Study Of The Characteristics, Reservoir Conditions And Enriched Rules Of Shallow Biogenic Gases

Over years ago, some geochemists estimated that the bio-gas reserves accountedfor about 20% of global natural gas resources, in other words, more than 20% of 66.4×10¹²m³ of natural gas reserves found is biogenic in the world, even reach 25% to30%. Eight of twenty-two giant gas fields of the globe are biogenic.At present, large amounts of biogenic gas fields are distributed in dozens ofcountries and regions of Russia, the United States, China, the Gulf of Mexico, Italy,Canada, Japan, etc. Especially with the continuously further study of the deepbiosphere in recent years, it has found microbes existence depth, long-time activities,and bio-gas reserves to be higher than previously estimated. Therefore, many expertspredict that the natural gas exploration in the future largely depends on biogenic gasdiscoveries.There are many Mesozoic and Cenozoic continental sedimentary basins in China,enriched in organic matterâ…¡-â…¢, better geologic setting of forming biogenic gases.Biogenic gas resources in the second resource assessment are 2.8×10¹²m³, whichaccounted for 5.3% of 53×10¹²m³ of the total amount of natural gas resources. This isa new field of the natural gas exploration with certain strategic value. A number oflarge-scale biogenic gas fields have been found in three-lake area in the eastern part ofthe Qaidam Basin and Ying-Qiong basin of South China Sea continental shelf.Biogenic gas fields are widely distributed in Mesozoic and Cenozoic basins likeYunnan Province etc., south of China, which indicate prospect of abundant bio-gasresources.According to technical routine of forming basin, hydrocarbon source rocks andreservoirs of oil and gas basin systems, based on the regional geological background and tectonic evolution in Qujing Basin, Through the stratigraphic classification andcorrelation, seismic facies analysis and identification of horizon, the isochronousstratigraphic sequence framework and basin fill sequence are established in this thesis;Deepened evaluation and understanding of immature source rocks to search for theeffective indexes of geochemical evaluation of them and the correspondinghigh-efficiency gas source rocks; The studies of tectonic characteristics, sedimentsystems and sedimentary facies of the basin to predict the advantageous trap types andreservoir distribution. Finally, combined the geological characteristics, reservoirconditions and formed reservoir rules of the domestic and overseas similar shallowimmature biogenic gas fields, and the geological characteristics of the two typicalbiogenic gas reservoirs that have been proved in Qujing Basin, to comprehensivelyanalyse and study the controlling factors of the formation of shallow biogenic gasesand the reservoir formed conditions of the traps, reservoirs, overlying formation,preservation, migration pathway, etc., and based on studying the migrated andaccumulated history and reservoirs formed model of biogenic gases, to summarizeand probe into the rules of reservoirs formed and enrichments of the shallow biogenicgases in Qujing Basin which belongs to continental,Tertiary, remnent andrift-subsidence basin.Therefore, the contents and achievements accomplished in this PhD thesis wouldbe great theoretical, practical and reference significance for the exploration anddevelopment of the biogenic gas reservoirs of Qujing Basin and even other areas ofthe world.