GEOLOGIC CHARACTERISTICS OF NATURAL GAS ACCUMULATIONS IN THE NORTHWEST OF GUIZHOU

The northwest of Guizhou is the main generation and distribution region for Lower Cambrian Niutitang Formation,Lower Silurian Longmaxi Formation and Upper Sinian Doushantuo Formation source rocks.Studies of source rock evolution histories in Guanling County,Zhuzang Town of Zhijin County and Yankong Town of Jinsha County have indicated that,petroleum generates and evolves slowly in Yankong Town and kerogen is degradated completely,which is favorable for hydrocarbon generation.Tectonic evolutions in the northwest of Guizhou are controlled by ancient tectonic effects leading by Middle Guizhou Uplift.Hydrocarbons mainly accumulate around source rocks.Middle Guizhou Uplift near petroleum generation center is favorable for petroleum migration and accumulation.Large lithologic and tectonic traps provided by ancient uplifts are main locations for oil and gas pools.Uprises and erosions in late Caledonian destroy early pools.Tectonic movements after Yanshanian are the keys for pool destroy and preservation.Cambrian and Silurian pressure system still exist in the northwest of Guizhou,where petroleum units may still exist.