studied the formation and development history of Qianmiqiao buried hills ,and indicate that the formation of Ordovician buried hills can be mainly divided into four periods, namely, stable uplift period , fold-thrust period , block-fault tilting period, and thermal subsidence and depression period .2.It is the first time to divide the structure of Qianmiqiao buried hills into three structural layers : buried hills thrust fault block, paleogeomorphic relict mountain and lowland, tilting horst block.3.It is discussed that the buried hill reservoir in this zone experienced karstification in Caledonian-early Hercynian , Indosinian and mid Yenshan movement period , and it is indicated that karst formed in late Indosinian and mid Yenshan movement period are the key periods to form fine reservoir. Karst formed in both periods piled up and formed the karst cave- pore reservoir of the Ordovician Fengfeng Formation and Upper Majiagou Formation in Qianmiqiao buried hills.4.Based on the research of geochemical characters of hydrocarbon source rock and comparison of oil and gas sources , it is indicated that the condensed oil and gas in buried hills mainly came from ES3 effective hydrocarbon source rock of type III kerogen - type II2 kerogen in Banqiao deprssion and Qikou depression beside both sides of the tilting horst ,and which is the main source of buried hill with early reservoir and late oil and gas source .5.With the help of thermal history of hydrocarbon source rock , and combined with the types , physical characters and homogeneous temperature distribution of organic and saltysolution fluid inclusion with different types in Ordovician limestones , the formation time and migration stages of oil and gas are determined. The formation of oil and gas experienced three periods with different temperature peak zone : first, 120-125 , oil generation period ; second, 140~150 , condensed oil generation period ; third , 160-190 , condensed oil and dry gas generation period .Likewise, the migration of oil and gas are divided into three stages : from early Esi to late Ng ,then from early Nm to mid Nm ,and last from late Nm to now . We can see clearly that oil and gas began to migrate with large scale after Nm .6.The character of hydrocarbon production and high gas-oil ratio show that the main migration facies in buried hills is gas facies (including condensed gas facies) . The earlymigration facies is condensed gas facies , later ,gas facies.7..Based on fluid inclusion and oil and gas geochemical character, it is concluded that low mature gas came from Banqiao depression and condensed gas and high mature gas came from Banqiao depression and Qikou depression. Futhermore, the formation of reservoir experienced four periods: the first, from Esi to Ed ; the second , from late Ng to early Nm ; the third , Nm ; the fourth , from late Nm to now .So we predict that exploration in Qianmiqiao should be mainly directed to condensed oil and gas reservoir nearby Banqiao depression and gas reservoir is more probably found near Qikou depression.8.Analogue of the conditions required for reservoir formation in Huanghua buried hills shows that,high quality and thick Es3 hydrocarbon source rock distributed richly in the middle area depression, and moderate quality sandstone distributed in south area, but...
|
PDF Full Text Request