Formation Conditions And Resource Evaluation Of Biogas Of Shallow Layers In Northern Songliao Basin

On the basis of present recognition of generation mechanism for biogas and chemistry, biochemistry and microbiology theories, this thesis sets up the calculation models of genetic association method of biogas and material balance method of biogas from original oil biodegradation. Generation history is studied quantificationally through material basis and geological, geochemistry conditions of biogas generation in shallow and middle depth layer in northern Songliao basin. Resoure quantity is calculated dynamically. At last ,the favorable exploration areas of biogas from source rock and bacterial decomposition gas from original oil arepredicted. Main conclusions are as follows:1,The geochemical condition and material basis of biogas in shallow layer are generalized. There are excellent geochemical conditions, good tectonic conditions, sedimentary conditions, temperature-pressure field and material basis for biogas generation - gray mudstone layers with immature and low maturity, high abundance and rich in hydrogen and oxygen in Songliao basin.2,Different genetic type biogas and with different calculation methods are studied. Calculation methods of biogas from source rock and bacterial decomposition gas from original oil are particularly studied.3,Distributive character of biogas is generalized. Gas source rock above 1500m layers mainly distributed in K₂n₁ and K₂n₂, k₂qn secondly, and K₂n₃, K₂n₄ and K₂m thirdly in profile. From plane view, gas generation intensity is highest around Sanzhao sag and east West slope of k₂qn Formation, and high of the whole Central depression of K₂n Formation. Bacterial decomposition gas mainly distributed in Taikang uplift, west overlap area and Putaohua area.4,Migration and accumulation coefficients of two typical projects are calculated. Migration and accumulation coefficient of Aonan oil field is 0.4029%,and Xinzhao is 0.3694%. So the average coefficient is 0.3862%. The coefficient before Nenjiang Formation is only 0.1786%.and after it is 2.0426%. Besides above,when Alaxin gas field is formed, migration and accumulation coefficient of bacterial decomposition from original oil gets to 67.28%.5,Biogas generation quantity and resource quantity of biogas from source rock and bacterial decomposition gas from original oil in Songliao basin is calculated. Two calculation methods-genetic relationship method and elment balance method are set up to calculate quantity of biogas from source rock. The result is 120.94×10¹²m³, Resource quantity of biogas from source rock is 1.058×10¹²m³ by dynamic calculation method, and 0.467×10¹²m³ by static calculation method. Total gas generation quantity of bacterial decomposition gas from original oil is 7.06×10¹¹m³. With 50% probability confidence level, the total resource of bacterial decomposition gas from original oil is 4.55×10¹¹m³,Taikang uplift belt is 2.83×10¹¹m³,western overlying belt is 1.13×10¹¹m³,and Putaohua area is 0.59××10¹¹m³, Total resource of biogas from source rock and bacterial decomposition gas from original oil in Songliao basin above 1500m layers is 1.513×10¹²m³.6,It is identified that Biogas can be found effectively by seismic bright point and low frequency. Through stratigraphic attribute analysis, seismic bright point character is discovered in sandstone reservoir. The distribution of biogas layer in the sandstones from mouth bar, and subsea distributary channel is predicted with the low frequency attribute.7,It is noted that there are biogas fields from source rock and bacterial decomposition gas from original oil by means of classic gas field dissection, which belong to structural-lithological gas fields. It is stated that the main play factors are gas source rock, reservoir and faults.8,The favorable exploration areas of biogas from source rock and bacterial decomposition gas from original oil are predicted. The favorable exploration area of biogas from source rock are: Sanzhao sag margin,Chao-Chang area, southwest Northeast uplift ,south Mingshui terrace, Daqing large anticline belt and West slope around Qijia-Gulong sag for middle and upper combination, West slope, belt between Qijia-Gulong sag and West slope, Heiyupao sag ,north plunge area and middle and northern Sanzhao sag for shallow combination. The favorable exploration area of bacterial decomposition gas from original oil are mostly West slope area for middle combination, and secondly south area of Daqing large anticline belt for middle and upper combination.