DISTRIBUTION AND GAS-BEARING CHARACTERISTICS OF THE CENOZOIC IGNEOUS ROCKS IN THE JIZHONG DEPRESSION

In the Jizhong Depression, the Cenozoic igneous rocks, distributing within the Eogene strata, trend to be younger in age but increase in thickness, and in area from the south toward the north. The maximum distributing area occurs in the Langgu Depression, approximate to 1000km², with a thickness exceeding 500m, dominated by diabases. The thermal alteration of the intrusions and erup tions improves the conditions of oil/gas generation, and provides favourable conditions for large amount of oil and gas accumulations. The reservoirs relating to igneous rocks consist of basalts, diabases, tuffs and spotted slates, mainly characteristic of secondary dissoluted pores and fissures, among which the spotted slates is the best one in property. As a result, three types of traps would be developed, i. e. updipping thin-out, lenticle and structure-lithology traps. The oil/gas pools discovered up to date are principally of structural lithological traps.