The Genetic Feature and Reservoir Forming Mode of Cracked Gas in China

At present,the proven reserves of kerogen cracked and oil cracked gases at high thermal evolution stage have accounted for about 26%of the total reserves in China,so it is important to carry out systematic analysis of the formation and distribution characteristics of natural gas.Based on a number of pyrolytic experiments on kerogen and oil at high thermal stage,,combined with the researches on cracked gas,this paper further analyzed the genetic characteristics of cracked gases from oil,marine-lacustrine mudstone and lacustrine coal measures,and proposed five gas accumulation modes.Crude oil cracking was generally thought to occur at temperature more than 150℃.Our experiment proves that it begins to form cracking gas at temperature more than 190℃ in some areas.Gas generation potential of marine mudstone would exhaust when ROapproaches 3%.However,lacustrine coal measures still have great methane generation potential when ROis near 2.5%-5%,and the gas amount generated at this stage accounts for more than 20% of the total generated gas.The cracking potential of lacustrine mudstone lies between the two formers,and the coal source rock has the greatest gas cracking potential.Cracking gas mainly has five accumulation modes,including ancient uplift crude oil cracked gas,ancient slope weathering karst cracking gas,dense sandstone coal source rock cracking gas,special reservoir cracking gas,and coal seam-shale source cracking gas.The ancient uplift and slope reservoir,the marine-terrestrial transitional basin dense sandstone reservoir and Meso-Cenozoic special reservoir are important potential exploration direction.