Geochemistical characteristics of butane gas in Tarim basin

Abstract：In order to study the effects of matrix type, thermal evolvement and migrational di- rection on geochemistical characteristics of butane gas in Tarim basin, the changes of compo- nent of butane and carbon isotope were analyzed. The results demonstrate that the content of butane changes obviously, ranging from 0.02% to 28.9% in terms of volume, and the average value is 1.89 %. The carbon isotope composition of butane is relatively stable with the main frequency of δ^13 C4 between -30%0 and - 280/000 in platform areas and between - 24% and --220/000 in foreland area. The iC4/nC4 of oil-type gas is lower than 0.8, and OlaC4 is lighter than --27.5%o. Whereas the iC4/nC4 of coal-type gas is higher than 0.8, and δ^13aC4 is heavier than -- 25.50/000. The value of δ^13iC4-δ^13nC4 of nature gas at the stage of high-thermal evolution is more than 0. The value of iC4/nC4 of nature gases which migrate in clastic rocks decreases along mi- grational direction, but the counterpart of natural gas diffused from cap or migrating through weathering crust of carbonate increases. Thus, the component and carbon isotope of butane could offer abundant geochemical information about the accumulation of oil and gas which in turn plays a significant role on the research associated with butane.